| 摘要 |
An apparatus comprising a tuning voltage-generating circuit (23) used as part of a voltage synthesizer (23,43) during a search operation of locate a broadcast signal, and thereafter as part of a phase-locked loop (23,57,59,61,63,71) to maintain the tuning frequency. The voltage-generating circuit (23) includes a window comparator (25), a charge pump (27) and a low-pass filter (29). An S curve signa is applied to the window comparator (25) to effectuate the searching operation until the receipt of a broadcasting signal. When the optimum tuning point is established, the local oscillation frequency at that time is counted to provide frequency division ratio data. The phase-locked loop (23,57,59,61,63,65,71) operates as a function of the frequency division ratio data to maintain the local oscillation frequency, whereby reception of the broadcasting signal is continued. Preferably, an automatic frequency control operation is performed before the phase-locked loop (23,57,59,61,63,65,71) is operated. |
