| 摘要 |
PURPOSE:To prevent a VCO from unnecessary variation of output frequency by sample-holding the output of a phase comparator at the leading edge or trailing edge of a vertically synchronizing pulse of a composite synchronizing signal and inputting the sample-holding value to the VCO as a control signal. CONSTITUTION:A vertical synchronization separating circuit 7 separates a vertically synchronizing signal from a composite cynchronizing signal inputted from an input terminal 1 and sends the separated signal to a synchronizing width extending circuit 8. The circuit 8 extends the pulse width of the vertically synchronizing signal and sends the extended signal to a sample holding circuit 4. The circuit 4 samples the output of an amplifier 3 at the trailing edge of the extended synchronizing pulse, holds the sampled voltage up to the leading edge of the pulse and outputs the held voltage to the VCO 5. When there is no extended synchronizing pulse, the signal inputted from the amplifier 3 is outputted to the VCO 5 as it is. Consequently, the VCO can be prevented from the influence of the output variation of a phase comparator 2 upon its output frequency. |
