JPH0344380U - - Google Patents

Description

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of a fully synchronous detection circuit according to the present invention, Fig. 2 is a circuit diagram showing a conventional completely synchronous detection circuit, and Fig. 3 is a circuit diagram of a voltage control circuit constituting the fully synchronous detection circuit. FIG. 3 is a circuit diagram showing an external tank circuit. 2...Intermediate frequency amplifier, 3...Phase detector, 4
... Synchronous detector, 5 ... Voltage controlled oscillator, 6 ...
Phase shifter, 7... Filter circuit, 10... Audio intermediate frequency detector, 12... PLL cutoff switch, 13
...PLL lock detection circuit.

Claims (1)

[Claims for Utility Model Registration] A synchronous carrier signal synchronized with the input video intermediate frequency signal to be detected is generated from a voltage controlled oscillator of a phase-locked loop circuit, and the synchronous carrier wave signal is used to generate the input video intermediate frequency signal. In a fully synchronous detection circuit that performs synchronous detection with a synchronous detector and detects an input audio intermediate frequency signal with the audio intermediate frequency detector using the synchronous carrier signal as a second local oscillation frequency signal, the phase locked loop circuit detects the input audio signal. A phase-locked loop lock state detection circuit detects that it is in a non-lock state with respect to an intermediate frequency signal, and a switch is inserted into the loop of the phase-locked loop circuit and receives a detection output from the phase-locked loop lock state detection circuit. a phase-locked loop disconnection switch circuit that is opened, and when the phase-locked loop circuit is in an unlocked state with respect to the input video intermediate frequency signal, the phase-locked loop disconnection switch circuit is opened to disconnect the phase-locked loop. Complete synchronization of a television receiver, characterized in that the loop of the circuit is cut off and the free-running oscillation frequency signal from the voltage controlled oscillator is used as a second local oscillation frequency signal to detect the input audio intermediate frequency signal. Detection circuit.