PHASE SYNCHRONOUS CIRCUIT

摘要

PURPOSE:To obtain the clock signals featuring a highly stable phase for the sampling synchronized with the reference phase signal contained in the analog input signal by detecting the phase error of the clock signal out of the digital signal corresponding to the reference phase signal. CONSTITUTION:The composite color TV signal supplied to input terminal 20 is converted into the digital signal through A/D converter 21 and then drawn out at output terminal 22. Burst extraction circuit 24 extracts only the digital signal corresponding to the color burst signal among the output signals of converter 21 based on the synchronous signal isolated through synchronous isolator circuit 23. Thus the error is calculated at digital arithmetic circuit 25 to the reference phase difference. The output of circuit 25 is converted into the analog signal through D/A converter 26 and then applied to voltage control oscillator 26 to control the oscillation frequency. And the output of oscillator 26 is supplied to converter 21 in the form of the clock signal.