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

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°. Designed analog front end achieves an input referred noise of 0.12 μ Vrms and SNR of 74 dB. It consumes power of 430 μ W from 1.8 V supply and occupies an area of 1.2 mm × 0.22 mm. Proposed circuit is designed and fabricated in 0.18 μ 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.