JPH03135186A - Color television receiver - Google Patents

Abstract

PURPOSE:To attain automatic white level adjustment without malfunction even at reception by providing a switch to an input terminal of a demodulation circuit for SECAM system color demodulation and bypassing a color signal from a reference signal period. CONSTITUTION:A color signal is outputted even at an output of a SECAM SW 29 by a color signal retarded by a 1H delay line 28 causing malfunction for automatic white color adjustment at the SECAM system reception. Then a 1st switch comprising a 1st capacitor 33 and a transistor(TR) 35 and a 2nd switch comprising a 1st capacitor 34 and a TR 36 are provided between an input of a color demodulation circuit 4 and the output of the SW 29. A timing generator 12 is operated to output a high level for a reference signal period, 1st and 2nd TRs 34, 35 are turned on and the 1st and 2nd switches are closed and an input terminal of the circuit 4 is bypassed to a common level. Since the color signal is not inputted to the circuit 4, the automatic white color adjustment is operated normally.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to color television receivers, and particularly to SEC
The present invention relates to an AM type color television receiver with an automatic white adjustment circuit.

[Conventional technology]

In general, in color television receivers, a certain standard white signal is the standard for color reproduction, and if the standard white signal deviates, the color of the subject and the picture reproduced by the television receiver will be blurred. appear. Therefore, this standard white color must be sufficiently adjusted, and is adjusted for each television receiver, but due to aging, the current ratio of each cathode, which determines the RGB output brightness of the cathode ray tube, may shift. As a result, the reference white color shifts and the screen becomes reddish or bluish.

In order to automatically keep this reference white constant, a conventional technique includes an automatic white adjustment circuit.

Hereinafter, the circuit operation will be explained using FIG. 5 and FIG. 6.

The power for the Y/C separation circuit with composite video input 22 is as follows:
It is connected to the input of the Y signal processing circuit 2, and its output is connected to the first input of the matrix 5. The output of the Y/C separation circuit 2 is connected to the first input of the chroma 5W25, and the second input of the chroma 5W25 is connected to the third output of the timing generator 12. chroma 5w
The output of 25 is connected to a BPA (band pass amplifier) 30 input, the pressure of which is connected to the input of a color demodulation circuit 4, the output of which is connected to the second input of matrix 5. Here, the blocks after matrix 5 are B
- Since both G and R outputs have the same system configuration, explaining only the B output, the B output of matrix 5 is:
It is connected to the first input of the drive regulator 8 through an adder 26, 27. The output of the drive adjustment 8 is connected to the first input of the cutoff adjustment, the output of which is the blanking 1
0 input, blanking 10 output is connected to CRT
It is connected to the input of amplifier 11.

The output of the CRT amplifier 11 is connected to the base of a PNP transistor 17, its emitter is connected to the cathode of the CRT, and its collector is connected to GND through a resistor 19 and to each first input of a comparator 13, 14. There is. Each second input of the comparator 13.14 is connected to a respective reference voltage 15.16, and the output of the comparator 13 is connected to a hold capacitor 20.
through GND and to the second input of the drive regulator 8. The output of the comparator 14 is connected through a hold capacitor 21 to GND and to the second input of the cutoff adjustment 9. A third input of the comparator 13 is connected to the adder 26 through the first output of the timing generator 12 and the reference voltage 6 . The third input of the comparator 13 is connected to the adder 27 through the second output of the timing generator 12 and the reference voltage 7 . It is connected to the adder 27 through the second output of the timing generator 12 and the reference voltage 7 . The timing generator 12 has a vertical blanking (■, BLK) input 23 and a horizontal blanking (HBLK) input 24.

The signal waveforms of each part in FIG. 5 are as shown in FIG. 6. That is, the composite video signal input to the Y/C separation circuit 1 has a waveform of only the Y signal when input to the Y signal processing circuit, and has a waveform of only the chroma signal when input to the chroma 5W25.

Here, the chroma SW 25 receives the chroma S field pulse shown in FIG. 5 during the reference signal period, and performs an operation that prohibits input of the chroma signal to the next stage B-P-A during this period. To do this, a signal without a chroma signal is input to the B-P-A input during the reference signal period, as shown in FIG. N.T.S.
In the case of C method, this chroma signal is sent to the next stage color demodulation circuit 4.
Since the output of matrix 5 is directly input to
Only the waveform of the Y signal without the color demodulation signal is output during the reference signal period, and the waveform obtained by combining the color demodulation signal and the Y signal is output during the other periods.

Hereinafter, in order to perform the operation as shown in 9 of JP-A-60-18087, the reference white is automatically kept constant without any problems, so as mentioned above, it is a good color that does not change over time. Automatic white adjustment was performed.

[Problem to be solved by the invention]

In the color television receiver having the conventional automatic white adjustment described above, when receiving the SECAM system, the output of the limiter 30 is input to the LH delay line 28 and the SECAM 5W 29 as shown in FIG.
Since the output of is input to the color demodulation circuit 4 via the SECAM 5W29, even if the chroma S field pulse is input to the chroma 5W25, the first IH period of the reference signal period is as shown in FIG. The chroma signal waveform will be input.

Therefore, since the output of matrix 5 is a composite of the color demodulated signal and Y signal during the first IH period of the reference signal period, when adding the next stage reference signal with the adder,
This means that the offset of only the color demodulated signal is superimposed,
Since the reference white color adjustment is performed using this signal as a reference, there is a drawback that the reference white color is shifted.

[Means to solve the problem]

The color television receiver of the present invention has an IH that causes a malfunction in automatic white adjustment when receiving the SECAM system.
In order to prevent the chroma signal delayed by IH by the delay line from being input to the color demodulation circuit, a switch is provided that provides a pulse to control the input of the color demodulation circuit to be bypassed to the ground during the reference signal period.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention.

In the figure, parts that are the same as a conventional color television receiver with automatic white adjustment are designated by the same numbers. As mentioned above, the color signal delayed by the IH delay line 28 causes the color signal to be outputted to the output of the SECUM 5W29, but between the input of the color demodulation circuit 4 and the output of the SECUM SW29, the first Capacitor 33 and first transistor 3
5 connected in series, and a second switch connected in series with a second capacitor 34 and a second transistor 36.
The bases of the first and second transistors 34 and 35 are connected to the timing generator 12 to determine the on/off state of the switches.
Driven by

The timing generator 22 operates to output a high level during the reference signal period, and during this reference signal period, the first
and the second transistors 34 and 35 are turned on and the first and second transistors 34 and 35 are turned on.
switch is turned on, the input terminal of the color demodulation circuit 40 is bypassed to the common potential, and no color signal is input to the color demodulation circuit 4.

The above-mentioned operation will be further explained with reference to FIG.

Since the color demodulation input is bypassed by the first and second switches during the reference signal period, nothing is input during the reference signal period, and as a result, the output of the CRT amplifier 11 is also the original reference signal. The output is showing that the automatic white adjustment is working properly.

Note that although a capacitor and a transistor connected in series are used as the first and second switches, it goes without saying that this may be replaced with other switch means.

FIG. 3 is a partial circuit diagram for concretely realizing the present invention. The color signal output from the limiter 30 is
Added to W29 and IH day line 28. The output of IH delay line 28 is added to SECAM 5W29,
SECOM 5W29 is set to limiter 3 by line discrimination circuit 31.
By alternately switching the output color signal of 0 and the output color signal of IH delay line 28 for each IH, B-Y and R-Y
The continuous color signals are outputted to the color demodulation circuit 4. Secum 5
A first capacitor 33 is connected to each of the two lines of color signals R-Y and B-Y between W29 and the color demodulation circuit 4.
and a second switch consisting of a series connection of a second capacitor 34 and a second transistor 36 are connected to a common ground potential. The bases of the Ml transistor 35 and the second transistor 36 are commonly connected to the timing generator 12. In this example, two capacitors 33,34 and two transistors 35,36
The remaining parts are necessary for conventional SECAM color television receivers, and require only a small number of additional parts.

FIG. 4 shows another specific circuit. In this example, transistors 35, 36 . A circuit of capacitors 33 and 34 is provided upstream of the SECUM switch 29.

〔Effect of the invention〕

As described above, the present invention has the advantage that automatic white adjustment can be performed without malfunction even during SECAM system reception.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a color television receiver of the present invention, Fig. 2 is a diagram for explaining the operation of Fig. 1, Fig. 3 is a circuit diagram of this embodiment, and Fig. 4 is another example. Figures 5 and 7 are block diagrams of an example of a conventional color television receiver, and Figures 6 and 8 are diagrams for explaining the operations of Figures 5 and 7, respectively. be. 1...Y/C separation circuit, 2...Y signal processing circuit, 3...Band pass amplifier, 4...
...Color demodulation circuit, 5...R-G-B matrix, 8...Drive adjustment, 9...Cutoff adjustment, 10...B Ranking circuit, 11
...CRT amplifier, 12 ...timing generator, 29 ...SECOM SW, 28 ...IH delay line, 30 ...limiter.

Claims (1)

[Claims] an insertion means for inserting a reference voltage into the reference signal period immediately after vertical blanking; and automatically using a voltage obtained by comparing the reference voltage with a voltage proportional to the cathode current of the CRT during the reference signal period. In a color television receiver that performs white adjustment, a switch means is provided at the input end of a demodulation circuit for SECAM color demodulation, and the switch means is turned on during the reference signal period to bypass the color signal. A color television receiver characterized by: