Frequency tracking arrangement, corresponding method of frequency tracking and a radio receiver embodying such an arrangement

摘要

A frequency tracking arrangement comprises an input (30) to a frequency translation means (32) whose output is coupled to a filter and demodulator (34) which has both frequency (36), and amplitude (38) outputs. The frequency output is fed via a low pass filter (42) to a variable gain stage (44). The output of the gain stage (44) is fed to a feedback input of the frequency translation means (32). The amplitude output (38) of the filter and demodulator is fed to a control input of the variable gain stage (44). The amplitude output of the filter and demodulator is used to vary the amplitude of the feedback signal in the frequency tracking loop. When the arrangement is used in an FM radio receiver for audio, as the input signal weakens the frequency translation means (32) stops attempting to track the incoming signal. The subjective effect is that as the output signal amplitude diminishes relative to the noise, the receiver is less likely to search adjacent frequency bands and lock on to unwanted signals.