An Undersampling Digital Microphone Utilising Second Order Noise Shaping

Abstract

Certain applications do not allow for feedback in delta-sigma converters due to circuit topologies and/or practical problems inherent to feedback loops. As a result, this paper presents the analysis and implementation of a digital microphone utilizing a feed-forward only sigma delta A/D converter comprising of a Schmitt trigger, capacitor and sampling D-FF to digitize data. The system is analyzed mathematically and performance results are given. To further improve upon the obtained results, the topology is extended to cascaded structure utilizing an all digital second modulator to obtain second-order noise shaping. This is a marked departure from prior art and results in significant improvements in the performance over a first-order topology.