A Delta Sigma-Modulated Sample and Average Common-Mode Feedback Technique for Capacitively Coupled Amplifiers in a 192-nW Acoustic Analog Front-End

Abstract

This work presents an acoustic analog front-end based on a delta sigma-modulated sample and average common- mode feedback technique. The proposed feedback offers a process and temperature stable high pass (HP) frequency corner, unity dc feedback gain, and a programmable HP frequency corner to reduce startup time. In addition, this article also presents an automatic saturation detection and recovery technique from in-band input artifacts. The proposed technique was imple- mented in the low-noise amplifier (LNA) and programmable gain amplifier (PGA) of an acoustic analog front-end fabricated in 180-nm CMOS. The technique achieved a maximum effective resistance of 100 T /Omega1. The HP frequency corner variation across temperature and process was reduced by 226 × and 4.38 ×, respectively, compared to a traditional pseudo-resistor feedback structure. Integrated noise in the 20 Hz–4 kHz speech signal band is reduced by 2.98 × using the lowest possible HP frequency corner. The amplifier recovery time from saturation due to artifacts was reduced by 10 ×. The total power consumption of the LNA, PGA, and analog to digital converter (ADC) in the acoustic front-end was 192 nW.