Frequency modulation-demodulation circuit

Claim 1

A broadband, low noise counter detector demodulator for a frequency modulation radio receiver in which an intermediate frequency FM signal is applied to said demodulator for detection comprising: a limiter circuit for producing substantially uniform height pulses at the same repetition frequency as the frequency of the applied intermediate frequency FM signal, said frequency being nominally in the center of the FM band, said pulses having a rise and fall time substantially smaller than the pulse width; a differential circuit responsive to said pulses produced by said limiter for producing relatively sharp pulses; a broad band, one-stage transistor pulse amplifier employing controlled feedback between collector and base and responsive to the pulses produced by said differential circuit, said pulse amplifier including a series capacitor for coupling to a succeeding stage from the transistor collector electrode, said amplifier for amplifying the pulses produced by said differential circuit without deteriorating pulse rise and fall time; a pulse expander circuit responsive to said amplified pulses using a single transistor of predEtermined storage characteristics, said transistor having its base electrode connected to a series circuit including a diode and a currentlimiting resistor, said series circuit being connected to circuit common, said base electrode being connected to said coupling capacitor of said amplifier stage, said coupling capacitor and series circuit forming a controlled biasing circuit for determining the amount of storage of said expander circuit so that the desired expansion of pulses is effected; and an integrating circuit responsive to the expanded pulses for producing a demodulated audio output signal.