A 100- to- 10-kHz 5.4- to- 216- μW Power-Efficient Readout Circuit Employing Closed-Loop Dynamic Amplifier for MEMS Capacitive Accelerometer

Abstract

Micro-electromechanical systems (MEMS) capacitive accelerometer for the Internet of Things (IoT) applications is required to operate at various sampling frequencies while keeping high power efficiency. To meet this requirement, dynamic amplifiers are used in the readout circuit of the accelerometer. However, the dynamic amplifier’s open-loop gain is low and varies with the sampling frequency of the readout circuit. This significantly deteriorates the gain accuracy of the readout circuit. In this article, the dynamic-amplifier-specific oversampling successive approximation (DA-OSA) readout technique is proposed to overcome this gain variation problem and make the dynamic amplifier applicable to the readout circuit. The DA-OSA-based readout circuit is fabricated in a commercial 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $</tex-math> </inline-formula> m 1.8-V CMOS process and tested with the MEMS accelerometer sensing element. The measurement results show that, with the sampling frequency varying from 10 kHz to 1 MHz, the proposed readout circuit achieves a variable signal bandwidth from 100 Hz to 10 kHz, a variable power consumption from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5.4$</tex-math> </inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm{216}\mu \mathrm{W}$</tex-math> </inline-formula> , and a low gain variation of 1.2%.