Low-Cost Complex Impedance Measurement Circuit for Guard-Sense Capacitive Sensors Operated in Loading Mode

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Low-Cost Complex Impedance Measurement Circuit for Guard-Sense Capacitive Sensors Operated in Loading Mode

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LAMESCH LAURENT

A microcontroller uses a combination of several synchronized PWM outputs to generate a low distortion sine wave by summing the PWM outputs and filtering the summed signal. The sine wave is used as a guard voltage. The unknown impedance is measured by impinging the guard voltage on the sense electrode by a transistor connected in common base configuration and then transferring the sense current through the common base connected transistor to a transimpedance amplifier made out of a second transistor connected in common emitter configuration. The output voltage at the collector of the second transistor is measured by an ADC input of the microcontroller. The microcontroller translates the ADC output values into the unknown impedance to be measured by doing a software demodulation of the ADC output values. A reference impedance can be connected in parallel to the unknown impeder to eliminate gain errors of the signal sensing circuit.

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Title :

Low-Cost Complex Impedance Measurement Circuit for Guard-Sense Capacitive Sensors Operated in Loading Mode

Contributors:

LAMESCH LAURENT (author)

Publication date :

2017-12-14

Type of media :

Patent

Type of material :

Electronic Resource

Language :

English

Classification :

IPC:

B60R Fahrzeuge, Fahrzeugausstattung oder Fahrzeugteile, soweit nicht anderweitig vorgesehen , VEHICLES, VEHICLE FITTINGS, OR VEHICLE PARTS, NOT OTHERWISE PROVIDED FOR / B60N SEATS SPECIALLY ADAPTED FOR VEHICLES , Sitze besonders für Fahrzeuge ausgebildet / G01D MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE , Anzeigen oder Aufzeichnen in Verbindung mit Messen allgemein