U.S. Philips Corporation

Willem A Sloof

Wolfdietrich G Kasperkovitz

Hendricus C De Ruyter

Wolter Bijker

Kaveh Kianush

An FM receiver having an RF section, a first tunable mixer stage for the frequency conversion of a desired RF FM reception signal into a first intermediate frequency signal, an IF device and an FM demodulator. In order to enhance the integration of the apparatus, while maintaining a signal processing ability which is free from distortion, the FM receiver includes circuitry incorporated in the signal path for converting a single-phase signal into a pair of signals in mutual phase quadrature. The pair of phase-quadrature signals is applied to in-phase and quadrature signal paths of the IF device. The IF device having a polyphase IF filter incorporated in the in-phase and quadrature signal paths and has a bandpass characteristic which is symmetrical around its resonance frequency. The polyphase IF filter is coupled to the FM demodulator.

FM receiver including a phase-quadrature polyphase if filter

An FM receiver includes an RF section, a first mixer stage for converting a desired RF reception signal into a first IF signal having a carrier frequency located on average at a first intermediate frequency, a first IF section for selecting the first IF signal, and a second mixer stage for converting the first IF signal into a second IF signal having a carrier frequency located on average at a second intermediate frequency. The second intermediate frequency is below the first intermediate frequency. A second IF section selects the second IF signal and is coupled to an FM demodulator for demodulating the baseband modulation signal of the desired RF reception signal, followed by a low-pass filter for selecting the baseband modulation signal. In order to enhance the signal processing of the FM receiver and to realize a receiver in a largely integrated form, to provide a substantially fully integrable IF stage which is easily exchangeable with the IF section of substantially all existing FM receivers of the superheterodyne type, and to realize a selectivity considerably greater than that of known IF filters, a third mixer stage is coupled between the second IF section and the FM demodulator for converting the second IF signal to a third IF signal having a carrier frequency located on average at a third intermediate frequency which is above the second intermediate frequency.

FM Receiver having multiple IF stages

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.

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Eindhoven, Netherlands

Willem A Sloof