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A stray-insensitive symmetrical capacitance-to-voltage converter for capacitive sensors is presented. By introducing a reference branch,a symmetrical readout circuit is realized.The linear input range is increased, and the systematic offsets of two input op-amps are cancelled.The common-mode noise and even-order distortion are also rejected.A chopper stabilization technique is adopted to further reduce the offset and flicker noise of the op-amps,and a Verilog-A-based varactor is used to model the real variable sensing capacitor.Simulation results show that the output voltage of this proposed readout circuit responds correctly,while the under-test capacitance changes with a frequency of 1 kHz.A metal-insulator-metal capacitor array is designed on chip for measurement, and the measurement results show that this circuit achieves sensitivity of 370 mV/pF,linearity error below 1%and power consumption as low as 2.5 mW.This symmetrical readout circuit can respond to an FPGA controlled sensing capacitor array changed every 1 ms.
A stray-insensitive symmetrical capacitance-to-voltage converter for capacitive sensors is presented. By introducing a reference branch, a symmetrical readout circuit is realized. Linear input range is increased, and the systematic offsets of two input op-amps are canceled. The common-mode noise and even-order distortion are also rejected. A chopper stabilization technique is adopted to further reduce the offset and flicker noise of the op-amps, and a Verilog-A-based varactor is used to model the real variable sensing capacitor.Simulation results show that the output voltage of this proposed readout circuit responds correctly, while the under-test capacitance changes with a frequency of 1 kHz. A metal-insulator-metal capacitor array is designed on chip for measurement, and the measurement results show that this circuit achieves sensitivity of 370 mV / pF, linearity error below 1% and power consumption as low as 2.5 mW. This symmetrical readout circuit can respond to an FPGA controlled sensing capacitor array changed every 1 ms.