Fm receiver with dynamic intermediate frequency (if) filter tuning

Abstract

An FM receiver with a modulation signal-dependent intermediate frequency (IF) filter tuning, comprising a radio frequency (RF) section, a tunable mixer stage for a down-conversion of a desired RF FM reception signal to an intermediate frequency (IF) FM signal, an IF section comprising a tunable IF filter, and an FM demodulator for demodulating the baseband modulation signal of the IF FM signal. The demodulator is coupled to a baseband signal processing device and an IF tuning control loop couples the FM demodulator to a tuning control input of the IF filter for an instantaneous tuning control of the IF filter by means of the baseband modulation signal. In order to enhance the tuning behaviour, the FM receiver includes a first amplifier-limiter connected in the IF tuning control loop between an output of the FM demodulator and the tuning control input of the IF filter. The gain of said first amplifier-limiter gradually decreases as the input signal increases. The first amplifier-limiter supplies an output signal whose amplitude increases monotonically to a limiting value for a continuous and gradual limitation of the tuning control signal in the IF tuning control loop at an increasing output signal amplitude of the FM demodulator.