Linearized capacitance sensor system
AssigneeSetra Systems, Inc.
InventorDennis K. Briefer
Life of this patent
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Abstract
A capacitive sensing circuit and system includes a variable capacitance sensing element as an active element in a circuit to measure changes in capacitance of the sensing element. A switching network in alternate cycles energizes a capacitor to develop a charge which effectively linearizes the sensor's capacitance response. In a push-pull circuit with two active sensing elements, a multi-channel switching network energizes two fixed correction capacitors to provide third or higher order correction, significantly extending the effective scale of the sensor. In a preferred embodiment, a single feedback signal is applied to all capacitors in different switching cycles. Examples include weight and pressure sensing systems.
Claims12
A capacitive sensing circuit comprising
- a first and a second capacitor with one end of each capacitor connected to a junction, at least said second capacitor being a sensing capacitor having a capacitance which varies in accordance with physically-induced change in plate position and which has a non-linear capacitance characteristic,
- first switching means for applying signals to non-common ends of said first and second capacitors in alternate switching cycles for developing a flow of charge through said capacitors such that the voltage present at the junction varies in functional dependence on the capacitance values of said first and second capacitors,
- a third capacitor having one end coupled to said junction,
- second switching means for coupling a signal to the non-common end of said third capacitor to develop a charge effective to substantially null the charge variation due to said non-linear capacitance characteristic of the sensing capacitor, and
- feedback means responsive to the voltage at said junction for providing a feedback signal to said first switching means to charge at least said second capacitor and maintain stationary the voltage present at the junction.
Dependencies are inferred from the claim text.