Full-Analog Parasitic Capacitance Compensation for AC-Excited Differential Sensors

• Capacitive sensors are popular, especially due to the possibility to be integrated together with the readout circuit. In particular, differential implementations are intrinsically insensitive to common-mode noise. Unfortunately, stray capacitances can significantly alter the sensor output value, worsening the performance. This article proposes a novel solution based on an autotuning feedback loop to compensate for parasitic effects, thus preserving measurement performance. In particular, a voltage-controlled negative impedance converter is driven by a feedback loop, in order to control the current flowing in the sensor. The proposed solution can work with the both linear and hyperbolic type of sensors and with any voltage-mode sensor interfaces. An experimental setup, comprising the proposed compensating circuit, a De-Sauty bridge-based sensor front end and an emulated sensor, has been arranged to evaluate obtainable performance. Results show that the linearity error is decreased from more than 10%, without compensation, to less than 1%, when the proposed system is applied. © 1963-2012 IEEE.

Nyckelord

Analog circuits

differential capacitive sensor

negative impedance converter (NIC)

parasitic capacitance compensation

Capacitance

Capacitive sensors

Error compensation

Common mode noise

Compensating circuits

Differential sensors

Linearity errors

Parasitic capacitance

Read-out circuit

Stray capacitances

Voltage-controlled

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