Design On Roic Of MEMS Piezoresistive Acceleromete

With the rapid development of MEMS and IC manufacturing process technology, the research on the integration of MEMS sensor and readout circuitry has become one of the main current development directions. The MEMS piezoresistive accelerometer has been widely used in aviation, aerospace, automotive and other fields for its many advantages such as good low-frequency characteristics, low input impedance, wide operating temperature range, good linear output, probability to be used to measure linear acceleration and simple circuit structure of back-end processing.Based on the study of the trends in MEMS sensors and the development of readout integrated at home and abroad, this paper has designed an ROIC used for a dual-beam structure MEMS piezoresistive acceleration sensor. This readout circuit mentioned above is mainly composed of the integration circuit and the switched capacitor sampling circuit which has high processing accuracy when deal with a weak signal. By the co-simulation of the equivalent electrical model of the acceleration sensor readout circuit and the readout circuit, we have verified the feasibility of this ROIC, and thus realized the optimization of the circuit performance. Here follows the main contents:(1) According to the model of the MEMS piezoresistive accelerometer Wheatstone bridge, we have built its equivalent electrical model. And we have generated the sensor module which can be called by using Verilog_A on Cadence.(2) The readout circuit is composed of the pre unity gain buffer, the integration circuit and the switch capacitor sampling circuit. The unity gain buffer uses folded-cascode op amps of direct input and output of the gate shorted to the op amp design. The integration circuit uses high gain, low noise, telescopic cascode structure design. This paper focuses on the voltage gain of the two op amps, output swing and the design to improve the performance of noise.(3) By analyzing various adverse factors which set a limit to the speed and accuracy of the switched capacitor sampling circuit, we have come up to a method which can improve the accuracy of the switched capacitor sampling circuit by using the CMOS complementary switch, increasing the virtual devices, and using the bottom plate sampling technique.(4) we have designed a timing generating circuit with an adjustable pulse width which is composed of a Gray code counter, a digital comparator and SR latches for the control timing of the switch.With the simulation of the equivalent electrical model of the acceleration sensor and the readout circuit, here are the results: the single-ended output swing of the equivalent electrical model are: 2.501 V ~ 2.544 V, 2.455 V ~ 2.499 V, the sensitivity of the output: 43.73μV/g, the output swing of the readout circuit: 2.519 V ~ 3.585 V, the sensitivity of the output: 1.066 mV / g, and the output signal has good linearity.