Adaptive signal to noise ratio scalable analog front-end continuous time sigma delta converter for digital hearing aids
A dual-channel directional digital hearing aid (DHA) front end using Micro Electro Mechanical System (MEMS) microphones and an adaptive-power analog processing signal chain is presented. The analog front end consists of a double differential amplifier (DDA) based capacitance to voltage conversion circuit, 40dB variable gain amplifier (VGA) and a continuous time sigma delta analog to digital converter (CT - &SIGMA;&DELTA; ADC). Adaptive power scaling of the 4th order CT - &SIGMA;&DELTA; achieves 68dB SNR at 120μW, which can be scaled down to 61dB SNR at 67μW. This power saving will increse the battery life of the DHA.