JPH05211621A - Waveform correcting circuit - Google Patents

Abstract

PURPOSE:To remove a sag from a video signal and generate a video signal which has no DC component variation by extracting and subtracting the sag from a supplied waveform. CONSTITUTION:The input waveform is supplied to a delay unit 11 and a sag detector 12, via a terminal 10 the delay time of the delay unit 11 is the same as the processing time of the sag detector 12, and their outputs are supplied to a subtracter 19, so that the sag-corrected waveform is outputted through a terminal 14. Namely, the input waveform is supplied to a reference range selecting circuit 15 to select a reference range and a mean calculation unit 16 calculates the mean of data on plural values within the reference range. The mean value calculated is stored in a storage circuit 17 and an interpolating circuit 18 outputs a value, obtained by connecting the mean value of the output of the storage circuit 17 by a line, to the subtracter 19 as an interpolated waveform. The subtracter 19 subtracts the output waveform of the interpolating circuit 18 from the output waveform of the delay unit 11 and outputs the sag- corrected waveform.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveform correction circuit for correcting sag of a video signal.

[0002]

2. Description of the Related Art In a television signal receiver, a video signal level at the time of reception is very low, and therefore it is necessary to amplify the video signal level. The configuration of this amplifier circuit is shown in FIG. In FIG. 9, the video signal is supplied to the amplifier 49 via the terminal 50. The amplifier 49 includes a capacitor C1, resistors R1 and R2, and an amplifier 51. The supplied video signal is supplied to the amplifier 51 after passing through the capacitor C1 and biased by the resistors R1 and R2. The signal amplified by the amplifier 51 is supplied to the next amplifier. The other amplifiers also have the same configuration as the amplifier 49, and these are connected in multiple stages to form one amplifier circuit. Since the HPF (high-pass filter) is composed of the capacitor C1 and the resistors R1 and R2 inside the amplifier 49, the low-pass gain of the amplified video signal is lowered.

Incidentally, the above-mentioned amplifier circuit is shown in FIG.
When a video signal as shown in Fig. 1 is supplied, its output is
Since the DC component is cut as shown in 0 (B), the signal becomes inclined. This kind of signal tilt is commonly read as "sag".

This sag causes various problems. For example, when a video signal in which sag is generated is displayed on the screen, the brightness is different between the left and right sides of the screen even though the images originally have the same brightness.
Signals with a particularly large influence are s for measuring transmission characteristics.
There are inx / x signals and the like.

Most of the waveform equalization processes in recent television signal receivers use sin x / x signals. For example, the sinx / x signal is used as a reference signal to remove a ghost component. An example of this signal waveform is shown in FIG. FIG. 11A is an example of a waveform that is not affected by sag,
FIG. 11 (B) shows the frequency spectrum of FIG. 11 (A). As shown in FIG. 11B, the sinx / x signal has a frequency component of a constant level from the direct current component to the high frequency component, and is a signal suitable for the measurement of the transmission system.

On the other hand, FIG. 11 shows an example of a waveform affected by sag.
(C) and the frequency spectrum at that time are shown in FIG.
It shows in (D). As shown in FIG. 11C, when the sag influences the waveform, the waveform is inclined. Also, the frequency spectrum changes from DC to low frequency components. Thus, the sag causes distortion in the transmission system.

A clamp circuit is generally known as a circuit for correcting sag. FIG. 12 shows an example of the clamp circuit. In FIG. 12, the NPN transistor 7
A power supply voltage Vcc is supplied to the collector of No. 2, and a DC voltage source 71 is connected to the base. The emitter is connected to the reference potential point via the resistor R0 and is also connected to the capacitor C0 and the terminal 73. Capacitor C0
A terminal 70 is connected to the other end of the.

A video signal having a lower negative polarity in synchronization is supplied to the terminal 70, and the DC component is cut by the capacitor C0.
The transistor 72 is turned on when the minimum level of the video signal, that is, the horizontal synchronizing pulse portion is supplied, so that the video signal is clamped and output from the terminal 73.

The clamp circuit removes the sag considerably, but also leaves the sag. Further, since the clamp circuit itself is a non-linear circuit, the low frequency component from the direct current may not be corrected in some cases, which is not sufficient to correct the sinx / x signal.

[0010]

When multistage amplification is applied to a video signal, it is affected by sag. This sag can usually be removed with a clamp circuit, etc.
It was insufficient for correction of signals used for measurement of transmission system such as inx / x signals.

It is an object of the present invention to provide a waveform correction circuit having sufficient accuracy in a circuit that corrects a waveform such as sag.

[0012]

Means according to the present invention include a sag detecting means for detecting a sag which is a low frequency component from a direct current of a video signal, a processing time of the sag detecting means supplied with the video signal. A delay means having an equalized delay time and a correction means for correcting sag in the video signal based on the sag detection means output and the delay means output.

[0013]

By the means described above, the sag is removed from the video signal, and a video signal without fluctuation of the DC component is generated.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the structure of a waveform equalizing circuit will be described before describing an embodiment of the present invention. FIG. 8 is a diagram showing the configuration of the waveform equalization circuit. In this figure, the video signal supplied from the terminal 40 is supplied to the equalization circuit 41 and the waveform acquisition circuit 42. The equalization circuit 41 is composed of a transversal filter or the like with a variable tap coefficient, and a video signal from which transmission distortion has been removed is output, and is output from the terminal 46 to the outside of the circuit and simultaneously supplied to the waveform capturing circuit 44. The waveform capturing circuits 42 and 44 respectively capture the reference waveform inserted in the video signal, and at the same time, perform sag correction, and the sag-corrected reference waveform is supplied to the control circuit 43. The control circuit 43 is also supplied with the reference waveform which is the output of the reference waveform generating circuit 45.
The comparison calculation is performed between the output reference waveforms of 2, 44 and the tap coefficient that minimizes the transmission distortion is set, and the equalization circuit 41 is set.
Is supplied to. Transmission distortion is removed by repeating the above operation a plurality of times.

As described above, the waveform equalization circuit performs waveform equalization processing based on the reference waveform inserted in the video signal. Therefore, if there is sag in the reference waveform, accurate waveform equalization processing cannot be performed, so sag correction is important.

The present invention relates to a waveform correction circuit for performing sag correction of a video signal and sag correction inside the waveform capturing circuits 42 and 44. Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing the configuration of a first embodiment according to the present invention. In this figure, the input waveform is transmitted through a terminal 10 to a delay device 11 and a sag detector 12
And supplied to. The delay time in the delay device 11 is equal to the processing time of the sag detector 12, each output is supplied to the corrector 13, and the sag-corrected waveform is output via the terminal 14.

FIG. 2 shows a specific example of FIG. In this figure, the sag detector 12 is composed of a reference range selection circuit 15, an average calculator 16, a storage circuit 17, and an interpolation circuit 18, and the corrector 13 is a subtractor 19. In FIG. 2, the input waveform has a delay device 11 and a reference range selection circuit 15 via a terminal 10.
And supplied to. The reference range selection circuit 15 selects the reference range of the supplied waveform, and the average calculator 16 calculates the average of the data of multiple values within the reference range. Then, a plurality of average values calculated by the storage circuit 17 are stored. The interpolation circuit 18 outputs a value obtained by connecting a plurality of average values output from the storage circuit 17 with a line to the subtracter 19 as an interpolation waveform. The subtractor 19 subtracts the output waveform of the interpolation circuit 18 from the output waveform of the delay device 11, and outputs a sag-corrected waveform.

Next, the transition of the waveform in FIG. 2 will be described with reference to FIG. The waveform as shown in FIG.
When supplied by the above, the reference range appears every horizontal scanning period. As the reference range, a sync tip A, a pedestal front porch B, a back porch C, and the like can be considered. For example, when the sync chips A and A'are used as the reference range, the average values of the plurality of values within the reference range are shown in FIG.
A and b. The interpolation circuit 18 outputs a waveform obtained by connecting the average values a and b to the subtractor 19 as an interpolation waveform. Therefore, the subtractor 19 subtracts the waveform of FIG. 3 (2) from the waveform of FIG. 3 (1) to generate a sag-corrected waveform as shown in FIG. 3 (3).

Next, a second embodiment according to the present invention will be described with reference to the drawings. The second embodiment shows sag correction in the case of a special waveform such as an impulse waveform. FIG. 4 is a diagram showing the configuration of the second embodiment. In this figure, the impulse waveform supplied from the terminal 10 is stored in the memory circuit 20 and then supplied to the peak position detector 21 and the delay device 11. The peak position detector 21 detects the peak position from the output of the storage circuit 20. After that, the right detector 22 and the left detector 24 respectively set the positions A and B sufficiently distant from the peak position on the right side and the left side, respectively, and the average calculator 23,
In 25, the average value of a plurality of values in the vicinity of A and B is calculated and supplied to the inclination calculator 26. The slope calculator 26 calculates the sag slope from the supplied average value at the points A and B and the time difference between the points A and B, and supplies the sag slope to the correction value calculator 27.
The correction value calculator 27 generates a correction waveform from the supplied value, and the subtractor 19 subtracts the correction waveform from the output of the delay device 11.
As a result, a sag-corrected waveform is generated.

FIG. 5 shows the transition of the waveform in FIG. In this figure, the vertical axis represents level and the horizontal axis represents time.
First, the peak position of the waveform is detected in FIG.
In (2), positions A and B are set to the right and left sides of the peak position, which are sufficiently distant from each other. Then, in FIG. 5 (3), the average value of a plurality of values near points A and B is calculated, and the time difference T0 between AB is detected. After that, as shown in FIG.
A correction waveform based on the peak position is generated from the average value of the multiple values near the point B and the time difference T0, and the correction waveform is subtracted from the waveform of FIG. 5 (1) to generate the sag as shown in FIG. 5 (5). Of waveforms are generated.

Next, a third embodiment according to the present invention will be described with reference to the drawings. The third embodiment shows sag correction in the case of a special waveform with a small change in the AC component. FIG. 6 is a diagram showing the configuration of the third embodiment. In this embodiment, the sag detector 12 of the first embodiment shown in FIG. 2 is composed of an LPF (low pass filter) 30, and the other structures are the same as those of FIG. The transition of the waveform in FIG. 6 will be described with reference to FIG. 7. In this figure, the vertical axis represents level and the horizontal axis represents time. When the waveform as shown in FIG. 7 (1) is supplied from the terminal 10, the output of the LPF 30 becomes sag as shown in FIG. 7 (2). Therefore, the subtractor 19 subtracts the waveform of FIG. 7 (2) from the waveform of FIG. 7 (1) to generate a sag-corrected waveform as shown in FIG. 7 (3).

As described above, in the present invention, the reference range is set in the first embodiment, and the sag is calculated from the average value of the adjacent reference ranges. In the second embodiment, the sag is calculated from the average value in the vicinity of the positions sufficiently distant from the reference peak position to the right and left sides and the time difference thereof. In the third embodiment, the sag is detected by extracting the DC component of the waveform with the LPF. Subtracting these sags from the original waveform produces a sag-free waveform.

When the sag of the video signal is removed, the direct current component is correctly displayed on the television receiver, so that there is no uneven brightness on the left and right of the screen. Further, since the sag is corrected in the transmission distortion measurement impulse waveform, sufficient performance can be obtained as a transmission distortion detection reference signal of the waveform equalizer.

The sag extraction method is not limited to the above-mentioned method. Further, in the present invention, the sag is extracted between two data, but it goes without saying that the accuracy can be improved by using a plurality of data.

[0025]

As described above, the sag is extracted and subtracted from the supplied waveform to generate the sag-removed waveform.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of a first embodiment according to the present invention.

FIG. 2 is a configuration diagram showing a configuration of a specific example of the first embodiment.

FIG. 3 is an explanatory diagram for explaining the transition of the waveform in FIG.

FIG. 4 is a configuration diagram showing a configuration of a second embodiment according to the present invention.

5 is an explanatory diagram for explaining the transition of the waveform in FIG.

FIG. 6 is a configuration diagram showing a configuration of a third embodiment according to the present invention.

FIG. 7 is an explanatory diagram for explaining the transition of the waveform in FIG.

FIG. 8 is a configuration diagram showing a configuration of a waveform equalization circuit.

FIG. 9 is a configuration diagram showing a configuration of an amplifier circuit.

FIG. 10 is an explanatory diagram for explaining the transition of the waveform in FIG.

FIG. 11 is an explanatory diagram for explaining the transition of the waveform and frequency spectrum in FIG. 9.

FIG. 12 is a configuration diagram showing a configuration of a clamp circuit.

[Explanation of symbols]

11 ... Delay device, 12 ... Sag correction circuit, 13 ... Correction device, 1
5 ... Reference range selection circuit, 16 ... Average calculator, 17 ... Storage circuit, 18 ... Interpolation circuit, 19 ... Subtractor.

Claims (2)

[Claims] 1. A sag detecting means for detecting a sag which is a low frequency component from a direct current of a video signal, a delay means which is supplied with the video signal and has a delay time equal to a processing time of the sag detecting means, A waveform correction circuit comprising: a correction unit that corrects sag in the video signal based on the sag detection unit output and the delay unit output. 2. The sag detecting means defines a plurality of reference positions from the video signal and selects a range in the vicinity of the reference positions; and an average for calculating an average value within the selected range. 2. The waveform correction according to claim 1, comprising a value calculation means and a correction waveform generation means for generating a correction waveform for correcting sag from a plurality of average value data output from the average value calculation means. circuit.