Download or read book Wide-temperature Range CMOS Interface Circuits for Capacitive MEMS Sensors written by Yucai Wang and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "Many applications require MEMS sensors to operate over wide temperature range, typically from -55 oC to 225 oC. It is desirable to place the sensor readout circuits in close proximity to the sensor devices to improve signal-to-noise ratio and system reliability. Therefore, the sensor readout circuits must also be able to function over the same temperature range as the sensor devices. The main challenges for designing CMOS sensor readout circuits working over wide-temperature range (especially at the high temperature end) include: 1) increased junction leakage current, 2) reduced carrier mobility, and 3) decreased threshold voltage in MOS transistors. In this thesis, constant-gm biasing and other design techniques are used to mitigate the circuit performance degradation at high temperatures and three readout circuits for capacitive MEMS sensors are developed using standard CMOS process which can operate over wide temperature range from -55 oC to 225 oC.First, several proof-of-concept core building blocks are designed and tested, including a constant-gm biasing circuit, a single-ended folded-cascode amplifier, and a fully-differential folded-cascode amplifier with a switched capacitor common mode feedback circuit. The single-ended folded-cascode amplifier showed DC gain of 68.5 dB at 225 °C and DC gain variation of 2.8 dB from -20 °C to 225 °C. The fully-differential folded-cascode amplifier with the switched capacitor common mode feedback circuit showed a DC gain of 68.9 dB and DC gain variation of 2.1 dB from -20 °C to 225 °C. Then, using these core building blocks, three readout circuits for capacitive MEMS sensors were constructed, including: 1) a differential capacitance to voltage readout circuit for sensors with a wide range of the steady-state capacitance values from 0.5 pF to 10 pF, 2) a capacitance to frequency readout circuit which converts the sensor capacitance into digital pulse signal modulated in frequency, and 3) a capacitance to digital readout circuit which uses a sigma-delta technique to convert the input ratio between sensor capacitance and reference capacitance into a high-accuracy digital output. All these three capacitive sensor readout circuits are simulated over temperature range from -55 °C to 225 °C and tested over temperature range from -20 °C to 225 °C. Measurement results show that these circuits have good accuracy and temperature stability over the wide temperature range.All the circuits developed in this thesis are implemented using IBM 0.13 [mu]m standard CMOS technology which incorporates a 2.5 V power for the advantages of high level of integration and low power consumption. The design techniques used here are universal and they can be readily ported to other standard CMOS processes and even SOI processes. Future improvement and development for these circuits are proposed. More sophisticated sensor readout circuits could be built based upon the prototypes developed in this thesis. " --