JP2002044169A - Digital demodulator - Google Patents

Abstract

(57) Abstract: Provided is a digital demodulation device having an automatic gain control function of adjusting a gain according to a reception state of a digital modulation signal. SOLUTION: In a digital demodulator (DSp) for amplifying a received digitally modulated signal wave (Sb) propagating in the air with a gain automatically adjusted to have a predetermined amplitude and demodulating it into a digital signal, a reception level is provided. A fluctuation detector (62) detects a reception level fluctuation (D, C / N) of the received digital signal wave (Sb), and a gain adjuster (1).
5, Sac) is the detected reception level fluctuation amount (D, C /
N) to adjust the gain.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital demodulator for receiving and demodulating a digitally modulated signal wave transmitted in the air, and more specifically to a receiving state of the digitally modulated signal. The present invention relates to a digital demodulation device having an automatic gain control function for adjusting a gain according to the following.

[0002]

2. Description of the Related Art FIG. 25 schematically shows a configuration of a conventional VSB demodulator. The VSB demodulator DSc is connected to the antenna 1
0, tuning tuner 11, down converter 12, AG
It includes a C amplifier 13, an AD converter 14, an AGC 15, a Hilbert filter 16, a detector 17, an interpolation filter 18, a roll-off filter 19, a waveform equalizer 1000, an error corrector 1001, and a C / N detector 1002. The antenna 10 receives a VSB modulated signal wave Sb transmitted from a broadcast station over a plurality of channels. The tuning tuner 11 selects a channel of a received signal to be tuned to the VSB modulated signal wave Sb over a plurality of channels input via the antenna 10. The down converter 12 is connected to the tuning tuner 11 and converts the frequency of the selected VSB modulated signal output from the tuning tuner 11 to a desired IF frequency.

[0003] The AGC amplifier 13 is a down converter 1
2 is a gain control amplifier (automatic gain control amplifier) for adjusting the gain of the IF signal output from 2 to a desired magnitude. The AD converter 14 is an AGC amplifier 1
The analog VSB modulated signal, which has been frequency-converted to the IF frequency output from 3 and gain-adjusted to a desired magnitude, is converted to a digital signal using a frequency twice the symbol frequency.

The AGC 15 is a gain controller (automatic gain control device), and a digital VSB modulation signal output from the AD converter 14 (hereinafter, unless otherwise required, simply referred to as a “VSB modulation signal”) Svsb. Is calculated, and a digital signal having a desired amplitude for normal operation as a VSB demodulator is generated. This digital signal is output to the AGC amplifier 13 as a control signal Sc. The AGC amplifier 13 adjusts the amplitude of the VSB modulation signal Svsb input from the down converter 12 based on the control signal Sc output from the AGC 15, and then outputs the adjusted signal to the AD converter 14. in this way,
AGC amplifier 13, AD converter 14, and AGC 15
A VSB modulated signal Svsb having a desired amplitude is obtained by the feedback circuit formed between the two.

[0005] The Hilbert filter 16 includes an AD converter 1
4 extracts the quadrature component of the VSB modulated signal Svsb output from the VSB 4 and outputs the quadrature component signal to the detector 17. Based on the VSB modulated signal Svsb output from the AD converter 14 and the quadrature component signal output from the Hilbert filter 16, the detector 17 transmits the transmitted VSB modulated signal Svsb and the frequency of the oscillator of the tuning tuner 11. The baseband signal is generated by detecting and correcting the error. The interpolation filter 18 converts the baseband signal output from the detector 17 into symbol rate frequency data based on the device clock frequency data.

The roll-off filter 19 calculates the symbol rate frequency data input from the interpolation filter 18
A low-frequency region signal is extracted at a desired roll-off rate. The waveform equalizer 1000 performs a waveform equalization process by removing distortion caused by a transmission path from the low frequency region symbol rate frequency signal output from the roll-off filter 19. The error corrector 1001 performs an error correction process on the waveform-equalized low frequency domain symbol rate frequency signal output from the waveform equalizer 1000 to correct an error due to a transmission path,
The transport stream is demodulated and an error correction signal indicating the number of error corrections is output. The demodulated transport stream is output to a subsequent MPEG decoder (not shown). The C / N detector 1002 calculates the noise component of the transmission path from the error correction processing by the error corrector 1001, and calculates the C / N amount.

FIG. 26 shows a detailed configuration of the AGC 15 described above. AGC 15 includes an amplitude calculator 21 and an average filter 2
2. Error detector 23, loop filter 24, PWM calculator 25, low-pass filter 26, and operational amplifier 27
including. The AGC 15 is, as described above, the AD converter 14.
A digital signal having a desired amplitude for normal operation as a device is calculated by using the output signal of
A control signal to be input to the converter is calculated, and the control signal is output to the AGC amplifier 13.

For this purpose, the amplitude calculator 21 uses the above-mentioned A
The amplitude is obtained by calculating the absolute value of the output value of the VSB modulation signal Svsb input from the D converter 14. Then, the amplitude calculator 21 outputs an amplitude signal representing the obtained amplitude.
The average filter 22 calculates an average value of the amplitude of the VSB modulated signal Svsb based on the amplitude signal input from the amplitude calculator 21 and outputs an average amplitude signal. Error detector 2
3 detects an error between the actual average amplitude value of the VSB modulation signal Svsb and a desired average amplitude value for normal operation of the entire VSB demodulator based on the average amplitude signal input from the average filter 22. And outputs an average amplitude error signal.

[0009] The loop filter 24 integrates the detected error based on the average amplitude error signal input from the error detector 23 to generate a stabilizing signal, thereby stabilizing the loop of the entire AGC 15. The PWM calculator 25 converts the output of the loop filter 24 into a square wave in which the ratio of square waves of 0 and 1 indicates error information. The low-pass filter 26 is
The low frequency component is extracted from the square wave input from the WM calculator 25 and settled to a stable and desired level. The operational amplifier 27 amplifies the output from the low-pass filter 26 to a value appropriate for the AGC amplifier 13 and inputs the amplified output to the AGC amplifier 13 in order to adjust the loop gain of the entire AGC 15.

FIG. 27 shows a detailed configuration of the averaging filter 22 described above. The average filter 22 includes a multiplier 31a, a multiplier 31b, a first coefficient adder 32, a second coefficient adder 33, an adder 34, and a delay unit 35. The first coefficient assigner 32 holds a reciprocal of a predetermined average number as a first average coefficient K, and outputs the first average coefficient K as required. The second coefficient assigner 33 holds a value obtained by subtracting the first average coefficient K from 1, that is, “1−K” as a second average coefficient. Is output.

As described above, the average filter 22 averages the amplitude values detected by the amplitude calculator 21. Therefore, the multiplier 31a multiplies the amplitude signal input from the amplitude calculator 21 by the first average coefficient K input from the first coefficient adder 32, and outputs the result to the adder 34. . The adder 34 adds the multiplication result input from the multiplier 31a and the output from the multiplier 31b, and outputs the result to the error detector 23 and the delay unit 35. Delay unit 35
Outputs the multiplication result input from the adder 34 with a delay of one control cycle period. The multiplier 31b multiplies the multiplication result delayed by one control cycle period by the second average coefficient 1-K input from the second coefficient assigner 33, and outputs the result to the adder 34. Output.

One control cycle is defined as VSB demodulator DS.
This refers to one sequence of control processing performed continuously in c and its components. The time required to execute one control cycle, that is, the period from the start of a certain control cycle to the start of the next control cycle.
In the present specification, a control cycle is represented by t, not only for the related art but also for the description of the embodiment of the present invention.
The control cycle period is represented by Pt. In other words, a past or future control cycle with respect to a certain control cycle t is represented by adding or subtracting a natural number to t, and a corresponding control cycle period Pt is similarly represented by adding or subtracting a natural number to t. As described above, the control cycle t is also a parameter indicating the relative time.

As described above, the value obtained by multiplying the average amplitude signal output from the multiplier 31a by the first average coefficient K is the value in the current control cycle t and the value one control cycle t earlier is added to the adder 34. Then, the average value of the amplitude of the VSB modulation signal Svsb can be obtained by repeatedly adding the control cycle t. Referring to FIG. 27, an amplitude signal input from amplitude calculator 21 to multiplier 31a is denoted by X1 (t),
The average amplitude signal output from the adder 34 is represented by X2 (t)
The processing in the averaging filter 22 will be described.
FIG. 27 illustrates a case where the control cycle t is 2. Note that, for simplicity of explanation, the control cycle t is simply referred to as “t” unless otherwise required.

A relationship expressed by the following equation (1) is established between the above signals. X2 (t) = K × X1 (t) + (1−K) × X2 (t−1) (1)

As shown in the above equation (1), when the average number is set to a predetermined number, for example, 300, the average coefficient K becomes 1 /
It will be 300. In this case, multiply K = 1/300,
A signal X2 is obtained by adding the result obtained by multiplying the integral sum by 299/300.

FIG. 28 shows a detailed configuration of the loop filter 24 described above. The loop filter 24 includes an integral term coefficient assigner 41, a multiplier 42, an adder 43, and a delay unit 44.
including. The integral term coefficient assigner 41 holds an integral term coefficient representing the loop sensitivity of the AGC loop, and outputs an integral term coefficient A as required. The multiplier 42 multiplies the average amplitude signal X2 (t) input from the error detector 23 by the integral term coefficient A input from the integral term coefficient adder 41 to obtain A × X
2 (t) is obtained and output to the adder 43. For the sake of simplicity, the average amplitude signal X is used unless otherwise necessary.
2 is simply referred to as “X2”. The adder 43 adds X2 (t−1) input from the delay unit 44 to A × X2 (t) input from the multiplier 42, and calculates A × X2 (t) + X2.
(T-1) is obtained, and a PWM calculator 2 is set as X3 (t).
5 and to the delay unit 44.

When t is 1, X which is the output of the delay unit 44 is used.
Since 2 (t-1 = 0) becomes zero, A × X2 (t) is output from the adder 43 to the delay unit 44 and is also output to the PWM calculator 25 as a stabilized signal X3 (t). You. When t is 2, A × X2 (t) + X2 (t−1)
Is output to the delay unit 44, and the stabilized signal X3
The result is output to the PWM calculator 25 as (t). Thereafter, the same processing is performed.

A relationship expressed by the following equation (2) is established between the above signals. X3 (t) = {A × X2 (t)} (2)

FIG. 29 shows a detailed configuration of the PWM calculator 25 described above. The PWM calculator 25 includes an adder 51 with overflow and a delay unit 52. For the sake of simplicity, unless otherwise required, the stabilized signal X3 and the square wave signal X4 are simply referred to as "X3" and "X4", respectively.

A relationship represented by the following equation (3) is established between the above signals. X4 (t) = {X3 (t)} (3)

The output signal X3 of the loop filter 24
Is a digital signal having a bit width of n bits (n is a predetermined natural number), at a certain time (control cycle t), the adder 51 with overflow outputs 1 only when the overflow exceeds n bits, Otherwise, 0 is output. So that 0 and 1
Is proportional to the signal X3 output from the loop filter 24.

Next, referring to FIG. 30, VSB demodulator D
The main operation of Sc will be described. VSB demodulator DS
When power is turned on and operation is started, p1
The "receive analog VSB modulated signal" subroutine of step # 100 is started.

In step # 100, the channel of the received signal to be tuned is selected by the tuning tuner 11 with respect to the VSB modulated signal over a plurality of channels input via the antenna. An analog VSB modulated signal of the selected channel is received. Then, the "down-convert" subroutine of the next step # 200 is started.

In step # 200, step # 1
The analog VSB modulated signal obtained in 00 is converted by the down converter 12 into an IF signal having a desired frequency. Then, the "amplification" subroutine of the next step # 300 is started.

In step # 300, step # 2
The IF signal generated in 00 is amplified by the AGC amplifier 13 with a predetermined gain. And the next step #
The "AD conversion" subroutine of 400 is started.

In step # 400, step # 3
The analog VSB modulated signal, which is the IF signal amplified in 00, is converted by the AD converter 14 into a digital VSB modulated signal Svsb. Then, the next step # 60
The "Hilbert Filtering" subroutine at 0 starts.

In step # 600, step # 4
Based on the VSB modulated signal Svsb generated at 00,
The Hilbert filter 16 generates a quadrature component signal. Then, the "detection" subroutine of the next step # 700 starts.

In step # 700, the detector 17
Is the VSB modulated signal Svs obtained in step # 400.
b is detected with the quadrature component signal obtained in step # 600 to generate a baseband signal. Then, the “storage filtering process” subroutine of the next step # 800 starts.

In step # 800, step # 7
00 is output to the interpolation filter 18.
Is converted into symbol rate frequency data. Then, the "roll-off filtering" subroutine of the next step # 900 starts.

In step # 900, step # 8
Based on the symbol rate frequency data obtained in 00, the roll-off filter 19 generates a low frequency region symbol rate frequency signal. Then, the next step # 10
The “Waveform equalization process” subroutine of 00 starts.

In step # 1000, the waveform equalizer 1000 removes distortion caused by the transmission line from the low frequency domain symbol rate frequency signal obtained in step # 900. Then, the "error correction" subroutine of the next step # 1100 starts.

In step # 1100, the error corrector 1001 performs an error correction process on the low frequency domain symbol rate frequency signal subjected to the waveform equalization process in step # 1000 to correct an error caused by a transmission path. As a result, the demodulated transport stream is output to an external MPEG decoder. Then, the "C / N detection" subroutine of the next step # 1200 starts.

In Step # 1200, Step #
Based on the error correction processing of the error corrector 1001 in 1100, the noise component of the transmission path is calculated and the C / N amount is calculated.

[0034]

However, the digitally modulated signal wave Sb transmitted from the broadcasting station is deteriorated by various interference factors before it propagates through the atmosphere and is received by the antenna 10. Obstruction factors include reflections and interruptions by giant fixed objects such as buildings, or airplanes and automobiles. Further, there is interference by radio waves transmitted from other radio wave sources, and electromagnetic field interference by natural phenomena and artificial factors.
Further, as a simple example, the reception level of the VSB modulated signal wave Sb received by the antenna 10 fluctuates remarkably only when a person moves around the antenna 10. Such a change in the reception level of the VSB modulated signal wave Sb is a deterioration in the quality of the VSB modulated signal wave Sb.
It greatly affects the demodulation performance of the demodulator.

One of the effects of the interference factor is a bit error rate at the time of error correction processing executed by the error corrector 1001. This bit error rate is determined by the AGC circuit (A
It can be controlled by the value of the average coefficient (first average coefficient K) of the average filter (average filter 22) of the GC 15). If the average coefficient is increased, it can be applied even if the amount of change in the reception level of the transmission radio wave at the antenna is large, but the thermal noise increases as the device and the bit error rate deteriorates. Conversely, when the averaging coefficient is reduced, the AGC circuit does not follow when the fluctuation amount of the radio wave reception level is large, but the thermal noise of the device is reduced, and the bit error rate is improved.

In a conventional digital demodulator, AGC
Since the averaging coefficient of the averaging filter of the circuit is uniquely determined, it cannot be satisfied at the same time both the performance with respect to the variation in the reception level of the radio wave sent to the antenna and the performance with respect to the bit error rate of the entire device. There's a problem. The present invention focuses on this point, and provides a digital demodulation device capable of appropriately and dynamically setting an average coefficient of an average filter in accordance with a variation amount of a radio wave reception level and a bit error rate of the entire device. Aim.

[0037]

According to a first aspect of the present invention, a received digitally modulated signal wave propagating in the air is amplified with a gain automatically adjusted so as to have a predetermined amplitude to obtain a digital signal. A digital demodulation device for demodulating, a reception level fluctuation amount detector for detecting a reception level fluctuation amount of a received digital signal wave, and a gain adjuster for adjusting a gain based on the detected reception level fluctuation amount. A digital demodulation device comprising:

As described above, in the first aspect, the automatic gain control amplification process is controlled in accordance with the reception state of the digitally modulated signal wave which fluctuates due to various interference factors in the process of propagating through the air. This makes it possible to demodulate the digital signal with high quality.

According to a second aspect, in the first aspect, the reception level fluctuation amount detector detects the reception level fluctuation amount based on the amplitude of the received digital signal wave.

In a third aspect based on the first aspect, the reception level fluctuation amount detector detects the reception level fluctuation amount based on the error rate of the received digital signal wave.

In a fourth aspect based on the first aspect, the reception level fluctuation amount detector generates a first digital modulation signal by extracting a digital modulation signal having a desired frequency from the received digital modulation signal wave. And a second digital amplifier having a desired amplitude value by amplifying the first digital modulation signal with a gain.
An automatic gain control amplifier that generates a digitally modulated signal of
The second digital modulation signal is converted into a digital signal and converted into a third signal.
An analog-to-digital converter that generates a digitally modulated signal of the first type, and a tuned signal received level variation detector that detects a received level variation of the first digitally modulated signal based on the amplitude of the third digitally modulated signal. The gain adjuster adjusts the gain on the basis of the detected reception level fluctuation amount of the third digital modulation signal.

In a fifth aspect based on the fourth aspect, the tuning signal reception level fluctuation amount detector further comprises: an amplitude detector for detecting an amplitude value of the third digital modulation signal; A first averaging filter that performs average filtering using a predetermined averaging coefficient to detect an average amplitude value, an error detector that detects an error between the detected average amplitude value and a desired average value, A loop filter for generating a stabilizing signal for stabilizing the automatic gain control amplification process by loop-filtering the error using a predetermined integral term coefficient, and the tuning signal reception level fluctuation amount detector detects the generated stabilizing signal. The amount of received level fluctuation is detected based on

In a sixth aspect based on the fifth aspect, the tuning signal reception level fluctuation amount detector further comprises: a binary difference detector for detecting a difference between any two values of the stabilized signal; By comparing the difference with a threshold value of a predetermined value, the reception level fluctuation amount is detected.

As described above, in the sixth aspect, by arbitrarily setting the value and the number of the threshold value, the gain can be finely adjusted according to the type and reception state of the digital modulation wave to be received. High-quality digital signals can be demodulated.

In a seventh aspect based on the sixth aspect, the tuning signal reception level fluctuation amount detector generates a level fluctuation amount signal having a value indicating a comparison result, and the gain controller based on the level fluctuation amount signal. And adjusting the gain.

In an eighth aspect based on the seventh aspect, the average filter is an adaptive average filter for adaptively setting an average coefficient value based on a level variation amount signal value. The digital signal can be demodulated with high quality by setting the average coefficient to an optimum value according to

As described above, in the eighth aspect, the averaging coefficient is set according to the reception level fluctuation, so that the applied average filtering corresponding to the reception level fluctuation can be performed.

In a ninth aspect based on the eighth aspect, the average filter has a first average coefficient and a second average coefficient larger than the first average coefficient, and the level variation signal is detected. The first average coefficient is selected when the level fluctuation amount is smaller than the threshold value, and the second average coefficient is selected when the level fluctuation amount at which the level fluctuation amount signal is detected is not smaller than the threshold value. I do.

In a tenth aspect based on the seventh aspect, the loop filter is an adaptive loop filter that varies the value of the integral term coefficient based on the value of the level variation signal.
A digital signal can be demodulated with high quality by setting the integral term coefficient coefficient to an optimum value according to the detected reception level fluctuation amount.

As described above, in the tenth aspect,
Since the integral term coefficient is set according to the reception level fluctuation, applicable loop filtering corresponding to the reception level fluctuation can be performed.

According to an eleventh aspect, in the tenth aspect,
The loop filter includes a first integral term coefficient and a second integral term coefficient larger than the first integral term coefficient. And selecting a second integral term coefficient when the level variation amount at which the level variation amount signal is detected is not smaller than the threshold value.

In a twelfth aspect based on the sixth aspect, the tuning signal reception level fluctuation amount detector further comprises a PWM calculator for converting the stabilized signal into a square wave signal represented by 0 and 1, A low-pass filter that extracts a low-frequency component from the wave signal to generate a low-frequency square wave signal, and the tuning signal reception level fluctuation amount detector detects a reception level fluctuation amount based on the low-frequency square wave signal. It is characterized by doing.

According to a thirteenth aspect, in the twelfth aspect,
The gain adjuster adjusts a gain based on the low-frequency square wave signal.

According to a fourteenth aspect, in the twelfth aspect,
The tuning signal reception level fluctuation amount detector further includes a gain adjustment signal generator that generates a gain adjustment signal that adjusts the gain of the automatic gain control amplifier based on the low-frequency square wave signal. The amount detector detects a reception level fluctuation amount based on the gain adjustment signal.

According to a fifteenth aspect, in the fourteenth aspect,
The gain adjuster adjusts the gain based on the gain adjustment signal.

In a sixteenth aspect based on the fourth aspect, the tuning signal reception level variation detector further comprises a Hilbert filter for generating an orthogonal component from the third digital modulation signal, A detector for detecting and correcting an error from the oscillation frequency of the tuner and converting the frequency to a baseband signal, an interpolation filter for converting the baseband signal to symbol rate frequency data based on the system clock frequency data, and a symbol rate frequency data A roll-off filter that extracts low-frequency components at a desired roll-off rate to generate low-frequency symbol rate frequency data, and a waveform equalizer that removes distortion caused by a transmission path from the low-frequency symbol rate frequency data, An error that corrects an error due to the transmission path in the waveform-equalized low-band symbol rate frequency data And righteous, based on the error correction, the third
And an error rate detector for detecting an error rate of the digital demodulated signal, wherein the reception level fluctuation detector detects the reception level fluctuation based on the detected error rate.

According to a seventeenth aspect, in the sixteenth aspect,
The tuning signal reception level fluctuation amount detector further includes an amplitude detector for detecting an amplitude value of the third digital modulation signal, and an average amplitude value obtained by averaging the detected amplitude value using a predetermined averaging coefficient. A first average filter for detecting the error, an error detector for detecting an error between the detected average amplitude value and a desired average value, and loop-filtering the detected error using a predetermined integral term coefficient. It is characterized in that a reception level fluctuation amount is detected by comparing a loop filter that generates a stabilizing signal for stabilizing the automatic gain control amplification processing with a threshold value of a predetermined value of the detected error rate.

According to an eighteenth aspect, in the seventeenth aspect,
The tuning signal reception level fluctuation amount detector generates a level fluctuation amount signal having a value indicating the comparison result, and the gain adjuster adjusts the gain based on the level fluctuation amount signal.

According to a nineteenth aspect, in the eighteenth aspect,
Average filter, an adaptive average filter that adaptively sets the value of the average coefficient based on the value of the level fluctuation signal, and provides high quality by setting the average coefficient to the optimum value according to the detected reception level fluctuation. A digital signal can be demodulated.

According to a twentieth aspect, in the nineteenth aspect,
The average filter includes a first average coefficient and a second average coefficient that is larger than the first average coefficient.
And selecting the second average coefficient when the level fluctuation amount at which the level fluctuation amount signal is detected is not smaller than the threshold value.

According to a twenty-first aspect, in the eighteenth aspect,
The loop filter, based on the value of the level variation signal,
An adaptive averaging filter that adaptively sets a value of an integral term coefficient, and is capable of demodulating a digital signal with high quality by setting an integral term coefficient coefficient to an optimum value according to a detected reception level fluctuation amount. I do.

According to a twenty-second invention, in the twenty-first invention,
The loop filter includes a first integral term coefficient and a second integral term coefficient larger than the first integral term coefficient. And selecting a second integral term coefficient when the level variation amount at which the level variation amount signal is detected is not smaller than the threshold value.

According to a twenty-third aspect, in the seventeenth aspect,
The tuning signal reception level fluctuation amount detector further includes a PWM calculator for converting the stabilized signal into a square wave signal represented by 0 and 1, and a low frequency square wave by extracting a low frequency component from the square wave signal. A low-pass filter that generates a signal, and a gain adjustment signal generator that generates a gain adjustment signal that adjusts the gain of the automatic gain control amplifier based on the low-frequency square wave signal,
The gain adjuster adjusts the gain based on the gain adjustment signal.

In a twenty-fourth aspect based on the second aspect, the reception level fluctuation amount detector extracts a digital modulation signal having a desired frequency from the received digital modulation signal wave and generates a first modulation signal.
And an automatic gain control amplifier for amplifying the first digital modulation signal with a gain to generate a second digital modulation signal having a desired amplitude value, and a second digital modulation An analog-to-digital converter that converts a signal into a digital signal to generate a third digital modulation signal; a tuning signal reception level fluctuation amount detector that detects a reception level fluctuation amount based on a received digital modulation wave amplitude; Wherein the gain adjuster adjusts the gain on the basis of the detected reception level fluctuation amount.

According to a twenty-fifth aspect, in the twenty-fourth aspect,
The tuning signal reception level fluctuation amount detector further includes an amplitude detector for detecting an amplitude value of the third digital modulation signal, and an average amplitude value obtained by averaging the detected amplitude value using a predetermined averaging coefficient. A first average filter for detecting the error, an error detector for detecting an error between the detected average amplitude value and a desired average value, and loop-filtering the detected error using a predetermined integral term coefficient. A loop filter for generating a stabilizing signal for stabilizing the automatic gain control amplification process, wherein the tuning signal reception level fluctuation amount detector detects the reception level fluctuation amount based on the detected stabilization signal. .

According to a twenty-sixth aspect, in the twenty-fifth aspect,
The tuning signal reception level fluctuation amount detector further includes a binary difference detector that detects a difference between any two values of the stabilized signal,
By comparing the value difference with a threshold value of a predetermined value, the reception level fluctuation amount is detected.

According to a twenty-seventh aspect, in the twenty-sixth aspect,
The tuning signal reception level fluctuation amount detector generates a level fluctuation amount signal having a value indicating the comparison result, and the gain controller adjusts the gain based on the level fluctuation amount signal.

According to a twenty-eighth aspect, in the twenty-seventh aspect,
The average filter is an adaptive average filter that adaptively sets the value of the average coefficient based on the value of the level variation signal,
The digital signal can be demodulated with high quality by setting the average coefficient to an optimum value according to the detected reception level fluctuation amount.

According to a twenty-ninth aspect, in the twenty-eighth aspect,
The average filter includes a first average coefficient and a second average coefficient that is larger than the first average coefficient.
And selecting the second average coefficient when the level fluctuation amount at which the level fluctuation amount signal is detected is not smaller than the threshold value.

According to a thirtieth aspect, in the twenty-seventh aspect,
The loop filter, based on the value of the level variation signal,
An adaptive averaging filter that adaptively sets a value of an integral term coefficient, and is capable of demodulating a digital signal with high quality by setting an integral term coefficient coefficient to an optimum value according to a detected reception level fluctuation amount. I do.

According to a thirty-first aspect, in the thirtieth aspect,
The loop filter includes a first integral term coefficient and a second integral term coefficient larger than the first integral term coefficient. And selecting a second integral term coefficient when the level variation amount at which the level variation amount signal is detected is not smaller than the threshold value.

According to a thirty-second aspect, in the twenty-sixth aspect,
The tuning signal reception level fluctuation amount detector further includes a PWM calculator for converting the stabilized signal into a square wave signal represented by 0 and 1, and a low frequency square wave by extracting a low frequency component from the square wave signal. A low-pass filter that generates a signal, and a gain adjustment signal generator that generates a gain adjustment signal that adjusts the gain of the automatic gain control amplifier based on the low-frequency square wave signal,
The gain adjuster adjusts the gain based on the gain adjustment signal.

According to a thirty-third aspect, a first digitally modulated signal is generated by extracting a digitally modulated signal having a desired frequency from a received digitally modulated signal wave propagating in the air, and converting the first digitally modulated signal into a predetermined signal. Automatic gain control amplification with a gain of, a second digital modulation signal having a desired amplitude value is generated, the second digital modulation signal is converted to a digital signal, and a third digital modulation signal is converted to a digital signal. An automatic gain control device for adjusting a gain of a digital demodulation device for demodulation, comprising an amplitude detector for detecting an amplitude value of a third digital modulation signal, and averaging the detected amplitude values by using a predetermined averaging coefficient. First method for detecting average amplitude value by filtering
An average filter, an error detector for detecting an error between the detected average amplitude value and a desired average value, and automatic gain control amplification processing by loop filtering the detected error using a predetermined integral term coefficient. A loop filter that generates a stabilization signal that stabilizes the signal, a reception level fluctuation amount detector that detects a reception level fluctuation amount based on the detected stabilization signal, and an average filter based on the detected reception level fluctuation amount. And an average coefficient adjuster that adaptively sets the value of the average coefficient of the automatic gain control.

According to a thirty-fourth aspect, a digital modulation signal having a desired frequency is extracted from a received digital modulation signal propagating in the air to generate a first digital modulation signal. Automatic gain control amplification with a gain of, a second digital modulation signal having a desired amplitude value is generated, the second digital modulation signal is converted to a digital signal, and a third digital modulation signal is converted to a digital signal. An automatic gain control device for adjusting a gain of a digital demodulation device for demodulation, comprising an amplitude detector for detecting an amplitude value of a third digital modulation signal, and averaging the detected amplitude values by using a predetermined averaging coefficient. First method for detecting average amplitude value by filtering
An average filter, an error detector for detecting an error between the detected average amplitude value and a desired average value, and automatic gain control amplification processing by loop filtering the detected error using a predetermined integral term coefficient. A loop filter that generates a stabilizing signal for stabilizing the signal, a receiving level fluctuation detector that detects a receiving level fluctuation based on the detected stabilizing signal, and a loop filter based on the detected receiving level fluctuation. And an integral term coefficient adjuster that adaptively sets the value of the integral term coefficient.

According to a thirty-fifth aspect, a first digitally modulated signal is generated by extracting a digitally modulated signal having a desired frequency from a received digitally modulated signal wave propagating in the air, and converting the first digitally modulated signal into a predetermined signal. Automatic gain control amplification with a gain of, a second digital modulation signal having a desired amplitude value is generated, the second digital modulation signal is converted to a digital signal, and a third digital modulation signal is converted to a digital signal. An automatic gain control device for adjusting a gain of a digital demodulation device for demodulation, comprising an amplitude detector for detecting an amplitude value of a third digital modulation signal, and averaging the detected amplitude values by using a predetermined averaging coefficient. First method for detecting average amplitude value by filtering
An average filter, an error detector for detecting an error between the detected average amplitude value and a desired average value, and automatic gain control amplification processing by loop filtering the detected error using a predetermined integral term coefficient. A loop filter that generates a stabilizing signal that stabilizes the received signal, a reception level fluctuation amount detector that detects a reception level fluctuation amount based on the amplitude of the received digital modulation signal wave, and a detection amount based on the detected reception level fluctuation amount. And an average coefficient adjuster that adaptively sets the value of the average coefficient of the average filter.

According to a thirty-sixth aspect, a digital modulation signal having a desired frequency is extracted from a received digital modulation signal wave propagating in the air to generate a first digital modulation signal, and the first digital modulation signal is converted to a predetermined digital modulation signal. Automatic gain control amplification with a gain of, a second digital modulation signal having a desired amplitude value is generated, the second digital modulation signal is converted to a digital signal, and a third digital modulation signal is converted to a digital signal. An automatic gain control device for adjusting a gain of a digital demodulation device for demodulation, comprising an amplitude detector for detecting an amplitude value of a third digital modulation signal, and averaging the detected amplitude values by using a predetermined averaging coefficient. First method for detecting average amplitude value by filtering
An average filter, an error detector for detecting an error between the detected average amplitude value and a desired average value, and automatic gain control amplification processing by loop filtering the detected error using a predetermined integral term coefficient. A loop filter that generates a stabilizing signal that stabilizes the received signal, a reception level fluctuation amount detector that detects a reception level fluctuation amount based on the amplitude of the received digital modulation signal wave, and a detection amount based on the detected reception level fluctuation amount. And an integral term coefficient adjuster that adaptively sets the value of the integral term coefficient of the loop filter.

[0077]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS. 1, 2, 3, 4, 5, 6, and 7. FIG.
A digital demodulator according to the embodiment will be described. A digital demodulator according to a second embodiment of the present invention will be described with reference to FIGS. 8, 9, 10, 11, 12, 13, and 14. FIG. FIG. 15, FIG.
Referring to FIG. 17, FIG. 18 and FIG.
A digital demodulator according to the embodiment will be described. A digital demodulation device according to a fourth embodiment of the present invention will be described with reference to FIGS. 20, 21, 22, 23, and 24.

(First Embodiment) FIG. 1 shows a first embodiment of the present invention.
1 shows an example in which a digital device according to an embodiment is configured as a VSB demodulator. The VSB demodulator DSp1 includes an antenna 10, a tuning tuner 11, a down converter 1
2, AGC amplifier 13, AD converter 14, adaptive AGC1
5A, Hilbert filter 16, detector 17, interpolation filter 18, roll-off filter 19, waveform equalizer 100
0, error corrector 1001, and C / N detector 1002
including.

The antenna 10 receives the VSB modulated signal wave Sb transmitted from the broadcasting station over a plurality of channels. The tuning tuner 11 tunes to a specific channel frequency and extracts a VSB modulated signal of a specific channel from the VSB modulated signal waves Sb over a plurality of channels received by the antenna 10. The down converter 12
The tuner 11 is connected to the tuner 11 for tuning.
The frequency of the tuned VSB modulation signal output from is converted to a desired IF frequency.

The AGC amplifier 13 is connected to the down converter 1
2 is a gain control amplifier that adjusts the gain of the IF signal output from 2 to a desired magnitude. AD
The converter 14 converts the analog VSB modulated signal, which has been frequency-converted to the IF frequency output from the AGC amplifier 13 and the gain has been adjusted to a desired magnitude, into a symbol frequency of 2
The signal is converted into a digital signal using the double frequency.

The adaptive AGC 15A is a gain controller, and is a digital VS output from the AD converter 14.
B modulated signal (hereinafter simply referred to as “VSB unless otherwise required”
Modulated signal ". ) The average value of the amplitude of Svsb is calculated, and the reception level fluctuation of the VSB modulation signal Svsb is evaluated to generate a digital signal having a desired amplitude for normal operation as a VSB demodulator. This digital signal is output to the AGC amplifier 13 as a control signal for setting the gain of the AGC amplifier 13 to a desired value.
This control signal is adapted to the reception level fluctuation of the VSB modulation signal Svsb, and in this sense, is called a reception level fluctuation adaptive control signal Sac. As will be described in detail later with reference to FIG. 2, in the present embodiment, the adaptive AGC 15A
Is the VSB modulated signal Sv output from the AD converter 14.
A desired amplitude value is calculated from sb, and the level fluctuation amount of the amplitude of the received digital modulation signal is calculated. When the fluctuation amount is small, the average coefficient of the average filter is reduced, and when the fluctuation amount is large, And an adaptive average filter for increasing the average coefficient of the average filter, and inputs the reception level variation adaptive control signal Sac to the AGC amplifier 13.

The AGC amplifier 13 adjusts the amplitude of the VSB modulated signal Svsb input from the down converter 12 based on the reception level fluctuation adaptive control signal Sac output from the adaptive AGC 15A, and outputs the adjusted signal to the AD converter 14. . Thus, the AGC amplifier 13 and the AD converter 1
4 and a VSB modulated signal S having a desired amplitude by a feedback circuit formed between adaptive AGC 15A.
vsb is obtained. This will be described later in detail with reference to FIG. 2, FIG. 3, FIG. 4, and FIG.

The Hilbert filter 16 is used for the AD converter 1
4 extracts the quadrature component of the VSB modulated signal Svsb output from the VSB 4 and outputs the quadrature component signal to the detector 17. Based on the VSB modulated signal Svsb output from the AD converter 14 and the quadrature component signal output from the Hilbert filter 16, the detector 17 transmits the transmitted VSB modulated signal Svsb and the frequency of the oscillator of the tuning tuner 11. The baseband signal is generated by detecting and correcting the error. The interpolation filter 18 converts the baseband signal output from the detector 17 into symbol rate frequency data based on the device clock frequency data.

The roll-off filter 19 converts the symbol rate frequency data input from the interpolation filter 18 into
A low-frequency region signal is extracted at a desired roll-off rate. The waveform equalizer 1000 performs a waveform equalization process by removing distortion caused by a transmission path from the low frequency region symbol rate frequency signal output from the roll-off filter 19. The error corrector 1001 performs an error correction process on the waveform-equalized low frequency domain symbol rate frequency signal output from the waveform equalizer 1000 to correct an error due to a transmission path,
Demodulate the transport stream. The demodulated transport stream is output to a subsequent MPEG decoder (not shown). The C / N detector 1002
Is connected to the error corrector 1001 and the error corrector 10
The C / N signal Scn is generated by calculating the noise component of the transmission path from the error correction processing by the C.01 and calculating the C / N amount.

Referring to FIG. 2, adaptive AGC 15A will be described. The adaptive AGC 15A includes an amplitude calculator 21, an adaptive average filter 22A, an error detector 23, a loop filter 24, a PWM calculator 25, a low-pass filter 26, an operational amplifier 27, and a level fluctuation amount detector 62A.
As described above, the adaptive AGC 15A calculates the average value of the amplitude using the output signal of the AD converter 14 and receives the digital signal having the desired amplitude for normal operation as a device for input to the AD converter. Level fluctuation adaptive control signal Sa
c, and outputs the reception level fluctuation adaptive control signal Sac to the AGC amplifier 13.

For this purpose, the amplitude calculator 21 uses the above A
The amplitude is obtained by calculating the absolute value of the output value of the VSB modulation signal Svsb input from the D converter 14. Then, the amplitude calculator 21 outputs an amplitude signal representing the obtained amplitude.
The adaptive average filter 22A calculates the average value of the amplitude of the VSB modulation signal Svsb based on the amplitude signal input from the amplitude calculator 21 and the level fluctuation signal Ssw input from the level fluctuation amount detector 62A. The adaptive average amplitude signal S is calculated according to the reception level fluctuation.
aa is output. The error detector 23 calculates the actual average amplitude value of the VSB modulated signal Svsb and V based on the adaptive average amplitude signal Saa input from the adaptive average filter 22A.
An error Ea from a desired average amplitude value for normal operation of the entire SB demodulator is detected, and an average amplitude error signal SEa is detected.
Is output.

The loop filter 24 integrates the detected error Ea based on the average amplitude error signal input from the error detector 23, generates a stabilized signal SSp, and
Stabilize the entire loop of C15A.

The level fluctuation amount detector 62A is based on the stabilization signal SSp output from the loop filter 24,
The reception level fluctuation of the VSB modulation signal Svsb is detected, and a level fluctuation signal Ssw representing the detected reception level fluctuation amount is generated. That is, when the level variation of the signal received by the antenna 10 is large, the variation of the output value of the loop filter 24 is large, and when the level variation is small, the variation of the output value of the loop filter 24 is small. The value of the stabilization signal SSp output from the loop filter 24 is calculated by the level change amount calculator 62A to generate the level change signal Ssw.

The adaptive averaging filter 22A changes the internal averaging coefficient based on the level fluctuation signal Ssw input from the level fluctuation amount detector 62A, thereby obtaining the VSB.
The averaging process according to the reception level fluctuation of the modulation signal Svsb is performed to generate the above-mentioned adaptive average amplitude signal Saa. In this sense, the level fluctuation signal Ssw can also be said to be an average coefficient control signal. The adaptive average filter 22A
Will be described later in detail with reference to FIG.

The PWM calculator 25 includes a loop filter 24
Is converted into a square wave signal Sr in which the ratio of square waves of 0 and 1 indicates error information. The low-pass filter 26 extracts a low-frequency component from the square-wave signal Sr input from the PWM calculator 25 and stabilizes the low-frequency component at a desired level to generate a low-frequency square-wave signal Srl. The operational amplifier 27 amplifies the low-frequency square wave signal Srl input from the low-pass filter 26 to an appropriate value for the AGC amplifier 13 in order to adjust the loop gain of the entire AGC 15, and adjusts the reception level fluctuation adaptive control signal. The signal is input to the AGC amplifier 13 as Sac.

Referring to FIG. 3, adaptive average filter 22A
Will be described. The adaptive average filter 22A includes a multiplier 31a, a multiplier 31b, a delay unit 35, a first small-level variation average coefficient providing unit 71, a first large-level variation average coefficient providing unit 72, a first changeover switch 73, It includes two small-level variation average coefficient assigners 74, a second large-level variation average coefficient assigner 75, and a second switch 76.

First small-level variation average coefficient assigning device 71
Holds the first small-level variation average coefficient KA, which is an average coefficient suitable when the level variation is small, and outputs the first small-level variation average coefficient KA as required. The first level fluctuation average coefficient assigning unit 72 holds a first large level fluctuation amount average coefficient KB which is an average coefficient suitable for a case where the level fluctuation amount is large. Output the quantity average coefficient KB.

The first changeover switch 73 includes an output port of the first small-level variation average coefficient assignment unit 71, an output port of the first large-level variation average coefficient assignment unit 72, and a multiplier 3.
1a and the output port of the level variation detector 62A. Then, based on the level fluctuation signal Ssw input from the level fluctuation amount detector 62A, the first changeover switch 73 switches the first small-level fluctuation average coefficient applying unit 71 or the first large-level fluctuation average coefficient applying unit. One of the output ports 72 is selected and connected to the input port of the multiplier 31a. As a result, the first
Of the small-level variation average coefficient KA or the first large-level variation average coefficient KB indicated by the level variation signal Ssw is input to the multiplier 31a.

The second small-level variation average coefficient assigning unit 74
Holds the value obtained by subtracting the first small-level variation average coefficient KA from 1, that is, “1-KA” as the second small-level variation average coefficient, and stores the second small-level variation amount as required. The average coefficient 1-KA is output. The second large-level variation average coefficient assigning unit 75 calculates the value obtained by subtracting the first first large-level variation average coefficient KB from 1, that is, “1-KB” as the second large-level variation average coefficient 1 -KB, and outputs the second small-level variation average coefficient 1-KB as required.

The second changeover switch 76 includes an output port of the second small-level variation average coefficient assigning unit 74, an output port of the second large-level variation average coefficient adding unit 75, and a multiplier 3.
1b, and an output port of the level fluctuation detector 62A.
Then, based on the level fluctuation signal Ssw input from the level fluctuation amount detector 62A, the output of one of the second small level fluctuation average coefficient applying unit 74 or the second large level fluctuation average coefficient applying unit 75 A port is selected and connected to the input port of the multiplier 31b. As a result, one of the second small-level variation amount average coefficient 1-KA and the second small-level variation amount average coefficient 1-KB, whichever is indicated by the level variation signal Ssw, is input to the multiplier 31a.

In the present embodiment, the amount of fluctuation in the reception level is large (KB, 1-KB) and low (KA, 1-KA).
Therefore, the level fluctuation signal Ssw generated by the level fluctuation amount detector 62A is preferably generated so as to have binary values corresponding to large and low, respectively. Further, as described later, the level fluctuation signal Ssw has a value corresponding to a large level fluctuation as an initial value. Note that the number of discrimination stages of the reception level fluctuation amount may be arbitrarily increased according to the required processing accuracy. For the sake of simplicity of description, the second small-level variation average coefficient 1-KA and the second large-level variation average coefficient 1-KB are each simply referred to as "1-KA" unless otherwise required. And "1-
KB ”.

In the following, regarding the internal processing of the adaptive average filter 22A, the amplitude signal S input from the amplitude calculator 21 will be described.
a will be described as X1 (t), and the adaptive average amplitude signal Saa output from the adaptive average filter 22A will be described as X2 (t).

First, the value of the level fluctuation signal Ssw is smaller than the level fluctuation threshold Lth, that is, the VSB modulation signal Sv
Consider a case where the reception level fluctuation of sb is small. In this case, the first changeover switch 73 selects the first small-level variation average coefficient assigning device 71, and the second changeover switch 76 selects the second small-level variation average coefficient adding device 74. As a result, the first small-level variation average coefficient KA is input to the multiplier 31a, and the second small-level average variation coefficient 1-KA is input to the multiplier 31b.

As a result, in the multiplier 31b, the delay 35
Is multiplied by 1−KA output from the second small-level variation average coefficient assigner 74 to obtain (1−KA) × KA × X2 (t−1). ) Is obtained. This (1-KA) * KA * X2 (t-1) is output to the adder 34. In the adder 34, the multiplier 3
KA × X1 (t) input from the input device 1a and the multiplier 31b
(1−KA) × X2 (t−1) input from the above are added, and KA × X1 (t) + (1−KA) × X2 (t−
1) is obtained. This KA × X1 (t) + (1-KA)
× X2 (t−1) is input to the delay unit 35,
The adaptive average amplitude signal Saa (X
2 (t)).

Next, the value of the level fluctuation signal Ssw is larger than the level fluctuation threshold Lth, that is, the VSB modulation signal Sv
Consider a case where the reception level fluctuation of sb is large. In this case, the first changeover switch 73 selects the first large-level fluctuation average coefficient assigning device 72, and the second changeover switch 76 selects the second large-level fluctuation average coefficient adding device 75. As a result, the multiplier 31a receives the first large-level variation average coefficient KB, and the multiplier 31b receives the second small-level variation average coefficient 1-KB.

The setting method of the threshold value Lth will be described by way of an example. The input VSB modulation signal S
When the level variation of vsb has an amplitude difference (value difference D) of 6 dB, the level variation threshold Lth is set to 10 Hz. The amplitude difference (value difference D) does not need to be 6 dB, and the level variation threshold Lth is 10H according to the amplitude difference (value difference D).
Needless to say, it is set to an appropriate value other than z.

As a result, in the multiplier 31b, the delay 35
Is multiplied by 1−KB input from the second large-level variation average coefficient assigning unit 75 to obtain (1−KB) × X2 (t−1). can get.
This (1−KB) × X2 (t−1) is output to the adder 34. In the adder 34, KB × X1 (t) input from the multiplier 31a and (1−KB) × X2 (t−1) input from the multiplier 31b are added, and KB × X1 (t−1) is added.
X1 (t) + (1−KB) × X2 (t−1) is obtained. This KB × X1 (t) + (1−KB) × X2 (t−
1) is input to the delay unit 35 and the error detector 2
3 is output as an adaptive average amplitude signal Saa (X2 (t)).

A relationship represented by the following equation (4) is established between the above signals. X2 (t) = KA × X1 (t) + (1−KA) × X2 (t−1)] = KB × X1 (t) + (1−KB) × X2 (t−1)] (4)

The above equation (4) represents the relationship between two consecutive control cycles t and t-1. In the present embodiment, the small level variation average coefficient KA and the large level variation average coefficient KB are set to 1/1000 and 1/200, respectively, as an example. When the level variation is small, 1/10
X2 (t) is obtained by multiplying by 00 and adding the result obtained by multiplying the sum by 999/1000. If the level variation is large, multiply by 1/200 and add the product of 199/200 times the integration sum to obtain X
2 (t) is required.

Next, referring to FIG. 4, VSB demodulator DS
The main operation of p1 will be described. VSB demodulator DS
When power is turned on and operation is started, p1
In step # 100, the "analog VSB modulation signal Svsb
The "receive" subroutine is started.

In step # 100, the channel of the received signal to be tuned is selected by the tuning tuner 11 with respect to the VSB modulated signal over a plurality of channels inputted via the antenna 10. An analog VSB modulated signal of the selected channel is received. Then, the "down-convert" subroutine of the next step # 200 is started.

In step # 200, step # 1
The analog VSB modulation signal Svsb obtained at 00 is
The down-converter 12 converts the signal into an IF signal having a desired frequency. Then, the next step # 300
Is started.

In step # 300, step # 2
The IF signal generated in 00 is amplified by the AGC amplifier 13 with a predetermined gain. And the next step #
The "AD conversion" subroutine of 400 is started.

In step # 400, step # 3
The analog VSB modulated signal, which is the IF signal amplified in 00, is converted by the AD converter 14 into a digital VSB modulated signal Svsb. Then, the next step # 50
A subroutine of “gain control based on reception level fluctuation detection based on VSB modulation signal and adaptive average filtering” of 0A is started.

In step # 500A, step #
Based on the reception level fluctuation of the VSB modulation signal Svsb generated in 400, the adaptive AGC 15A generates the reception level fluctuation adaptive control signal Sac, and the above-described step # 30
The gain value of the AGC amplifier 13 at 0 is controlled. That is, in the first step # 300 after the start of the operation of the VSB demodulator DSp1, the AGC amplifier 13 uses a predetermined gain value. After this step, the AGC amplifier 13 uses the gain value controlled by the adaptive AGC 15A. The "Hilbert filtering" subroutine of the next step # 600 starts.

In Step # 600, Step # 4
Based on the VSB modulated signal Svsb generated at 00,
The Hilbert filter 16 generates a quadrature component signal. Then, the "detection" subroutine of the next step # 700 starts.

In step # 700, the detector 17
Is the VSB modulated signal Svs obtained in step # 400.
b is detected with the quadrature component signal obtained in step # 600 to generate a baseband signal. Then, the "waveform processing" subroutine of the next step # 800 starts.

In step # 800, step # 7
00 is output to the interpolation filter 18.
Is converted into symbol rate frequency data. Then, the "roll-off filtering" subroutine of the next step # 900 starts.

In step # 900, step # 8
Based on the symbol rate frequency data obtained in 00, the roll-off filter 19 generates a low frequency region symbol rate frequency signal. Then, the next step # 10
The "interpolation filtering process" subroutine of 00 starts.

In step # 1000, the waveform equalizer 1000 removes distortion caused by the transmission path from the low frequency domain symbol rate frequency signal obtained in step # 900. Then, the "error correction" subroutine of the next step # 1100 starts.

In step # 1100, the error corrector 1001 performs an error correction process on the low frequency domain symbol rate frequency signal subjected to the waveform equalization process in step # 1000 to correct an error due to a transmission path. As a result, the demodulated transport stream is output to an external MPEG decoder. Then, the "C / N detection" subroutine of the next step # 1200 starts.

In step # 1200, step #
Based on the error correction processing of the error corrector 1001 in 1100, the noise component of the transmission path is calculated and the C / N amount is calculated.

As described above, in the VSB demodulation device DSp1, based on the reception level fluctuation of the VSB modulated signal Svsb generated in step # 400, step # 5 is performed.
At 00A, the adaptive AGC 15A controls the gain value of the AGC amplifier 13 in step # 300 by appropriately setting the adaptive average filter 22A. Thus, a high-quality digital signal can be demodulated by amplifying the VSB modulation signal Svsb with an appropriate gain corresponding to the reception fluctuation level.

Next, referring to the flowchart shown in FIG. 5, the above-mentioned "gain control by reception level fluctuation detection based on VSB modulated signal and adaptive loop filtering" subroutine of step # 500A mainly executed by adaptive AGC 15A. Will be described in detail. If the VSB modulated signal Svsb generated in step # 400 is A
From the D converter 14, the amplitude calculator 21 of the adaptive AGC 15A
, The process of step # 500A starts.

First, in step S2, the amplitude calculator 21 calculates the amplitude of the input VSB modulation signal Svsb, generates an amplitude signal Sa, and outputs the signal to the adaptive average filter 22A. Then, the process proceeds to the next step S4A.

In step S4A, the adaptive averaging filter 22A receives the first large-level variation average coefficient KB and the second large-level variation based on the level variation signal Ssw input from the level variation detector 62A. The average coefficient 1-KB is set as an initial value. As described above, the level fluctuation detector 62A outputs the VSB modulated signal Sv
This is because the VSB demodulator DSp1, which does not detect the reception fluctuation level of sb, is set to output a level fluctuation signal Ssw having a value indicating a large level fluctuation at the start of operation.

More specifically, the first changeover switch 73
Selects the first large-level variation average coefficient applicator 72,
The first large-level variation amount average coefficient KB is input to the multiplier 31a. The second changeover switch 76 selects the second large-level variation average coefficient assigning unit 75 and inputs the second large-level variation average coefficient 1-KB to the multiplier 31b. Then, the process proceeds to the next step S6.

In step S6, an averaging process is performed on the basis of the first large-level variation average coefficient KB and the second large-level variation average coefficient 1-KB selected in step S4A, and KB × X1 (T) + (1-KB) ×
X1 (t-1) is obtained, and the adaptive average amplitude signal Sa is obtained.
It is output to the error detector 23 as a. Then, the process proceeds to the next step S8.

After the predetermined time has been measured in step S8, the process proceeds to the next step S10. this is,
Until the value of the adaptive average amplitude signal Saa output from the adaptive average filter 22A becomes stable, processing over a predetermined number n of control cycles t is required, so that the process waits for a period of n × Pt.

In step S10, the error detector 23
Is the adaptive average amplitude signal Sa obtained in step S6.
a (KB × X1 (t) + (1-KB) × X1 (t−
An error Ea is obtained based on 1)). Then, an average amplitude error signal SEa is generated and output to the loop filter 24.

In step S12, the loop filter 24 integrates the average amplitude error signal SEa generated in step S10 to generate an adaptive average amplitude signal Saa, and outputs the same to the level fluctuation detector 62A.

In step S14, the level fluctuation detector 62A acquires the values of two unspecified points of the adaptive average amplitude signal Saa generated in step S.

In step S16, the level fluctuation detector 62A obtains the value difference D of the two points acquired in step S14.

In step S18, the level fluctuation detector 62A determines whether the value difference D obtained in step S16 is larger than a predetermined level fluctuation threshold Lth.
If the determination is Yes, the process proceeds to step S20.

In step S20, the level fluctuation detector 62A generates a level fluctuation signal Ssw indicating that the level fluctuation is large, and outputs it to the adaptive average filter 22A. Then, this subroutine ends.

On the other hand, if No is determined in step S18, the process proceeds to step S22. Then, in step S22, the level fluctuation amount detector 62
A generates a level fluctuation signal Ssw indicating that the level fluctuation is small, and outputs it to the adaptive average filter 22A.
Then, this subroutine ends.

Note that the above steps S20 and S22
Respectively, the level fluctuation amount detector 62A outputs the level fluctuation signal Ss representing the large reception level fluctuation and the small reception level fluctuation.
Generate and output w. As a result, when the process of step S4A is executed again in the next control cycle t, steps S20 and S2 are executed in the previous control cycle t-1.
Based on the level variation signal Ssw generated in step 2, either the large-level variation average coefficient (KB, 1-KB) or the small-level variation average coefficient (KA, 1-KA) is set in the adaptive average filter 22A. Is done.

Note that the above steps S14, S16, S
18, S20 and S22 are the main features of the present invention, the VSB executed by the level variation detector 62A.
This corresponds to a process (step # 550A) of detecting and evaluating the reception level fluctuation of the modulated signal Svsb. Then, in steps S20 and S22, a level fluctuation signal Ssw having any one of two types of values is generated. In this embodiment, the level fluctuation signal Ssw is generated inside the adaptive average filter 22A. This is because two types of average coefficients are prepared. Therefore, the VSB demodulator D
According to the demodulation quality desired in Sp1, three or more types of average coefficients may be used.
Needless to say, the value of sw is diversified accordingly.

Referring to FIG. 6, a first modification of adaptive AGC 15A according to the present embodiment will be described. The adaptive AGC 15A_1 according to this modification includes an amplitude calculator 21, an adaptive average filter 22A, an error detector 23, a loop filter 24, and a P, similarly to the adaptive AGC 15A shown in FIG.
WM calculator 25, low-pass filter 26, operational amplifier 2
7, an adaptive averaging filter 22A and a level variation detector 62A. As described above, in the adaptive AGC 15A, the level fluctuation detector 62A detects and evaluates the reception level fluctuation of the VSB modulated signal Svsb based on the output of the loop filter 24, and evaluates the received level fluctuation.
Set the average coefficient of A.

However, in adaptive AGC 15A_1, level fluctuation detector 62A detects and evaluates the reception level fluctuation of VSB modulated signal Svsb based on low frequency square wave signal Srl output from low-pass filter 26. , The average coefficient of the adaptive average filter 22A is set. Except for this point, the configuration and operation of the adaptive AGC 15A_1 and the adaptive AGC 15A
The operation of the VSB demodulator DSp1 incorporating the GC15A_1 is basically the same as that described in the first embodiment.

Referring to FIG. 7, a second modification of adaptive AGC 15A according to the present embodiment will be described. The adaptive AGC 15A_2 according to the present modification includes an amplitude calculator 21, an adaptive average filter 22A, an error detector 23, a loop filter 24, and a P, similarly to the adaptive AGC 15A shown in FIG.
WM calculator 25, low-pass filter 26, operational amplifier 2
7, an adaptive averaging filter 22A and a level variation detector 62A. As described above, in the adaptive AGC 15A, the level fluctuation amount detector 62A uses the VS voltage based on the stabilization signal SSp output from the loop filter 24.
The reception level fluctuation of the B modulation signal Svsb is detected and evaluated, and the average coefficient of the adaptive average filter 22A is set.

However, in the adaptive AGC 15A_2, the level fluctuation detector 62A is
, Detects and evaluates the reception level fluctuation of the VSB modulation signal Svsb based on the reception level fluctuation adaptive control signal Sac output from the controller, and sets the average coefficient of the adaptive averaging filter 22A. Except for this point, the configuration and operation of the adaptive AGC 15A_2 and the adaptive AGC 15A instead of the adaptive AGC 15A
The operation of the VSB demodulator DSp1 incorporating the GC15A_2 is basically the same as that described in the first embodiment.

(Second Embodiment) FIGS. 8 to 1
4, the VSB according to the second embodiment of the present invention
The demodulation device will be described. As shown in FIG. 8, the VSB demodulator DSp2 according to the present example has the same configuration as the VSB demodulator DSp1 already described with reference to FIG. 1, except that the adaptive AGC 15A is replaced with the adaptive AGC 15B. .

Referring to FIG. 9, adaptive AGC 15B will be described. The adaptive average filter 22A is the average filter 2
2 except that the loop filter 24 is replaced with an adaptive loop filter 24A, and the configuration is the same as that of the adaptive AGC 15A shown in FIG. That is, in the adaptive AGC 15B, unlike the adaptive AGC 15A, the average filter 22 outputs the VSB modulated signal Svsb.
The average signal Sa input from the amplitude calculator 21 is average-filtered with a predetermined average coefficient regardless of the reception level fluctuation to generate Saa.

On the other hand, the adaptive loop filter 24A receives the level fluctuation signal S input from the level fluctuation amount detector 62A.
Based on sw, the integral term coefficient is adaptively changed, and the average amplitude error signal SEa input from the error detector 23 is loop-filtered to generate the adaptive stabilization signal SSa. In this sense, the level fluctuation signal Ssw can also be said to be an integral term coefficient control signal.

Referring to FIG. 10, adaptive loop filter 2
4A will be described. The adaptive loop filter 24A includes:
It includes a multiplier 43, an adder 44, a delay unit 45, a small-level variation integral term coefficient assigner 111, a large level variation integral term coefficient assigner 112, and a changeover switch 103. The small-level variation integral term coefficient adder 111 holds a small-level variation integral term coefficient AA which is an integral term coefficient suitable when the level variation is small, and converts the small-level variation integral term coefficient AA as required. Output. Large-level variation integral term coefficient assigner 1
Numeral 12 holds a large-level variation integral term coefficient AB, which is an integral term coefficient suitable when the level variation is large, and outputs the large-level variation integral term coefficient AB as required.

The changeover switch 103 is connected to the output port of the small-level variation integral term coefficient applicator 111, the output port of the large-level variation integral term coefficient applicator 112, the input port of the multiplier 43, and the level variation detector 62A. Have been. Then, based on the level fluctuation signal Ssw input from the level fluctuation amount detector 62A, the changeover switch 103 outputs one of the output of one of the small level fluctuation integral term coefficient applicator 111 and the large level fluctuation integral term coefficient applicator 112. A port is selected and connected to the input port of the multiplier 43. As a result, either the small-level variation amount integration term coefficient AA or the large-level variation amount integration term coefficient AB, which is indicated by the level variation signal Ssw, is input to the adder 44.

In the following, regarding the internal processing of the adaptive loop filter 24A, the average amplitude error signal SEa input from the error detector 23 is X5 (t), and the stabilized signal SSa output from the adaptive loop filter 24A is X6 ( This will be described as t).

First, the level fluctuation signal Ssw is smaller than the level fluctuation threshold Lth, that is, the VSB modulation signal Svsb.
Let us consider a case in which the reception level fluctuation is small. In this case, the changeover switch 103 selects the small-level variation integral term coefficient applicator 111. As a result, the small-level variation integral term coefficient AA (hereinafter simply referred to as “AA” unless otherwise required) is input to the multiplier 43. The multiplier 43 multiplies X5 (t) input from the error detector 23 by AA input from the changeover switch 103 to obtain AA ×
X5 (t) is output to the adder 44.

As a result, in adder 44, X5 (t-1) output from delay unit 45 and AA × X5 (t) output from multiplier 43 are added, and AA × X5 (t) is added.
+ X5 (t-1) is obtained. This AA × X5 (t) +
X5 (t-1) is input to the delay unit 45 and P5
The stabilization signal SSa (X5
(T)).

Next, the level fluctuation signal Ssw is larger than the level fluctuation threshold Lth, that is, the VSB modulation signal Svsb.
Let us consider a case where the reception level fluctuation is large. In this case, the changeover switch 103 selects the large-level variation integral term coefficient applicator 112. As a result, the large-level variation integral term coefficient AB (hereinafter simply referred to as “AB” unless otherwise required) is input to the multiplier 43. The multiplier 43 multiplies X5 (t) input from the error detector 23 by AB input from the changeover switch 103 to obtain AB ×
X5 (t) is input to the adder 44.

As a result, in adder 44, X5 (t-1) output from delay unit 45 and AB × X5 (t) output from multiplier 43 are added, and AB × X5 (t)
+ X5 (t-1) is obtained. This AB × X5 (t) +
X5 (t-1) is input to the delay unit 45 and P5
The stabilization signal SSa (X5
(T)).

A relationship expressed by the following equation (5) is established between the above signals. X5 (t) = Σ [AA × X1 (t)] = Σ [AB × X1 (t)] (5)

Referring to FIG. 11, V according to the present embodiment
The main operation of the SB demodulator DSp2 will be described. V
The main operation of the SB demodulation device DSp2 is as follows:
500A "gain control by detection of fluctuation in reception level based on VSB modulated signal and adaptive loop filtering"
The operation of the VSB demodulator DSp1 described with reference to FIG. 4 is the same as the operation of the VSB demodulator DSp1 except that the subroutine is replaced with the “gain control by reception level fluctuation detection and adaptive loop filtering based on the VSB modulation signal” subroutine of step # 500B. Is the same.

As a result, in the VSB demodulator DSp2, the VSB modulated signal Sv generated in step # 400
Step # 500B based on the reception level fluctuation of sb
In the adaptive AGC 15B, the adaptive loop filter 24
By appropriately setting the integral term coefficient of A, the gain value of the AGC amplifier 13 in step # 300 is controlled. Thus, a high-quality digital signal can be demodulated by amplifying the VSB modulation signal Svsb with an appropriate gain corresponding to the reception fluctuation level.

Next, referring to the flow chart shown in FIG. 12, the above-mentioned subroutine "gain control by reception level fluctuation detection based on VSB modulated signal and adaptive loop filtering" of step # 500B mainly executed by adaptive AGC 15B. Will be described in detail. As is clear from FIG. 12, in the processing in this subroutine, step S4A and step S6 are performed in step S6.
B, except that step S11 is added between step S10 and step S12.
Is the same as the processing in the subroutine # 500A “Gain Control by Adaptive Loop Filtering Based on Reception Level Fluctuation” shown in FIG.

That is, the V generated in step # 400
The SB modulated signal Svsb is supplied from the AD converter 14 to the adaptive AG
At the time when the data is input to the amplitude calculator 21 of C15B, the process of step # 500B starts. Then, step S2
In, the amplitude calculator 21 calculates the amplitude of the input VSB modulation signal Svsb, generates an amplitude signal Sa, and outputs it to the adaptive average filter 22A. Then, the process proceeds to the next step S6B.

In step S6B, the average filter 2
2 performs an averaging process on the amplitude signal Sa based on a predetermined averaging coefficient. As a result, the obtained average amplitude signal Sav is output to the error detector 23. Then, the processing goes through the above-described step S8, and in S10, the average amplitude error signal S
Ea is output to the loop filter 24. Then, the process proceeds to the next step S11.

In step S11, the adaptive loop filter 24A determines which of the small-level variation integral term coefficient AA or the large-level variation integral term coefficient AB based on the level variation signal Ssw input from the level variation detector 62A. Or set. In the present embodiment, as described above, the level fluctuation signal Ssw is configured to indicate a high reception level fluctuation as an initial value. Therefore, after the operation of the VSB demodulation device DSp2 is started, the step S1 is performed for the first time.
When 1 is executed, the large-level variation integral term coefficient AB is selected. Then, the process proceeds to the next step S12.

In the step S12, the adaptive loop filter 2
4A is the average amplitude error signal S generated in step S10.
Ea is integrated to generate an adaptive average amplitude signal Saa,
Output to the level fluctuation detector 62A. Then, the above steps S14, S16, S18, S20, and S2
2, a process of detecting and evaluating the reception level fluctuation of the VSB modulation signal Svsb executed by the level fluctuation amount detector 62A (step # 550A).

In steps S20 and S22 described above, level fluctuation detector 62A generates and outputs a level fluctuation signal Ssw representing a high reception level fluctuation and a low reception level fluctuation, respectively. As a result, when the processing of step S11 is executed again in the next control cycle t, the small level fluctuation amount is calculated based on the level fluctuation signal Ssw generated in steps S20 and S22 in the previous control cycle t-1. Integral term coefficient AA or large-level variation integral term coefficient A
Either B is set in the adaptive loop filter 24A. The integral term coefficient is adaptively switched according to the reception level of the VSB modulation signal Svsb. However, it is not necessary to particularly limit the level variation to two types, large and small, and it is also possible to set two or more types. This is the same as the average coefficient in the first embodiment.

Referring to FIG. 13, a first modification of adaptive AGC 15B according to the present embodiment will be described. The adaptive AGC 15B_1 according to the present modification includes an amplitude calculator 21, an average filter 22, an error detector 23, an adaptive loop filter 24A, like the adaptive AGC 15B shown in FIG.
It includes a PWM calculator 25, a low-pass filter 26, an operational amplifier 27, and a level fluctuation amount detector 62A. As described above, in the adaptive AGC 15B, the level variation detector 62A uses the VSB modulated signal S based on the adaptive stabilization signal SSa output from the adaptive loop filter 24A.
A variation in the reception level of vsb is detected and evaluated, and the integral term coefficient of the adaptive loop filter 24A is set.

However, in adaptive AGC 15B_1, level fluctuation detector 62A detects and evaluates the reception level fluctuation of VSB modulated signal Svsb based on low frequency square wave signal Srl output from low-pass filter 26. , The integral term coefficient of the adaptive loop filter 24A is set. Except for this point, the configuration and operation of the adaptive AGC 15B_1 and the VSB demodulator DSp2 incorporating the adaptive AGC 15B_1 instead of the adaptive AGC 15B
Is basically the same as that described in the second embodiment.

Referring to FIG. 14, a second modification of adaptive AGC 15B according to the present embodiment will be described. The adaptive AGC 15B_2 according to the present modification includes an amplitude calculator 21, an average filter 22, an error detector 23, an adaptive loop filter 24A, and the like, similarly to the adaptive AGC 15B shown in FIG.
It includes a PWM calculator 25, a low-pass filter 26, an operational amplifier 27, and a level fluctuation amount detector 62A. As described above, in the adaptive AGC 15A, the level fluctuation amount detector 62A
The reception level fluctuation of the VSB modulated signal Svsb is detected and evaluated, and the integral term coefficient of the adaptive loop filter 24A is set.

However, in adaptive AGC 15B_2, level fluctuation detector 62A is connected to operational amplifier 27A.
Of the VSB modulated signal Svsb based on the output of the adaptive loop filter 2
Set the integral term coefficient of 4A. Apart from this point, adaptation A
Configuration, operation, and adaptive AGC 15B of GC15B_2
The operation of the VSB demodulator DSp2 incorporating the adaptive AGC 15B_2 in place of the above is basically the same as that described in the second embodiment.

(Third Embodiment) Hereinafter, a third embodiment of the present invention will be described.
15, FIG. 16, FIG. 17, FIG.
8 and FIG. First, as shown in FIG. 15, the VSB demodulator DSp3 according to the present example includes:
Adaptive AGC 15A is replaced by Adaptive AGC 15C,
Further, except that the adaptive AGC 15C is also connected to the antenna 10, the VSB already described with reference to FIG.
The configuration is the same as that of the demodulation device DSp1.

Referring to FIG. 16, adaptive AGC 15C will be described. The adaptive AGC 15C includes an amplitude calculator 21, an adaptive average filter 22A, an error detector 23, a loop filter 24, and a P, similarly to the adaptive AGC 15A shown in FIG.
It includes a WM calculator 25, a low-pass filter 26, and an operational amplifier 27. However, the level fluctuation detector 62A is replaced by a level fluctuation detector 62C. The level fluctuation detector 62C is basically a level fluctuation detector 6
It is configured similarly to 2A. However, adaptive AGC1
In 5C, the level fluctuation detector 62C is not connected to the loop filter 24, but is connected to the antenna 10. That is, the level fluctuation amount detector 62C detects and evaluates the reception level fluctuation based on the VSB modulated signal wave Sb before tuning input to the tuning tuner 11 instead of the stabilized signal SSa, and evaluates the level fluctuation. A signal Ssw is generated and output to the adaptive average filter 22A. Note that the stabilizing signal SSa is used for the adaptive AGC 15C to function normally.

Referring to FIG. 17, VSB demodulator DSp
3 will be described. VSB demodulator DSp
The main operation in Step # 3 is “VSB” in Step # 500A.
Except that the "gain control by detecting reception level fluctuation based on modulation signal and adaptive loop filtering" subroutine is replaced by the "gain control by detecting antenna reception level fluctuation of VSB modulation signal wave and adaptive average filtering" subroutine in step # 500C. For example, the operation is the same as the operation in the VSB demodulation device DSp1 described with reference to FIG.

Next, with reference to the flowchart shown in FIG. 18, the above-described "gain control by detection of fluctuation in antenna reception level of VSB modulated signal wave and adaptive average filtering" in step # 500C, mainly executed by adaptive AGC 15C. The details of the subroutine will be described.
As is clear from FIG. 18, the processing in this subroutine is different from the “substrate level detection / evaluation evaluation of VSB modulated signal” subroutine of step # 550A including steps S14, S16, S18, S20 and S22 in step S550.
2 are processed in parallel to generate a level fluctuation signal Ssw. Then, processing is performed in the same manner as the processing in step # 500A shown in FIG. 5, except that the average coefficient of the adaptive averaging filter 22A is set in step S4A based on the same level fluctuation signal Ssw.

In the present embodiment, step # 550
FIG. 5A shows the first point shown in FIG. 5 in that the evaluation of the reception level fluctuation and the generation of the level fluctuation signal Ssw are performed based on the reception wave before being received by the antenna and input to the tuning tuner 11. This is different from the case according to the embodiment. That is, in the first embodiment, the digital VSB modulated signal Svsb is a processing target in step # 550A, whereas the third embodiment is different only in that an analog reception wave is a target. The content itself is Step # 5
Same as 50A. That is, in the present embodiment, high-quality digital demodulation can be performed by adaptively changing the average coefficient of the adaptive average filter 22A according to the level fluctuation amount of the VSB modulated signal wave Sb at the antenna 10.

Referring to FIG. 19, a modification of adaptive AGC 15C according to the present embodiment will be described. The adaptive AGC 15C_1 according to this modification is the adaptive AGC 15C_1 shown in FIG.
Similarly to C15B, the amplitude calculator 21, the average filter 2
2. Error detector 23, adaptive loop filter 24A, PW
It includes an M calculator 25, a low-pass filter 26, and an operational amplifier 27. However, the level fluctuation detector 62A is replaced by a level fluctuation detector 62C. The level fluctuation detector 62C is basically configured in the same manner as the level fluctuation detector 62A. However, the level fluctuation amount detector 62A outputs the VS output from the AD converter 14.
While detecting the reception level fluctuation of the B modulation signal, the level fluctuation amount detector 62C detects and evaluates the reception level fluctuation of the VSB modulation signal wave Sb input from the antenna 10, and evaluates the reception level fluctuation of the adaptive loop filter 24A. Set the integral term coefficient.

Except for this point, the configuration and operation of adaptive AGC 15C_1 and VSB demodulator DSp3 incorporating adaptive AGC 15C_1 instead of adaptive AGC 15B.
Is basically the same as that described in the second embodiment.

(Fourth Embodiment) Hereinafter, a fourth embodiment of the present invention will be described.
20, FIG. 21, FIG. 22, FIG.
3 and FIG. First, as shown in FIG. 20, the VSB demodulator DSp4 according to the present example includes:
Adaptive AGC 15C is replaced by Adaptive AGC 15D,
Except that the adaptive AGC 15D is connected to the C / N detector 1002 instead of the antenna 10, the configuration is the same as that of the VSB demodulator DSp3 described with reference to FIG. That is, based on the C / N signal Scn output from the C / N detector 1002, the VSB demodulation device DSp4 detects and evaluates the reception level fluctuation of the VSB modulation signal and controls the gain of the AGC amplifier 13.

Referring to FIG. 21, adaptive AGC 15D will be described. The adaptive AGC 15D includes an amplitude calculator 21, an adaptive average filter 22A, an error detector 23, a loop filter 24, and a P, similarly to the adaptive AGC 15A shown in FIG.
It includes a WM calculator 25, a low-pass filter 26, and an operational amplifier 27. However, the level fluctuation detector 6
2A is replaced by a level variation detector 62D. The level fluctuation detector 62D is not connected to the loop filter 24, but is connected to the C / N detector 1002.
Connected to. That is, the level fluctuation amount detector 62D
Based on the C / N information Scn input from the C / N detector 1002 instead of the stabilization signal SSa, a reception level fluctuation is detected and evaluated to generate a level fluctuation signal Ssw,
Output to the adaptive average filter 22A.

Referring to FIG. 22, VSB demodulator DSp
4 will be described. VSB demodulator DSp
The main operation in step # 4 is “VSB” in step # 500C.
Except for the point that "gain control by detection of fluctuation in antenna reception level of modulated signal wave and adaptive averaging filtering" is replaced by subroutine # 550D "gain control by detection of fluctuation in reception level based on C / N ratio and adaptive averaging filtering". The operation is the same as that in VSB demodulator DSp3 (# 500C) described with reference to FIG.

Next, with reference to the flowchart shown in FIG. 23, the above-described "gain control by reception level fluctuation detection based on C / N ratio and adaptive average filtering" of step # 500D mainly executed by adaptive AGC 15D. The details of the subroutine will be described. As is clear from FIG. 23, the processing in this subroutine is # 55
The “Reception level fluctuation detection and evaluation of VSB modulation signal” subroutine of 0A is replaced by a “Reception level fluctuation detection and evaluation of VSB modulation signal” subroutine based on the C / N of # 550D.

Step # 550D is the same as step S15,
Steps S18D, S20, and S22 are included. In step S15, C input from C / N detector 1002
A CN value is obtained based on the / N signal Scn. Then, in step S18D, the CN acquired in step S15 is compared with a threshold CNth. Then, in steps S20 and S22, processing is performed as described above to generate an average coefficient control signal Ssw.
A is output to A.

In step S4A, except that the average coefficient of the adaptive average filter 22A is set based on the average coefficient control signal Ssw, step # 500D shown in FIG. The processing is the same as the processing in the "gain control by average filtering" subroutine.

As described above, in the VSB demodulator according to the present invention, the received level fluctuation amount of the received VSB modulated signal wave Sb is determined by using the VSB modulated signal wave Sb itself, the digital VSB modulated signal, or the CSB of the VSB modulated signal. / N information is detected based on the / N information, and the internal parameters of the automatic gain control process are adjusted according to the detected reception level fluctuation amount, whereby digital demodulation with high quality can be performed. As an example of the digital demodulator, an example in which the present invention is applied to the VSB demodulator has been described above. However, the present invention
VSB represented by OFDM demodulator and QAM demodulator
It is apparent that the present invention can be similarly applied to a digital demodulator other than the demodulator.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a VSB demodulator according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a detailed configuration of an adaptive AGC of FIG. 1;

FIG. 3 is a block diagram showing a detailed configuration of the adaptive average filter of FIG. 2;

FIG. 4 is a flowchart showing a main operation of the VSB demodulator of FIG. 1;

FIG. 5 is a flowchart showing a detailed operation in step # 500A shown in FIG. 4;

FIG. 6 is a block diagram showing a first modification of the adaptive AGC 15 of FIG. 2;

FIG. 7 is a block diagram showing a second modification of the adaptive AGC 15 of FIG. 2;

FIG. 8 is a block diagram illustrating a VSB demodulator according to a second embodiment of the present invention.

FIG. 9 is a block diagram illustrating a detailed configuration of the adaptive AGC of FIG. 8;

FIG. 10 is a block diagram showing a detailed configuration of an adaptive loop filter 24A of FIG.

FIG. 11 is a flowchart showing a main operation of the VSB demodulator of FIG. 8;

FIG. 12 is a flowchart showing a detailed operation in step # 500B shown in FIG. 11;

FIG. 13 is a block diagram showing a first modification of the adaptive AGC of FIG. 9;

FIG. 14 is a block diagram showing a second modification of the adaptive AGC of FIG. 9;

FIG. 15 is a block diagram showing a VSB demodulator according to a third embodiment of the present invention.

16 is a block diagram showing a detailed configuration of the adaptive AGC of FIG.

FIG. 17 is a flowchart showing a main operation of the VSB demodulator of FIG.

FIG. 18 is a flowchart showing a detailed operation in step # 500C shown in FIG.

FIG. 19 is a block diagram showing a modification of the adaptive AGC of FIG.

FIG. 20 is a block diagram showing a VSB demodulator according to a fourth embodiment of the present invention.

21 is a block diagram illustrating a detailed configuration of the adaptive AGC of FIG.

FIG. 22 is a flowchart showing main operations of the VSB demodulator of FIG.

FIG. 23 is a flowchart showing a detailed operation in step # 500D shown in FIG. 22;

FIG. 24 is a block diagram showing a modification of the adaptive AGC of FIG. 21.

FIG. 25 is a block diagram showing a conventional VSB demodulator.

26 is a block diagram illustrating a detailed configuration of the adaptive AGC of FIG. 25.

FIG. 27 is a block diagram illustrating a detailed configuration of the average filter of FIG. 26;

FIG. 28 is a block diagram showing a detailed configuration of the loop filter of FIG. 26;

FIG. 29 is a block diagram showing a detailed configuration of a PWM calculator 25 in FIG. 26;

FIG. 30 is a flowchart showing main operations of the VSB demodulator of FIG. 25;

[Explanation of symbols]

DSp1, DSp2, DSp3, DSp4, DSc V
SB demodulator 10 Antenna 11 Tuner for tuning 12 Downconverter 13 AGC amplifier 14 AD converter 15 AGC 15A, 15A_1, 15A_2, 15B, 15B_
1, 15B_2, 15C, 15C_1, 15D Adaptation A
GC 16 Hilbert filter 17 Detector 18 Interpolation filter 19 Roll-off filter 1000 Waveform equalizer 1001 Error corrector 1002 C / N detector 21 Amplitude calculator 22 Average filter 22A Adaptive average filter 23 Error detector 24 Loop filter 24A Adaptive loop Filter 25 PWM calculator 26 Low-pass filter 27 Operational amplifier 31 Multiplier 32 First coefficient assigner 33 Second coefficient assigner 34 Adder 35 Delayer 41 Integral term coefficient A 42 Multiplier 43 Adder 44 Delayer 51 With overflow Adder 52 Delay unit 61 Adaptive average filter 62, 62A, 62C, 62D Level variation calculator 71 First small level variation average coefficient assigner 72 First large level variation average coefficient assigner 73 First changeover switch 74 Second small level Variation average coefficient applier 75 second large level variation average coefficient applier 76 second changeover switch 103 over switch

Continued on the front page (72) Inventor Hisaya Kato 1006 Kazuma Kadoma, Osaka Pref. Matsushita Electric Industrial Co., Ltd. Person Hiroaki Ozeki 1006 Kadoma Kadoma, Kadoma-shi, Osaka Matsushita Electric Industrial Co., Ltd. (72) Inventor Kazuya Ueda 1006 Kadoma Kadoma, Kadoma-shi Osaka Pref. LA08 LA10 LA11 QA01 SA02 5K004 AA03 DA15 DC02 DC05 DF04 DG01

Claims (36)

[Claims] 1. A digital demodulator for amplifying a received digitally modulated signal wave propagating in the air with a gain automatically adjusted to have a predetermined amplitude and demodulating the signal into a digital signal. A digital demodulation device comprising: a reception level fluctuation amount detection unit that detects a reception level fluctuation amount of a signal wave; and a gain adjustment unit that adjusts the gain based on the detected reception level fluctuation amount. 2. The digital demodulation device according to claim 1, wherein the reception level fluctuation amount detection unit detects the reception level fluctuation amount based on an amplitude of the received digital signal wave. . 3. The reception level variation detection unit according to claim 1, wherein the reception level variation detection unit detects the reception level variation based on an error rate of the received digital signal wave.
3. The digital demodulator according to claim 1. 4. A tuning means for extracting a digital modulation signal of a desired frequency from the received digital modulation signal wave to generate a first digital modulation signal, wherein the reception level fluctuation detection means comprises: Automatic gain control amplification means for amplifying the digitally modulated signal of the above with the gain to generate a second digitally modulated signal having a desired amplitude value; and converting the second digitally modulated signal into a digital signal to produce a third digitally modulated signal. Analog-to-digital conversion means for generating a digitally modulated signal, and tuning signal reception level fluctuation amount detection means for detecting a reception level fluctuation amount of the first digitally modulated signal based on an amplitude of the third digitally modulated signal. Wherein the gain adjustment means adjusts the gain based on the detected reception level fluctuation amount of the third digital modulation signal. Digital demodulating apparatus according to claim 1. 5. The tuning signal reception level fluctuation amount detection means further comprising: an amplitude detection means for detecting an amplitude value of the third digital modulation signal; and a predetermined averaging coefficient using the detected amplitude value. Average filtering means for performing average filtering to detect an average amplitude value; error detecting means for detecting an error between the detected average amplitude value and a desired average value; and a predetermined integration term for the detected error. Loop filtering means for generating a stabilizing signal for stabilizing the automatic gain control amplification process by loop filtering using a coefficient, wherein the tuning signal reception level fluctuation amount detecting means is configured to generate the stabilizing signal based on the generated stabilizing signal. The digital demodulation device according to claim 4, wherein a reception level fluctuation amount is detected. 6. The tuning signal reception level fluctuation amount detecting means, further comprising: a binary difference detecting means for detecting a difference between any two values of the stabilizing signal; By comparing
The digital demodulator according to claim 5, wherein the reception level variation is detected. 7. The tuning signal reception level fluctuation amount detecting means generates a level fluctuation amount signal having a value indicating the comparison result, and the gain adjusting means adjusts the gain based on the level fluctuation amount signal. The digital demodulation device according to claim 6, wherein the digital demodulation is performed. 8. The average filtering means is an adaptive averaging filter that adaptively sets the value of the averaging coefficient based on the value of the level variation signal, and performs averaging in accordance with the detected reception level variation. 8. The digital demodulation device according to claim 7, wherein the digital signal can be demodulated with high quality by setting the coefficient to an optimum value. 9. The average filtering means includes a first average coefficient and a second average coefficient larger than the first average coefficient, and the level fluctuation amount at which the level fluctuation amount signal is detected is equal to the threshold value. If it is smaller, the first average coefficient is selected, and if the level fluctuation amount at which the level fluctuation amount signal is detected is not smaller than the threshold value, the second average coefficient is selected. The digital demodulator according to claim 8. 10. The loop filtering means is an adaptive loop filter for varying the value of the integral term coefficient based on the value of the level variation signal, and the integral filter is adapted in accordance with the detected received level variation. 8. The digital demodulation device according to claim 7, wherein the digital signal can be demodulated with high quality by setting the coefficient to an optimum value. 11. The level change amount, wherein the loop filtering means includes a first integral term coefficient and a second integral term coefficient larger than the first integral term coefficient, and wherein the level change amount signal is detected. Is smaller than the threshold value, the first integral term coefficient is selected. If the level variation amount at which the level variation amount signal is detected is not smaller than the threshold value, the second integral term coefficient is selected. Characterized by the fact that
The digital demodulation device according to claim 10. 12. The tuning signal reception level fluctuation amount detecting means further comprises: a PWM calculating means for converting the stabilizing signal into a square wave signal represented by 0 and 1, and a low frequency component from the square wave signal. And a low-pass filtering means for generating a low-frequency square wave signal by extracting the received signal.The tuning signal reception level fluctuation amount detection means detects the reception level fluctuation amount based on the low frequency square wave signal. The digital demodulation device according to claim 6, characterized in that: 13. The digital demodulator according to claim 12, wherein said gain adjusting means adjusts said gain based on said low frequency square wave signal. 14. A gain adjusting signal generating means for generating a gain adjusting signal for adjusting the gain of the automatic gain control amplifying means based on the low frequency square wave signal. 13. The tuning signal reception level fluctuation amount detection means detects the reception level fluctuation amount based on the gain adjustment signal.
3. The digital demodulation device according to claim 1. 15. The gain adjustment unit adjusts the gain based on the gain adjustment signal.
The digital demodulation device according to claim 14. 16. The tuning signal reception level variation detection means further includes: a Hilbert filtering means for generating a quadrature component from the third digital modulation signal; a frequency of the third digital modulation signal and an oscillation frequency of the tuning means. A detection means for detecting and correcting an error between the baseband signal and the frequency conversion into a baseband signal; an interpolation filtering means for converting the baseband signal into symbol rate frequency data based on system clock frequency data; Roll-off filtering means for extracting low-frequency components at the roll-off rate to generate low-frequency symbol rate frequency data, and waveform equalizing means for removing distortion caused by a transmission path from the low-frequency symbol rate frequency data, The waveform-equalized low band symbol rate frequency data An error correction means for correcting an error caused by a transmission path; and an error rate detection means for detecting an error rate amount of the third digital demodulated signal based on the error correction. 5. The digital demodulation device according to claim 4, wherein the detection unit detects the reception level fluctuation amount based on the detected error rate. 17. The tuning signal reception level fluctuation amount detecting means, further comprising: an amplitude detecting means for detecting an amplitude value of the third digital modulation signal; and a predetermined averaging coefficient using the detected amplitude value. Average filtering means for performing average filtering to detect an average amplitude value; error detecting means for detecting an error between the detected average amplitude value and a desired average value; and a predetermined integration term for the detected error. A loop filtering means for generating a stabilizing signal for stabilizing the automatic gain control amplification processing by loop filtering using a coefficient, and comparing the detected error rate with a threshold value of a predetermined value, thereby obtaining the reception level fluctuation amount. 17. The digital demodulation device according to claim 16, wherein 18. The tuning signal reception level variation detection means generates a level variation signal having a value indicating the comparison result, and the gain adjustment means adjusts the gain based on the level variation signal. The digital demodulator according to claim 17, wherein the digital demodulation is performed. 19. The average filtering means, which is an adaptive average filter that adaptively sets the value of the average coefficient based on the value of the level variation signal, wherein the average filter is configured to calculate the average coefficient in accordance with the detected reception level variation. 19. The digital demodulation device according to claim 18, wherein a digital signal can be demodulated with high quality by setting to an optimum value. 20. The average filtering means according to claim 1, wherein
And a second average coefficient larger than the first average coefficient, and when the level fluctuation amount at which the level fluctuation amount signal is detected is smaller than the threshold, the first average coefficient is selected. If the level fluctuation amount at which the level fluctuation amount signal is detected is not smaller than the threshold value, the second
20. The digital demodulation device according to claim 19, wherein an averaging coefficient is selected. 21. The loop filtering means is an adaptive averaging filter that varies a value of the integral term coefficient based on a value of the level variation signal, and an integral term according to the detected reception level variation. 19. The digital demodulation device according to claim 18, wherein the digital signal can be demodulated with high quality by setting the coefficient to an optimum value. 22. The loop filtering means, comprising: a first integral term coefficient and a second integral term coefficient larger than the first integral term coefficient, wherein the level variation amount is detected when the level variation amount signal is detected. Is smaller than the threshold value, the first integral term coefficient is selected. If the level variation amount at which the level variation amount signal is detected is not smaller than the threshold value, the second integral term coefficient is selected. Characterized by the fact that
A digital demodulator according to claim 21. 23. The tuning signal reception level fluctuation amount detecting means further includes a PWM calculating means for converting the stabilizing signal into a square wave signal represented by 0 and 1, and a low frequency component from the square wave signal. A low-pass filtering means for extracting a low-frequency square wave signal to extract a low-frequency square wave signal; 18. The digital demodulation apparatus according to claim 17, further comprising: a gain adjustment unit that adjusts the gain based on the gain adjustment signal. 24. The tuning means for extracting a digital modulation signal of a desired frequency from the received digital modulation signal wave to generate a first digital modulation signal, wherein the reception level fluctuation amount detection means comprises: Automatic gain control amplification means for amplifying the digital modulation signal of the above with the gain to generate a second digital modulation signal having a desired amplitude value; and converting the second digital modulation signal into a digital signal to produce a third digital modulation signal. Analog-to-digital conversion means for generating a digitally modulated signal, and tuning signal reception level fluctuation amount detection means for detecting the reception level fluctuation amount based on the received digital modulation wave amplitude, wherein the gain adjustment means The digital demodulator according to claim 2, wherein the gain is adjusted based on the detected reception level fluctuation amount. 25. The tuning signal reception level fluctuation amount detecting means, further comprising: an amplitude detecting means for detecting an amplitude value of the third digital modulation signal; and a predetermined averaging coefficient using the detected amplitude value. Average filtering means for performing average filtering to detect an average amplitude value; error detecting means for detecting an error between the detected average amplitude value and a desired average value; and a predetermined integration term for the detected error. Loop filtering means for generating a stabilizing signal for stabilizing automatic gain control amplification processing by loop filtering using a coefficient, wherein the tuning signal reception level fluctuation amount detecting means is configured to perform 25. The digital demodulation device according to claim 24, wherein a reception level fluctuation amount is detected. 26. The tuning signal reception level fluctuation amount detecting means, further comprising: a binary difference detecting means for detecting a difference between any two values of the stabilizing signal; By comparing
26. The digital demodulator according to claim 25, wherein the amount of change in the reception level is detected. 27. The tuning signal reception level variation detection means generates a level variation signal having a value indicating the comparison result, and the gain adjustment means adjusts the gain based on the level variation signal. The digital demodulation device according to claim 26, wherein the digital demodulation is performed. 28. The average filtering means is an adaptive averaging filter that adaptively sets the value of the averaging coefficient based on the value of the level variation signal, and performs averaging in accordance with the detected reception level variation. 28. The digital demodulation device according to claim 27, wherein a digital signal can be demodulated with high quality by setting a coefficient to an optimum value. 29. The average filtering means, comprising:
And a second average coefficient larger than the first average coefficient, and when the level fluctuation amount at which the level fluctuation amount signal is detected is smaller than the threshold, the first average coefficient is selected. If the level fluctuation amount at which the level fluctuation amount signal is detected is not smaller than the threshold value, the second
29. The digital demodulation device according to claim 28, wherein an average coefficient is selected. 30. The loop filtering means is an adaptive averaging filter that varies the value of the integral term coefficient based on the value of the level variation signal, and integrates the integral term according to the detected received level variation. 28. The digital demodulator according to claim 27, wherein the digital signal can be demodulated with high quality by setting the coefficient coefficient to an optimum value. 31. A level fluctuation amount including a first integral term coefficient and a second integral term coefficient larger than the first integral term coefficient, wherein the level fluctuation amount is detected. Is smaller than the threshold value, the first integral term coefficient is selected. If the level variation amount at which the level variation amount signal is detected is not smaller than the threshold value, the second integral term coefficient is selected. Characterized by the fact that
A digital demodulator according to claim 30. 32. The tuning signal reception level fluctuation amount detecting means further includes: a PWM calculating means for converting the stabilizing signal into a square wave signal represented by 0 and 1, and a low frequency component from the square wave signal. A low-pass filtering means for extracting a low-frequency square wave signal to extract a low-frequency square wave signal; 27. The digital demodulation device according to claim 26, further comprising: the gain adjustment means adjusting the gain based on the gain adjustment signal. 33. A digital modulation signal having a desired frequency is extracted from a received digital modulation signal wave propagating in the air to generate a first digital modulation signal, and the first digital modulation signal is converted with a predetermined gain. Automatic gain control amplification to generate a second digital modulation signal having a desired amplitude value, convert the second digital modulation signal into a digital signal, convert it into a third digital modulation signal, and demodulate the digital signal An automatic gain control device for adjusting a gain of a digital demodulation device, comprising: an amplitude detection unit configured to detect an amplitude value of the third digital modulation signal; and averaging the detected amplitude values using a predetermined averaging coefficient. Average filtering means for filtering to detect an average amplitude value; error detecting means for detecting an error between the detected average amplitude value and a desired average value; Loop filtering means for generating a stabilizing signal for stabilizing the automatic gain control amplification process by loop filtering using a predetermined integral term coefficient, and the received level fluctuation amount based on the detected stabilized signal. An automatic gain control device comprising: a reception level fluctuation amount detection unit to detect; and an average coefficient adjustment unit that adaptively sets a value of an average coefficient of the average filtering unit based on the detected reception level fluctuation amount. 34. A received digitally modulated signal wave propagating in the air, a digitally modulated signal of a desired frequency is extracted to generate a first digitally modulated signal, and the first digitally modulated signal is generated at a predetermined gain. Automatic gain control amplification to generate a second digital modulation signal having a desired amplitude value, convert the second digital modulation signal into a digital signal, convert it into a third digital modulation signal, and demodulate the digital signal An automatic gain control device for adjusting a gain of a digital demodulation device, comprising: an amplitude detection unit configured to detect an amplitude value of the third digital modulation signal; and averaging the detected amplitude values using a predetermined averaging coefficient. Average filtering means for filtering to detect an average amplitude value; error detecting means for detecting an error between the detected average amplitude value and a desired average value; Loop filtering means for generating a stabilizing signal for stabilizing the automatic gain control amplification process by loop filtering using a predetermined integral term coefficient, and the received level fluctuation amount based on the detected stabilized signal. An automatic gain control device comprising: a reception level fluctuation amount detecting unit to detect; and an integral term coefficient adjusting unit that varies a value of an integral term coefficient of the loop filtering unit based on the detected reception level fluctuation amount. 35. A received digitally modulated signal wave propagating in the air, extracting a digitally modulated signal of a desired frequency to generate a first digitally modulated signal, and converting the first digitally modulated signal with a predetermined gain. Automatic gain control amplification to generate a second digital modulation signal having a desired amplitude value, convert the second digital modulation signal into a digital signal, convert it into a third digital modulation signal, and demodulate the digital signal An automatic gain control device for adjusting a gain of a digital demodulation device, comprising: an amplitude detection unit configured to detect an amplitude value of the third digital modulation signal; and averaging the detected amplitude values using a predetermined averaging coefficient. Average filtering means for filtering to detect an average amplitude value; error detecting means for detecting an error between the detected average amplitude value and a desired average value; And based on the amplitude of the loop filtering means and said received digital modulated signal wave for generating a stabilization signal for stabilizing an automatic gain control amplification process loops filtered using a predetermined integral term coefficient,
A reception level fluctuation amount detection unit that detects the reception level fluctuation amount; and an average coefficient adjustment unit that adaptively sets a value of an average coefficient of the average filtering unit based on the detected reception level fluctuation amount. Automatic gain control device. 36. A digital modulation signal having a desired frequency is extracted from a received digital modulation signal wave propagating in the air to generate a first digital modulation signal, and the first digital modulation signal is converted with a predetermined gain. Automatic gain control amplification to generate a second digital modulation signal having a desired amplitude value, convert the second digital modulation signal into a digital signal, convert it into a third digital modulation signal, and demodulate the digital signal An automatic gain control device for adjusting a gain of a digital demodulation device, comprising: an amplitude detection unit configured to detect an amplitude value of the third digital modulation signal; and averaging the detected amplitude values using a predetermined averaging coefficient. Average filtering means for filtering to detect an average amplitude value; error detecting means for detecting an error between the detected average amplitude value and a desired average value; And based on the amplitude of the loop filtering means and said received digital modulated signal wave for generating a stabilization signal for stabilizing an automatic gain control amplification process loops filtered using a predetermined integral term coefficient,
Automatically comprising: a reception level fluctuation amount detecting means for detecting the reception level fluctuation amount; and an integral term coefficient adjusting means for fluctuating a value of an integral term coefficient of the loop filtering means based on the detected reception level fluctuation amount. Gain control device.