Capacitance-to-voltage transformation circuit
First Claim
1. A capacitance-to-voltage transformation circuit for providing an output voltage variation related to capacitance variations in a variable capacitor element, comprising:
- means for applying a reference voltage potential;
circuit means coupled to said applying means for charging said variable capacitor element to said reference potential;
switching means for cyclically connecting said variable capacitor element to said circuit means and to a ground potential; and
impedance means coupled between said circuit means and said switching means for conducting the charging current provided by said circuit means to said variable capacitor during a predetermined portion of each of said switching cycles and for developing an output voltage variation related to the variations in capacitance of said variable capacitor.
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Abstract
A capacitance-to-voltage transformation circuit for providing an output voltage proportional to capacitive variations includes a variable capacitor, a reference voltage source, and circuit means for charging the variable capacitor to the reference potential. A switch means alternately connects the variable capacitor to the charging means and to ground at a cyclical rate determined by an oscillator clock. An impedance means coupled between the charging and switch means, develops a voltage drop thereacross of a magnitude directly proportional to capacitance variations of the variable capacitor.
In accordance with another aspect of the invention, the circuit includes a compensating means for nullifying any fixed capacitance component of the variable capacitor.
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Citations
12 Claims
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1. A capacitance-to-voltage transformation circuit for providing an output voltage variation related to capacitance variations in a variable capacitor element, comprising:
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means for applying a reference voltage potential; circuit means coupled to said applying means for charging said variable capacitor element to said reference potential; switching means for cyclically connecting said variable capacitor element to said circuit means and to a ground potential; and impedance means coupled between said circuit means and said switching means for conducting the charging current provided by said circuit means to said variable capacitor during a predetermined portion of each of said switching cycles and for developing an output voltage variation related to the variations in capacitance of said variable capacitor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A capacitance-to-voltage transformation circuit for providing an output voltage variation which is directly proportional to variations in capacitance comprising:
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a variable capacitor having first and second terminals, said first terminal being coupled to ground potential, and characterized by a fixed capacitance component and a variable capacitance component; first means for applying a first reference voltage potential; circuit means coupled to said applying means for charging said variable capacitor to said reference potential; first switch means for cyclically connecting said second terminal to said circuit means and to ground potential; a fixed capacitor having first and second terminals, said first terminal being coupled to said variable capacitor second terminal; second means for applying a second reference voltage potential; second switching means operating in synchronism with said first switching means for cyclically connecting said fixed capacitor second terminal to said second voltage source when said variable capacitor second terminal is connected to said charging means, and to said variable capacitor second terminal when said variable capacitor second terminal is connected to ground potential to effectively cancel said fixed capacitance component of said variable capacitor; and impedance means coupled between said circuit means and said first and second switching means for conducting the charging current provided by said circuit means to said variable capacitor during each said switching cycle and for providing an output voltage which is directly proportional to the variations in capacitance of said variable component of said variable capacitor.
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Specification