Abstract

This paper presents a fully-integrated wireless bondwire accelerometer using a closed-loop readout interface that effectively reduces the noise from electrical circuits and long-term frequency drifts. The proposed accelerometer was fabricated using 0.18- μm CMOS technology without micro electromechanical systems (MEMS) processing. To reduce manufacturing errors, the bondwire inertial sensors are wire-bonded on the chip pads, thereby enabling a precisely-defined length and space between sensing bondwires. The proposed wireless accelerometer using a pair of 15.2 μm and 25.4 μm bondwires achieves a linear transducer gain of 33 mV/g, bandwidth of 5 kHz, a noise floor of 700 μg/√Hz, and 4.5 μg bias stability. The acceleration data is digitalized by an energy-efficient 10-bit SAR ADC and then wirelessly transmitted in real time to the external reader by a low-power on-off shift keying (OOK) transmitter. The proposed architecture consumes 9 mW and the chip area is 2 mm × ۲٫۴ mm.

Introduction

MEMS accelerometers have enjoyed translational success in a wide range of applications, such as infrastructure monitoring, automotive systems, wearable healthcare devices, and customer electronics for gaming and mobiles. Most inertial sensors rely on changes in material characteristics or mechanical structures to detect force and acceleration, and usually cannot be directly fabricated by a conventional CMOS process. With the advent of advanced CMOS-MEMS technologies, sensors and interface circuits can be integrated on a small silicon chip using special post-processing mechanisms. Capacitive [1], [2] and resonant [3]–[۵] are the most commonly used MEMS accelerometer types that sense capacitance changes and resonant frequency deviations caused by applied acceleration, respectively. The capacitive MEMS accelerometer has been widelyused in automotive systems and consumer electronics due to its low temperature sensitivity, miniature size, and low power consumption. In comparison, the resonant accelerometer can achieve high precision, a dynamic input range, and radiation insensitivity [4].