A Charge Amplifier Based Complementary Metal-Oxide-Semiconductor Analog Front End for Piezoelectric Microphones in Hearing Aid Devices

Abstract

In this paper, a low noise and low power analog front end for piezoelectric microphones used in hearing aid devices is presented. It consists of a Charge Amplifier, followed by a Variable Gain Amplifier and an Analog-to-Digital Converter. At the core of charge amplifier a two stage opamp with modified cascode current mirror is designed which achieves a gain of 93 dB and phase margin of 62 degrees. Designed analog front end achieves an input referred noise of 0.12 mu Vrms and SNR of 74 dB. It consumes power of 430 mu W from 1.8 V supply and occupies an area of 1.2 mm x 0.22 mm. Proposed circuit is designed and fabricated in 0.18 mu m CMOS process. Designed circuit is interfaced with a sensor model of piezoelectric microphone, which mimics Ormia ochracea's auditory system, and its performance is successfully verified against simulation results.