JPS63123283A - Differential phase compensating circuit - Google Patents

Abstract

PURPOSE:To attain compensation without affecting linearity by a luminance signal by providing a BPF to take out a frequency band including a color sub-carrier component from the output of a compensating signal generating means in a color sub-carrier differential compensating circuit. CONSTITUTION:A non-linear circuit 1 extracts a level range to need a compensation from the level range from the white level to the black level of an inputted video signal, and applies the non-linear processing to this. Out of the compensating signals applied with non-linear processing, the signal of the frequency band with a color sub-carrier as a center is extracted by a BPF 2. After this extracting signal is phase-shifted to 90 deg. by a phase shifting circuit 3, the signal is added through a delaying circuit 4 to an original input video signal by a synthesizing circuit 5. Thus, since a luminance component is not included to the compensating signal, only the differential phase of the color sub-carrier can be compensated without giving an influence to the linearity of the luminance signal.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a differential phase compensation circuit used in a television video transmitter, and particularly to a differential phase compensation circuit that compensates for the differential phase of a color subcarrier in a video band. Regarding.

[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 a television video transmitter.

The source of nonlinear distortion is mainly a high frequency power amplifier, and compensation for this should be performed in an 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.

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, a video band linearity compensation circuit 11 and an intermediate frequency band linearity compensation circuit 13 are shown.
As a result, the device compensates for non-linear distortion generated in the high frequency power amplifier l5.

Nonlinear distortion includes amplitude distortion and phase distortion, and depending on the way the distortion appears or the method of measurement,
It has various names. For example, when the phase of a color subcarrier superimposed on a luminance signal changes depending on the luminance signal level, this phenomenon is called differential phase and is a typical example of phasic nonlinear distortion.

Conventionally, differential phase compensation circuits as shown in FIGS. 3(a) to 3(C) have been used for the purpose of compensating differential phase in a video band. In the figure, (a) shows a system diagram, (b) shows a simplified system diagram, and (C) shows a vector diagram. In the system diagram (a), the input signal V is applied separately to a non-inverting amplifier 21 and an inverting amplifier 22, and the respective output signals vl and -v1 are combined after passing through a resistor R and a coil L to generate a high It is received by the impedance and becomes the output signal V.

As shown in the vector diagram (C), the signal VR at both ends of the resistor and the signal 2 at both ends of the coil are always at right angles, and the amplitude of the output signal V0 is constant regardless of the frequency. In such a system, if the resistance value of the resistor R is configured to change depending on the voltage of the input signal, the output signal V
. The phase of changes depending on the input voltage. Therefore, when a signal obtained by superimposing a color subcarrier on a luminance signal is input, the phase of the color subcarrier changes at the output depending on the luminance signal level, and differential phase compensation is performed.

[Problems to be solved] The conventional differential phase compensation circuit described above affects the entire frequency band of the input signal, so it has the disadvantage that adjusting the differential phase compensation affects the luminance component. There is.

Therefore, it is an object of the present invention to provide a differential phase compensation circuit capable of compensating only the differential phase of a color subcarrier without affecting the linearity of a luminance signal, as a video band linearity compensation circuit. .

[Means for Solving Problems] A differential phase compensation circuit of the present invention that solves the above conventional problems includes a nonlinear circuit that receives an input video signal and outputs a compensation signal, and a nonlinear circuit that receives the compensation signal output from the nonlinear circuit. a band pass filter for extracting a signal in a frequency band containing a color subcarrier component, a phase shift circuit for receiving the output signal of the band pass filter and giving a phase rotation of approximately 90 degrees, and a nonlinear filter for the input video signal. The circuit includes a delay circuit that provides a delay corresponding to the delay time of the bandpass filter and the phase shift circuit, and a synthesis circuit that synthesizes the output signal of the delay circuit and the output signal of the phase shift circuit. ing.

[Examples] Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a differential phase compensation circuit according to an embodiment of the present invention.

In the figure, 1 is a nonlinear circuit that receives an input video signal and performs nonlinear processing, 2 is a bandpass filter that extracts a signal in a frequency band centered on the color subcarrier, and 3 is 90 degrees to the color subcarrier. 4 is a delay circuit that provides the input video signal with a delay amount corresponding to the delay time of the nonlinear circuit 1, bandpass filter 2, and phase shift circuit 3; 5 is a phase shift circuit This is a synthesis circuit that adds the output signal of No. 3 to the output signal of the delay circuit 4.

In such a configuration, the operating characteristics of the nonlinear circuit 1 are such that it can extract 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, and adjust its polarity and amplitude. That's fine. This corresponds to the level region to be compensated, compensation polarity, and compensation amount, and the output signal of the nonlinear circuit 1 can be called a compensation signal. The basic configuration of the present invention is to create a compensation signal from an input video signal, extract a signal in a frequency band centered on the color subcarrier from this compensation signal, and
After passing through a 90 degree phase shift circuit, it is added to the input video signal again. Since no luminance component is added, only the differential phase of the color subcarrier can be compensated for without affecting the linearity of the luminance signal.

Note that the phase shift circuit 3 performs differentiation by adjusting the phase of the color subcarrier of the output signal of the bandpass filter 2 and the phase of the color subcarrier of the output signal of the delay circuit 4 to have a phase difference of 90 degrees. It is used to ensure that only the differential phase is compensated with minimal impact on gain.

Further, in the configuration of the present invention, a similar effect can be expected even if a bypass filter that passes a frequency band including a color subcarrier component is used instead of the bandpass filter 2.

[Effects of the Invention] As described above, according to the present invention, there is a nonlinear circuit that receives an input video signal and outputs a compensation signal, and a frequency band that includes a color subcarrier component that receives the compensation signal output from the nonlinear circuit. a bandpass filter for extracting a signal from the bandpass filter; a phase shift circuit for receiving an output signal of the bandpass filter and giving a phase rotation of about 90 degrees; and a phase shifter for the nonlinear circuit and the bandpass filter for the input video signal. Since the configuration includes a delay circuit that provides a delay corresponding to the delay time of the circuit, and a synthesis circuit that synthesizes the output signal of the bandpass filter with the output signal of this delay circuit, the linearity of the luminance signal is not affected. It is possible to realize a differential phase compensation circuit capable of compensating only the differential phase of the color subcarrier without using the differential phase of the color subcarrier.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a differential phase compensation circuit according to an embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of a television video transmitter, and FIGS. FIG. 3 is a diagram for explaining the operation of the differential phase compensation circuit. 1: Nonlinear circuit 2: Bandpass filter 3: Phase shift circuit 4: Delay circuit 5: Synthesis circuit

Claims (1)

[Claims] A nonlinear circuit that receives an input video signal and outputs a compensation signal, a bandpass filter that receives the compensation signal output from this nonlinear circuit and extracts a signal in a frequency band containing a color subcarrier component, and an output of this bandpass filter. a phase shift circuit that receives a signal and provides a phase rotation of about 90 degrees; a delay circuit that provides a delay corresponding to the delay time of the nonlinear circuit, the bandpass filter, and the phase shift circuit to the input video signal; A differential phase compensation circuit comprising: a synthesis circuit for synthesizing the output signal of the delay circuit and the output signal of the phase shift circuit.