JPS57193174A - Generator of scanned optical modulated timing clock - Google Patents

Abstract

PURPOSE:To eliminate a shift of a dot position, by detecting a delay of time between a scan start position synchronizing signal and a modulated timing clock and then compensating the shift of phase. CONSTITUTION:The output of a light detector 6 is divided to a latch circuit 22 and a tmer 24 by a synchronizing circuit 20. The circuit 22 delivers a pulse having a prescribed time of delay as the pulse duration to a charging/discharging circuit 28. The circuit 28 delivers the signal holding the duration of the input pulse to an analog subtractor 30. The subtractor 30 subtracts the analog voltage of the circuit 28 from a reference voltage source 32 and delivers the signal to a pulse position modulator 34. On the other hand, the timer 24 discharges the circuit 28 when the time during which a light beam reaches the blanking region requiring no modulation timing after starting the scan and finishes the scan of a photoreceptor elapses from the synchronizing position signal. As a result, a shift of a dot position due to the variance of the phase shift between a scan start position synchronizing signal and a modulated timing clock can be eliminated.