Claims Analysis
Total Claims: 6
Claim 1
Independent Claim
181 words
An FM receiver comprising a radio frequency (RF) section, means 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, an FM demodulator for demodulating the baseband modulation signal of the IF FM signal, which demodulator is coupled to a baseband signal processing device, and an IF tuning control loop via which the FM demodulator is coupled 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, characterized in that a first amplifier-limiter is arranged 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 decreasing at an increasing input signal amplitude and supplying 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.
Claim 2
Dependent Claim
125 words
An FM receiver as claimed in Claim 1, characterized in that the FM demodulator comprises a multiplier circuit and means for deriving, from the IF FM signal, a pair of FM-modulated signals having a mutually equal modulation signal and a phase difference which is 90 degrees on average at the carrier frequency and which varies with the FM modulation signal, said means comprising a tunable frequency-dependent phase-shifting circuit having a tuning control input, said FM demodulator also comprising a demodulator tuning control loop including a low-pass filter via which an output of the multiplier circuit is coupled to the tuning control input of the frequency-dependent phase-shifting circuit, the gain in the IF tuning control loop being smaller than that in the demodulator tuning control loop.
Claim 3
Dependent Claim
140 words
An FM receiver as claimed in Claim 2, characterized in that the demodulator tuning control loop of the FM demodulator incorporates a second amplifier-limiter, an output of which is coupled to the tuning control input of the tunable frequency-dependent phase-shifting circuit and to the baseband signal processing device, the gain of said second amplifier-limiter gradually decreasing at an increasing input signal amplitude and supplying an output signal whose amplitude increases monotonically to a limiting value for a continuous and gradual limitation of the tuning control signal in the demodulator tuning control loop at an increasing output signal amplitude of the FM demodulator, the tuning frequency deviation in the frequency-dependent phase-shifting circuit occurring at the limiting value of the second amplifier-limiter being larger than the tuning frequency deviation in the IF filter occurring at the limiting value of the first amplifier-limiter.
Claim 4
Dependent Claim
46 words
An FM receiver as claimed in Claim 2 or 3, characterized by a loop filter which is common for said two tuning control loops and is arranged between an output of the multiplier circuit of the FM demodulator and inputs of the first and second amplifier-limiters.
Claim 5
Dependent Claim
28 words
An FM receiver as claimed in any one of the preceding Claims 3 to 4, characterized in that each of the two amplifier-limiters comprises an emitter-coupled transistor pair.
Claim 6
Dependent Claim
157 words
An FM receiver as claimed in any one of the preceding Claims 2 to 5, characterized in that the IF filter and the frequency-dependent phase-shifting circuit comprise first and second cascade-arranged resonance amplifiers, respectively, each having in-phase and quadrature inputs and outputs, said in-phase and quadrature inputs of the first resonance amplifier receiving in-phase and quadrature components of the IF signal, said in-phase and quadrature outputs of the first resonance amplifier being coupled to first inputs of first and second multiplier stages of the multiplier circuit, and in-phase and quadrature outputs of the second resonance amplifier being coupled to second inputs of the second and first multiplier stages, respectively, outputs of the two multiplier stages being coupled to inputs of a superposition circuit for a mutual superposition of the output signals of the first and second multiplier stages, said superposition circuit being coupled to low-pass filter which is arranged in common in said two tuning control loops.