| 摘要 |
PURPOSE:To ensure the high-speed elimination of jitter, by produding through a PLL a continuous signal synchronized in phase with a synchronous signal extracted out of a composite video signal to be reproduced and increasing the sensitivity of a phase comparator included in the PLL only when a head is switched. CONSTITUTION:A switch SW1 is made to conduct for a certain period of a corresponding synchronous signal by a horizontal synchronous signal which is as an output of a synchronous signal separating circuit 32. A constant current source I1 is connected to the common emitter of transistors (TR)Q1 and Q2 of a differential switching circuit. The n-division output given from a dividing circuit 36 turns on either TRQ1 or Q2. The current flows into or out of a low pass filter 38 through a phase comparator 35. Thus a variable frequency scillating circuit 37 is controlled, and a multivibrator 101 triggered by a jitter detection output changeovers a switch SW2. As a result, the detecting capacity of phase difference of a comparator 35 is increased to ensure a high-speed elimination of jitter. |
