Design of CMOS capacitance to frequency converter for high-temperature MEMS sensors

We present a CMOS capacitance to frequency convertor for capacitive MEMS sensors working in high temperature environments. Many MEMS sensors are needed to work at the extended military temperature range from -55 ^oC to 175^oC and require a suitable readout circuitry to detect, process, and transmit the sensor measurement data. The proposed CMOS circuitry uses a current to frequency conversion circuit to convert the sensor capacitance output into a digital output modulated in frequency. Pulse width control is implemented on-chip to control the pulse width of the output digital signal. The circuitry is implemented using IBM 0.13μm CMOS technology. Simulation results show that the circuitry has excellent stability over wide temperature range, good accuracy and high sensing resolution. The novelty in this work lies in the fact that a digital output is achieved without using complex analog to digital converter (ADC).