JPS6165689A - Color television carrying color signal gain control circuit - Google Patents

Abstract

PURPOSE:To realize a current color demodulation by providing a memory circuit in which a conversion factor is stored in advance when converting from an average peak value output from an average value circuit to an amplitude of a standard color burst signal, and a multiplication circuit multiplying an input carrying color signal to the conversion factor output from the memory circuit. CONSTITUTION:Peak value outputs of positive and negative color burst signals each fetched in the 1st and 2nd registers, 1, 2 are supplied to a subtracter 3. The positive and negative peak value outputs outputted from the subtracter 3 is fed to an absolute value circuit 4, and herein changed to peak value outputs of an absolute value. In a memory circuit B, a conversion factor to be converted into an amplitude of a standard color burst signal is stored preliminary with respect to the average peak value output from the third register 6. The memory circuit B outputs a conversion factor output corresponding to the average peak value output outputted from an average value circuit A to a multiplier C.The multiplier C multiplies the conversion factor output from the memory circuit B to a carrying color signal in input color signals and outputs the multiplication output as a standardization carrying color signal.

Description

Detailed Description of the Invention Technical Field The present invention relates to technology for digitally processing color television signals, and in particular to a color television carrier color signal gain control circuit that controls the carrier color signal gain of a color television signal. Regarding.

<Prior Art> In a color television receiver, it is necessary to create a color subcarrier synchronized with a color burst signal in a color television signal.
This was realized using analog circuits such as the Phase Control (Phase Control) method. However, both of these circuits
The color burst signal sent from the transmitting side is extracted and used as is. Therefore, variations in the color burst signal due to external factors such as variations in received field strength, impedance mismatch between the antenna and receiver, and internal factors such as variations in the local oscillation frequency will affect the color subcarrier as the output. Therefore, the color g11 carrier wave is added to the carrier color signal and becomes a noise component in the demodulation circuit that demodulates the color.
This will impede accurate demodulation. Furthermore, fluctuations in the color burst signal, which occur for the same reason, are caused by ACC (Autoaati
c Chroma Contr61) Since it is also added as an input to the circuit, the amplitude ratio between the luminance signal and the chromaticity signal is constant, but it is no longer a positive value, and the error due to noise components and color saturation changes is also reduced. Live.

<Object of the Invention> The present invention makes it possible to realize more accurate color demodulation that follows the influence of fluctuations in color burst signals due to factors outside and inside the receiver using a digital circuit configuration. The purpose is to

<Configuration of the Invention> In order to achieve the above object, the present invention samples the peak values of an input color burst signal extracted from a color television signal, and calculates the average value of the peak values as an average peak value. an average value circuit that outputs a value output; a storage circuit that stores in advance a conversion coefficient for converting the average peak value output from the average value circuit into the amplitude of a standard color burst signal; and a conversion coefficient from the storage circuit. A multiplication circuit that multiplies the coefficient output by an input carrier color signal is provided, and the output of the visiting multiplication circuit is made into a standardized carrier color signal.

<Example> Hereinafter, the present invention will be described in detail based on an example shown in the drawings. FIG. 1 is a block diagram showing the overall configuration of an embodiment of the present invention. In FIG. 1, symbol A is an average value circuit that samples the peak value of an input color burst signal extracted from a color television signal and outputs the average value of the peak values as an average peak value output,
B is a storage circuit, such as a programmable ROM, in which a conversion coefficient for converting the average peak value output from the average value circuit A to the amplitude of a standard color burst signal is stored in advance, and C is a storage circuit such as a programmable ROM. This is a multiplication circuit that multiplies the conversion coefficient output from the input carrier color signal.

The average value circuit A receives the first color burst signal whose peak value is sampled. The second register 1.2 and the first register 1.2. a subtracter 3 for subtracting the output of the second renostar 1.2;
An absolute value circuit 4 that takes the absolute value of the output of this subtracter 3, an adder 5 that adds the output of this absolute value circuit 4, a third renostar 6 that takes in the output of this adder 5, and a color to be averaged. A counter 7 for counting the number of peak values of the burst signal; and a gate circuit 8 that controls the third register 1.2.6.

Next, the operation will be explained with reference to the time chart of the color burst signal and clock signal shown in FIG. FIG. 2(a) is a time chart of an input color burst signal sampled at, for example, four times the color subcarrier frequency CLO, and FIG. 2nd Reno Star 1.
1. Controls the operation timing of 2. Second clock CL
1. It is a time chart of Cl3. Here, the first clock CLI is generated with a period of 2T from time El, and is transmitted from the gate circuit 8 to the second reno star 1.
and the second clock CL2 is given at time t2Q2.
=tl +T) with a period of 2T, and is given to the second register 2 from the gate circuit 8. The time point corresponds to the positive peak value of the color burst signal, and the time t2 corresponds to the negative peak value of the color burst signal. The period T is half the period 2T of the color burst signal.

First, the operation of the average value circuit A will be explained. 1st゜Second clock CL1. At the timing responsive to Cl3, the second register 1 receives the positive peak value output of the color burst signal, and the second register 2 receives the negative peak value of the color burst signal. The positive and negative peak value outputs of the color burst signals respectively taken into each renoster 1.2 are given to a subtracter 3. In the subtracter 3, the first . The outputs from the second register 1.2 are subtracted from each other. That is, if the positive peak value output is 10P1 and the negative peak value is -P2, this subtracter 3 outputs 10PI
-(-P2)-+Pl+P2 or -P2-(+P I
) = -P 1 - P2 will be subtracted, so if the absolute values of Pl and -P2 are equal, the output of the subtracter will be the value of each peak P1. -It will be twice as much as P2. This peak value is halved by the subtracter 3. The positive and negative peak values output from the subtracter 3 are sent to the absolute value circuit 4, where they are converted into absolute peak value outputs. The current peak value output from the absolute value circuit 4 is sent to the adder 5.
After being added to the previous summed peak value output from the third register 6, it is inputted to the third renostar 6 as a final summed peak value output.

Here, the number of additions in the adder 5 is counted by a counter 7, and when the number of additions n that has been set in advance is reached, a control signal is supplied from the counter 7 to the gate circuit 8, and the gate of the gate circuit 8 is closed. Then, the output of the third register 6 is held in the third renoster 6 until the gate of the gate circuit 8 is opened next time.

In this way, time t1. t2. ...has passed,
When the number of additions by the adder 5 reaches n, the output of the adder 5 is divided by the number of additions n in a third renostar 6 having a division function. This division value becomes an average peak value output obtained by taking the average of the peak values of the color burst signals of nl[4. Note that the purpose of dividing by n after one addition is inserted to integrate instantaneous noise.

This average value is input to storage circuit B. This memory circuit B
For the average peak value output from the third renostar 6,
A conversion coefficient to be converted into the amplitude of a standard color burst signal is stored in advance, and the storage circuit B outputs the conversion coefficient corresponding to the average peak value output from the average value circuit A to the multiplier C. do.

Multiplier C multiplies the carrier color signal in the human color signal by the conversion coefficient output from storage circuit B, and outputs the multiplication output as a standardized carrier color signal.

Therefore, if color demodulation is performed using the standardized carrier color signal from the multiplier circuit C, more accurate color demodulation becomes possible.

Note that in the above embodiment, the first. The period of the second clock is 2
T and matches the period 2T of the color burst signal, but for example, this is set to 4, which is twice the period of the color burst signal.
Good as T. In this case, every other peak value of the color burst signal is averaged.

<Effects of the Invention> Since the present invention is configured as described above, it is possible to obtain an automatic color signal gain control circuit that follows fluctuations in a color burst signal based on factors outside the receiver and inside the receiver. Therefore, more accurate demodulation of the color turpentine signal is possible.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the overall configuration of an embodiment of the present invention, and axis-1≠→ in FIG. 2 is a time chart of signals for explaining the operation of the embodiment of FIG. A is an average value circuit, B is a memory circuit, and C is a multiplier.

Claims (1)

[Claims] (1) An average value circuit that samples the peak value of a color burst signal extracted from a color television signal and outputs the average value of the peak values as an average peak value output, and an average value output from the average value circuit. A storage circuit in which a conversion coefficient for converting a peak value output to the amplitude of a standard color burst signal is stored in advance, and a multiplication circuit that multiplies the conversion coefficient output from the storage circuit by an input carrier color signal, A color television carrier chrominance signal gain control circuit characterized in that a multiplier circuit output is a standardized carrier chrominance signal.