Burst/continuous wave converting apparatus for generating continuous wave in response to bursts

Abstract

Abstract A color synchronizing circuit (120) of a color television receiver comprises a PLL circuit comprising a phase detector circuit (12b), an LPF (12c), a VCO (12d) and a 1/4 frequency divider (12f). Color bursts extracted from a composite chrominance signal by a burst gate circuit (12a) are directly applied to an input of the PLL circuit through an adder (12g) in a burst period while being circulated through a loop including a delay circuit (12h) by a switch (12i). The delay circuit has a delay time which is equal to a period of the back porch of a horizontal synchronizing signal having the color burst inserted thereinto and is equal to integer multiples of a cycle of a chrominance subcarrier. Thus, the repetition frequency of the color burst sequentially supplied to the PLL circuit while being circulated through the above described loop becomes 16 times a horizontal frequency f H . As a result, the sidebands which appear at the intervals of f H in the frequency spectrum of the color bursts is decreased, so that the capture range of the PLL circuit becomes wide.

Inventors

• 👤 Nobukazu Hosoya

Bibliographic Details