JPS58223B2 - Irofukuchiyou Kairono Tokuseikan Sokusouchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a color demodulation method that allows adjustment of the demodulation phase and demodulation level of a color demodulation circuit of a color television receiver with high precision and high efficiency using an easily observed Lissajous waveform. The present invention provides a circuit characteristic observation device.

The present invention will be described below based on the illustrated embodiments, but before that, a color demodulation circuit to be adjusted and a conventional example will be described.

FIG. 1 is a block diagram showing an example of a general color demodulation circuit.

In the figure, A is a color signal input terminal, and B is a horizontal pulse input terminal.

Further, 1 is a burst gate circuit including a color signal amplifier, 2 is a demodulation carrier generation circuit using a phase control loop, 3 is a color signal phase shifter, 4 is a demodulation carrier phase shifter, 5 is an RY axis demodulator, 6 is a matrix circuit for G-Y axis synthesis, 7 is B-
Y-axis demodulator, 8, 9, 10 are amplifiers with DC component regeneration function, C, D, E are R-Y output terminals, G
-Y output terminal and B-Y output terminal.

Most recent color demodulation circuits using monolithic ICs are of the demodulation type shown in FIG.

To adjust this color demodulation circuit. adjusting the demodulation phase by adjusting the phase shifters 3 and 4 so as to supply the demodulation carrier inputs (signal lines e and f) of the correct phase to the demodulators 5 and 7 with respect to the chrominance signal input (signal line d); There is demodulation gain adjustment in which the gains of amplifiers 8 and 9 are adjusted so that the ratio of demodulation gains for each axis becomes a specified value.

Conventionally, the adjustment of such a color demodulation circuit is carried out as shown in FIG.
As shown in C.2, this was done by observing the waveforms of the demodulated outputs of each axis on the time axis of an oscilloscope when an offset color bar signal was received.

That is, for the B-Y output, the sixth color bar (
Center CW 180°) is maximum, R-Y output is 3
The demodulation phase was adjusted so that the color bar (center CW 90°) was maximized, and the demodulation gain was adjusted by reading the amplitude of the output waveform of each axis.

However, this method using offset color bar signals
Due to the transient response of the color signal path, it is difficult to obtain a clear observed waveform as shown in Figure 2, and the original waveform itself has low reading accuracy in terms of phase and amplitude, and is difficult to read, resulting in poor adjustment accuracy and work efficiency. There were drawbacks.

The present invention overcomes the drawbacks of the prior art by using a new configuration of signal sources in place of the offset color bar signal and by displaying R-Y and B-Y output surge waveforms on an oscilloscope. This is how it was done.

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 3 to 5.

First, in FIG. 3, this shows a block diagram of an embodiment of the present invention, and 11 in the figure has a frequency of 3.579545 MH.
a carrier oscillator which is a reference phase signal generating means for generating a reference phase (CWOo) signal of z; 12 is an amplitude modulator;
3 is a delay circuit which is a signal delay means for creating a signal CW90° whose phase is delayed by 90° from the amplitude modulated CWO° signal; 14 is a gate circuit for multiplexing the signals of the amplitude modulator 12 and the delay circuit 13; and 15 is a gate circuit. In the color demodulation circuit to be adjusted, terminals A, B, C, and E in the color demodulation circuit 15 correspond to terminals A, B, C, and E of the circuit illustrated in FIG. 1, respectively.

Reference numeral 16 denotes a modulated wave generation circuit 17 that generates pulses φ1 and φ2 that cause the gate circuit 14 to perform a switching operation, and a horizontal pulse B and a modulated wave φ that are supplied to the color demodulation circuit 15.
18 is a pulse generation circuit that generates pulses to be supplied to Y
It is assumed that the oscilloscope has axis and Y-axis input terminals, and its input sensitivity is calibrated so that the input levels of the X-axis and Y-axis are 1:1 on the cathode ray tube surface when adjustment is completed.

FIG. 4 shows signal waveforms at various parts in FIG. 3, and the reference numerals in the figure correspond to the respective reference numerals in FIG. 3.

When the modulation wave φM is a sawtooth wave as shown in the figure, the output waveform of a correctly adjusted color demodulation circuit will be as shown by the solid lines shown in C and E in Figure 4, and the phase of the demodulation circuit will be shifted. If so, the waveform will look like the dashed line.

From these outputs, a surge waveform as shown in FIG. 5 is obtained on the cathode ray tube surface of the oscilloscope 18.

This Lissajous waveform consists of two straight lines that intersect at the origin, and exhibits the following properties.

The angle between the straight line by the CWO° signal and the -X axis is R-Y
Indicates the direction of deviation of the demodulation axis, and the angle formed between the straight line by the CW90° signal and the Y axis indicates the direction of deviation of the B-Y demodulation axis. When one demodulation axis is correct, the net deviation angle for the other shows.

In addition, the lengths of these straight lines indicate the respective demodulated output levels, and these waveforms indicate that the color signal is 1 horizontal (1H).
) Since the waveform observation method uses conventional offset color bars, there are far fewer transient phenomena, and highly accurate observed waveforms can be obtained using clear fixed phase signals.

As is clear from the above description, according to the present invention, R-Y
Also, the phase and level of B-Y demodulation can be directly observed, which is extremely effective when adjusting or inspecting the color demodulation circuit.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an example of a color demodulation circuit to be adjusted, Fig. 2 A, C, and 2 are color demodulation characteristic observation waveform diagrams for explaining a conventional example, and Fig. 3 is an embodiment of the present invention. An example circuit configuration diagram, FIG. 4 is a signal waveform diagram of each part of FIG. 3, and FIG. 5 is a diagram showing an example of observed waveforms obtained by the present invention. 11...Carrier oscillator, 12...Amplitude modulator, 13...
...Delay circuit, 14...Gate circuit, 15...Color demodulation circuit, 16...Pulse generation circuit, 17...Modulated wave generation circuit,
18...Oscilloscope.

Claims (1)

[Claims] 1. A reference phase signal generating means for generating a reference phase signal of a predetermined frequency, an amplitude modulator for amplitude modulating the reference phase signal from the reference phase signal generating means, and an amplitude modulated reference phase. A signal delay means for obtaining a signal whose phase is delayed by 90 degrees from the signal, an output signal of the amplitude modulator and an output signal of the signal delay means are input, and switching is performed to obtain a burst signal and a color signal. Works and shakes above. A gate circuit is provided for obtaining a signal sequentially containing the output signal of the width modulator and the output signal of the signal delay means for each horizontal period, and the output signal of the gate circuit is used for color demodulation of an NTSC color television receiver. A Lissajous waveform is projected onto the cathode ray tube of the oscilloscope by inputting the B-Y output and R-Y output of the color demodulation circuit to the X-axis and Y-axis of the oscilloscope, respectively. Characteristic observation device for color demodulation circuit.