| 摘要 |
A circuit for receiving an incoming RF signal incurring frequency drift and producing a local signal for tracking the incoming signal includes a phase-locked loop and means incorporated in the loop which compensate or correct for the frequency drift so as to maintain the loop locked on the incoming signal. The loop is defined by a phase detector, a DC amplifier and a voltage controlled oscillator connected in series. The correction means is coupled in parallel with the loop amplifier between the loop detector and amplifier at its one end and between the amplifier and a DC bias voltage supply terminal for the amplifier at its opposite end. The correction means is responsive to low frequency components of a DC voltage produced by the detector for changing, within preset limits, the DC bias voltage applied to the loop amplifier from the supply terminal as offsets in the DC voltage from the detector are caused by frequency drift of the incoming signal so as to maintain operation of the loop amplifier within its optimum bandwidth range.
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