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Capacitive Transducer Electronics

IP.com Disclosure Number: IPCOM000076974D
Original Publication Date: 1972-May-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 50K

Publishing Venue

IBM

Related People

Buckley, F: AUTHOR

Abstract

The capacitive transducer electronics described provides an output transition when the transducer capacitors cross (C1=C2) in either direction.

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Capacitive Transducer Electronics

The capacitive transducer electronics described provides an output transition when the transducer capacitors cross (C1=C2) in either direction.

Differential pair 1, sources I2 and I3, and amplifiers 4, 5 and 6, 7 form a generator with two (out-of-phase) outputs, A and A, which swing plus and minus a diode drop around ground with a period of approximately 1 microsecond. These signals drive the end legs of the capacitive transducer 20. When capacitor C1 is larger than C2, voltage B is in phase with A. When C1 is smaller than C2, B is out-of-phase with A. Buffer amplifier 8, differential pair 9 and amplifier 10, 11 shape voltage B into a signal similar to A, but with transitions when B is near zero. Transistors 12, 13 and amplifier 14, 15 form the exclusive OR D of A and C. When A and C are in the same state, D is negative, and when A and C are in opposite states, D is positive. If D has been negative (C1 larger than C2) for some time, E will be negative and both G and F will be positive (one, and a half-diode drops, respectively). When capacitance C1 becomes smaller than C2, and remains so for several cycles of A, E will eventually cross F and both G and F will go negative. The time constant between D and E is designed (with respect to the two levels of F) such that even if C had no transitions indefinitely, E would never cross F. No output transition will occur until D remains in one state or the other for some time.

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