US 4,729,042 AGranted

Clock signal generating circuit for digital signal recording device

AssigneePioneer Electronic Corporation

InventorHidehiro Ishii

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Abstract

A clock signal generating circuit for a data reproducing device, such as a device in which an audio signal is digitized and recorded in multiplex form together with other signals such as video signals, on a magnetic recording medium, wherein the stability of the frequency of the clock signal is maintained even in the presence of drop-out of the audio, video or other signals. The clock signal generating circuit includes a voltage-controlled oscillator receiving as a frequency-control input signal the output of a phase comparator comparing the output of the voltage-controlled oscillator with a pulse train signal extracted from the RF signal read from the recording medium. The voltage-controlled oscillator receives a second control signal which causes it to maintain its present frequency. The second control signal is produced by ORing drop-out signals generated when FM signals obtained by subjecting the video and audio signals to frequency modulation are no longer present in the RF signal.

Claims3

Dependent claims

A data reproducing device, comprising;

pick up means for reading out an RF signal recorded on a recording medium;
filter means for separating said RF signal into an FM video signal component, an FM audio signal component, and a digital audio pulse train signal;
first drop-out detection means for detecting drop-out in said FM video signal component to produce a first drop-out detection signal;
second drop-out detection means for detecting drop-out in said FM audio signal component to produce a second drop-out detection signal;
oscillator means for producing an oscillating output at a frequency determined in response to a first control signal, and including means for holding a current frequency in response to a second control signal;
phase comparison means for comparing the phase of said oscillating output with the phase of said pulse train signal to produce said first control signal, said first control signal having a level corresponding to a phase difference between said oscillating output and said pulse train signal;
hold signal generating means coupled to at least said first and second drop-out detection means for producing said second control signal in response to at least one of said first and second drop-out detection signals;
and
means for demodulating said pulse train signal using said oscillating output as a clock signal.

6 more elements

Dependencies are inferred from the claim text.