| 摘要 |
<p>A horizontal synchronization circuit (10) includes a horizontal AFC circuit (16), which receives a horizontal synchronizing signal from a synchronization separator circuit (12). The horizontal AFC circuit, a VCO (20) and a horizontal countdown circuit (22) form a PLL, and the horizontal AFC circuit generates the control voltage for the VCO. An LPF (30) is set to have a time constant τ1, while an LPF (32) is set to have a time constant τ2 smaller than the time constant τ1. When a composite video signal is supplied from a VCR and a head is switched, a comparator (34) produces a high-level output voltage while a comparator (36) produces a low-level output voltage. Specifically, the high-level signal is applied to the horizontal AFC circuit during vertical retrace periods to increase the loop gain of the PLL.</p> |
