| 摘要 |
PURPOSE: To prevent the distortion or bent of the upper pattern of a screen pattern even when a horizontal period is deviated from a regular state. CONSTITUTION: The phase of a horizontal synchronizing signal subjected to synchronization separation is compared with the phase of a reference pulse from a horizontal system count-down circuit 17 by a phase detection circuit 15 and its error component is fed to a control terminal of an oscillator 16 as a frequency control voltage. The output of the oscillator 16 is fed to the horizontal system count-down circuit 17. A reference bias depending on the combined parallel resistance of resistors R1, R2 is set equal to the frequency control voltage in the regular horizontal synchronization state. A switch SW1 is open for a V mask period to eliminate an equivalent pulse for a vertical blanking period and an offset is provided to the frequency control voltage, and when an input horizontal frequency is offset, a large deviation from the control voltage in the lock state is suppressed. |
