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US 6,456,477 B1Granted
Linear capacitance detection circuit
OwnerRobert B. McIntosh, Winfield Hillinventors
Life of this patent
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Abstract
A differential transconductance amplifier detects changes of the variable capacitor in a low-impedance, bridge circuit and feeds back current to balance the bridge. The voltage that controls the feedback current is proportional to capacitance over a wide dynamic range.
Claims22
An electrical circuit that measures a difference in capacitance between a first capacitor and a second capacitor comprising:
- a. a generator of periodic pulses of positive amplitude with respect to a reference potential, said generator connected to a first and second isolation means;
- b. said first isolation means connected to a first node connected to said first capacitor and to a current sourcing means connected in parallel to said reference potential;
- c. said second isolation means connected to a second node connected to said second capacitor connected to said reference potential;
- d. a transconductance amplifier with an input terminal connected to said first node and an input terminal of opposing polarity connected to said second node and an output connected to said second node, whereby feedback current maintains a voltage at said second node substantially equal to a voltage at said first node.
1 more element
A capacitive bridge network comprising at least one variable capacitor:
- a. a first node connected to a first and second isolation means;
- b. said first isolation means connected to a second node, and a first capacitor and a current sourcing means connected in parallel between said second node and a third node to form a first side of said bridge network;
- c. said second isolation means connected to a fourth node, and a second capacitor and a voltage-controlled current sourcing means connected in parallel between said fourth node and said third node to form a second side of said bridge network.
Dependencies are inferred from the claim text.