An ASIC Design For Butterfly Accelerometer

Micro-accelerometer is the most representative sensor in MEMS.Among them,the pendulous micro-accelerometer has the characteristics of differential detection.butterfly micro-accelerometer with "double pendulum " structure has the advantage of "double differential",it is a great potential micro-accelerometers.In this paper,we designed an Application Specific Integrated Circuit(ASIC)for the butterfly micro-accelerometer.The main work was as follows:1.Based on the working principle analysis for the butterfly micro-accelerometer’s mechanical structure,the relationship between the measured acceleration and the change of the capacitance is summed up.And the electrical model of the mechanical structure is given.The ASIC project about "Switched Capacitor C/V Conversion + Open-loop Detection " of the butterfly micro-accelerometer is proposed.2.In the design of the switched capacitor C/V conversion circuit,a fully differential C/V conversion circuit structure with "common mode input feedback" and " compensation of bias capacitor " based on "differential switched capacitor detection" is proposed.A "Folded Cascode" operational amplifier with "gain boosting" is designed for C/V conversion.The op amp’s open-loop gain is 121 dB,bandwidth is 14.8MHz,phase margin is 85°,slew rate is 3.5V/ ?s.And the gain of C/V conversion circuit is 10V/pF,the density of input reference noise is 0.83?V/ Hz.3.The sampling and switched capacitor filter after C/V conversion is designed;The necessary circuits including reference,clock generation is introduced briefly.The layout based on 0.6?m CMOS is completed.4.The essential test of ASIC chip is completed.The circuit test of the chip shows that the gain of C/V conversion is about 10V/pF,which basically meets the design requirements.The joint test with the mechanical structure of the butterfly micro accelerometer shows that the function of ASIC chip is correct,and the scale factor of the butterfly micro accelerometer is measured as 318.8mV/g,the bias stability is measured as 0.484 mg.In summary,the first ASIC chip for butterfly micro-accelerometer in our laboratory is compeleted.It is tested that the basic functions is achieved.