Phase modulator circuit
First Claim
1. A phase modulator circuit comprising means for applying a modulating signal to the circuit;
- a ramp generator for generating a ramp signal in response to the receipt of an edge of a timing signal, the level, relative to a nominal reference voltage, from which the ramp is generated, varying in response to the amplitude of an applied modulating signal; and
a level detector, having a defined switching level, coupled to the ramp generator, which detector produces an output edge signal in response to the ramp passing the switching level in a given direction, the position in time of the edge signal being related to the amplitude of the modulating signal;
characterized in that the ramp generator comprises a capacitor;
a constant current source connectable to one side of the capacitor in response to the receipt of an edge of a timing signal; and
means for establishing the reference voltage on the other side of the capacitor, the modulating signal being also applied to the other side of the capacitor.
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Accused Products
Abstract
A problem with phase modulators particularly when modulating high frequency signals with signals of audio frequency is that noise is generated during the production of a free running ramp signal and noise is present on the modulating signal so that accurate detection of the modulating signal is not possible. In order to avoid this problem a fast ramp signal is generated by charging a low value capacitor (12) from a constant current source (13) in response to the edge of an applied timing signal. The starting voltage of the ramp signal is related to the phase of a modulating signal derived from a source having a low output impedance (25). The ramp signal is applied to a level detector (16) having a defined switching level, which detector produces an output edge signal in response to the ramp signal traversing the switching level in a given direction.
8 Citations
7 Claims
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1. A phase modulator circuit comprising means for applying a modulating signal to the circuit;
- a ramp generator for generating a ramp signal in response to the receipt of an edge of a timing signal, the level, relative to a nominal reference voltage, from which the ramp is generated, varying in response to the amplitude of an applied modulating signal; and
a level detector, having a defined switching level, coupled to the ramp generator, which detector produces an output edge signal in response to the ramp passing the switching level in a given direction, the position in time of the edge signal being related to the amplitude of the modulating signal;
characterized in that the ramp generator comprises a capacitor;
a constant current source connectable to one side of the capacitor in response to the receipt of an edge of a timing signal; and
means for establishing the reference voltage on the other side of the capacitor, the modulating signal being also applied to the other side of the capacitor. - View Dependent Claims (2, 3, 4, 5, 6, 7)
- a ramp generator for generating a ramp signal in response to the receipt of an edge of a timing signal, the level, relative to a nominal reference voltage, from which the ramp is generated, varying in response to the amplitude of an applied modulating signal; and
Specification