JPS62272768A - Distortion removal circuit - Google Patents

Abstract

PURPOSE:To remove distortion such as undershoot, etc. from a video signal by removing the high frequency components from the video signal, and clipping the video signal only at the time the difference between thus generated signal and an original video signal exceeds a prescribed level. CONSTITUTION:In case a video signal whose brightness signal has an undershoot reaching the level of a synchronizing signal as shown in figure (a) is inputted to an input terminal 1, a video signal whose waveform is deformed as shown in figure (b) by attenuating the undershoot is outputted by a low-pass filter LPF to the base of a transistor Tr 15. As far as the transistor Tr 15 does not operate, a video signal outputted from a transistor 9 directly undergoes a resistor 11 and is inputted to a synchronizing signal separator circuit. In the undershoot part shown in the figure (a), the potential difference between the base terminal of the Tr 15 and the output terminal of the Tr 9 i.e. the base-emitter potential difference of the Tr 15 reaches an active level, and the potential of the emitter of the Tr 15 is clipped at a voltage level determined by the voltage of the base of the Tr 15, to be made a video signal free from the undershoot shown in figure (c).

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a circuit for removing distortion such as undershoot from a video signal.

[Prior Art] In a circuit that separates a synchronization signal from a video signal, a method has been used in which the video signal is clamped, and the synchronization signal is extracted by slicing the video signal at a constant voltage. , undershoot, etc., and when it reaches the voltage level of the synchronization signal, there is a problem in that the undershoot is mistaken for the synchronization signal and the slices are separated.

Therefore, in order to eliminate this, conventionally, a low-pass filter (LPF) or the like having characteristics sufficient to attenuate the sag contained in the video signal has been inserted at the front stage of the synchronization signal separation circuit.

[Problems to be Solved by the Invention] However, in such conventional techniques, there is a time delay in the separated synchronization signal with respect to the synchronization signal included in the original video signal, and the amount of separation is large.

There is a drawback in that the phase of the phase signal is affected by the brightness level of the video signal in front of the front porch.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a distortion removal circuit that eliminates the above-mentioned drawbacks.

[Means for Solving the Problems] The present invention provides a high-frequency removal means for removing a predetermined high-frequency component from a video signal, and a high-frequency removal means for removing a predetermined high-frequency component from a video signal. and means for clipping the video signal.

[Function] According to the present invention, the video signal is improved by removing high-frequency components from the video signal and clipping the video signal when the difference between the removed signal and the original video signal exceeds a predetermined level. Remove distortions such as undershoot.

[Example code] The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a specific circuit diagram of the same embodiment, and FIG. 3 shows signal waveforms of the main parts of FIG. 2.

In Fig. 1, 1 is an input terminal, which is a negative polarity video signal (the synchronization signal is a positive polarity signal, and the luminance signal is a negative polarity signal).
is input. A buffer amplifier 2 outputs the video signal input to the input terminal 1 as a low impedance signal. Reference numeral 3 denotes an LPF, which has a characteristic of removing undershoot and the like of the video signal inputted to the input terminal 1. 4 is a limiter which compares the DC level of the signal output from buffer amplifier 2 and the DC level of the signal output from LPF 3, and determines that the output of buffer amplifier 2 is higher than the output of LPF 3 by a certain voltage or more. Sometimes, the signal from the buffer amplifier 2 is clipped within a certain level range.

This is a synchronization signal separation circuit that separates a synchronization signal from the video signal from the 5-digit limiter 4. Reference numeral 6 denotes an output terminal for outputting the synchronization signal separated by the synchronization signal separation circuit 5.

In FIG. 2, resistors 7, 8, 10 and a transistor (Tr) 9 are emitter followers that constitute a buffer amplifier 2, and resistors 12, 13 and a capacitor 14 constitute an LPF 3.

Resistor 11 and Tr 15 constitute limiter 4.

Capacitor 16. Resistors 17, 18, 20, 22 and Tr19.21 constitute a synchronizing signal separation circuit 5.

When a video signal having an undershoot that reaches the synchronization signal level in the luminance signal as shown in a in FIG. 3 is input to the input terminal 1, the undershoot is attenuated from the LPF 3 as shown in FIG. A video signal with a rounded (smooth) waveform is input to the base of Tr15. As long as Tr15 does not operate, the video signal output from Tr9 is directly input to the synchronization signal circuit through the resistor 11, but in the undershoot portion shown in Figure 3a, the base terminal of Tr15 and the output of Tr9 are connected to each other. The potential difference with the terminal, that is, the potential difference between the base and emitter of Tr is reaches the active region, and the potential of the emitter of Tr15 is clipped to the level determined by the voltage of the base of Tr15, as shown in FIG. 3C. A video signal from which undershoot has been removed is output to the synchronization signal separation circuit 5. In this way, Tr15 is not operated when there is a potential difference in the synchronizing signal part, and Tr9 is operated only when there is an undershoot such as that which occurs when the video signal changes from a high brightness level to a low brightness level.
The output DC level of the resistor 12 and the division ratio of the resistors 12 and 13 may be adjusted.

In addition, although the explanation was given using LPF in this example, LP
A similar effect can be obtained by using a delay line instead of F by outputting the difference between the delayed signal and the original signal, and clipping the original signal when the difference exceeds a predetermined level. That is self-evident.

As described above, even if the video signal contains a distortion signal such as undershoot that is inappropriate for separating the synchronization signal, only the undershoot can be removed.
There is no need to dull or delay the synchronization signal.

[Effects of the Invention] As described above, according to the present invention, distortion such as undershoot can be removed from a video signal.

[Brief explanation of the drawing] FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a specific circuit diagram of the same embodiment, FIG. 3 is a waveform diagram of points a, b, and c in FIG. 2. 1...input terminal, 2...Buffer amplifier, 3...LPF. 4...Limiter, 5...Synchronization signal separation circuit, 6...Output terminal. Figure 2

Claims (1)

[Scope of Claims] High-frequency removal means for removing a predetermined high-frequency component from a video signal; and clipping the video signal when a difference between an output signal from the high-frequency removal means and the video signal exceeds a predetermined level. A distortion removal circuit characterized in that it comprises means for.