JPS6151832B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a color television receiver capable of receiving two types of color television signals having different color subcarrier frequencies.

Some color television signals have two types of color subcarrier frequencies (for example, 3.58MHz and 4.43MHz), and when receiving such color television signals, two systems of color demodulation circuits must be prepared. , it is necessary to switch this depending on the received color television signal. At this time, it is natural to share functionally common circuits as much as possible and to switch only the minimum necessary circuits. Therefore, by switching the oscillation frequency of the local oscillator for performing color demodulation and the hue adjustment circuit, it is possible to demodulate each color television signal.

In the process of switching the necessary circuits described above, this invention determines whether the switching state is correct for the received color television signal, and if the switching state is correct, it maintains this state, and if it is The purpose is to correct this condition and significantly simplify the circuit.

Hereinafter, this invention will be explained in detail using the drawings. In the figure, reference numeral 1 denotes a composite color television signal input terminal, to which two types of color television signals having different color subcarrier frequencies, such as 3.58MHz and 4.43MHz, are applied. 2 is a bandpass filter that separates the color subcarrier frequency from the composite color television signal; 3 is a bandpass amplifier; 4 is a color control amplifier; 5 is an input terminal to which a color control voltage is applied; 6 is a demodulation circuit;
Demodulated outputs of RY and BY appear at terminals 7 and 8, respectively. 9 is a burst gate circuit, and a burst gate pulse 11 is applied to a terminal 10. 12 is an automatic frequency and phase control circuit (hereinafter referred to as
(referred to as AFPC circuit), 13 is AFPC filter, 1
4 is a local oscillation circuit. 15 and 16 are respectively
3.58MHz and 4.43MHz crystal oscillators, 17 is a switch for selectively capturing the crystal oscillators 15 and 16. Reference numeral 18 indicates a phase shift circuit, and reference numeral 19 indicates a color killer detection circuit, which generates an output and controls the color control amplifier 4, usually when receiving monochrome broadcasting. 2
0 is a hue adjustment circuit, which is connected to the demodulation circuit 6 and whose hue is adjusted by a hue control voltage applied to a terminal 21. Sub-hue adjustment circuits 22 and 23 correspond to 3.58 MHz and 4.43 MHz, respectively, and are selectively switched by a switch 24. The switch 24 and the switch 17 are operated in conjunction with each other by a flip-flop 25. Reference numeral 26 denotes an AND gate, into which a flip-flop trigger pulse 28 such as a vertical synchronizing signal and a color killer voltage obtained from the color killer circuit 19 are respectively inputted via an input terminal 27 .

Next, we will explain the functions in detail.

First, assume that a 3.58MHz color television signal is arriving at terminal 1. At this time, the switches 17 and 24 are in the illustrated position, i.e.
Assuming that the 3.58MHz crystal oscillator and 3.58MHz sub-hue adjustment circuit are connected, the output of the color killer detection circuit is at a low level (hereinafter referred to as L, the reverse is referred to as H), and gate 2
6 output does not appear.

Therefore, the output state of the flip-flop 25 remains the same, and is in the correct demodulation state of the 3.58 MHz color television signal.

Next, in this state, when a 4.43MHz color television signal is received, the crystal oscillator 15
Since the 3.58MHz connection state is established, the AFPC circuit 12 is not locked and the color killer detection circuit 1
The output 29 of 9 becomes H. Therefore, a flip-flop trigger pulse is generated at the output of the AND gate 26, and the flip-flop 25 receives this trigger pulse 28 and changes its state. Therefore, the switches 17 and 24 are in the opposite state as shown, and a 4.43 MHz crystal resonator is connected to the local oscillation circuit 14. Therefore, the AFPC circuit 12 is locked, and the output of the color killer detection circuit 19 is L.
becomes. Therefore, no output appears at the AND gate 26, and the flip-flop 25 remains in its current state, maintaining the correct demodulation state of the 4.43 MHz color television signal.

In this way, the switching circuit is automatically switched so as to always maintain the correct demodulation state for the incoming signal.

In the above embodiment, the switching circuits 17 and 24 are controlled by the AND gate 26 and the flip-flop 25, but the switching circuits 17 and 24 can be similarly implemented by other control circuits.
In addition, although we have explained the NTSC system, which has two different color subcarrier frequencies of 3.58MHz and 4.43MHz, it is also possible to configure a similar automatic switching circuit for the PAL system, and it is also possible to configure a local oscillator circuit. This embodiment is not limited to the combination of AFPC circuits, but can also be applied to a ringing method or an injection method by switching the crystal oscillator.

As described above, according to the present invention, it is possible to automatically switch the color demodulation of two types of color television signals having different color subcarrier frequencies with an extremely simple configuration, and the practical value of the present invention is great.

[Brief explanation of the drawing]

The figure is a block diagram showing the main parts of a color television receiver which is an embodiment of the present invention. In the figure, 1 is a composite color television signal input terminal, 6 is a demodulation circuit, 9 is a burst gate circuit, 1
4 is a local oscillation circuit, 15 and 16 are crystal oscillators, 19 is a color killer detection circuit, 17 and 24
25 is a flip-flop, 26 is an AND gate, 28 is a flip-flop, 26 is an AND gate, and 28 is a flip-flop trigger pulse.

Claims (1)

[Claims] 1. In a color television receiver capable of receiving two types of color television signals having different color subcarrier frequencies, a gate circuit for extracting a signal of the color subcarrier frequency from the received color television signal; An oscillator that generates two types of signals each having the same frequency as the carrier frequency, a switch that selectively switches the output of this oscillator, and a detection means that detects a frequency matching state between the output of the gate circuit and the selected output of the oscillator. , a color television receiver comprising control means for maintaining the selection of the switch when frequency matching is detected by the output of the detection means, and changing the selection of the switch when frequency matching is not detected.