JPH0380613A - Transmission distortion eliminater - Google Patents

Abstract

PURPOSE:To enable tap coefficient correction which is fast in converging speed, stable, and hardly affected by noise by performing proportional control in the beginning of a tap coefficient and then performing constant-increment control when the number of times of the tap coefficient correction reaches the specific number of times. CONSTITUTION:A tap coefficient correction frequency counting means 15 counts the number of times of tap coefficient correction by a proportional control type correction arithmetic means. A control means 12 obtains a cancellation signal by performing the tap correction by the proportional control type correction arithmetic means in the beginning of the tap correction and then performs the tap correction by a constant- increment control type correction arithmetic means after the counted value of a tap coefficient correction frequency counting means 15, i.e., the number of times of the tap correction under the proportional control reaches the specific value. Thus, the proportional control is employed in the beginning of the tap correction and then switched to the constant-increment control to securely remove transmission distortion without being affected by a noise. Consequently, the fast convergence and high stability of the proportional control and constant-increment control are obtained and while residual distortion is reduced, the convergence time is shortened, so that stable continuous operation becomes possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to a transmission distortion removal device, and particularly to a transmission distortion removal device suitable for ghost removal in television broadcasting.

(Prior Art) Recently, in television broadcasting, GCR (ahost cancel) is used as a reference signal for ghost cancellation.

r reference ) signal (Takayama et al., rGCR
Regarding Signal System Specification Settings”, Television Society Technical Report, ITEJ Technical Report, V
0113.8032. pp19-24June 198
9) has been decided to be inserted into the vertical retrace interval, and a television receiver AM has been developed that utilizes this GCR signal to perform waveform equalization and remove ghosts.

FIG. 3 is a block diagram showing a conventional transmission distortion removal device that performs such ghost removal.

A video signal subjected to ghost interference is input to an input terminal 1. A GCR signal for removing ghosts is inserted into this video signal. The input video signal is sent to an analog/digital converter (hereinafter referred to as A/D converter) 2
The signal is sampled every second per unit time, converted into a digital signal, and applied to the subtracter 3. The subtracter 3 subtracts the digital input video signal and a ghost cancellation signal, which will be described later, to remove the ghost component and outputs the ghost cancellation signal to the output terminal 4, the output waveform memory 5, and the transversal filter 6. Note that the clock CK for the entire system is generated by the timing signal generation circuit 7 based on the input video signal.

The N-tap transversal filter 6 that outputs a ghost cancellation signal includes a delay circuit group 8 consisting of N unit time delay circuits connected in series, a multiplier group 9, an adder 10, and a tap coefficient memory 11. There is. The tap coefficients stored in the tap coefficient memory 11 are applied to each multiplier in the multiplier group 9 to determine the coefficients of each multiplier. Subtractor 3
The output of is sequentially delayed by each delay circuit of delay circuit group 8, and each delayed signal is applied to each multiplier of multiplier group 9 to be given a tap coefficient. The output of each multiplier is added by an adder 10 and output to a subtracter 3. The tap coefficients are corrected every unit time T by the microprocessor 12 performing a predetermined calculation using the ROM 13, RAM 14, and output waveform memory 5. Note that the ROM 13 stores the same reference signal as the GCR signal inserted into the input video signal.

Next, correction of tap coefficients will be explained with reference to the flowchart of FIG. 4 and the timing chart of FIG. 5. 5(a) shows the ghost removed signal @Y・(GCR signal) taken into the output waveform memory 5, FIG. 5(b) shows the difference signal y・, and FIG. 5(C) shows the ROM 13 5(d) shows the error signal e.

The timing signal generation circuit 7 obtains a waveform capture start signal from the input video signal and outputs it to the output waveform memory 5.

First, in step S1 in FIG. 4, the output waveform memory 5 outputs the GCR signal (FIG. 5(a)) inserted into the ghost removal signal from the subtracter 3 at the timing of this waveform acquisition start signal). Note that at this point, the ghost component has not been removed, and the ghost removed signal (GCR
signal) contains a negative proximity ghost and a positive normal delay ghost.

In the next step S2, the microprocessor 12 uses the GCR signal stored in the output waveform memory 5 and the RO
An error signal e. is obtained from the reference signal stored in M13. That is, the microbrosena 12 firstly
By sequentially calculating the difference between the GCR signals before and after the 1-unit spacing shown in equation (1) below, the difference signal y shown in FIG. 5(b) is obtained.
get.

y・-Y, -Y, ...(1)l
1+l 1 Then the following (
By the operation q shown in equation 2), an error signal e shown in FIG. 5(d) is obtained.

”1=yi 'i...(2>However,
``.'' is a sample value of the reference signal in the ROM 13 shown in FIG. 5(C).

Next, in step S3, the error signal ei of equation (2)
Descend the tap coefficient from . Specifically, the microprocessor-2 calculates the tap coefficient C. by the calculation shown in equation (3) below.

C・L/+ 1 = C・ν+αe, ...(3
〉1 1 1 However, α
is a positive correction coefficient, and ν is the number of corrections of the tap coefficient.

By using this tap coefficient C, it is possible to remove a ghost whose delay time is 1 Tsec, that is, when the error signal @e is delayed, it is 1f! The generation timing of the waveform capture start signal is set so that the ghost component is l i T sec. Note that these operations are performed by the microprocessor 2 using the RAM 14.

Next, in step S4, the tap coefficients C and LJ+1 stored in the tap coefficient storage area of the RAM 14 are given to the tap coefficient memory 1. This tap coefficient is applied to each multiplier in the multiplier group 9 to add a coefficient to the delayed signal, which is added in an adder 10 to generate a ghost cancellation signal.

Thereafter, steps S1 to S4 are repeated. Through these steps S1 to S4, a tap coefficient is generated based on the magnitude of the error signal every unit time T, that is, a tap coefficient is generated so that the error signal converges to approximately 0, and the ghost cancellation signal is corrected. to remove ghosts from the input video signal.

Incidentally, the tap coefficient modification shown in equation (3) above is based on proportional control based on the magnitude of the error signal. In proportional control, as described in "Digital Signal Processing" (edited by Haka Miyayo, Institute of Electronics and Communication Engineers, Corona Publishing), the amount of correction is proportional to the magnitude of the error signal e, so the convergence speed is fast. There is an advantage. However, proportional control is easily affected by noise, and there are problems in that coefficients are generated in taps that are unrelated to ghost removal, and the recursive transversal filter 6 may oscillate.

Now, the amount of variation (standard deviation) of the tap coefficient of proportional control is σ
Let P be the noise fluctuation ff1 (standard deviation). Then, “＾Novel＾automatic Ghost C
anceller J (Shinichi Hak
ino and others, IE [E Trans CE-2f3 N
o3. pD629~. σP and σ as described in Aua, 1980). has the relationship shown in the following equation (4).

σp=(α/2)V2・σ, ...(4)
That is, as shown in equation (4), the amount of variation σρ of the tap coefficient of proportional control is the amount of variation σ of the noise. It is directly proportional to , and proportional control is easily affected by noise.

Therefore, the microprocessor-2 may employ constant incremental control based on the polarity of the error signal.

In this case, the microprocessor-2 performs the calculation shown in equation (5) below to obtain the tap coefficient C1.

C, l/+ 1, C, L'+Δ-5on(e,)-
(5) However, Δ is a positive correction coefficient and sgn is a coding function.

Equation (5) indicates "tap coefficient correction by constant incremental control, and in this case, the amount of variation in the tap coefficient σ. and the amount of variation in noise σ. have a relationship shown in the following equation (6).

σ・=0.79・(Δ・σ)l/2 ...(
6) As shown in equation (6) above, in constant incremental control, the tap coefficient fluctuation amount σ is the noise fluctuation amount σ. is proportional to the square root of In this way, in terms of the amount of practical noise, constant incremental control is less affected by noise than proportional control. However, constant incremental control has a slow convergence speed.

(Problems to be Solved by the Invention) As described above, in the conventional transmission distortion removal device described above, when tap coefficient correction by proportional control is adopted,
Although the convergence speed is fast and transmission distortion can be quickly removed, it lacks stability and is strongly affected by noise when the S/N is low. Also, after the tap coefficient converges, due to noise,
There is a problem in that tap coefficients that do not contribute to transmission distortion removal tend to appear, making it difficult to operate stably and continuously.

On the other hand, when tap coefficient correction by constant incremental control is adopted, it is stable and is not easily affected by noise, but there is a problem in that the convergence speed is slow.

The present invention has been made in view of such problems, and includes:
It is an object of the present invention to provide a transmission distortion removal device that can perform tap coefficient correction that is fast in convergence speed, stable, and less susceptible to noise.

[Structure of the Invention] (Means for Solving the Problems) A transmission distortion removal device according to the present invention includes a delay circuit group, a multiplier group, an adder, and a tap coefficient memory with variable tap coefficients, and periodically outputs a reference signal. a transversal filter that introduces a video signal into which is inserted and outputs a cancellation signal for removing transmission distortion included in the video signal; and a transversal filter that modifies the tap coefficient in proportion to the magnitude of the transmission distortion component. proportional control type correction calculation means; constant incremental control type correction calculation means for correcting the tap coefficient based on the polarity of the transmission distortion component; and counting the number of times the tap coefficient is corrected by the proportional control type correction calculation means. A tap coefficient correction number counting means, and when the count value of the tap coefficient correction number counting means reaches a predetermined value, the tap coefficient correction is changed from the tap coefficient correction by the proportional control type correction calculation means to the tap coefficient correction by the constant incremental control type correction calculation means. and control means for causing the transition to occur.

(Operation) In the present invention, the tap coefficient modification number counting means counts the number of times the tap coefficient is modified by the proportional control type modification calculation means. In the initial stage of tap correction, the control means performs tap correction by the proportional control type correction calculation means to obtain a cancellation signal. When the count value of the tap coefficient correction number counting means indicates that the number of tap corrections by proportional control has reached a predetermined value, the control means thereafter performs tap correction by the constant incremental control type correction operation means. By adopting proportional control at the beginning of tap correction, tap coefficient convergence can be made faster.
Thereafter, by switching to constant incremental control, the remaining transmission distortion that was not removed by proportional control is reliably removed without being affected by noise.

(Example) Hereinafter, an example of the present invention will be described in detail based on the drawings. Fig. 1 is a block diagram showing a transmission distortion removal device according to a first example of the present invention. This is applied to ghost removal equipment.

Components in FIG. 1 that are the same as those in FIG. 3 are given the same reference numerals.

A video signal into which an OCR signal has been inserted is input to an input terminal 1. This video signal is applied to a transversal filter 6 via an A/D converter 2 and a subtracter 3, and is also applied to a timing signal generation circuit 7. The timing signal generation circuit 7 uses the clock GK (period T (T is approximately 70 nsec = 1/4 fsc) of the device).
and a waveform capture start signal.

As in FIG. 3, the transversal filter 6 includes a delay circuit group 8' consisting of N unit time delay circuits connected in series, a multiplier group 9, an adder 10, and a tap coefficient memory 1.
1, and outputs a ghost cancellation signal for removing ghost signals.

A ROM 13 that stores a reference signal having the same waveform as the GCR signal inserted into the input video signal, and a working RAM 13 that temporarily stores waveform data obtained by various calculations described later.
14. The configuration of the output waveform memory 5 for temporarily storing the ghost removed signal from the subtracter 3 is the same as the conventional one. In this embodiment, the microprocessor 12 uses these ROMs.
13. In addition to the RAM 14 and the output waveform memory 5, a tap coefficient modification count means 15 is controlled to modify the tap coefficients. The tap coefficient modification number counting means 15 is adapted to count the number of times the tap coefficient is modified. Note that the microprocessor 12 is a RAM
By setting the specified location of RAM 14 to “0”,
can also be used as a tap coefficient modification number counter; in this case, the tap coefficient modification number counting means 1
5 can be omitted.

Next, the operation of the transmission distortion removing device configured as described above will be explained with reference to the flowchart of FIG. 2. Second
The figure shows the tap coefficient modification algorithm.

First, in step S5 of FIG. 2, the output waveform memory 5 receives the ghost removal signal (GC
R signal).

Next, in step S6, by calculating the difference between the GCR signals before and after 11 unit times as shown in equation (7) below,
Obtain the difference signal y.

y・=Y, −Y・ . . . (7) 1+1 Next, the error signal e・ is obtained by performing the calculation shown in the following equation (8>).

ei=yi 'i...〈8)
In the next step S7, it is determined whether the number of times the tap coefficient has been corrected is equal to or greater than a predetermined number of times.

That is, for each tap coefficient correction operation, the tap coefficient B
The count value of the iJE number counting means 15 has been updated, and if this count value has not reached the predetermined number of times, the microprocessor 12 executes the process in step S8.
to move to.

In step S8, a proportional control type tap coefficient correction calculation is performed. That is, the microprocessor 12 executes the following (
9> Calculate the tap coefficient by performing the calculation shown in the formula.

C1ν+1−c, Cαe, ...(9) Above (
8) The tap coefficient determined by the formula is determined in step 31.
0 to the tap coefficient memory 11, and the coefficients of each multiplier in the multiplier group 9 are determined.

Next, the process moves to step S5, and the same process is repeated.

On the other hand, in step S7, if the count value of the tap coefficient correction number counting means 15 indicates that the number of correction operations has exceeded the predetermined number, the microcomputer 12 shifts the process to step S9. , tap correction is performed by constant incremental control.The tap coefficient C in this case is expressed by the following equation <10>.

C,l/+ 1-C,L'-Δ-sgn(e,)・(
10) In this way, in this embodiment, the proportional control type tap coefficient correction, which has a fast convergence speed, is employed only for a short period of time at the beginning of the tap coefficient correction, and it is possible to remove the tap coefficient correction by the proportional control type tap correction. Ghosts that could not be detected are removed by constant incremental control type tap correction, reducing the influence of noise and improving convergence speed.

Next, a second embodiment of the present invention will be described.

This embodiment differs from the embodiment shown in FIG. 1 in that instead of the fixed incremental control correction calculation shown in step S9 in FIG. 2, a constant incremental control correction calculation using leakage is performed. The tap coefficient is expressed by the following equation (11).

C0ν+' = C-'-7-8(Jn (C,'')1
1
1-Δ·Sgn(e,> (11) where γ is a leakage coefficient.

Leakage is determined by the second term on the right side of equation (11) above. In this way, in this embodiment, constant incremental control is used in combination with constant incremental leak, and the leak amount is determined only by the coefficient γ, regardless of the tap coefficient. Therefore, the smaller the tap coefficient, the greater the leakage effect. At the time when the tap coefficients have substantially converged, the tap coefficients of taps related to ghost removal have relatively large values, and the tap coefficient values of taps unrelated to ghost removal have relatively small values. therefore,
The leakage effect is weak for tap coefficients related to ghost removal, and the leakage effect is high for tap coefficients unrelated to ghost removal.This makes it possible to reliably remove residual ghosts and eliminate unnecessary taps due to noise. It can be seen that the coefficient occurs in 021,
Enables stable continuous operation.

Next, a third embodiment of the present invention will be described.

This embodiment is a combination of the above-described second embodiment with a proportional leak. In proportional control type tap coefficient correction, it is common to apply a leak proportional to the magnitude of the tap coefficient. The tap coefficient in this case is as follows (12)
It is shown in the formula.

C, L/+ 1 == C,! /-β, C, l/α・
e, (12) where β is the coefficient of proportional leakage.

In this embodiment as well, as in the first and second embodiments described above, proportional control type tap correction is performed at the initial stage of correction. That is, after repeating the tap coefficient correction based on the above equation (12) a predetermined number of times, the above equation (10) or (y)
11) Switch to the tap coefficient correction shown in equation 11) and perform ghost removal using constant incremental control.

In the case of proportional leakage, the leakage is proportional to the magnitude of the tap coefficient, so if the tap coefficient is adopted at the beginning of correction when the tap coefficient is relatively small, as in this embodiment, the shift will be extremely rightward.

Note that the present invention is not limited to the above embodiments,
For example, although the tap coefficients were obtained using an error calculation method, they may also be obtained using a correlation calculation method or the like.

Furthermore, proportional control and constant incremental leakage may be performed as ()I,
Further, constant incremental control and proportional leakage may be used together, and stability can be improved in either case.

[Effects of the Invention] As explained above, according to the present invention, proportional control is performed at the initial stage of the tap coefficient, and when the number of corrections of the tap coefficient reaches a predetermined number, constant incremental control is performed. As a result, it is possible to obtain high-speed convergence and high stability of proportional control and constant incremental control, reduce residual distortion, shorten convergence time, and enable more stable continuous operation. play.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a transmission distortion removal device according to the present invention, FIG. 2 is a flowchart showing a tap coefficient correction algorithm, and FIG. 3 is a block diagram showing a conventional transmission distortion removal device. FIG. 4 is a flowchart for explaining the operation of the conventional example, and FIG. 5 is a timing chart for explaining the operation of the conventional example. DESCRIPTION OF SYMBOLS 1... Input terminal, 2... A/D converter, 3... Subtractor, 4... Output terminal, 5... Output waveform memory, 6... Transversal filter, 7... - Timing signal generation circuit, 8... Delay circuit group, 9... Multiplier group, 10... Adder, 11... Tap coefficient memory, 12... Microprocessor, 13
...ROM, 14...RAM. 15...Means for counting the number of tap coefficient corrections. Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] A video signal is introduced which is composed of a delay circuit group, a multiplier group, an adder, and a tap coefficient memory with variable tap coefficients, and in which a reference signal is periodically inserted. a transversal filter that outputs a cancellation signal for removing the transmission distortion component; a proportional control correction calculation means that modifies the tap coefficient in proportion to the magnitude of the transmission distortion component; a constant incremental control type correction calculation means for correcting the tap coefficient; a tap coefficient correction number counting means for counting the number of times the tap coefficient is corrected by the proportional control type correction calculation means; and a count value of the tap coefficient correction number counting means is set to a predetermined value. A transmission distortion removing device characterized by comprising: control means for causing a transition from tap coefficient correction by the proportional control type correction calculation means to tap coefficient correction by the constant incremental control type correction calculation means when a value is reached.