High accuracy direct reading capacitance-to-voltage converter
First Claim
1. A circuit for providing an accurate measurement of the capacitance of a capacitor, said circuit comprising:
- clock signal generator means for providing a signal which alternates between relatively high and low signal levels, said signal generator means interconnected with a first plate of said capacitor to supply said clock signal thereto;
operatonal amplifier means having first input terminal means connected to a summing node, second input terminal measn connected to ground, and output terminal means providing an output voltage signal, said capacitor being discharged into said summing node at the first input terminal means of said operational amplifier means; and
means for successively charging and discharging said capacitor as said clock signal alternates between relatively high and low signal levels, said charging and discharging means including switch means connected between the second plate of said capacitor and said summing node;
the magnitude of the voltage signal at the output terminal means of said operational amplifier means providing a measurement of the capacitance of said capacitor.
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Accused Products
Abstract
A relatively simple circuit for implementing a low-cost, low power, highly accurate capacitance-to-voltage converter by which to measure the unknown capacitance of a capacitor. The circuit is characterized by the ability to eliminate error due to stray capacitance sources. The circuit is implemented by a crystal controlled clock generator which produces multi-phase clock signals to control the operation of a pair of series connected field effect transistors and a buffer amplifier. The field effect transistors are alternately switched on and off to periodically charge and discharge the capacitor under measurement between a source of reference potential and the inverting input terminal of a precision operational amplifier. The output voltage of the operational amplifier tracks the capacitance of the capacitor under measurement, such that an accurate indication of its capacitance is obtained by merely reading the output of the operational amplifier.
231 Citations
18 Claims
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1. A circuit for providing an accurate measurement of the capacitance of a capacitor, said circuit comprising:
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clock signal generator means for providing a signal which alternates between relatively high and low signal levels, said signal generator means interconnected with a first plate of said capacitor to supply said clock signal thereto; operatonal amplifier means having first input terminal means connected to a summing node, second input terminal measn connected to ground, and output terminal means providing an output voltage signal, said capacitor being discharged into said summing node at the first input terminal means of said operational amplifier means; and means for successively charging and discharging said capacitor as said clock signal alternates between relatively high and low signal levels, said charging and discharging means including switch means connected between the second plate of said capacitor and said summing node; the magnitude of the voltage signal at the output terminal means of said operational amplifier means providing a measurement of the capacitance of said capacitor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A capacitance-to-voltage converter circuit for providing an accurate measurement of the capacitance of a capacitor, said circuit comprising:
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clock means for supplying a clock signal which alternates between relatively high and relatively low voltage levels; operational amplifier means having input and output terminal means; and means for successively charging and discharging said capacitor including a buffer amplifier interconnected between said clock means and one plate of said capacitor for charging said capacitor during a first portion of the clock signal, and multi-terminal semiconductor switch means interconnected between said operational amplifier means and the second plate of said capacitor for discharging said capacitor to the input terminal means of said operational amplifier means during a second portion of the clock signal; the magnitude of the voltage at the output terminal means of said operational amplifier means providing a measurement of the capacitance of said capacitor. - View Dependent Claims (14, 15, 16, 17, 18)
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Specification