JPS57186840A - Phase synchronizing oscillator - Google Patents

Abstract

PURPOSE:To obtain an output which stably follows an input varied within a range decided in advance, by providing a phase shifter for providing a fixed phase displacement to an oscillator output, and a switching device for selecting the nearest signal to phase of an input AC signal, in its phase shifter output and the oscillator output. CONSTITUTION:A phase difference of a subcarrier in a color burst period of an input signal from an input terminal 51, and an output of a switching device 56 is derived by a phase difference circuit 52 and is smoothed by a filter 53. By an output of this filter 53, oscillation frequency of an oscillator 54 is controlled so that an output of the circuit 52 becomes zero. Also, information of the color burst period is provided to the circuit 52 by a synchronizing signal from an input terminal 59, an output of the oscillator 54 is inputted to the switching device 56 and a phase shifter 55, and a phase value of + pi radian is provided by the phase shifter 55. Subsequently, in the switching device 56, the input subcarrier, an output of the oscillator 54 and an output of the phase shifter 55 are compared as to each phase, a signal being near the input subcarrier is selected, is supplied to the circuit 52, and simultaneously is outputted as an output of a phase synchronizing oscillator from an output terminal 58.