Highly programmable temperature compensated readout circuit for capacitive microaccelerometer

Abstract

This paper describes a capacitive microaccelerometer system and readout circuit topology with a high programmability and a low temperature dependency. The MEMS sensing element is fabricated using the Sacrificial Bulk Micromachining (SBM) process and the Wafer Level Hermetic Packaging (WLHP) process, to achieve high reliability, low noise and low bias instability. The readout circuit exploits a highly programmable capacitive sensing architecture with an on-chip EEPROM in order to calibrate the output offset and the scale factor. The temperature compensated sub-circuits, including a bandgap reference, a current reference, and an oscillator, are designed to enhance the temperature characteristics. The supply voltage variations are compensated for by using an on-chip voltage regulator. The reverse voltage protection circuit is also designed to enhance the electrical reliability. After calibrating the scale factor and the offset by using the programmable circuits, the scale factor error and the offset error are compensated to 1.2%FSO and 3.3%FSO, respectively. The temperature coefficient of the offset is measured to be 43 ppm/°C in the temperature range from −40 °C to 125 °C. The bias instability and the noise equivalent resolution are measured to be in the range from 16.1 μg to 135.2 μg, and from 93.5 μ g/ Hz to 514.0 μ g/ Hz , respectively.