Imec, Holst MEMS readout chip eschews customization

August 22, 2011 — Imec and Holst Centre have developed an ultra-low-power readout ASIC for capacitive micro and nano electro mechanical system (MEMS/NEMS) sensors. While most available readout chips are customized to particular sensors, this architecture can interface with various MEMS/NEMS devices without draining power.

The system reads accelerometers and strain sensors in a half-bridge configuration, with gain controlled by integrating pulses from the excitation voltage, controlling the signal-to-noise (SNR) ratio. The system has also been designed to cancel residual motion artifacts.

The readout architecture has the lowest reported equivalent acceleration noise level and the highest bandwidth, Imec states, offering SNR, bandwidth, and power tradeoffs. The team achieved a figure-of-merit of 4.41×10-20 F√(W/Hz) for a sensor range of ±2.0g and ±20,000με over a 100Hz bandwidth. The readout chip handles sensors with different sensitivities, offsets and mismatch via modifications to timing and duty cycle of the excitation pulses.

"Innovative, flexible and power-efficient readout architectures," which read signals from a wide range of capacitive devices (such as accelerometers and strain sensors with different actuation voltages, sensitivities and resolutions), enable MEMS use in building-monitoring networks for seismic-active areas, among other uses where various sensors operate on restricted power sources, Imec reports. Resolution requirements can be 1mg and 10με for the accelerometer and strain sensor respectively, and a range of ±2.0g and ±20,000με over a 100Hz bandwidth.

The ASIC was fabricated on TSMC 0.25μm CMOS with metal-insulator-metal capacitors. Total power consumption of the 3 channels is 15μW. The clock and excitation voltages for the sensors are external.

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