JPS62292079A - Automatic waveform equalizer - Google Patents

Abstract

PURPOSE:To use a proper reference waveform signal by providing a reference waveform storage means generating plural signals which have the different timing of a reference waveform sample value in a transversal filter type automatic waveform equalizer. CONSTITUTION:An error signal ei (k) at the time when the respective reference waveform signals from a reference waveform storage means 22 are used is inputted in a decision circuit 23 and the sum of the absolute value of the error signals corresponding to the respective reference waveform signals is found out so as to detect the least value in the respective sums of the absolute values. And a reference waveform memory which issues the least value is decided from reference memories 231-23N. According to the result of the decision, the decision circuit 23 controls a switch 21 and connects the reference waveform memory which issues the least value to a subtracter 15. Thus the proper reference waveform signal can be used.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Object of the Invention] (Industrial Application Field of the Invention) This invention relates to a transversal filter type automatic waveform etc. for correcting waveform distortion of a television signal. Concerning conversion equipment.

(Prior Art) When a television signal is transmitted via cable or radio waves, the signal is distorted due to the influence of the transmission path (e.g., echo, ghost, phase distortion, etc.). In order to correct this distortion, a baseband automatic waveform equalizer using a transversal filter has conventionally been used.

FIG. 8 shows a conventional automatic waveform equalizer. The received television signal is converted into a digital television signal by an analog-to-digital converter 11 via an input terminal 10, and is supplied to a transversal filter 12. The analog-to-digital converter 11 performs digital conversion using a clock having a frequency four times that of the color subcarrier, for example.

Further, the output of the digital-to-analog converter 11 is supplied to a tap gain memory control circuit 16. This tap gain memory control circuit 16 provides a gain control signal to the coefficient multiplier of each tap of the transversal filter 12 to control the filter characteristics of the transversal filter. As a result, the waveform distortion of the output of the transversal filter 12 is corrected, and the output is transferred to the digital-to-analog converter 13.
The signal is input to the input terminal 17, is converted into an analog signal, and is outputted to an output terminal 17 as an analog television signal.

By the way, as shown in FIG. 9, the television signal includes a reference signal ro (t) in the vertical retrace interval, and this reference signal ro (t) has a tap gain of the transversal filter. used for control. That is, the output of the transversal filter 12 is supplied to the subtracter 15. In this subtracter 15, the reference waveform memory 14
The reference waveform signal "i" from
Obtain i(k). The reference waveform signal ri has the same waveform as the reference pulse sent from the transmitting side.

Therefore, obtaining the error signal ei(k) means detecting whether a component that requires correction still remains in the output of the transversal filter 12. error signal e
VB in i(k), where k means the number of reference pulses, and i means the sample number of the signal.

11 Tap gain cl, c2 of transversal filter 12
．． c3...cM are modified each time a reference pulse arrives. This modification is performed so that the error signal et(k) is minimized.

As a correction method at this time, for example, the method shown by the following equation is generally adopted.

C-(K+1)=C-CK)-aΣxt(K)e
(1+j)(K).

Coco j-1, 2,... Wings...
(1) However, α is an appropriate integer, and xi(k) is ro (t
) is the sample value of the input signal.

As described above, by correcting the tap gain so that the error signal between each reference pulse and the reference waveform signal is minimized, the distortion of the video signal is corrected.

(Problems to be Solved by the Invention) One of the problems with the conventional system described above is the sampling timing in the analog-to-digital converter 11 and the timing when reading and using the reference waveform signal from the reference waveform memory 14. This will be raised if there is a deviation.

The normal reference pulse has an impulse-like waveform as shown in FIGS. 9(a) and 9(b). On the other hand, the reference waveform memory 14 stores reference waveform sample values having the same waveform as the reference pulse, and outputs the reference waveform sample values in synchronization with the input of the reference pulse to the subtracter 15.

Now, to make the explanation easier to understand, consider a case where there is no signal distortion and the CMO as the main tap has an initial value of 1. Assuming that the initial values of taps other than CMO are zero, the signal passes only through the CMO taps and is output, so the output yi at that time is y i - x (i - MO) - (2) . In other words, the input signal is delayed by xO (Fig. 9(c)
) It will come as yf. Here, the reference waveform signal ri is
Ideally, the peak value should be read out to match the peak value of the previous signal yi (FIG. 9(d)). In this case, if the two peak values are equal, the error signal ei(K) from the subtracter 15 becomes zero.

However, if the phase of the reference signal yi from the transversal filter is shifted with respect to the reference waveform signal ri, that is, the sampling point is shifted, as in the example of the leaf size Q(e), a maximum of 0. A deviation of 57 (T is the sampling period) occurs. In such a case, the tap gain of the equalizer is formed into a tap gain pattern as shown in FIG. 10(b) for error recognition of this 0.5T timing shift.

The characteristics shown in FIG. 10(b) are the same as those of an interpolation filter that realizes a time shift of 0.5T in a so-called sample value system.

By the way, when the characteristics of the transversal filter having the tap gain shown in FIG. 10(b) are compared with the characteristics in the case of no timing shift, that is, the case of FIG. 10(b), the following can be said.

First, in FIGS. 10(a) and 10(b), the input and output characteristics are basically the same except for the difference in the fixed delay line. However, in terms of actual application, the case shown in FIG. 10(b) has the following problems compared to the case shown in FIG. 10(a).

■Since it is established by a combination of many tap gains, the output signal is more susceptible to the influence of quantization errors.

(2) Since the tap gain that should normally be used to correct distortion components is simply used for timing shifting, the margin for distortion correction becomes small.

■Since a considerable number of taps are required, the hardware increases.

Therefore, in this invention, for an input signal with little distortion, an automatic tap gain pattern is created so that there is no deviation in the sampling point of the peak value between the reference waveform signal and the reference signal, and an ideal tap gain pattern is always formed. The purpose is to provide a waveform equalizer.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a transversal filter to which an analog-to-digital converted input signal is supplied, and a tap gain control circuit for setting the tap gain of the transversal filter. In order to correct the tap gain information stored in this control circuit, the reference signal in the output of the transversal filter and the reference waveform sample value are subtracted to obtain an error signal, and this error signal is The waveform equalizer corrects the tap gain information so as to minimize the tap gain information, and the waveform equalizer includes reference waveform storage means capable of generating a plurality of sample values of the reference waveform signal with different timings; detecting a reference waveform signal in which the sum of absolute values of the error signal or the sum of absolute values of the tap gains is the smallest when each reference waveform signal is used;
This reference waveform signal is used as a reference waveform signal for subsequent use.

(Function) By providing a reference waveform storage means that can generate multiple reference waveform sample values with different timings as described above, an appropriate reference waveform signal can be used, and the transversal filter can be used efficiently. You can get a lot of use out of it.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, in which an analog video signal supplied to an input terminal 11 is converted into a digital video signal by an analog/digital converter 11, and then
The signal is supplied to the transversal filter 12. Waveform equalization is performed in this transversal filter 12,
This output is input to the digital-to-analog converter 13. And the analog converted video signal is output terminal 1.
7.

Further, the output of the transversal filter 12 is transmitted to the subtracter 1
5. The other input terminal of the subtracter 15 is supplied with a reference waveform sample value from the switch 21 . In this subtracter 15 , subtraction processing is performed between the reference pulse yf being output from the transversal filter 12 and the reference waveform signal ri, and the error signal ei(k) is supplied to the tap gain control circuit 16 . The tap gain control circuit 16 corrects the tap gain of the transversal filter 12 so that the error signal is minimized. Here, the present invention includes a reference waveform storage means 22 capable of outputting various waveforms having different sampling positions as reference waveform signals. This reference waveform storage means 22 has, for example, N waveform memories 231 to 23n, and the sampling positions of the reference waveform sample values stored in each waveform memory are stored with the readout timings slightly shifted. There is. Therefore, in the present invention, tap gains are set in each case using reference waveform signals having different sampling positions. Then, the error signal ei (k) when each reference waveform signal is used is input to the determination circuit 23, and the error signal absolute value sum (e i (k), i-1 to i ) is calculated, and the smallest value is detected from each absolute value sum. The reference waveform memory that produced this minimum value is then determined. Based on this determination result, the determination circuit 23:
The switch 21 is controlled to connect the reference waveform memory that has generated the minimum value to the subtracter 15 side.

The sample positions of the reference waveform sample values in each of the reference waveform memories 231 to 23n are shifted as shown in FIG. 2, for example. The position of the circle mark is the sample position, N is the number of reference waveform memories, and T is the sampling period.

In this way, selecting the reference waveform memory that produced the minimum value as the error signal ei(k) means using the reference waveform signal closest to the phase of the reference pulse yi. Therefore, the generation of unnecessary taps in the transversal filter 12 and the tap gain control circuit 16 can be suppressed to a minimum.

The present invention is not limited to the above-described embodiment, but may be configured as shown in FIG. 3.

The embodiment of FIG. 1 utilizes the error signal ei(k) to detect the reference waveform signal closest to the phase of the reference pulse. However, as shown in FIG. 3, the sum of the absolute values of the tap gains accumulated in the tap gain control circuit 16 (the sum of the absolute values of the tap gains of the transversal filter determined by one reference waveform) is determined by another reference waveform signal. The determination circuit 23B may determine whether the tap gain is larger or smaller than the sum of absolute values of the tap gains of the transversal filter. Then, the reference waveform signal that caused the smallest absolute value sum is detected, and the reference waveform memory storing this reference waveform signal is transferred to the switch 21.
It is connected to the subtracter 15 via.

As mentioned above, selecting the reference waveform signal with the smallest sum of absolute values of the tap gains of the transversal filter is to prevent unnecessary tap gain of the transversal filter from occurring and an increase in the number of taps used. Yes, this means that the transversal filter has been effectively used.

In this embodiment, the other parts are the same as those in the embodiment shown in FIG. 1, so the same reference numerals as in FIG. 1 will be given and the explanation will be omitted.

FIG. 4 shows yet another embodiment of the invention. In the case of the above embodiment, a plurality of reference waveform memories are prepared and the contents of each reference waveform memory are read out via a switch, but as shown in FIG. A configuration may also be adopted in which a plurality of different reference waveform signals are stored and read out using address data from the address counter 31. In this embodiment, the determination circuit 23C includes the accumulator 32. It consists of a latch circuit 33 to which this output is supplied, and a comparator 34, and this comparator 34 compares the output of the latch circuit 33 and the output of the accumulator 32. Now, let the output of the latch circuit 33 be 81 and the output of the accumulator 32 be 82, and if the comparison result is Sl>32, increase the upper bit of the address counter 31 by 1, and if 51<52, decrease the upper bit by 1. . Changing the upper bits in this way means selecting another reference waveform signal in the reference waveform memory. Once a reference waveform signal is selected, an error signal is calculated using sample values of this reference waveform signal. In this case, in this example, the reference pulse is
The one held in the output waveform memory 35 is used. That is, the output waveform memory 35 extracts the reference pulse from the output of the transversal filter 12 and holds it. As shown in FIG. 5, from time t-TO, reference pulses for M samples are stored by addressing the output waveform memory 35 by the address counter 37. The address counter 37 is controlled by timing and control signals from a synchronization separation and clock recovery circuit 38 and a control signal generation circuit 39 that constitute the sequence controller 40.

The reference pulse stored in the output waveform memory 35 is once read out at a low speed and input to the peak determination circuit 36. Note that the output waveform memory 35 may cumulatively add the reference signal a plurality of times to attenuate noise in order to improve the S/N ratio of the signal components.

The peak determination circuit 36 determines the sample number MO having the peak value of the reference pulse. When this sample number MO is known, the peak determination circuit 36 uses the address counter 31 .
37, and sets the start position of the address so that the reading timing of the reference pulse and the peak value of the reference waveform signal coincide with each other and are supplied to the subtracter 19. Error signal e resulting from subtraction of each sample value of the reference pulse and reference waveform signal
i is accumulated in the accumulator 32. Next, the address counter 31 counts up or down the upper address in accordance with the output of the comparator 34.

As shown in FIG. 6, the address counter 31 specifies a reference waveform signal (0-N) by its upper address, and specifies the sample number (0-M) of the reference waveform signal by its lower address.
can be specified. The upper address of address counter 31 is changed by comparator 34 as described above, and the lower address is automatically changed by a control signal from control signal generation circuit 39.

As described above, the reference waveform memory 30
The respective reference waveform signals within are compared, and the operating procedure at this time is expressed as shown in FIG. 7, for example.

That is, from steps sll to s13, the initial values of the address counters 31 and 37 are set, and the results of subtraction using each sample value, that is, the error signals are accumulated. The cumulative result is compared with the previous one in comparator 34 (step 514).
Ru. If Sl<32, it is determined in step s15 whether the upper address is N or not, and if it is not N, the process moves to step s16 and the upper address is changed in the direction of increasing. If the upper address is N, as shown in FIG. 6, it has come to the last address, so in step s17, move to the first address of 0, and then set the upper address to 0 and go to step s21. Move. Further, if 81<S2 in step s14, step S
At 1g, it is determined whether the upper address is O or not. If it is not 0, the process goes to step S19, and the address is changed in the direction of decreasing. Also, if the upper address is O, the 6th
As shown in the figure, since the upper address has reached O without being changed in the decreasing direction, the address is changed to the maximum N and the process moves to step s'21.

Step s21 is to determine whether the change of the upper address has been repeated eight times, which means to determine whether all the reference waveforms stored in the reference waveform memory have been compared with the reference pulse. That's true. By setting such a processing procedure, if there is a reference waveform closest to the phase of the reference pulse, each time the reference waveforms before and after this reference waveform in the storage section are processed, Sl<S
2. The determination result of Sl>S2 is repeated, and when the number of repetitions reaches a predetermined number, the system determines the reference waveform to be used.

[Effects of the Invention] As explained above, the present invention automatically selects the reference waveform closest to the phase of the reference signal waveform and uses it as the reference waveform, regardless of the timing of the sample position of the input signal. It can also be used as a signal, and it can suppress the increase in the number of unnecessary core taps due to the timing difference between the two signals.
This can contribute to obtaining higher performance waveform equivalence.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, FIG. 2 is a waveform explanatory diagram showing a detailed explanation of the invention, and FIG. 3 is a circuit diagram showing another embodiment of the invention. 4 is a circuit diagram showing another embodiment of the present invention, FIG. 5 is a signal waveform diagram shown to explain the operation of the embodiment of FIG. 4, and FIG. 6 is a circuit diagram of the address counter of FIG. 4. 7 is a diagram showing the operating procedure of the circuit in FIG. 4, FIG. 8 is a circuit diagram showing a conventional transversal filter, and FIG. 9 is a reference pulse diagram. FIG. 10 is a diagram showing the distribution of tap gain due to differences in reference waveforms. DESCRIPTION OF SYMBOLS 11... Analog-digital converter, 12-) - Lanceversal filter, 13... Digital-analog converter, 15... Subtractor, 16... Tap gain control circuit, 22... Reference waveform Storage means, 23...determination circuit. Applicant's agent Patent attorney Takehiko Suzue CI C2---CMO Figure 10

Claims (2)

[Claims] (1) A transversal filter to which an analog-to-digital converted input signal is supplied, a tap gain control circuit that sets the tap gain of this transversal filter, and the tap gain information stored in this control circuit is corrected. a waveform equalizer that performs subtraction processing using a reference signal and a reference waveform signal in the output of the transversal filter to obtain an error signal, and corrects the tap gain information so that this error signal is minimized. In the case where a reference waveform storage means capable of generating a plurality of sample values of the reference waveform signal with different timings and each reference waveform signal from the reference waveform storage means are used,
Reference waveform determining means for detecting a reference waveform signal in which the sum of absolute values of the error signal or the sum of absolute values of the tap gains is the smallest, and supplying this reference waveform signal to the subtracter as a reference waveform signal to be used thereafter. An automatic waveform equalizer characterized by: (2) The automatic waveform etc. according to claim 1, wherein the reference waveform determining means includes an address counter that controls an address of the reference waveform storage means that stores the plurality of reference waveform signals. Maker.