JPS62284584A - Linearity compensating circuit for luminance signal - Google Patents

Abstract

PURPOSE:To compensate only the linearity of a luminance signal by synthesizing a signal of the output signal of a delay circuit which delays an input video signal corresponding to the delay time of a nonlinear circuit and a low-pass filter and the output of the low-pass filter. CONSTITUTION:The video signal is compensated by the nonlinear circuit 1 and a low-frequency luminance signal is extracted by the low-pass filter 2 and supplied to a synthesis circuit 4. The video signal, on the other hand, is delayed by the time corresponding to the delay time of the nonlinear circuit 1 and low-pass filter 2 through the delay circuit 3 and supplied to the synthesis circuit 4. The synthesis circuit 4 synthesizes the signal of the output signal of the low-pass filter 2 and the output signal of the delay circuit 3 and the synthesized signal is outputted. Thus, no chrominance subcarrier component is added, so a defferential gain is not affected and only the linearity of the luminance signal is compensated.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a linearity compensation system used in a television video transmitter, and in particular to a linearity compensation system for improving the linearity of a luminance signal in a video band. The present invention relates to a luminance signal linearity compensation circuit for compensation.

[Prior Art] Conventionally, an intermediate frequency band linearity compensation circuit and a video band linearity compensation circuit have been used in combination for the purpose of compensating for nonlinear distortion occurring in television video transmitters.

FIG. 2 shows a system diagram of a television video transmitter including a linearity compensation system to which the present invention relates. In the figure, 11 is a video band linearity compensation circuit, 12 is a modulator, 13 is an intermediate station waveband linearity compensation circuit, 14 is a frequency converter, and 15 is a high frequency power amplifier.

Generally, the source of nonlinear distortion is mainly the high frequency power amplifier 15, and compensation for this should be performed in the intermediate frequency band. However, in the intermediate frequency band, it is difficult to perform sufficient compensation in detail, so a video band linearity compensation circuit is also used. All of these were configured to perform equal compensation over the entire frequency band of the video signal. In other words, in the television video transmission shown in FIG. Preliminary compensation is provided.

[Problems to be Solved] However, with respect to the nonlinear distortion generated in the high frequency power amplifier 15, it is often seen that there is a difference in the amount of distortion for the luminance signal and the amount of distortion for the color subcarrier. For example, the linearity of the luminance signal and the differential gain of the color subcarrier are not equal.

Here, the differential gain of the color subcarrier indicates the rate at which the amplitude of the color subcarrier multiplied by the luminance signal changes depending on the luminance signal level. On the other hand, the linearity of the luminance signal represents the proportional relationship between the human power level of the luminance signal itself and the output level, and can be considered as the differential gain when a sufficiently low frequency signal is multiplied. Therefore, the difference in distortion for the luminance signal and the chrominance subcarrier is considered to be the difference in distortion for the low frequency region of the video signal and the high frequency region centered on the chrominance subcarrier.

In such cases, conventional compensation circuits compensate evenly over the entire frequency band of the video signal.
It is difficult to optimally compensate for both the linearity of the luminance signal and the differential gain of the chrominance subcarrier at the same time, and when one is properly compensated, the other becomes insufficiently compensated.

In this way, conventional compensation circuits are configured to perform equal compensation over the entire frequency band of the video signal, so compensation for the linearity of the luminance signal and compensation for the differential gain of the chrominance subcarrier are performed separately. Therefore, it is difficult to perform optimal compensation for both characteristics at the same time.

SUMMARY OF THE INVENTION An object of the present invention is to provide a luminance signal linearity compensation circuit capable of compensating only the linearity of a luminance signal without affecting the differential gain of a color subcarrier, as a video band linearity compensation circuit. It is something.

[Means for Solving Problems] In order to achieve the above object, the present invention includes a nonlinear circuit that receives an input video signal and generates a compensation signal, and a nonlinear circuit that receives the compensation signal and generates a signal in a frequency band containing a color subcarrier component. A low-pass filter that removes only the luminance signal component,
comprising: a delay circuit that provides a delay corresponding to the delay time of the nonlinear circuit and the low-pass filter to the input video signal; and a synthesis circuit that adds the output signal of the delay circuit and the output signal of the low-pass filter. It is characterized by

[Embodiment] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a luminance signal linearity compensation circuit according to an embodiment of the present invention.

In this figure, 1 is a nonlinear circuit that applies nonlinear processing to an input video signal. That is, this nonlinear circuit 1 extracts a signal in a level region that requires compensation from the level range from the white level to the black level of the input video signal, compensates its polarity and amplitude, and converts the compensated signal into a low-pass signal. Supplied to filter 2. The low-pass filter 2 removes the color subcarrier from the compensation signal, extracts only the luminance signal in the low frequency region, and supplies it to the synthesis circuit 4.

On the other hand, 3 is a delay circuit which applies a delay 2 corresponding to the delay time of the nonlinear circuit 1 and the low-pass filter 2 to the input video signal, and supplies the delay circuit 3 to the synthesis circuit 4. A synthesis circuit 4 adds the signal output from the low-pass filter 2 to the output signal from the delay circuit 3.

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In the above configuration, the video signal is compensated by the nonlinear circuit 1, and then the low-frequency region luminance signal is extracted by the low-pass filter 2 and supplied to the synthesis circuit 4.

On the other hand, the video signal is delayed by the delay circuit 3 by a time corresponding to the delay time of the nonlinear circuit 1 and the low-pass filter 2, and then supplied to the synthesis circuit 4. In the synthesis circuit 4,
The output signal of the low-pass filter 2 and the output signal of the delay circuit 3 are combined and output.

In this manner, in the present invention, since no color subcarrier component is added, only the linearity of the luminance signal can be compensated for without affecting the differential gain. Note that in the configuration of the present invention, the same effect can be expected even if a band-removal filter that removes a frequency band centered on the color subcarrier is used instead of the low-pass filter 2.

[Effects of the Invention] As explained above, according to the present invention, a nonlinear circuit receives an input video signal and creates a compensation signal, and receives the compensation signal and removes a signal in a frequency band including a color subcarrier component to generate a luminance signal. a low-pass filter that extracts only the component; a delay circuit that provides a delay corresponding to the delay time of the nonlinear circuit and the low-pass filter to the input video signal; and an output signal of the delay circuit and an output signal of the low-pass filter. Since it is composed of a combining circuit that adds the signals, it is possible to realize a luminance signal linearity compensation circuit that can compensate only the linearity of the luminance signal without affecting the differential gain of the color subcarrier.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a luminance signal linearity compensation circuit according to an embodiment of the present invention, and FIG. 2 is a system diagram showing a television video transmitter including a linearity compensation system according to the present invention. 1: Nonlinear circuit 2: Low pass filter 3: Delay circuit 4: Synthesizing circuit 11: Video band linearity compensation circuit 12: Modulator 13: Intermediate layer waveband linearity compensation circuit 14: Frequency converter 15: High frequency power amplifier

Claims (1)

[Claims] a nonlinear circuit that receives the input video signal and creates a compensation signal; a low-pass filter that receives the compensation signal and removes the signal in the frequency band including the chrominance subcarrier component to extract only the luminance signal component; Luminance signal linearity characterized by comprising a nonlinear circuit, a delay circuit that provides a delay corresponding to the delay time of the low-pass filter, and a synthesis circuit that adds the output signal of the delay circuit and the output signal of the low-pass filter. Compensation circuit.