JPS5674805A - Dropout compensating circuit for sampling pulse - Google Patents

Abstract

PURPOSE:To always ensure a steady reproduced picture, by producing the pulse of the same frequency as the sampling pulse immediately before the production when the dropout is produced to the sampling pulse which is extracted out of the reproduced video signal. CONSTITUTION:The photoelectric transducer 1 the disk or the like of which is scanned by the laser beam reproduces the FM video signal. The tuning circuit 5 extracts the sampling pulse out of the video signal demodulated through the FM demodulator 4, and the bistable-multi 22 of the dropout compensating circuit 10 delivers logic 1. Said extracted sampling pulse is applied to the multi 22. Thus the FF23 is hit to close the loop of the PLL circuit 6 via the comparison circuit 7 or the like, and then the pulse of the same frequency as the sampling pulse is delivered from the voltage control oscillator 9 of the circuit 6. While in case when the dropout occurs to the sampling pulse, the output of the multi 22 is inverted to the logic 0 after the time lapse of the time constant formed with the resistance R and the capacitor C. Thus the loop of the circuit 6 is opened, and the oscillator 9 generates the pulse of the same frequency as the sampling pulse right before occurrence of the dropout. As a result, a steady reproduced picture can always be formed.