A capacitance sensing method with trans-impedance based readout circuit and adaptive filtering for micro-gyro.

Trans-impedance amplifier (TIA) based capacitance-voltage (C-V) readout circuit is an attractive choice for micro-machined gyroscope for its simplicity and superior performance. In this work, the noise and the C-V gain characteristics of the TIA circuit are analyzed in detail. Then, a TIA based readout circuit with a C-V gain of about 286 dB is designed, and a series of experiments are conducted to test the performance of the circuit. Both the analysis and test results show that T-network TIA should be avoided as far as possible for its poor noise performance. All results also show that there is a signal-to-noise ratio (SNR) limit for the TIA based readout circuit, and the SNR can only be further improved by filtering. Hence, an adaptive finite impulse response filter is designed to further improve the SNR of the sensed signal. For a gyroscope with a peak-to-peak variable capacitance of about 200 aF, a SNR of 22.8 dB can be achieved by the designed circuit and a SNR of 47 dB can be obtained by further adaptive filtering. Finally, the solution presented in this paper achieves a capacitive sensing resolution of 0.9 aF.