A low-noise high-sensitivity readout circuit for MEMS capacitive sensors

This paper presents a differential low-noise highresolution switched-capacitor readout circuit that is intended for capacitive sensors. Amplitude modulation/demodulation and correlated double sampling are used to minimize the adverse effects of the amplifier offset and flicker (1/f) noise and improve the sensitivity of the readout circuit. In order to simulate the response of the readout circuit, a Verilog-A model is used to model the variable sense capacitor. The interface circuit is designed and laid out in a 0.8 µm CMOS process. Postlayout simulation results show that the readout interface is able to linearly resolve sense capacitance variation from 2.8 aF to 0.3 fF with a sensitivity of 7.88 mV/aF from a single 5V supply (the capacitance-to-voltage conversion is approximately linear for capacitance changes from 0.3 fF to~1.2 fF). The power consumption of the circuit is 9.38 mW.

[1]  Behzad Razavi,et al.  Design of Analog CMOS Integrated Circuits , 1999 .

[2]  Haigang Yang,et al.  A low-noise readout circuit for MEMS vibratory gyroscope , 2008, 2008 3rd IEEE International Conference on Nano/Micro Engineered and Molecular Systems.

[3]  Henrik Rödjegård,et al.  A differential charge-transfer readout circuit for multiple output capacitive sensors , 2005 .

[4]  Min-Hang Bao,et al.  Micro Mechanical Transducers: Pressure Sensors, Accelerometers and Gyroscopes , 2000 .

[5]  Kari Halonen,et al.  Fully integrated charge sensitive amplifier for readout of micromechanical capacitive sensors , 2005, 2005 IEEE International Symposium on Circuits and Systems.

[6]  Gabor C. Temes,et al.  High-accuracy circuits for on-chip capacitance ratio testing or sensor readout , 1994 .

[7]  Z. Ignjatovic,et al.  An interface circuit for measuring capacitance changes based upon capacitance-to-duty cycle (CDC) converter , 2005, IEEE Sensors Journal.

[8]  F. N. Toth,et al.  Ultra-linear, low-cost measurement system for multi-electrode pF-range capacitors , 1995, Proceedings of 1995 IEEE Instrumentation and Measurement Technology Conference - IMTC '95.

[9]  Stilianos Siskos,et al.  Noise optimised charge-sensitive CMOS amplifier for capacitive radiation detectors , 2008, IET Circuits Devices Syst..

[10]  Gabor C. Temes,et al.  Circuit techniques for reducing the effects of op-amp imperfections: autozeroing, correlated double sampling, and chopper stabilization , 1996, Proc. IEEE.

[11]  Liter Siek,et al.  Designing CMOS folded-cascode operational amplifier with flicker noise minimisation , 2001 .

[12]  H.P. Chou,et al.  A Novel Interface Circuit for Capacitive Sensors Using Correlated Double Sampling Demodulation Technique , 2008, 2008 Second International Conference on Sensor Technologies and Applications (sensorcomm 2008).