JPS56169423A - Phase synchronizing circuit - Google Patents

Abstract

PURPOSE:To eliminate the phase jitter of clocks, by adding a fluctuating signal to an output of a voltage controlled oscillator and producing a sample clocks through slicing. CONSTITUTION:An NTSC signal 11 at an input terminal is fed to a synchronizing separation circuit 4 and fed to an A/D converter 2 and digitized for output. A part of this output is fed to a burst pickup circuit 5 and the color burst signal is picked up by the output of the circuit 4. The shift of phase between the color burst signal and the reference is detected at an operation circuit 6 to control a voltage controlled oscillator 8 via a D/A converter 7. Further, a step fluctuation signal in which the level corresponding to the 3rd cycle of the color burst signal is zero and the level before and after it is changed positive or negative with a given step, is produced at a production circuit 41 and it is added by an addition circuit 42 to the output of an oscillator 8, and sampled clocks are formed by slicing it at a given level with a slicer 43. Thus, the phase comparison characteristics are in bang bang control and the phase jitter of clock can be eliminated.