| 摘要 |
A synchronizing signal detector for detecting a received television synchronizing signal includes a synchronizing signal separator for separating the synchronizing signal from a received composite television signal. A phase-locked loop is provided, including an adjustable oscillator and a phase comparator for comparing the difference between the output of the synchronizing signal separator and the output of the local oscillator to produce an error signal. A sensor senses this error signal to indicate that the output of the synchronizing signal separator is, in fact, the synchronizing signal, when the error signal is of a predetermined value. In an AFT circuit, the error signal is used to control the tuning condition of the tuning section included in the television receiver. In one embodiment, the tuning section is an electronic tuner whose tuning condition is determined by a digital count. This count is changed until the error signal is sensed as being of the predetermined value, whereupon the digital count is inhibited from changing further.
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