JPS55115775A - Synchronizing signal generator - Google Patents

Abstract

PURPOSE:To produce the horizontal and vertical synchronizing signal without jitter, by resetting the counter with the control signal when external synchronizing signal is present at the period when the window pulse is fed and with the external synchronizing signal other than the case. CONSTITUTION:In the external synchronism by means of the synchronizing signal generator of various standard system such as NTSC and PAL systems, the reference signal So of the reference signal oscillator 1 is frequency-divided with the counters 2...5 to obtain the horizontal and vertical synchronizing signals SH, SV. The counter 3 is provided with the control circuit 21 for reset pulse and the forming circuit 20 of window pulse, and to the circuit 21, the control signal PHI based on the signal SH and the external synchronizing signal PHE are fed and the window pulse signal PW is fed. Further, if the signal PHE is present at the period when the pulse PW is fed, the counter 3 is reset with the signal PHI and in other case, with the signal PHE. Thus, if the signal PHE is fluctuated with the presence of transmission system, signals SH, SV can be formed without jitter.