JPH05284389A - Waveform equalizing circuit - Google Patents

Abstract

PURPOSE:To reduce the change of the picture quality before and after waveform equalization, and to mitigate the sense of incompatibility by controlling a tap coefficient of a transveral filter in the waveform equilizing circuit, thereby adjusting the picture quality of an output signal. CONSTITUTION:A signal inputted from a video input terminal 1 is converted to a digital signal by an A/D converter 2, and inputted to a transversal filter 3 and an adder 4. An output of the adder 4 is inputted to a waveform memory 7. In the waveform memory 7, only a certain period of a GCR signal in a vertical period of a video signal is stored. The stored GCR signal is read out to a difference circuit 8, subjected to one clock difference, and compared with a reference waveform stored in a reference waveform memory 9 by an adder 10. This result is inputted to a tap coefficient generating circuit 11, and a distortion is detected from an obtained error, and the tap coefficient is generated, and stored in a memory. When the coefficient is obtained for all taps, the coefficient is read out from a tap coefficient memory, and the coefficient is written in the filter 3. In this case, until the tap coefficient is finally obtained, no coefficient is generated from a picture quality adjustment coefficient generating circuit 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveform equalizing circuit for removing distortion in a signal processing circuit for video signals such as television and video.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional waveform equalizing circuit and image quality adjusting circuit. Reference numeral 1 is a video signal input terminal, 15 is a waveform equalizing circuit, 16 is an image quality adjusting circuit, and 17 is a video signal output terminal.

First, the waveform equalizing circuit 15 will be described. The waveform equalizer circuit uses a vertical synchronizing signal of a video signal and a ghost removing reference signal (Ghost) inserted in a vertical blanking period.
Cancel Reference signal: hereafter, GC
Abbreviated as R signal. ) Is used to detect distortions or ghosts generated in a transmission line, the characteristics of a filter that compensates for the distortions are obtained on the receiver side, and waveform distortions are to be removed by passing the filter. A block diagram of this conventional waveform equalization circuit is shown in FIG. In FIG. 3, 1 is a video signal input terminal, 2 is an A / D converter, 3 is a transversal filter, 4 is an adder, 5 is a D / A converter, 6 is a video signal output terminal, 7 is a waveform memory, Reference numeral 8 is a difference circuit, 9 is a reference waveform memory, 10 is an adder, 11 is a tap coefficient generation circuit, and 14 is a delay circuit.

First, the overall operation will be described. The signal input from the video input terminal 1 is converted into a digital signal by the A / D converter 2 and input to the transversal filter 3 and the delay circuit 14. The output passes through the adder 4, and the GCR signal portion inserted in the video signal is stored in the waveform memory 7. The signal stored in the waveform memory 7 becomes a difference signal by the difference circuit 8 and is compared with the reference waveform stored in the reference waveform memory 9 by the adder 10. The error output from the adder 10, that is, the distortion included in the input signal is input to the tap coefficient generation circuit 11. The tap coefficient generating circuit 11 calculates the tap coefficient of the transversal filter so as to remove the distortion of the input signal from the obtained error and stores it in the built-in tap coefficient memory. The tap coefficient is output to the transversal filter and written in the transversal filter.

Now, a tap coefficient control algorithm for making the characteristics of the transversal filter such that distortion of the input signal is removed will be described. As this algorithm, the Zero Forcing method (hereinafter, Z
The F method) and the correlation method are generally known.
Here, the ZF method will be described. Now, assuming that the tap coefficient of the nth tap is C (n), the output Y (n) for the input X (n) of the transversal filter is

[0006]

[Expression 1] Y (n) = ΣC (i) · X (i) If the reference signal is Rn, the error E (n) between the output signal and the reference signal is

[0007]

## EQU2 ## E (n) = Y (n) -R (n). From the tap coefficient C (n) {m} at the m-th processing time to the tap coefficient C (n) {m + 1} at the m + 1-th processing,

[0008]

[Equation 3] C (n) {m + 1} = C (n) {m} −α · E (n) {m} (Α is a correction coefficient, α <1) By performing the sequential processing in this way, the values converge to the optimum values. (reference:
Ghost canceller based on adaptive ZF method Takaguchi et al. 198
Proceedings of the 9th Annual Conference of the Television Society of Japan p247
-) Thus, normally, the tap coefficient is not determined by one calculation, but the final tap coefficient is determined by several calculations. Therefore, in the first tap coefficient calculation, since all the tap coefficients are 0, the input signal is stored in the waveform memory 7 as it is. When calculating the tap coefficient for the second time, the characteristics of the transversal filter are based on the tap coefficient given by the first tap coefficient calculation, and the signal with less distortion than the output for the first time is used. Then, it is stored in the waveform memory 7. The second tap coefficient calculation is performed using this signal. Thereafter, the tap coefficient is calculated in the same manner and the final characteristic is obtained. Therefore,
Finally, the input signal is distortion-free and converted into an analog signal by the D / A converter 5, and the video output terminal 6
Will be output.

As an example of the method using the correlation method, there is JP-A-3-117979.

Since the characteristic of the output signal is based on the GCR signal built in the tap coefficient generating circuit, it becomes the same as the characteristic of this signal. The frequency characteristic of this GCR signal is shown in FIG. The frequency characteristic is flat up to 4 MHz.

Next, the image quality adjusting circuit 16 will be described. The image quality adjustment circuit is a circuit for adjusting the image quality by emphasizing a specific frequency. FIG. 5 shows an image quality adjustment circuit. In FIG. 5, 18 is an input terminal, 19 is a delay element, 20 is an adder, 21 is a multiplier, 22 is a delay element, 23 is an adder, and 24 is an output terminal. The signal input from the input terminal 18 passes through the differential circuit including the delay element 19 and the adder 20 in two stages and becomes a secondary differential signal. This signal is multiplied by the coefficient β (β <1) by the multiplier 21, and the delay element 2
The input signal that has passed through 2 is added by the adder 23, and is obtained from the signal output terminal 24 in which the contour is emphasized. The circuit shown as an example is a digital circuit, but an analog circuit can be realized by adding signals that have been secondarily differentiated.

By changing the polarity of the coefficient β, on the contrary, the contour portion can be smoothed and a soft image quality can be obtained.

As described above, the conventional waveform equalizing circuit and the image quality adjusting circuit are connected in series as separate circuits.

[0014]

Since the input video signal contains distortion and the like, it has various frequency characteristics. Since this has the same frequency characteristic as the reference waveform signal in the waveform equalizing circuit, the characteristic of the output signal becomes constant. However, the appearance of the output signal after waveform equalization depends on the characteristics of the input signal, even though the frequency characteristics of the output signal are constant.
It depends on the characteristics of the input signal. For example, if the image of the input signal looks blurry due to distortion, it becomes a sharp image after waveform equalization, but on the other hand, it looks rough, and on the contrary, the image of the input signal looks garbled. At one point, it looks blurry after waveform equalization,
I felt uncomfortable before and after the waveform equalization process.

Further, in order to adjust the image quality according to the taste, a separate image quality adjusting circuit is required, and the setting must be changed for each channel.

An object of the present invention is to eliminate distortion by a waveform equalization circuit, detect the uncomfortable feeling before and after the waveform equalization, and adjust the image quality so as to mitigate this.
Another object is to adjust the image quality according to preference by the waveform equalization circuit.

[0017]

In order to achieve the above object, the magnitude of distortion in a frequency band related to the image quality of an input signal is detected and used for image quality adjustment control. Also, the magnitude of distortion in the frequency band related to image quality is detected from the tap coefficient after waveform equalization, and this is used for image quality adjustment control.

As another means, the image quality is adjusted by adding the output of the tap coefficient generating circuit for image quality adjustment to the tap coefficient of the transversal filter and adding the image quality adjustment coefficient after waveform equalization.

[0019]

Function: The frequency band related to the image quality is from the middle band to the high band. Therefore, conversely, the distortion related to this frequency band can be detected from the delay time. Alternatively, from the magnitude of the tap coefficient after the waveform equalization, the characteristic of the frequency band related to the image quality can be known by the waveform equalization. Therefore, this can be used to detect a change in image quality before and after waveform equalization.

Further, the output signal after operating the waveform equalizing circuit is a flat signal having no distortion and having a flat frequency characteristic, and is constant regardless of channels or the like. By controlling the tap coefficient of the transversal filter at this time, a specific frequency can be emphasized or attenuated, and the image quality can be adjusted.

[0021]

EXAMPLE An example of the present invention will be described. FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 1, 1 is a video input terminal, 2 is an A / D converter, 3 is a transversal filter, 4 is an adder, 5 is a D / A conversion circuit, 6 is a video output terminal, 7 is a waveform memory, and 8 is A difference circuit, 9 is a reference waveform memory, 10 is a difference circuit, 11 is a tap coefficient generation circuit, 12 is an image quality adjustment coefficient generation circuit, 13 is an adder, and 14 is a delay circuit.

First, the operation will be described.

First, the signal input from the video input terminal 1 is converted into a digital signal by the A / D converter 2 and input to the transversal filter 3 and the adder 4. The output of the adder 4 is input to the waveform memory 7. The waveform memory 7 is controlled so that only a certain period of the GCR signal in the vertical period of the video signal is stored.

Next, the GCR signal stored in the waveform memory 7 is read out by the difference circuit 8, subtracted by one clock, and compared with the reference waveform stored in the reference waveform memory 9 by the adder 10. The comparison result is input to the tap coefficient generation circuit 11. The tap coefficient generation circuit 11 detects the distortion from the obtained error, generates the tap coefficient, and stores the tap coefficient in the memory. When the coefficients are obtained for all taps, the coefficients are read from the tap coefficient memory and the coefficients are written in the transversal filter 3. At this time, the image quality adjustment coefficient generation circuit 1 is used until the tap coefficient is finally obtained.
No coefficient is generated from 2. After that, when the coefficients are sequentially corrected, the tap coefficient having the optimum characteristic for finally removing the distortion can be obtained.

Now, the image quality adjustment coefficient generating circuit 12 will be described. FIG. 6 shows a block diagram. In FIG.
25 is an image quality adjustment signal input terminal, 26 is a tap coefficient input terminal, 27 is a delay element, 28 is an adder, 29 is a multiplier, 3
Reference numeral 0 is an image quality coefficient generation circuit, and 31 is a coefficient output terminal. The operation will be described. First, the tap coefficient input from the tap coefficient input terminal 26 is input to the image quality coefficient generation circuit 30,
Detects whether distortion affects image quality. This is done by weighting and adding the magnitudes of the tap coefficients corresponding to a specific frequency band. The obtained detection result and the image quality adjustment signal input terminal 25 preset externally
The signals input from are added to generate the image quality coefficient. The generated coefficient is added to the tap coefficient delayed by the delay element 27 by the adder 28, weighted by the multiplier 29, and output from the coefficient output terminal 31. The principle will be described with reference to FIG. FIG. 7 shows a transversal filter portion. In FIG. 7, 32 is a delay element,
33 is a multiplier and 34 is an adder. Here, the tap coefficient of the i-th tap output from the tap coefficient generating circuit is C
(I), and the tap coefficient obtained by adding the image quality adjustment coefficient to this is c (i). Now, it is assumed that a signal A having no distortion is input. Then, since there is no distortion, the tap coefficients C (i) are all 0. Here, when the tap to which the image quality adjustment coefficient β is added is an image quality adjustment tap, the B and C signals are input to the adder 34 from this tap and added to the original signal to enhance the contour D. The signal is obtained. Arbitrary image quality can be obtained by changing the size and polarity of the image quality adjustment coefficient β.

On the other hand, if there is distortion,

[0027]

## EQU00004 ## The tap coefficient such that c (i) = C (i) +. Beta..multidot. {C (i-1) + C (i + 1)} is input to the transversal filter. Also, the coefficient of the image quality adjustment tap is

[0028]

## EQU00005 ## c (i) = C (i) +. Beta..multidot. {C (i-1) + C (i + 1)} +. Beta. (Where i = -1 or i = + 1). Here, for the sake of explanation, the image quality adjustment taps are the + 1st tap and the -1st tap, but in reality, the sampling clock frequency is 14.
If the frequency is 3 MHz (4 fsc), the component at 3.58 MHz (fsc) can be emphasized or attenuated by setting the + 2nd tap and the −2nd tap.

An image quality coefficient generation circuit 30 for detecting a change in image quality due to waveform equalization will be described with reference to FIG. In FIG. 8, 35 is a tap coefficient input terminal, 36 is a latch circuit, 3
Reference numeral 7 is a multiplier, 38 is an adder, and 39 is a detection output terminal. Of the tap coefficients input from the tap coefficient input terminal 35, the tap coefficients corresponding to the frequency band that affects the image quality, that is, the coefficients of the several taps before and after the center tap with the delay time of 0 are latched by the latch circuit 36 and the multiplier 37
Are weighted by, added by the adder 38, and output from the output terminal 39 as a detection output. When this detection output is positive, it means that the frequency band corresponding to this tap has been raised, so it can be seen that the gain of this frequency band of the input signal was small. In this case, on the screen, the blurred screen looks rough after waveform equalization. That is,
This is because the S / N becomes worse because the frequency characteristics are raised and the noise component is also raised. In such a case, S /
N is not a concern, and the uncomfortable feeling of image quality before and after waveform equalization is alleviated. On the other hand, when the detection output was negative, the screen was glaring, but the screen seemed to be blurred.
In this case, it is better to sharpen the image quality. Therefore,
An image quality adjustment coefficient β is created from this detection result, and the image quality is adjusted according to the principle described above.

An example of another image quality coefficient generating circuit is shown in FIG.
In FIG. 9, 40 is an error input terminal, 41 is a multiplier, and the same as FIG. 8 below. The error between the difference waveform of the input signal and the reference waveform is input from the error input terminal 40. here,
The multiplier 41 multiplies the coefficient γ for standardization according to the amplitude of the input signal, and thereafter, the frequency characteristic of the input signal is detected in the same manner as the circuit of FIG. 8 described above. Even if the image quality is adjusted using this detection result, the same operation is performed.

According to the present embodiment, the change in image quality before and after waveform equalization is detected from the delay time and the magnitude of the tap coefficient, the distortion is removed, and the change in image quality is suppressed to be small after waveform equalization. It is possible to reduce the discomfort of the screen.

Further, a change in image quality can be detected from the tap coefficient. Furthermore, the frequency characteristic of the input signal can be estimated from the error of the input signal, and the image quality adjustment circuit can be controlled from this result.

Further, the operation of the image quality adjusting circuit can be performed by the waveform equalizing circuit, whereby the external image quality adjusting circuit can be eliminated and the circuit can be simplified.

[0034]

According to the present invention, the image quality can be adjusted by adding the image quality adjustment coefficient to the tap coefficient of the transversal filter of the waveform equalization circuit. Further, there is an effect that the change in image quality before and after waveform equalization can be known from the delay time and the magnitude of the tap coefficient, and the sense of discomfort due to this can be reduced.

Further, since it is not necessary to provide an image quality adjusting circuit outside, the circuit can be simplified.

[Brief description of drawings]

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

FIG. 2 is a block diagram of a conventional circuit.

FIG. 3 is a block diagram of a waveform equalization circuit.

FIG. 4 is a diagram showing frequency characteristics of a GCR signal.

FIG. 5 is a block diagram of an image quality adjustment circuit.

FIG. 6 is a block diagram of an image quality adjustment coefficient generation circuit.

FIG. 7 is a diagram showing a principle of image quality adjustment.

FIG. 8 is a block diagram of an image quality adjustment coefficient generation circuit.

FIG. 9 is a block diagram of another embodiment of the image quality adjustment coefficient generation circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Video input terminal, 2 ... A / D converter, 3 ... Transversal filter, 4 ... Adder, 5 ... D / A conversion circuit, 6 ... Video output terminal, 7 ... Waveform memory, 8 ... Difference circuit, 9 Reference waveform memory, 10 ... Adder, 11 ... Tap coefficient generation circuit, 12 ... Image quality adjustment coefficient generation circuit, 13 ... Adder, 14 ... Delay circuit, 15 ... Waveform equalization circuit, 16 ... Image quality adjustment circuit, 17 ... Video signal output terminal, 18 ... Input terminal, 19 ... Delay element, 20 ... Adder, 21 ... Multiplier, 22 ... Delay element, 23 ... Adder, 24 ... Output terminal, 25 ... Image quality adjustment signal input terminal, 26 ... Tap coefficient input terminal, 27 ... Delay element, 28 ... Adder, 29 ... Multiplier, 30 ... Image quality coefficient generation circuit, 31 ... Coefficient output terminal, 32 ... Delay element, 33 ... Adder, 34 ... Adder, 35 ... Tap coefficient input terminal , 36 ... Latch circuit, 37 ... Multiplier, 38 ... Adder, 39 ... Detection output terminal, 40 ... Error input terminal, 41 ... Multiplier.

Claims (3)

[Claims] 1. A transversal filter capable of obtaining an output video signal having a desired characteristic by controlling the tap coefficient, and a tap coefficient generating means for generating a coefficient given to a tap of the transversal filter, In the waveform equalization circuit that removes distortion of the input video signal by controlling the tap coefficient of the transversal filter, a coefficient generation circuit for image quality adjustment is provided. A waveform equalization circuit, characterized in that the image quality of an output video signal is adjusted by adding the tap coefficient obtained by the coefficient generation means and inputting the result into a transversal filter. 2. A change in image quality before and after waveform equalization is detected by calculating a tap coefficient corresponding to a frequency affecting image quality among the tap coefficients output from the tap coefficient generating means, and this image quality is detected. 2. The waveform equalization circuit according to claim 1, wherein the image quality adjustment coefficient generation circuit is controlled so as to reduce the change of the waveform. 3. A change in the image quality after waveform equalization is estimated by calculating the magnitude of the delay time distortion that affects the image quality among the distortions included in the input signal, and this change in the image quality is reduced. 2. The waveform equalizing circuit according to claim 1, wherein the image quality adjusting coefficient generating circuit is controlled so as to do so.