| 摘要 |
PURPOSE:To reduce the circuit component and to improve the noise immunity by providing a tri-state gate circuit in a horizontal synchronizing circuit of a television equipment so as to allow the tri-state gate circuit to apply phase comparison. CONSTITUTION:The tri-state gate circuit 13 compares the phase of a horizontal synchronizing pulse generated by a frequency divider 16 with that of a horizontal synchronizing signal and given the phase comparison output to a low pass filter 44. A phase difference signal filtered by a low pass filter 14 controls the oscillation frequency of a voltage controlled oscillator 15. The tri-state gate circuit applies the phase comparison, and the feature of the phase comparison operation, no phase comparison is applied while the tri-state gate circuit is not in operation. That is, the phase comparison is independently of the noise included in the synchronizing signal 52. Thus, the comparison output 53 is hardly affected by the noise included in the synchronizing signal and stable synchronizing state is kept as a PLL.
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