A low noise sigma-delta microaccelerometer interface circuit

Abstract

A closed-loop sigma-delta ('") capacitive microaccelerometer interface circuit is proposed in this work based on the time shared multiplexing electrostatic feedback and correlated-double-sampling (CDS) techniques. The noise analysis of the proposed low noise capacitance detection circuit is presented. The interface circuit is fabricated in a standard CMOS process and the active area is 13 mm 2 . The chip consumes 20 mW from a 5 V supply and the sampling frequency is 250 kHz. The measured results show that the sensor achieves a noise floor of 6 µg/Hz 1/2 in a closed-loop operation over a 1.5 kHz bandwidth, and the achieved figure of merit (FOM, 53 pW/Hz) is better than the previously reported '" interfaces.

A low-distortion ΣΔ capacitive microaccelerometer with self-test circuit

“…The target performance of the proposed microaccelerometer is to achieve a overall noise floor of lower than 10 µg/Hz 1=2 , sensing range of larger than AE1:5 g, low power dissipation of lower than 15 mW, DR of larger than 100 dB and bandwidth of larger than 300 Hz, respectively. Additionally, we want to obtain a self-test circuit with distortion of lower than −90 dB [1,6]. Fig.…”

“…An important objective for designing a AEÁ sensor is to implement the digital feedback without compromising the noise performance of the underlying open-loop system. In addition, AEÁ interface circuits for microaccelerometers are easy to be obtained in CMOS process [1,2]. A new control structure for an electromechanical AEÁ modulator based on the dual quantization technique is presented in [3], and the proposed MASH2-0 structure achieved a noise-floor level of −130 dB, which shows its potential as a closed-loop interface for high-performance capacitive MEMS inertial sensors.…”

“…The authors of [4] reports a novel six-order AEÁ closed-loop accelerometer with extended bandwidth in vacuum environment, and a noise acceleration value of 1.2 µg/Hz 1=2 is achieved. Most of the published microaccelerometers employ topologies of distributed feedback or that with feedforward paths [1,3,4,5,6]. These topologies have signal paths bypassing the sensor element, therefore, compensating zeros are determined by feedback coefficients as well as the parameters of sensor, and the position of the zeros are influenced by the variations of sensor's parameters [2].…”

A closed-loop ΣΔ modulator for micromechanical capacitive sensors

“…As a result, a one-bit internal quantizer is enough for this design, and prevents complexity and power dissipation of a multi-bit quantizer with corresponding dynamic element matching (DEM) or any other linearization technique [4]. Besides, only quantization noise is processed in the modulation loop, which also significantly decreases the output swing of integrators and relaxes the requirements for operational amplifiers [5]. In order to gain high precision, double-sampling technique is employed.…”

A high-order sigma-delta accelerometer interface circuit

“…High-resolution capacitive accelerometers have gained increasing popularity operating as electromechanical AEÁ closed-loop, which provides direct digital output and has good compatibility with the CMOS process [3,4]. Previous AEÁ microaccelerometers have focused on low-order system with high-Q sensor element and high-order low-Q system, so the sensor resolution is limited by the quantization noise or the mechanical noise.…”