Efficient CMOS Preamplifier Dedicated for a MEMS-Based Electrostatic Field Sensor

This paper presents a preamplifier for the MEMS-based electrostatic field sensor (EFS). Being different from the conventional way of using an operational amplifier with a feedback resistor, this preamplifier takes advantage of the cascode structure to realize current to voltage conversion more efficiently. With its main conversion part containing only eight transistors, this preamplifier can realize a transimpedance as high as 10⁹. To improve the temperature performance and stabilize the output DC level, biasing circuit and feedback network are developed. Theoretical calculation is done to give a thorough understanding of the circuit, which meanwhile reveals that the transimpedance is equal to the output cascode impedance. Moreover, the band pass filter profile of this circuit makes it especially suitable for the EFS. The simulation result in Spectre using standard CMOS technology is obtained to confirm the theory.