JPS59191942A - Turn-on sequence AGC method demodulator - Google Patents

Abstract

PURPOSE:To correct the set error of an AGC for a demodulator which performs the AGC with a training signal by detecting the switching between an AB period (when data A and B are repeated regularly and alternately) and a CD period (when data C and D are repeated at random by a certain produced polynomial) respectively. CONSTITUTION:An input signal is received and demodulated via an AGC circuit 1, a demodulator 2, an LPF3 and an automatic equalizer 4. When a training signal is received, the level of the training signal is detected by a level detector 5. Then a high-speed AGC is applied by an AGC control circuit 6. When the training signal shifts to a CD period from an AB period, an AB/CD switching detector 7 detects this shift. Then a high-speed AGC is applied again by the circuit 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a turn-on sequence AGC type demodulator.

[Background of the invention]

Demodulators with built-in automatic equalizers that perform synchronization using a training signal have conventionally existed. In this demodulator,
A turn-on sequence AGC method is used to correct input level errors of training signals using signal patterns.

In a data demodulator that receives a signal obtained by modulating a training signal and a data signal with a carry signal, and has a built-in waveform equalization function for the received signal, generally before equalizing the waveform of the information data, that is, immediately before the data. Initialization and pull-in are performed so that normal equalization can be performed using the training signal placed in .

FIGS. 1(a) and 1(b) are diagrams explaining initialization using a training signal. FIG. 2 is a block diagram of a conventional turn-on sequence AGC device. FIG. Phase planes are shown, A, C, D.

~-1 indicates data, each of which corresponds to data A, , C, D, -m- in FIG. 1(b).

The training signal is the no-signal period NOXMT.

The period ALT (also referred to as the AB period) in which data A and B in FIG. It is placed immediately before the data DA which is constituted by a scramble data section SCR in which all the data existing on the phase plane are randomly arranged.

Figure 2 shows an AGC circuit 1, a demodulator 2, and a low-pass filter 3.
, automatic equalizer 4, level detector 5. It consists of an AGC control circuit 6. This operation is as follows.

(2) In a state where no data is input, initialize the tap coefficient of the equalizer 4 and set the minimum level signal of the AGC circuit 1 to the gain to be detected.

(2) When the AB period ALT signal "ABAB---" is input, the level detector 5 performs level detection. The AGC control circuit 6 takes this in, changes the gain of the AGC circuit 1 at high speed, and sets the AGC gain according to the detection level. High-speed AGC gain change means that the setting can be completed in about one or two times.

This fast setting of the gain is said to stabilize the input level before the automatic equalizer 4 is adjusted. After that, A
The GC is controlled so that it becomes an AGC circuit with a slow time constant.

(2) When the level is optimal and the training signal shifts from the ALT period to the AE period, the pull-in operation of the equalizer 4 is performed using the aforementioned binary irregularly arranged data group.

(2) Next, the multi-value random data signal of the scrambling period is input to the equalizer 4, and the tap coefficients converged with the binary random data are further updated to perform fine-grained equalization.

According to the above, the training signal is used to complete the acquisition, and thereafter the data is subjected to waveform equalization.

At this time, the AGC circuit becomes an AGC that updates the initial setting level, which was preset at high speed at the beginning of the AL'[' period, with a long time constant.

On the other hand, in systems that transmit and receive data via a modulator/demodulator with a built-in equalizer and perform predetermined information processing, there are Due to the attenuation distortion that occurs, deviations in the received frequency spectrum occur.

Here, a problem with the conventional system is that the total power of the AB double signal for setting the AGC circuit 1 is reduced compared to the data random signal. This is because the signal point arrangement in Figure 1(a) is set in CCITT recommendation V29, and the frequency spectrum of the ALT section is:
Carrier frequency 1700Hz, Poultry) 240
Since it is 0 BA UD, 500Hz, 1700
Hz, and 2900 Hz O-line spectrum. The attenuation distortion of the communication line at this time is the valley link (1 link, 3
As the number of links increases, the spectrum of 500Hz and 2900Hz is attenuated, and the total power decreases.

As mentioned above, due to the decrease in the power of AB,! 11
．． The value of the AB signal high-speed level set will be incorrect.
If the level setting deviates during the adjustment pattern of the automatic equalizer in the CD section, it will interfere with the island pull-in operation. In the worst case, retraction may not be possible.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a turn-on sequence AGc type demodulation device which corrects an AGC setting error with a 1-equalizer adjustment pattern and establishes automatic equalizer pull-in.

[Summary of the Invention] In the present invention, from the ALT period (AB period) to the AE period (C
By detecting the change point in period D) and performing fine-grained high-speed settings of the AGC again before starting adjustment of the automatic equalizer, deterioration of the rise probability due to level error of the automatic equalizer was prevented.

[Embodiments of the invention]

FIG. 4 shows an embodiment of the turn-on sequence AGC device of the present invention. In this embodiment, an AGC circuit 1, a demodulation circuit 2
, low-pass filter (LPF) 3, automatic equalizer 4,
Level setter 5. It consists of an AGC control circuit 6 and an ABCD switching detector 7. Among this element, ABCD switching detector 7
is an element added in this embodiment.

This ABCD switching detector 7 has a function of detecting switching from the AB period to the CD period. This switching detection signal is input to the AGC control circuit 6, and the AGC control circuit 6
Perform necessary AGC control.

The operation at turn-on in FIG. 4 will be explained. If no data is input, the same operation as the conventional example shown in FIG. 2 is performed. Next, when receiving ALT during the AB period, the current level is detected from the level detector 5, and the control port N6 calculates the amount of level fluctuation to set the standard level using the set gain of the AGC, and the level is set at high speed. Settings are made. At this time, other necessary timing and carrier initial settings are made. However, due to line attenuation distortion, etc., the AGC is set assuming that the power is less than the actual power.

Next, when the training signal is shifted from the AB times signal to the CD period, the equalizer is pulled in.

These nine switching points are made by the detection signals detected by the ABCD switching detector 7. That is, the power at this time is remeasured, a reset request signal is output to the AGC control circuit 6, and the CD
Fine-grained, high-speed settings are made at the beginning of the signal.

As a result, the equalizer is set at an optimal level in the lead-in section of the fixture A, resulting in a configuration with good start-up stability.

Note that the switching point between the AB double signal and the CD signal can be detected by simple filtering because the alternate AB signal frequency spectra are different.

〔Effect of the invention〕

According to the present invention, the AGC level setting error due to the influence of attenuation distortion of the line where the input signal exists can be finely absorbed by the signal of the turn-on sequence of the training signal. Therefore, the adjustment of the automatic equalizer can be performed efficiently, and the synchronization establishment is improved.

[Brief explanation of the drawing]

1(a) and 1(b) are explanatory diagrams of the operation of the conventional example, FIG. 2 is a diagram of the conventional example, FIG. 3 is a characteristic diagram thereof, and FIG. 4 is a diagram of an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... AGC circuit, 2... Demodulation circuit, 3... Low pass filter (LPF), 4... Automatic equalizer, 5...
...Level detector, 6...AGC control circuit, 7...
ABCD switching detector. O l Figure (α) O 2 Figure 3 Figure 11a Figure 4

Claims (1)

[Claims] An AGC circuit that receives a signal modulated by a carrier signal by a training signal and a data signal, and a repeating signal between two points in the data point arrangement diagram following the no signal of the training signal that is the output of the AGC circuit. an AGC control circuit that performs gain control, a demodulator that inputs the output of the AGC circuit and performs demodulation, and an automatic equalizer that takes in the output of the demodulator and automatically equalizes the output of the demodulator. means for capturing the output and detecting a switching point υ of a two-point randomly repeated isolator signal following the alternatingly repeated signal;
The detection signal is input to the AGC control circuit and the AGC
Turn-on sequence AGC method % type % equipped with means for controlling the gain of the circuit