SERVO CONTROL OSCILLATION CIRCUIT

摘要

PURPOSE:To stabilize the operation of a VCO by applying on/off control periodically to the oscillation of a voltage controlled variable frequency oscillation circuit (VCO). CONSTITUTION:The VCO 3 uses a control pulse SCB from an input terminal 14B to apply on/off control of its oscillation in a servo control oscillation circuit 12B. The control pulse SCB consists of a pulse PB at a high level for a prescribed period including a sampling pulse SP in the vertical blanking period VBLK and a pulse PB' at a high level during each other line including a video line LB of a B-Y signal. The VCO 3 is oscillated during a high level period of the control pulse SCB and the oscillation is stopped at a low level period. The phases of reference pulses Sb at the leading point of time of the pulse PB of the control pulse SCB are set so that they are always equal at all the vertical blanking periods VBLK, the VCO 3 stops the oscillation at a low level period of the control pulse SCB at the low level period of the control pulse SCB and starts the oscillation at the leading from the low to the high level, and the phase of an output signal VR-Y is always kept constant at the oscillation start point of time.