Pulse shaping FM demodular with low noise where capacitor charge starts on input signal edge

摘要

A receiver having, arranged in this order, an input section, an FM demodulator, to which a frequency-modulated input signal is applied, and an LF section, which FM demodulator includes a pulse shaper and a low- pass filter, the pulse shaper comprising a series arrangement of at least a load and a capacitance, the base-emitter junction of a transistor being arranged across the capacitance, and further including a switching device for charging and discharging the capacitance. The pulse shaper generates a low-noise pulse in that charging of a capacitance is started upon an edge of the input signal. The capacitance voltage is measured by a single transistor and when the transistor is turned on, the charging current of the capacitance is diverted via the transistor, so that the capacitance voltage is limited. The capacitance is discharged upon a second edge, after which the cycle is repeated. The output signal of the pulse shaper is a signal which varies with the current through the capacitance.