JP2843690B2 - Waveform equalization circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention
The present invention relates to a waveform equalizing circuit that removes a proximity ghost generated near a main signal of a video signal as signal distortion and outputs the signal.

[0002]

2. Description of the Related Art A conventional waveform equalizing circuit will be described.
The waveform equalization circuit includes a vertical synchronizing signal of a video signal and a ghost removal reference signal (Ghost Cance Cance) inserted in a vertical blanking period.
l Reference signal: Hereinafter, abbreviated as GCR signal. ) To detect distortions and proximity ghosts caused by transmission lines, etc.
The characteristic of a filter for compensating for this is obtained on the receiver side, and an image signal is passed through the filter to remove waveform distortion (including proximity ghost) and the like.

FIG. 15 shows a block diagram of this conventional waveform equalizing circuit. 15, 51 is a video signal input terminal, 52 is an A / D converter, 59 is a transversal filter, 56 is a D / A converter, 57 is a video signal output terminal,
62 is a difference circuit, 60 is a noise removal circuit, 61 is a waveform memory, 66 is a tap coefficient generation circuit, and 67 is a tap coefficient memory.

First, the overall operation will be described. The signal input from the video input terminal 51 is converted into a digital signal by the A / D converter 52, passes through the transversal filter 59, and is input to the noise removal circuit 60. Here, the GCR signal inserted into the video signal is noise-removed and stored in the waveform memory 61. As will be described in detail later, the GCR signal is inserted into the video signal in the form of an eight-field sequence, that is, a sequence signal covering eight fields.

Next, the signal stored in the waveform memory 61 is converted into a pulse signal by obtaining a difference signal (the GCR signal has a step waveform, so that a difference of one sample is obtained. Therefore, the difference signal is a pulse waveform). Is input to the tap coefficient generation circuit 66. The tap coefficient generation circuit 66 compares the difference signal with a reference waveform stored in advance, detects an error (distortion), and calculates a tap coefficient of the transversal filter 59 so as to remove the distortion of the input signal. Then, it is stored in the tap coefficient memory 67. The tap coefficients are output to the transversal filter 59 and written to the transversal filter 59.

Here, a description will be given of a tap coefficient control algorithm for changing the characteristics of the transversal filter 59 so as to remove the distortion of the input signal. As this algorithm, Zero Forcing method (hereinafter abbreviated as ZF method), Mean Square Err
Although the or method (MSE method) and the like are generally known, the ZF method will be described here.

Now, when the tap coefficient of the n-th tap among a plurality of taps in the transversal filter is Cn, the output Yn with respect to the input Xn of the transversal filter is obtained.
Is represented by Yn = ΣCi · Xi (1) If the reference signal held in advance is Rn, the error (distortion) En between the output signal and the reference signal becomes En = Yn-Rn (2). From the m-th tap coefficient Cn (m) to the (m + 1) -th tap coefficient Cn in the tap coefficient correction operation
(M + 1) is obtained by Cn (m + 1) = Cn (m) −α · En (m) (3) (Α is a correction coefficient, α <1) The tap coefficient converges to the optimum value by performing the processing sequentially and repeating the correction operation as described above. (Reference: Ghost canceller by adaptive ZF method Takaguchi et al. 1989 National Convention of the Institute of Television Engineers of Japan, p247-)

As described above, usually, the tap coefficient is not determined by one calculation (correction operation), but the final tap coefficient is determined by repeating the calculation several times. Therefore, since the tap coefficients are all 0 at the time of the first tap coefficient calculation, the output of the transversal filter is output as it is, input to the noise removal circuit 60, and stored in the waveform memory 61.

In the second tap coefficient calculation, the characteristics of the transversal filter are based on the tap coefficients given by the first tap coefficient calculation, and the output of the transversal filter is the first output coefficient. This is a signal with less distortion than that of the signal. This signal is input to the noise removal circuit 60 and stored in the waveform memory 61. The second tap coefficient calculation is performed using this signal. Thereafter, tap coefficients are calculated in the same manner to obtain final characteristics.

The signal input to the transversal filter having the final characteristics is output as a signal from which distortion has been removed (a signal from which a nearby ghost has been removed), and is converted into an analog signal by the D / A converter 56. , AGC (automatic gain control circuit) 76 and output from a video output terminal 57.

Here, the noise removing circuit 60 will be described. The noise elimination circuit is a circuit that reduces noise by canceling random noise by performing synchronous addition. The noise elimination circuit includes a so-called cyclic noise elimination circuit and a non-cyclic noise elimination circuit.

FIG. 16 is a block diagram showing a cyclic noise elimination circuit. In the figure, 15 is an input terminal, 16 and 1
7 is a multiplication circuit, 18 is an adder, and 19 is an output terminal.
This noise elimination circuit is called a cyclic noise elimination circuit. The noise elimination circuit divides a signal input from an input terminal 15 by a multiplier 1.
6 and a waveform memory 61 (k <1).
Are multiplied by (1-k) by the multiplier 17 and added by the adder 18 and stored in the waveform memory 61. This makes it possible to remove noise that is randomly input.

As described above, the recursive noise elimination circuit multiplies the input signal by k times (k <1) by the multiplier, and multiplies the signal stored in the memory by (1-k). This is a circuit that removes noise by repeating addition of the multiplied value by an adder and storage in a memory. On the other hand, the non-recursive noise elimination circuit is a circuit that adds an input signal n times and finally divides the signal by n to eliminate noise. The greater the number of additions in both circuits, the greater the effect of noise removal. However, as a matter of course, it takes time as the number of times increases.

As described above, it takes a long time to sufficiently remove noise. However, since the current GCR signal is an 8-field sequence signal described below, it takes more time to remove the noise.

Next, an 8-field sequence will be described. The eight-field sequence is a signal format designed to be able to correctly detect distortion without being affected by a large delay time distortion (distant ghost). FIG. 17 shows a GCR signal waveform expressed in an 8-field sequence format. As shown, 8
For each field in the field, sin
It can be understood that the (X) / X bar signal and the pedestal level signal are alternately inserted, and the order of the sin (X) / X bar signal and the pedestal level signal is reversed every four fields. Would. In order to eliminate the influence of the signal of the previous line, the horizontal synchronizing signal, and the color burst signal from this signal, it is necessary to remove them by using the fact that the phase of the color burst signal is inverted every frame. .

This is accomplished by taking the sum of the first and third fields and taking the difference between this and the sum of the second and fourth fields, and similarly in the fifth, sixth, seventh and seventh fields. By calculating eight fields, the signals before and after are canceled, and a signal of only the sin (X) / X bar signal is obtained. However, this requires a memory for eight fields, and furthermore, it is necessary to know what field the stored signal is. If this is incorrect, the phase of the detected GCR signal is inverted. Problems arise.

.., S
8, and the detected GCR signal is S (GCR). S (GCR) = ((S1 + S3)-(S2 + S4)-(S5 + S7) + (S6 + S8)) / 4 (4) Therefore, even if there is a long-range ghost, in order to obtain a correct GCR signal once without being affected by the ghost, 8
Requires a sequence across fields. Therefore,
Japanese Patent Application Laid-Open No. 1-284179 discloses a technique in which a fetched GCR signal is stored in a memory and used in order to reduce the time required for the noise removal circuit.

FIG. 18 is a block diagram showing details of the tap coefficient generation circuit 66. In the figure, 20 is an input terminal, 21 is a reference waveform memory, 22 and 24 are adders, 23
Is a multiplier, 67 is a tap coefficient memory, 26 is an output terminal,
27 is a distortion (error) detection circuit. Reference waveform memory 21
In advance, a signal waveform obtained by calculating the difference between GCR signals without distortion is stored as a reference waveform.

The adder 22 takes the difference between the output signal of the reference waveform memory 21 and the signal stored in the waveform memory 12 to detect distortion. The detected distortion is multiplied by α (α <1) in the multiplier 23 and stored in the tap coefficient memory 67 through the adder 24. The signal stored in the tap coefficient memory 67 is input to the transversal filter through the output terminal 26. The distortion detection circuit 27 is a circuit that controls so that the tap coefficient memory 67 is not rewritten when the distortion becomes a certain level or less.

FIG. 19 shows a transversal filter 59.
FIG. 4 is a block diagram showing the details of. In the figure, 28 is a one-clock delay circuit, 29 is a multiplier for multiplying a given tap coefficient, 30 is an adder, 31 is a delay circuit, 32 is an input terminal, and 33 is an output terminal. Tap coefficients C1, C2, C3,..., Cn stored in the tap coefficient memory 67.
Each of the signals is supplied to the corresponding multiplier 29 as a coefficient of multiplication, and the signal input from the input terminal 32 is the signal delayed by the one-clock delay circuit 28 as C1, C
2, C3,..., Cn times. These signals are added to adder 30
Create a signal that cancels the distortion of the input signal by adding
By adding the signal delayed by the delay circuit 31, a signal from which distortion has been removed is output from the output terminal 33. A document describing such a conventional circuit example is disclosed in JP-A-1-1378.
No. 85 can be mentioned.

[0021]

The noise superimposed on the GCR signal of the input signal stored in the waveform memory is regarded as a distortion. The S / N ratio must be improved beforehand. Here, in order to improve the S / N ratio, it is necessary to increase the number of additions in the noise elimination circuit. But,
The GCR signal is inserted during the vertical retrace interval, and
Since it is inserted in a field sequence format, it takes eight fields for one addition, and it takes several to several tens of fields to obtain a GCR signal from which noise has been removed.

In a conventional circuit, the GCR signal is taken into the waveform memory every time the tap coefficient is calculated.
That is, the signal is passed through the transversal filter to which the tap coefficient is given, the noise removal circuit is operated on the output signal, the GCR signal is fetched into the waveform memory, and the tap coefficient is calculated using this signal. In order to obtain the final tap coefficient, the noise elimination circuit had to be operated many times, which was very time-consuming.

An object of the present invention is to provide a waveform equalizing circuit capable of shortening the time until the tap coefficient of the transversal filter becomes optimal.

Therefore, even if this point is solved by shortening the time required for noise removal using the stored GCR signal by using a memory, the tap coefficient correction operation is repeated, and as a result, the residual error is reduced. If the operation of correcting the tap coefficient is stopped when the (residual distortion) falls within the allowable range, the following problem arises.

First, if the allowable value of the residual error is set to a small value, it is easy to shift to a mode in which correction is performed again due to a change in an input signal, even if the allowable value of the residual error is once less than the allowable value level. There is a problem that the tap coefficient is corrected after returning to the screen where there is, and switching of the screen is worrisome.

Further, when the allowable value level of the residual error is set large, there is a problem that the residual error is large and the distortion cannot be completely removed. If the error is just outside the allowable range, there is still a problem that the residual error is large and the mode is likely to be corrected immediately.

Further, since the GCR signal is once fetched into the waveform memory, then fetched and input to the transversal filter, the input of the transversal filter is limited in the number of bits. That is, even if the waveform memory obtains a bit precision of about 16 bits, when the input of the transversal filter is 8 bits, there is a problem that the distortion detection precision is reduced and the equalization capability is reduced. Further, there is a problem that a memory is required for eight fields in order to perform the eight-field sequence processing, and the circuit scale becomes large.

Further, since the input video signal in the analog signal format is converted into a digital signal for signal processing, A /
Depending on the phase of the sampling clock in the D converter,
In some cases, the phase of the acquired signal in the waveform memory is different from the phase of the reference waveform prepared in advance. Then, even if there is no distortion, there is a problem in that there is a case where an error due to the phase difference is regarded as distortion and equalization is performed, so that a tap coefficient which degrades image quality is calculated.

Further, since the distortion is detected by using the difference signal of the acquired signal waveform, there is a problem that the signal amplitude becomes small and the sensitivity of detecting the distortion becomes low. Further, once the tap coefficient is obtained, the distortion becomes large. For example, when the tap needs to be corrected again, the screen becomes an image with an initial large distortion, and sometimes shakes greatly.

As described above, another object of the present invention is to reduce the time required until the tap coefficients of the transversal filter become optimal and to generate a waveform or the like capable of generating tap coefficients that minimize distortion. To provide a conversion circuit.

Another object of the present invention is to provide a waveform equalizing circuit capable of performing an 8-field sequence process with a smaller memory and reducing a required circuit scale. It is another object of the present invention to provide a waveform equalizing circuit capable of aligning the phase of an input GCR signal with the phase of an internal reference waveform, suppressing the generation of unnecessary tap coefficients, and effectively using taps. It is still another object of the present invention to provide a waveform equalization circuit capable of improving distortion detection sensitivity and improving equalization performance.

[0032]

In order to achieve the first object, the input signal of the transversal filter is switched by a switch, and the output signal of the A / D converter is used at the time of capturing the waveform at the time of the first tap coefficient calculation. During the second and subsequent tap coefficient calculations, waveform acquisition is not performed, and the output signal of the first captured waveform memory is input.Furthermore, the output signal of the transversal filter is output without passing through the waveform memory. Direct input to the tap coefficient generator.

In order to achieve the another object, the input signal of the transversal filter is switched, and further, as means for controlling a switch for switching the input signal,
The number of times or time until the correction of the tap coefficient sufficiently converges is used. Further, after the tap coefficient is obtained by the above-mentioned means, in order to eliminate the influence of rounding, a fixed number of times or a fixed time correction is performed regardless of the presence or absence of residual distortion.

The calculation of the 8-field sequence is simplified by detecting the presence or absence of the GCR signal. Further, the phase of the sampling clock is detected from the signal stored in the waveform memory, and the output of the clock generation circuit is controlled to match the phase of the internal reference waveform.

Further, the phase of the sampling clock is detected from the signal stored in the waveform memory, and a reference waveform having a phase corresponding to this phase is used for comparison. Further, a signal having a characteristic that makes it hard to be affected by distortion for the detection of the phase of the reference waveform and that has a characteristic of high distortion detection sensitivity is used for calculating the tap coefficient.

Further, once the tap coefficients are obtained, the tap coefficients are corrected so that the initial image is not shown. Further, a delay circuit equal to the delay time of the transversal filter is provided so that the screen does not fluctuate when the switch is switched.

[0037]

The GCR signal initially stored in the waveform memory is
Since the signal passes through the transversal filter in which zero is written as the tap coefficient, it is the same signal as the input signal whose S / N ratio is improved by the noise removal circuit. Therefore, if this signal is input to the transversal filter in which the tap coefficient is written, the conventional input signal passes through the transversal filter in which the tap coefficient is written, passes through the noise removing circuit, and is stored in the waveform memory. The signal equivalent to is obtained.

Therefore, if this signal is used, the tap coefficient can be calculated without considering noise. In other words, there is no need to use the signal after re-inputting it to the waveform memory to remove the noise, thereby reducing the time required for the GCR signal fetching and the noise removing circuit. Further, by performing the calculation of the tap coefficient until the convergence is sufficiently achieved, the tap coefficient which minimizes the distortion can be obtained.

Further, after the tap coefficient is obtained by the above method and the tap is corrected irrespective of the magnitude of the distortion, GC
Since the distortion detection accuracy of the R signal can be corrected with high accuracy, low-frequency distortion with low sensitivity can be removed. In addition, the operation between each field can be made a simple calculation of addition and subtraction depending on the presence or absence of the GCR signal, and the memory required for the 8-field sequence processing can be reduced.

Further, since the input signal is sampled at a phase close to that of the reference waveform memory, even smaller distortion can be detected, and the effect of improving the signal after equalization can be improved. Furthermore, since the tap coefficient calculation is performed by changing the difference filter, correction with a large signal amplitude and higher sensitivity can be performed.

Further, once the tap coefficients are obtained, the tap coefficients can be corrected without switching the screen, so that it is not necessary to switch to an image having an initial distortion. Further, by providing a delay circuit equal to the delay time of the transversal filter, no fluctuation occurs at the transition between the initial screen and the screen from which distortion has been removed.

[0042]

An embodiment of the present invention will be described. FIG. 1 is a block diagram showing one embodiment of the present invention. In the figure, 3 is a delay circuit, 4, 6, and 13 are switches, 11
Is a GCR signal detection switch.

First, the operation will be described. The signal input from the video signal input terminal 1 passes through the switch 4 and is input to the transversal filter 5. The output of the transversal filter 5 is input to the noise removal circuit 10 through the switch 11 and stored in the waveform memory 12. The switch 11 detects a certain period of the GCR signal in the vertical blanking period of the video signal, closes only during this period, and outputs only the GCR signal to the waveform memory 12. The waveform memory 12 stores a signal having an improved S / N ratio as in the conventional circuit.

Next, the signal stored in the waveform memory 12 is input to the difference circuit 9 and, after being differentiated, the switch 13
Is input to the tap coefficient calculation circuit 14 through. Here, tap coefficients are calculated, and the tap coefficients are output to the transversal filter 5 and written. Next, the switch 4 is connected from the side of the A / D conversion circuit 2 to the side of the difference circuit 9 opposite to the side of the A / D conversion circuit 2.
The output signal of the waveform memory 12 obtained by the difference is input. At the same time, the switch 13 is connected from the difference circuit 9 to the opposite side. Transversal filter 5
Since the tap coefficient is written, the output is output as a signal obtained by correcting the input signal, and is input to the tap coefficient calculation circuit 14 through the switch 13. Here, the tap coefficient is calculated again.

Thereafter, by repeating the operation in the same manner, the optimum tap coefficients for removing the distortion of the characteristics of the transversal filter are written. During this time, since the transversal filter 5 outputs the GCR signal, the switch 6 is connected to the delay circuit 3 having a delay time equal to the delay amount of the transversal filter until the tap coefficient of the transversal filter becomes optimal. A signal obtained by converting the input signal as it is into a digital signal by the D / A converter 7 is output.

As described above, the operation of the waveform equalization circuit is roughly classified into two modes. One is a mode for capturing a GCR signal, and the other is a mode for calculating a tap coefficient using the captured signal.

Here, the GCR signal capturing mode will be described. As described above, FIG. 17 shows a GCR signal waveform. The GCR signal is designed to be able to capture the GCR signal so as not to be affected by the signals of the preceding line and the following line in an 8-field sequence system. For each field, a sin (X) / X bar signal and a pedestal level are used. The signal is inserted alternately, and the order of the sin (X) / X bar signal and the pedestal level signal is reversed every four fields. In order to eliminate the influence of the signal of the previous line, the horizontal synchronizing signal and the color burst signal from this signal, it is possible to use the fact that the phase of the color burst signal is inverted for each frame by using the first field and the third field. By taking the sum and taking the difference between this and the sum of the second and fourth fields, and similarly calculating the fifth, sixth, seventh and eighth fields,
A signal of only the sin (X) / X bar signal in which the preceding and succeeding signals have been canceled is obtained.

Accordingly, since one GCR signal can be obtained in eight fields, the addition and integration in the noise elimination circuit means that the number of integration times eight fields, which is very time-consuming. One tap coefficient calculation mode depends on the time required for one tap calculation, but since the time is multiplied by the number of taps, it is almost negligible compared to the waveform acquisition mode.

FIG. 2 shows a diagram comparing the operation mode of the embodiment with the operation mode of the conventional circuit. FIG. 2A shows a conventional example, and FIG. 2B shows an operation mode of the embodiment of the present invention. In the conventional circuit, there is a tap coefficient calculation mode after the GCR signal capturing mode, and a mode in which the tap coefficients are once written in the transversal filter and then the GCR signal capturing mode is repeated is repeated. As described above, since it takes time mainly to capture the GCR signal, it takes a very long time to calculate one tap coefficient, and it may take several tens of seconds until the optimum tap coefficient is obtained.

On the other hand, in the present invention, the time required for obtaining the optimum tap coefficient is short because the waveform acquisition mode which takes the longest time is performed only once at the beginning. Further, since the tap coefficient correction mode is not synchronized with the input video signal, the time until an optimum tap coefficient is obtained can be short.

FIG. 3 shows another embodiment. In this figure, the operation of the circuit is the same as that of the embodiment shown in FIG. In FIG. 3, the difference circuit 9 is provided after the switch 13, so that the signal input to the transversal filter is the signal itself stored in the waveform memory, which is subjected to the difference after passing through the transversal filter and used for calculating the tap coefficient. Can be Further, as another embodiment, a difference circuit is connected between the noise removal circuit and the waveform memory, and G is added to the waveform memory.
The difference waveform of the CR signal may be stored.

Another embodiment is shown in FIG. The operation will be described with reference to FIG. The noise removal circuit 10 is connected to the A / D converter 2 and constantly improves the S / N ratio of the input signal. The signal with the improved S / N ratio is stored in the waveform memory 1
2 is stored. The signal stored in the waveform memory 12 is input to the transversal filter 5 through the switch 4. The signal whose distortion has been reduced by the transversal filter 5 takes a difference in the difference circuit 9 and is input to the tap coefficient calculation circuit 14. The tap coefficient calculation circuit 14 calculates the tap coefficients so that the characteristics of the transversal filter become more optimal, and outputs the tap coefficients to the transversal filter. The signal of the waveform memory is input via the switch 4 to the transversal filter in which the new tap coefficient is written, and thereafter, the same operation is performed to determine the optimum tap coefficient.

As another embodiment, instead of the GCR signal or when the GCR signal is not inserted,
By taking in the vertical synchronizing signal in the waveform memory, the distortion of the input signal can be removed in the same manner as in the above embodiment.

According to the present embodiment, the time required to capture the GCR signal is only one time at the beginning, and the tap coefficient can be calculated asynchronously with the input signal. However, there is an effect that the time until the tap coefficient of the transversal filter is obtained can be reduced.

Another embodiment of the present invention will be described. FIG. 5 is a block diagram showing another embodiment of the present invention. FIG. 6 is an explanatory diagram showing the operation in the embodiment of FIG. 5, reference numeral 51 denotes a video input terminal; 52, an A / D converter; 53, a delay circuit; 55, a switch;
Is a D / A conversion circuit, 57 is a video output terminal, 58 is a switch (SW), 59 is a transversal filter, 60 is a noise elimination circuit, 61 is a waveform memory, 62 is a difference circuit, 6
3 is a switch, 66 is a tap coefficient generation circuit, 67 is a tap coefficient memory, 68 is a clock phase detection circuit, 69 is a clock generation circuit, and 76 is an AGC circuit.

First, the operation will be described. As shown in FIG. 6, the operation of this embodiment is roughly divided into a normal correction mode, an intermittent correction mode, and a monitoring mode. Hereinafter, each operation will be described. Returning to FIG. 5, first, a signal input from the video input terminal 51 is converted into a digital signal by the A / D converter 52, and
8 and is input to the transversal filter 59. The output of the transversal filter 59 is input to the waveform memory 61 through the noise removal circuit 60. The waveform memory 61 is controlled so that only a certain period of the GCR signal in the vertical blanking period of the video signal is stored. By repeating this operation a predetermined number of times, a signal with an improved S / N ratio is stored in the waveform memory 61.

Next, the GCR signal stored in the waveform memory 61 is read out by the difference circuit 62, a one-clock difference is performed, and a difference signal is output. Here, it is detected whether or not the sample phase of the signal stored in the waveform memory 61 is the optimum phase. If it is detected that the phase is not optimal, a signal is sent to the clock generation circuit 69 so as to change the phase, and the waveform memory 61 again stores the GCR signals of the sample points having different clock phases.

If it is detected that the phase is optimal, the difference circuit 62 outputs the G signal stored in the waveform memory 61.
The CR signal is subtracted by two clocks and output to the tap coefficient generation circuit 66 through the switch 63. The tap coefficient generation circuit 66 detects the distortion of the GCR signal stored in the waveform memory 61 by comparing with a reference waveform stored in advance therein, generates a tap coefficient, and generates a tap coefficient.
7 is stored. When the coefficients are obtained for all taps, the coefficients are read from the tap coefficient memory 67 and the coefficients are written to the transversal filter 59. This is the first tap coefficient correction.

The second and subsequent tap coefficient corrections are slightly different from the first tap coefficient correction path. After the second time, the signal obtained by the two-clock difference by the difference circuit 62 is input to the transversal filter 59 through the switch 58 as in the first time, and the operation is performed using the tap coefficient obtained by the previous coefficient correction. The output of the transversal filter 59 is input to the tap coefficient generation circuit 66 through the switch 63. Hereinafter, the same operation as the first time is performed.

Thereafter, when the repetition coefficients are corrected for the third and fourth times, tap coefficients having characteristics optimal for removing distortion can be obtained. In the present embodiment, the correction is performed a predetermined number of times, and a residual error (residual distortion) at this time is detected. If the residual error is equal to or less than a predetermined value, it is considered that distortion has been removed, and the tap coefficient correction operation is stopped. This is called a normal correction mode.

During this time, the transversal filter 5
The switch 55 is connected to the delay circuit 53 having the same delay time as that of the transversal filter until the tap coefficient of the transversal filter becomes optimum because the output of 9 is a GCR signal. The converted signal is directly converted into an analog signal by the D / A converter 56, and the converted signal is output to the video output terminal 57. After the tap coefficients are obtained, the switch 55 is connected to the output side of the transversal filter 59, and the signal from which the distortion has been removed is adjusted in amplitude by the AGC circuit 76 and output.

After the tap coefficients are obtained, the waveform memory 6
1, the switch 58 is connected to the A / D converter 52, and the switch 63 is connected to the difference circuit 62.
Side. Then, the first operation of the correction is performed. Thereafter, the process does not proceed to the second correction operation but returns to the GCR signal capturing operation. This is called an intermittent correction mode.

The intermittent correction mode is performed because the signal stored in the waveform memory 61 has a signal amplitude of about 16 bits.
Since the tap coefficient correction is performed via the line 9, the correction must be performed with an 8-bit amplitude, and is easily affected by a rounding error or the like. In addition, a DC residual error may occur, and the original error may not be sufficiently removed.

Therefore, by repeating this intermittent correction mode several times, distortion that cannot be completely removed in the normal correction mode is removed. After repeating the predetermined number of times, the GCR signal is taken in, the difference is compared with a reference waveform, and if the error (residual distortion) is smaller than a certain value by the error detection circuit (in the tap coefficient generation circuit 66). Assuming that there is no error, the process returns to the GCR signal capturing operation without correcting the tap coefficient. This is called a monitoring mode. Here, the threshold value for detecting the presence or absence of an error is larger than the threshold value in the normal correction mode, so that the intermittent correction mode is less likely to be set.

FIG. 7 is a diagram comparing the operation of this embodiment in the normal correction mode with the operation of the conventional circuit. In FIG.
TA is the GCR waveform capture time, and TB is the tap coefficient calculation time and the tap coefficient write time to the transversal filter. The conventional circuit has a tap coefficient calculation mode after the GCR signal capture mode, and once the tap coefficients are written in the transversal filter,
The mode for taking in the GCR signal was repeated. As described above, since it takes time mainly to capture the GCR signal, it takes a very long time to calculate one tap coefficient, and it may take several tens of seconds until an optimum tap coefficient is obtained.

On the other hand, according to the present invention, the waveform acquisition mode which takes the longest time is only required once, so that the time required for obtaining the optimum tap coefficient is short. Further, since the tap coefficient correction mode is not synchronized with the input video signal, the time until an optimum tap coefficient is obtained can be short.

Here, the tap coefficient determination time according to the conventional circuit is T (sub), and the tap coefficient determination time according to the present invention is T
Assuming that (book), T (sub) = N · (TA + TB) (5) T (book) = TA + N · TB (6)

When the numbers are concretely entered, the GCR
If the number of waveform acquisitions is 120, the time is 120 fields, so TA = 120/60 = 2 (seconds). On the other hand, TB is about 100 (μsec), depending on the number of taps of the transversal filter. Therefore, TA
>> From TB, T (sub) = N · TA (7) T (book) = TA (8) Therefore, the greater the number of corrections N, the greater the effect.

Each circuit in FIG. 5 will be described in detail. First, the noise removal circuit 60 and the waveform memory 61
Will be described. The feature of this circuit is an 8-field sequence and sampling clock phase detection circuit. First, an 8-field sequence circuit will be described.

As described above, the GCR signal is designed to be able to capture the GCR signal in an 8-field sequence system without being affected by the signals of the preceding line and the following line. /
X bar signal and pedestal level signal are inserted alternately,
Further, the order of the sin (X) / X bar signal and the pedestal level signal is reversed every four fields.
In order to eliminate the influence of the signal of the previous line, the horizontal synchronizing signal, and the color burst signal from this signal, it is necessary to remove them by using the fact that the phase of the color burst signal is inverted every frame.

This is accomplished by taking the sum of the first and third fields and taking the difference between this and the sum of the second and fourth fields, as well as the fifth, sixth, seventh, By calculating the eighth field, the signals before and after are canceled, and a signal of only the sin (X) / X bar signal is obtained. However, this requires a memory for eight fields, and it is necessary to know what field the stored signal is.

Therefore, when the above equation (4) is expanded,
A circuit that can calculate the eight-field sequence more easily by utilizing the fact that the sign is positive when the sin (X) / X bar signal is present in the GCR signal and the sign is negative when the GCR signal is the pedestal level signal is considered. Was.

FIG. 8 is a block diagram showing a noise removing circuit (and an eight-field sequence circuit). In the figure, 77 is an input terminal, 78 is a GCR signal detection circuit, 79
Is a buffer memory, 80 is a multiplier, 81 is a switch, 8
2 is an adder, 83 is a divider, and 84 is an output terminal.

In operation, first, the GCR signal input from the input terminal 77 is input to the buffer memory 79. in the meantime,
This field is sin by the GCR signal detection circuit 78.
(X) / X bar signal or pedestal level signal is detected. If the signal is a sin (X) / X bar signal, if the signal is a pedestal level signal, the signal whose sign is inverted by the multiplier 80 is switched to the switch 8.
1 is input to an integrating circuit composed of the adder 82 and the waveform memory 61. This operation is repeated for 128 fields to integrate. Thereafter, by performing 1/64 by the divider 83, a sin (X) / X bar signal from which noise has been removed is obtained from the output terminal 84.

Next, the sampling clock phase detection circuit will be described. FIG. 9 is a diagram showing an analog waveform of the sin (X) / X pulse signal, sampling points, and digital data. For the same analog waveform,
(A) is a sample of the peak (maximum value),
(B) and (d) show the case where the sampling position is slightly shifted from the peak, and (c) shows the case where the sampling position is shifted 180 degrees from (a).

Now, assuming that the digital data in FIG. 9A is the same as the reference waveform signal, (b), (c), (d)
In the signal sampled as described above, even if there is no distortion, any error is detected, and the tap coefficient of the transversal filter is calculated so as to have the same shape as the waveform of (a).

Although the data finally has the same shape as the data of (a), digital signal processing is performed on a signal originally having no distortion, so that S / N deterioration such as a rounding error occurs. Therefore, in order to prevent such image quality deterioration, the sampled signal waveform and the reference waveform should have the same shape as much as possible.

Then, the phase of the sampling clock at that time is detected from the sampled signal waveform, and if it is not the desired phase of the sampling clock, a signal for shifting the phase is sent to the clock generation circuit (69 in FIG. 5). This clock phase detection circuit (68 in FIG. 5).

FIG. 10 shows a block diagram of the clock phase detection circuit 68. In the figure, 85 is an input terminal, 86,
87 and 88 are latches, 89 is an adder, 90 is a phase determination circuit, and 91 is an output terminal. The differential signal of the GCR signal is input from the input terminal 85, the maximum value of the amplitude is set to the peak value P0, and the data before and after the peak value are (P-1) and (P +
1) is stored in the latches 35, 36 and 37. (P-
1)-(P + 1), (P0)-(P-1), and (P
From 0)-(P + 1), the phase is determined by the phase determination circuit 90, and a signal as to whether or not to shift the phase of the clock is output from the output terminal 91 to the clock generation circuit 69.

Next, switching of the difference circuit 62 (switching of the clock difference) in FIG. 5 will be described. The GCR signal stored in the waveform memory 61 is subjected to a signal processing by removing the DC component by a difference by a difference circuit 62. FIG.
5A shows a waveform and a sample point near the rising edge of the GCR signal as (A), a one-clock difference signal from the sample point as (B), and a two-clock difference signal as (C).

First, the difference at the time of detecting the clock phase will be considered. As described above, the phase detection uses the peak value of the difference signal and three data before and after the peak value. Therefore, when considering the signal before the difference, the number of data related to the phase detection is 5 data in the case of 1 clock difference and 7 data in the case of 2 clock difference. Here, a correct phase cannot be detected if the data contains distortion at the time of phase detection. Then, since the possibility of distortion being included in the 7 data is higher than that of the 5 data, the probability of malfunction is lower when phase detection is performed with one clock difference.

On the other hand, when the tap coefficients are calculated, as is clear from FIG.
Clock differences are advantageous. Therefore, the circuit is switched so as to use one clock difference which is less affected by distortion when detecting the clock phase and to use two clock differences which can take a large amplitude when calculating the tap coefficients.

Next, tap coefficient generating circuit 6 in FIG.
6 will be described with reference to FIG. In FIG.
71 is an input terminal, 65 is a reference waveform memory, 72 and 74 are adders, 73 is a multiplier, 67 is a tap coefficient memory, 75
Is an output terminal, and 70 is a residual distortion (error) detection circuit.

The reference waveform memory 65 stores in advance a signal obtained by calculating a difference between GCR signals without distortion.
The output signal of the reference waveform memory 65 and the waveform memory 61
The difference between the signal stored in the differential circuit 62 and the signal stored in the differential circuit 62 is calculated by an adder 72 to detect distortion. The detected distortion is multiplied by α (α <1) in the multiplier 73, integrated by passing through the adder 74, and stored in the tap coefficient memory 67. The signal stored in the tap coefficient memory 67 is input to the transversal filter through the output terminal 75. Residual distortion (error) detection circuit 7
Reference numeral 0 denotes a circuit that detects how much distortion remains and outputs a detection signal.

Next, another specific example of the tap coefficient generation circuit 66 is shown in FIG. The operation of the circuit in FIG. 13 will be described. In FIG. 13, the clock phase detection circuit 68 is connected to the reference waveform memory 65 of the tap coefficient generation circuit 66 via the selector 92. The reference waveform memory 65 stores reference signals sampled at several types of phases, and selects a reference waveform sampled at the phase closest to the phase determined by the clock phase detection circuit 68 to the selector 92.
Select by. As a result, there is no error from the reference waveform caused by the shift of the sample phase.

FIG. 14 shows another embodiment of the present invention. FIG.
4 will be described. The noise removal circuit 60 is A
/ D converter 52, which is always connected to the S /
The N ratio is improved, and the signal with the improved S / N ratio is stored in the waveform memory 61. The signal stored in the waveform memory 61 is input to a transversal filter 59 through a switch (SW) 58. The signal whose distortion has been reduced by the transversal filter 59 takes a difference in the difference circuit 62 and is input to the tap coefficient generation circuit 66. The tap coefficient generation circuit 66 calculates the tap coefficients so that the characteristics of the transversal filter become more optimal, and outputs the tap coefficients to the transversal filter. The transversal filter 59 in which the new tap coefficient is written is connected to the waveform memory 6 via the switch 58.
1 is input, and thereafter, the same operation is performed to determine an optimum tap coefficient.

According to this embodiment, the time required to capture the GCR signal is only one time at the beginning, so that the time required to obtain the tap coefficient of the transversal filter can be shortened. Is calculated until convergence is achieved, so that there is an effect that an optimum tap coefficient can be obtained. Further, after the tap coefficients are determined, further correction is performed, so that low-frequency distortion can be removed. Further, since the phase of the sampled GCR signal and the phase of the reference waveform can be matched, an extra tap coefficient is not calculated, and S
There is an effect that interference such as / N deterioration is not given.

Further, the operation of the difference circuit is switched so that the difference circuit uses one clock difference when detecting the phase of the clock and uses the two clock difference when calculating the tap coefficients, so that the phase is not affected by the distortion. Can be detected,
And a signal with high sensitivity can be obtained. Further, by switching and adding the sign between the presence of the sin (X) / X bar signal of the GCR signal and the pedestal level, an eight-field sequence process can be performed with a small memory.

[0089]

According to the present invention, it is not necessary to take in an input waveform every time the tap coefficient of the transversal filter is calculated and eliminate noise, so that the time required for calculating the tap coefficient can be reduced as compared with the conventional case. Since the calculation is performed until the coefficient converges, there is an effect that a more optimal tap coefficient can be obtained. Further, since the correction is performed irrespective of the magnitude of the distortion, there is an effect that the remaining undetectable distortion can be removed.

Another effect is that the sampled data and the reference waveform have the same phase.
An extra tap coefficient is not calculated, and interference such as S / N deterioration is not given. In addition, since the differential operation of the differential circuit is switched between the detection of the clock phase and the calculation of the tap coefficient, there is no malfunction due to the distortion, and the detection sensitivity of the distortion can be increased. Further, the GCR signal can be extracted by the 8-field sequence processing with a small memory capacity.

[Brief description of the drawings]

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

FIG. 2 is an explanatory diagram showing a comparison between an operation mode according to the present invention and an operation mode according to the related art.

FIG. 3 is a block diagram showing another embodiment of the present invention.

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

FIG. 5 is a block diagram showing still another embodiment of the present invention.

FIG. 6 is an explanatory diagram showing an operation mode of the embodiment shown in FIG.

FIG. 7 is an explanatory diagram showing a comparison of required time between an operation according to the present invention and an operation according to the related art.

FIG. 8 is a block diagram illustrating details of a noise removal circuit.

FIG. 9 is an explanatory diagram showing a relationship between an analog waveform and a digital waveform as viewed from a sampling point.

FIG. 10 is a block diagram illustrating a specific example of a clock phase detection circuit.

FIG. 11 is a waveform diagram showing output waveforms of one clock difference and two clock differences in the difference circuit.

FIG. 12 is a block diagram illustrating a specific example of a tap coefficient generation circuit.

FIG. 13 is a block diagram showing another specific example of the tap coefficient generation circuit.

FIG. 14 is a block diagram showing still another embodiment of the present invention.

FIG. 15 is a block diagram showing a conventional example of a waveform equalization circuit.

FIG. 16 is a block diagram illustrating details of a noise removal circuit.

FIG. 17 is a signal waveform diagram illustrating an 8-field sequence.

FIG. 18 is a block diagram illustrating details of a tap coefficient generation circuit.

FIG. 19 is a block diagram showing details of a transversal filter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Video signal input terminal, 2 ... A / D converter, 3 ... Delay circuit, 4, 6, 11, 13 ... Switch, 5 ... Transversal filter, 7 ... D / A converter, 8 ... Output terminal, 9 …
Difference circuit, 10: noise removal circuit, 12: waveform memory, 1
4: Tap coefficient calculation circuit, 51: Video signal input terminal, 5
2: A / D converter, 53: delay circuit, 55, 58, 63
... Switch, 56 ... D / A converter, 57 ... Output terminal, 5
9: transversal filter, 60: noise removal circuit,
61: Waveform memory, 62: Difference circuit, 66: Tap coefficient generation circuit, 67: Tap coefficient memory, 68: Clock phase detection circuit, 69: Clock generation circuit, 76: AGC circuit

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshinori Murata 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside the Hitachi Media Research Laboratory, Inc. Inside Hitachi Image Information Systems Co., Ltd. (72) Katsumi Hishiyama 292, Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside Yokohama Plant, Hitachi, Ltd. (72) Morikage Akiyama 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Prefecture Shares (56) References JP-A-1-284179 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) H04N 5/14-5/217

Claims (16)

(57) [Claims] A waveform equalization circuit which receives a video signal, removes a nearby ghost generated in the vicinity of a main signal of the video signal as signal distortion and outputs the signal, and outputs a transversal filter (5); A ghost detection signal included in the ghost detection signal is removed by removing noise accompanying the ghost detection signal, a waveform memory (12) having a noise elimination circuit is stored, and a waveform of the ghost detection signal included in the output of the transversal filter is given. And a tap coefficient calculation circuit (14) for calculating a tap coefficient for eliminating the signal distortion, which is the difference between the reference waveforms, and applying the calculated tap coefficient to the transversal filter. The ghost detection signal read from the waveform memory instead of the input video signal will A first switch (4) for leading the output signal of the transversal filter to the waveform memory with a noise elimination circuit for the first time, but a second switch (11) for disconnecting the next time without leading. The first time, the ghost detection signal read from the waveform memory is led to the tap coefficient calculation circuit and input, but after the next time, the ghost detection signal included in the output signal of the transversal filter is led instead. And a third switch (13) for inputting. 2. The waveform equalizing circuit according to claim 1, further comprising a difference circuit (9) for obtaining a difference waveform for the ghost detection signal read from the waveform memory and outputting the difference signal on the output side of the waveform memory. A waveform equalization circuit characterized by the above-mentioned. 3. The waveform equalization circuit according to claim 1, wherein a difference circuit (9) for taking a difference waveform for the ghost detection signal and outputting the difference waveform is provided on an input side of the tap coefficient calculation circuit. Waveform equalization circuit. 4. A waveform equalization circuit according to claim 1, 2 or 3.
In a road, the ghost detection signal is included in a video signal.
Ghost removal reference signal (GCR signal)
A waveform equalization circuit, comprising: 5. A waveform equalization circuit according to claim 1, 2 or 3.
The ghost detection signal is included in the video signal.
Waveforms, etc., characterized by rare vertical synchronization signals
Circuit. 6. A video signal is inputted, and a main signal of the video signal is inputted.
Removes ghosts near the signal as signal distortion
In a waveform equalizing circuit that outputs a signal, a transversal filter (59) and an input video signal
Remove the included ghost detection signal and the accompanying noise
Waveform with noise elimination circuit that retrieves and stores the waveform
A memory (61) and an output of the transversal filter;
Ghost detection signal waveform included in force and given reference wave
Compared to the shape, a signal that eliminates the signal distortion that is the difference
Calculate the top coefficient and apply it to the transversal filter.
Tap coefficient generation circuit (66)
Signal to the transversal filter.
Is read from the waveform memory in place of the input video signal
Ghost detection signal to the transversal filter
A first switch (58) for guiding and the first time the waveform memory
Ghost detection signal read from the
Lead to the raw circuit to input, but instead of next time,
Included in the output signal of the transversal filter
A second switch for guiding and inputting a ghost detection signal
(63) and a tap in the tap coefficient generation circuit.
When the number of occurrences of correction of the coefficient reaches a predetermined number of times,
Means for switching back the first and second switches.
A waveform equalizing circuit, comprising: 7. A waveform equalizing circuit according to claim 6, wherein
Then, the first and second switches are switched to switch the waveform memo.
The ghost detection signal read from the
To the transversal filter.
Ghost detection signal included in the filter output signal.
By leading the input to the tap coefficient generation circuit,
To optimize the characteristics of the transversal filter.
A first step, and switching back the first and second switches to release the waveform note;
The ghost detection signal read from the
The transformer is input to the generator by
A second step of optimizing the characteristics of the versal filter; and a tap coefficient generation circuit through the first step.
, And then the second step
Correction of tap coefficients in the tap coefficient generation circuit
And a waveform equalizing circuit. 8. The waveform equalizing circuit according to claim 7, wherein
The operation of correcting the tap coefficient in the second stage is as follows:
The magnitude of the residual strain, the number of correction operations, or
Complete or resume depending on the length of time spent
A waveform equalization circuit comprising control means. 9. A waveform equalizing circuit according to claim 8, wherein
The control means performs a correction operation depending on the magnitude of the residual strain.
When the operation is restarted, the threshold value is
Greater than the level of residual strain achievable by normal operation
A waveform equalization circuit characterized by the above-mentioned. 10. A waveform equalizing circuit according to claim 6, wherein
To sample the video signal waveform.
Clock phase detecting means (68) for detecting the phase of the clock
And a sampling phase controlled according to the detected phase.
Clock generating means (69) for generating a ring clock
And the tap coefficient generation circuit (66)
The phase of the given reference waveform is read from the waveform memory.
If it does not match the waveform phase of the ghost detection signal
The clock phase detecting means and the clock generating means
Waveform equalization characterized by using matching
circuit. 11. A waveform equalizing circuit according to claim 6, wherein
To sample the video signal waveform.
Clock phase detecting means (68) for detecting the phase of the clock
And a plurality of types having different phases as the given reference waveform.
Reference waveform storage means for storing a reference waveform,
The reference according to the phase detected by the clock phase detecting means
Read the reference waveform of the optimal phase from the waveform storage
A waveform equalization circuit. 12. A waveform equalizer according to claim 6, wherein:
And the output of the waveform memory (61) with the noise elimination circuit.
The ghost detection signal read from the waveform memory
A differential circuit (62) which takes a differential waveform and outputs
A waveform equalization circuit, which is provided. 13. A waveform equalizing circuit according to claim 2,
Therefore, the output of the difference circuit is sent to the tap coefficient calculation circuit.
From the above, the two-clock difference is calculated as the difference circuit.
A waveform equalizing circuit characterized by using a differential circuit. 14. A waveform equalizing circuit according to claim 12,
Wherein the output of the difference circuit is the clock phase detection means.
From (68), one clock is used as the difference circuit.
Waveform characterized by using a difference circuit that takes a block difference
Equalization circuit. 15. A waveform equalizing circuit according to claim 6, wherein
The ghost detection signal is stored in the waveform memory (61).
Signal, the ghost detection signal has eight fields.
Consists of sequence GCR signal, included in input video signal
The signal amplitude of the signal is detected, and the detection result
By performing addition or subtraction, the required
Ghost detection signal
Waveform equalization characterized by extracting the GCR signal
circuit. 16. A circuit according to claim 7, wherein:
During the first stage, the input video signal is
At the delay required to pass through the transversal filter
Through a delay circuit having a delay time equal to
Output to the output side by bypassing the sversal filter.
And a waveform equalizing circuit.