Pulse shaping FM demodular with low noise where capacitor charge starts on input signal edge
First Claim
1. A receiver comprising, arranged in this order, an input section, an FM demodulator, to which a frequency-modulated input signal is applied, and an LF section, said FM demodulator comprising a pulse shaper and a low-pass filter, characterized in thatthe pulse shaper comprises:
- a series arrangement of at least a load and a capacitance, said load being coupled to a first supply terminal;
a switching device which charges said capacitance in a first state, initiated by a first edge of the frequency-modulated input signal, and which discharges said capacitance in a second state, initiated by a second edge following the first edge;
a first transistor having a base-emitter junction arranged across said capacitance, and having a collector coupled to the first supply terminal for limiting a voltage across said capacitance; and
output means for generating an output signal which varies with a current through said capacitance, wherein a charging time and a discharging time of said capacitance are smaller than a minimum time between two successive edges of the frequency-modulated input signal.
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Abstract
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.
111 Citations
10 Claims
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1. A receiver comprising, arranged in this order, an input section, an FM demodulator, to which a frequency-modulated input signal is applied, and an LF section, said FM demodulator comprising a pulse shaper and a low-pass filter, characterized in that
the pulse shaper comprises: -
a series arrangement of at least a load and a capacitance, said load being coupled to a first supply terminal; a switching device which charges said capacitance in a first state, initiated by a first edge of the frequency-modulated input signal, and which discharges said capacitance in a second state, initiated by a second edge following the first edge; a first transistor having a base-emitter junction arranged across said capacitance, and having a collector coupled to the first supply terminal for limiting a voltage across said capacitance; and output means for generating an output signal which varies with a current through said capacitance, wherein a charging time and a discharging time of said capacitance are smaller than a minimum time between two successive edges of the frequency-modulated input signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An FM demodulator comprising a pulse shaper, characterized in that said pulse shaper is implemented as an integrated circuit in a semiconductor material and comprises:
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a series arrangement of at least a load and a capacitance, said load being coupled to a first supply terminal; a switching device for charging the capacitance in a first state, initiated by a first edge of the frequency-modulated input signal, and for discharging the capacitance in a second state, initiated by a second edge following the first edge; a first transistor having a base-emitter junction arranged across the capacitance, and having a collector coupled to the first supply terminal or to a second supply terminal for limiting a voltage across said capacitance; and output means for supplying an output signal to an output terminal intended to have a low-pass filter coupled thereto, said output signal varying with a current through the capacitance, a charging time and a discharging time of the capacitance being smaller than a minimum time between two successive edges of the frequency-modulated input signal.
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10. A receiver comprising, arranged in this order, an input section, an FM demodulator, to which a frequency-modulated input signal is applied, and an LF section, said FM demodulator comprising a pulse shaper and a low-pass filter, characterized in that
the pulse shaper comprises: -
a series arrangement of at least a load and a capacitance, said load being coupled to a first supply terminal; a switching device which charges said capacitance in a first state, initiated by a first edge of the frequency-modulated input signal, and which discharges said capacitance in a second state, initiated by a second edge following the first edge; a first transistor having a base-emitter junction arranged across said capacitance, and having a collector coupled to a second supply terminal for limiting a voltage across said capacitance; and output means for generating an output signal which varies with a current through said capacitance, wherein a charging time and a discharging time of said capacitance are smaller than a minimum time between two successive edges of the frequency-modulated input signal.
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Specification