Detection And Self-test Circuit Design For Closed-loop Capacitive Acceleration

With the continuous improvement of the MEMS technology and all kinds ofsensor widely used, the application of micro acceleration sensor is becomingmore and more widely. But because of its small volume lead to its output signalis very weak, we must cooperate with signal detection circuit together to play itsdue function. So the design of signal detection circuit with the high precision,stability circuit performance for acceleration sensor is very important.The detection circuit chose continuous time detection principle, can bedetect the coherent variation signal of acceleration in continuous time, improvethe detection precision. The input terminal of circuit using sensitive chargeamplifier realize C-V conversion, which is effectively avoid the switch noise ofswitch capacitance detection principle. The acceleration signal through themechanical module transform to capacitance change. Then the signal through thesensitive charge amplifier, in-phase amplifier, synchronous demodulation circuitand low pass filter transform to a output voltage signa l which is linearrelationship with the acceleration signa l. And the output signal through the PIcontroller feedback to the in-phase end of sensitive charge amplifier whichrealize closed-loop testing, so that the signal detection circuit has good dynamicresponse characteristics and eliminate static error at the same time. When a dcvoltage imported the activity plate, we will detect a corresponding dc voltage inoutput terminal, which realize the self-test function of the signal detection circuit.Using0.5μm CMOS library completion the parameters setting of thecircuit each transistor, simulation, parameter adjustment and validation to thedetect circuit with using Cadence software. Get the simulation results ofdetection circuit performance: the open-loop gain of Operational amplifier is85.96dB, phase margin is62.8°, equivalent input noise is3.632nV/HZ. Fullscale range of the closed-loop system in±2.5V voltage is±30g, the detection sensitivity is16.2mV/g, the design goal subject achieve the anticipated.