| 摘要 |
A horizontal countdown system is described for developing horizontal scan drive pulses in a color television receiver. The system includes a counter for counting the cycles of a color oscillator signal, various decoders for sensing the state of the counter, and a gate coupled to a selected one of the decoders for developing a horizontal scan drive pulse and for resetting the counter. Also included is a detector for sensing when a non-standard signal is received and when a dynamic phase error exists between composite sync and the receiver's flyback pulse. Depending on the extent and direction of any dynamic phase error, one or more of the decoders are successively coupled to the gate to reduce the phase error. When a non-standard signal is sensed, an analog phase locked loop generates phase-corrected pulses which are coupled to the gate to develop horizontal scan drive pulses until the presence of a standard signal is sensed.
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