JP2003179514A - Correction circuit of intermediate-frequency filter of receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a receiver wherein the configurations for correcting thereby the variations of the characteristic of its IF-filter are provided additionally. <P>SOLUTION: In the receiver, an IF-filter 1 so limits the pass band of an intermediate-frequency signal as to obtain its selective characteristic from spurious and adjacent-channel responses. A limiter 2 so extracts the phase and amplitude components of the intermediate-frequency signal from it as to give by A/D converters 3, 4 the converted digital signals to an orthogonal demodulator 5. The orthogonal demodulator 5 demodulates an I-signal and a Q-signal based on the amplitude and phase components. An amplitude-level sensor 9 senses the amplitude-level of the amplitude component converted into the digital signal by the A/D converter 4. A control portion 10 corrects the amplitude characteristic of the IF-filter 1 by using digital filters 6, 7 in response to the amplitude-level sensed by the amplitude-level sensor 9. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver,
In particular, the present invention relates to a receiver having an IF (intermediate frequency) filter for band limitation in an intermediate frequency circuit.

[0002]

2. Description of the Related Art FIG. 8 is a block diagram showing a configuration from an IF stage to a demodulation section of a conventional receiving device. In FIG.
The IF filter 1 limits the band of the intermediate frequency signal in order to obtain the spurious characteristic and the adjacent channel selection characteristic, and the limiter 2 extracts the phase component and the amplitude component from the intermediate frequency signal.
The phase component and the amplitude component are converted into digital signals by the A / D converters 3 and 4 and given to the quadrature demodulator 5.
The quadrature demodulator 5 demodulates the I signal and the Q signal based on the phase component and the amplitude component. The I signal and the Q signal are supplied to the digital filters 6 and 7, respectively, and the components not band-limited by the IF filter 1 are removed and the demodulator 8
And is demodulated.

Incidentally, depending on the receiving device, the digital filters 6 and 7 may be omitted.

[0004]

In the receiver shown in FIG. 8, since the IF filter 1 is an analog filter, there are variations in filter amplitude characteristics and group delay characteristics. Due to such characteristic variations, there is a problem that the reception performance during demodulation deteriorates. Therefore, a main object of the present invention is to provide an intermediate frequency correction circuit for a receiving device, which has a configuration for correcting variations in the characteristics of the IF filter.

[0005]

SUMMARY OF THE INVENTION The present invention provides an amplitude characteristic detecting means for detecting an amplitude characteristic of an intermediate frequency signal output from an intermediate frequency filter in a receiving device having an intermediate frequency filter for band limiting, Equipped with a digital filter that corrects the amplitude characteristic of the intermediate frequency filter according to the detection output of the amplitude characteristic detection means.The digital filter sweeps an unmodulated wave signal to the input of the receiving device within the band of the intermediate frequency filter, and The amplitude characteristic is set so as to correct the amplitude characteristic.

Further, the digital filter is characterized in that a plurality of filters having different amplitude characteristics are prepared, and a filter suitable for correcting the amplitude characteristics is selected.

Furthermore, the digital filter includes a phase detecting means for detecting the phase characteristic of the intermediate frequency filter, the digital filter is provided with a filter for correcting the phase characteristic according to the detection output of the phase detecting means, and the digital filter is connected to the input of the receiving apparatus. When the unmodulated wave signal is swept within the band of the intermediate frequency filter,
The phase characteristic is set so as to correct the phase characteristic for each frequency.

The digital filter is characterized in that a plurality of filters having different phase characteristics are prepared, and a filter suitable for correcting the phase characteristics is selected.

Further, at least the amplitude level detecting means and the digital filter are constituted by a digital signal processor.

According to another aspect of the present invention, there is provided a receiving device equipped with an intermediate frequency filter for band limiting, comprising: a phase characteristic detecting means for detecting a phase characteristic of an intermediate frequency signal outputted from the intermediate frequency filter; and a phase characteristic detecting means. Equipped with a digital filter that corrects the phase characteristics of the intermediate frequency filter according to the detection output.The digital filter corrects the phase characteristics for each frequency when a non-modulated wave signal is swept to the input of the receiver within the band of the intermediate frequency filter. The phase characteristic is set so that

[0011]

FIG. 1 is a block diagram of an embodiment of the present invention. In FIG. 1, the IF filter 1, the limiter 2, the A / D converters 3 and 4, the quadrature demodulator 5, the digital filters 6 and 7, and the demodulator 8 are configured in the same manner as in FIG. A level detector 9 and a control unit 10 are newly provided.

The amplitude level detector 9 detects the amplitude level converted into a digital signal by the A / D converter 4.
The control unit 10 changes the amplitude characteristic of the IF filter 1 according to the amplitude level detected by the amplitude level detector 9 to IF.
The correction is performed by the digital filters 6 and 7 within the band of the filter.

FIG. 2 is a waveform diagram showing an example of the correction of the amplitude characteristic by the digital filter, and FIG. 3 is a waveform diagram showing another example of the correction of the amplitude characteristic by the digital filter.

2 and 3, (a)
Shows the amplitude characteristic of the IF filter, (b) shows the amplitude characteristic of the digital filter, and (c) shows the waveform of the amplitude characteristic after combination.

It is desirable that the IF filter 1 has a flat amplitude without attenuation in the band and is symmetrical with respect to the center frequency f ₀ , and attenuates sharply outside the band. However, the IF filter 1 has variations in amplitude characteristics,
As shown in FIG. 2A, the amplitude characteristic is not flat and is downward leftward, or as shown in FIG. 3A, some frequency components in the band are attenuated and become asymmetric with respect to the center frequency. It has become. In order to correct this, it is necessary to detect how much attenuation is required.

For this purpose, an unmodulated wave is input to sweep the used band, the amplitude at that time is detected by the amplitude level detector 9, and the control unit 10 determines the IF based on the detection result.
The characteristics of the digital filters 6 and 7 are automatically changed so as to correct the amplitude of the filter 1. In this case, prepare various digital filters with different amplitude characteristics in advance,
A filter having a desired characteristic may be selected from them.

For example, as shown in FIG.
If the amplitude characteristic of the filter is lower left,
As shown in (b), a filter is selected so that the amplitude characteristic of the digital filter is downward-sloping. This allows
When the amplitude characteristic of the IF filter and the amplitude characteristic of the digital filter are combined, the amplitude characteristic in a predetermined band can be flattened and symmetrical with respect to the center frequency f _{0 as shown} in FIG.

If some frequency components within the band are attenuated as shown in FIG. 3 (a), a digital filter whose frequency components are raised as shown in FIG. 3 (b) is selected. It As a result, when the amplitude characteristic of the IF filter and the amplitude characteristic of the digital filter are combined, FIG.
As shown in, the amplitude characteristic in the predetermined band can be made flat and can be made symmetrical with respect to the center frequency f ₀ .

By thus correcting the amplitude characteristic of the IF filter 1 with the digital filters 6 and 7, it is possible to reduce individual variations in the receiving characteristic, and to reduce the cost by loosening the IF specifications.

FIG. 4 is a block diagram showing another embodiment of the present invention. In the embodiment shown in FIG. 1, the amplitude level is detected to correct the variations in the amplitude characteristics of the digital filters 6 and 7. However, in this embodiment, not only the amplitude level but also the phase is detected and the IF filter 1 It is intended to correct variations in phase characteristics. For this purpose, the amplitude level detector 9 is connected to the output of the A / D converter 4, and
The phase detector 11 is connected to the output of the A / D converter 3.
The phase detector 11 detects the phase of the phase signal converted into the digital signal by the A / D converter 3, and the control unit 12 causes the digital filters 6 and 7 to detect the IF signal 1 based on the detection output of the phase detector 11. Correct the phase variation of.

For this reason, in order to detect the amplitude characteristic and the phase characteristic of the IF filter 1, a non-modulated wave is input and swept in the used band, and the amplitude at that time is detected by the amplitude level detector 9
And the phase is detected by the phase detector 11,
Based on the detection result, the characteristics of the digital filters 6 and 7 are automatically changed so as to correct the amplitude and phase of the IF filter 1. In this case, various digital filters having different amplitude characteristics and phase characteristics may be prepared in advance, and a filter having a desired characteristic may be selected from them.

FIG. 5 is a waveform diagram showing an example of the correction of the phase characteristic by the digital filter, and FIG. 6 is a waveform diagram showing another example of the correction of the phase characteristic by the digital filter.

5 and 6, (a) respectively.
Shows the phase characteristic of the IF filter, (b) shows the phase characteristic of the digital filter, and (c) shows the waveform of the combined phase characteristic.

It is desirable that the phase characteristics of the IF filter be constant within the band and decrease outside the band. However, as shown in FIG. 5A, the IF filter has a phase characteristic that is not flat within a predetermined band, and the center frequency f
There are cases where the phase characteristic decreases from the left side to the right side of ₀ , or there are cases where the phase characteristic is wavy as shown in FIG.

In such a case, the digital filters 6 and 7
As shown in FIG. 5 (b), the phase characteristic of is increased from the right side to the left side of the center frequency f ₀ , or the phase characteristic of FIG.
As shown in FIG. 6B, the one having the wavy characteristic is selected, which is the reverse of FIG. By this. If the phase characteristic of the IF filter and the phase characteristic of the digital filter are combined, the result is
(C), it can be corrected to have a flat phase characteristic as shown in FIG. 6 (c).

FIG. 7 is a block diagram showing still another embodiment of the present invention. This embodiment includes a quadrature demodulator 5 shown in FIG. 4, digital filters 6 and 7, a demodulator 8, and
The processing of the amplitude level detector 9, the control units 10 and 12, and the phase detector 11 is performed by a DSP (digital signal processor).
It is realized digitally at 20.

The DSP 20 is a digital filter 6 shown in FIG.
It has a function of correcting the amplitude characteristic and the phase characteristic of the IF filter 1 in the same manner as 7, and when an unmodulated wave is input to sweep the used band, the amplitude at that time is detected and the phase is changed. The amplitude and phase of the IF filter 1 are detected and corrected based on the detection result, and the corrected amplitude characteristic and phase characteristic are automatically changed.

The embodiments disclosed this time are to be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and is intended to include meanings equivalent to the claims and all modifications within the scope.

[0029]

As described above, according to the present invention, the amplitude characteristic of the intermediate frequency signal output from the intermediate frequency filter is detected, and the amplitude characteristic of the intermediate frequency filter is corrected according to the detected output. With the digital filter, when the unmodulated wave signal to the input of the receiving device is swept within the band of the intermediate frequency filter, the amplitude characteristic is set so as to correct the amplitude characteristic for each frequency.
It is possible to suppress variations in reception characteristics.

More preferably, in addition to the correction of the amplitude characteristic, the phase characteristic of the intermediate frequency filter is detected, and when the digital filter sweeps the unmodulated wave signal at the input of the receiving device within the band of the intermediate frequency filter, The phase characteristic is set so as to correct the phase characteristic for each of the above, and by correcting the phase characteristic of the intermediate frequency filter according to the detected output of the phase, it is possible to suppress not only the amplitude characteristic but also the variation of the phase characteristic. it can.

As described above, since the amplitude characteristic or the phase characteristic can be corrected, the specification of the component as the IF filter can be simplified, the circuit can be simplified, and the reception performance can be improved by reducing the component variation. Can be planned.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a waveform diagram showing an example of correction of amplitude characteristics by a digital filter.

FIG. 3 is a waveform diagram showing another example of correction of amplitude characteristics by a digital filter.

FIG. 4 is a block diagram showing another embodiment of the present invention.

FIG. 5 is a waveform diagram showing an example of correction of phase characteristics by a digital filter.

FIG. 6 is a waveform diagram showing another example of the correction of the phase characteristic by the digital filter.

FIG. 7 is a block diagram showing still another embodiment of the present invention.

FIG. 8 is a block diagram showing a configuration from an IF stage to a demodulation unit of a conventional receiving device.

[Explanation of symbols]

1 IF filter, 2 limiter, 3,4 A / D converter, 5 quadrature demodulator, 6,7 digital filter, 8
Demodulator, 9 amplitude level detector, 10, 12 control unit, 1
1 phase detector, 20 DSP.

Claims (6)

[Claims] 1. A receiving device having an intermediate frequency filter for band limitation, comprising: an amplitude characteristic detecting means for detecting an amplitude characteristic of an intermediate frequency signal output from the intermediate frequency filter; and a detecting by the amplitude characteristic detecting means. A digital filter that corrects the amplitude characteristics of the intermediate frequency filter according to the output is provided, and the digital filter sweeps a non-modulated wave signal into the input of the receiving device within the band of the intermediate frequency filter, for each frequency. An intermediate frequency filter correction circuit for a receiver, wherein the amplitude characteristic is set so as to correct the amplitude characteristic. 2. The digital filter is provided with a plurality of filters having different amplitude characteristics, and a filter suitable for correcting the amplitude characteristics is selected. Frequency filter correction circuit of the receiving device of. 3. The phase detecting means for detecting the phase characteristic of the intermediate frequency filter, the digital filter comprises a filter for correcting the phase characteristic according to the detection output of the phase detecting means, and the digital filter is The phase characteristic is set so as to correct the phase characteristic for each frequency when a non-modulated wave signal is swept within the band of the intermediate frequency filter at the input of the receiving device. The intermediate frequency filter correction circuit of the receiver according to 1. 4. The digital filter according to claim 3, wherein a plurality of filters having different phase characteristics are prepared, and a filter suitable for correcting the phase characteristics is selected. Frequency filter correction circuit of the receiving device of. 5. At least the amplitude level detecting means,
The intermediate frequency filter correction circuit according to any one of claims 1 to 4, wherein the digital filter is configured by a digital signal processor. 6. A receiver provided with an intermediate frequency filter for band limiting, a phase characteristic detecting means for detecting a phase characteristic of an intermediate frequency signal output from the intermediate frequency filter, and a detection by the phase characteristic detecting means. A digital filter that corrects the phase characteristics of the intermediate frequency filter according to the output is provided, and the digital filter sweeps a non-modulated wave signal into the input of the receiving device within the band of the intermediate frequency filter, for each frequency. An intermediate frequency filter correction circuit for a receiver, wherein the phase characteristic is set so as to correct the phase characteristic.