Design Of MEMS Acceleration Sensor Readout Circuit

MEMS acceleration sensor has been widely used in military and commercialequipment for its superior performance, which includes two parts: MEMS sensor and IC.Because of its high precision and high stability， it was also specially applied in precisionexploration in recent years, such as oil exploration. MEMS acceleration sensors, alsoknown as micro-accelerometers, have several kinds of structures like piezoresistive type,capacitive type…but the capacitive micro-accelerometer enjoy the optimal performancebased on all aspects of the situation. At the same time, the read-out circuit technology,which was used to detect differential capacitance change, is very mature now. There aretwo kinds of controlling way in read-out circuit: open-loop control and closed-loopcontrol. Among which the open-loop control style has simple structure, takes a veryimportant position in applications of the impact acceleration measurement; and theclosed-loop control way, the presence of electrostatic force feedback on it ensure manyadvantages like high linearity, good dynamic performance, non-noise sensitive…, waswidely used in many field. Read-out circuit’s structure was mainly divided into three type:first one, the continuous-time voltage read-out circuit, which was based on modulationand demodulation technique;second one, the continuous-time current read-out circuit,based on operational transconductance amplifier; third one, switched capacitor electriccharge readout circuit.The Full chip system adopt closed-loop readout circuit structure, this article is just partof its work, here we mainly analyzes the structure and design concept of the senseamplifier, and its auxiliary circuit: the reference voltage, the reference current,multi-phase clock synchronizing circuit, the editable compensation capacitor array andread-out amplifier’s auxiliary circuit, the Low power design for sense amplifier. Thesense amplifier can be run in high power/low power consumption state based on differentcontrol signal, with the main design idea working in high power consumption state under“Sensing” period, and remaining3/4cycles in low power consumption state, which willeffectively save the power source’s consumption. The sense amplifier adopt CDS(Correlated Double Sampling) technology to realize offset cancellation, this paperconducted the derivation of its main operational principle and the calculating formula,and also listed out effect factor of sense amplifier’s linearity. The low noise requirementis also the key part of entire chip system design, like the noise of reference voltage may transmitter to the output of system, therefore the reference basis for low noiseperformance is very important. the reference voltage module have a built-in chip resistorinside, there is an external330μF capacitor connected at its output terminal, which formsa low pass filter, greatly reduces the output noise of reference basis, there is no need toadd other complex designs on it.This design followed standard integrated circuit design process, finished pre and postsimulation under various process corners changes, also the work of taping out, packagingand testing. The testing mainly focus on indicators of test reference voltage, the linearityof read out amplifier circuit and so on, the results show that all indicators meet the designrequirements.