Fully Differential Difference Amplifier based Microphone Interface Circuit and an Adaptive Signal to Noise Ratio Analog Front end for Dual Channel Digital Hearing

ii ABSTRACT A dual-channel directional digital hearing aid (DHA) front-end using a fully differential difference amplifier (FDDA) based Microphone interface circuit (MIC) for a capacitive Micro Electro Mechanical Systems (MEMS) microphones and an adaptive-power analog font end (AFE) is presented. The Microphone interface circuit based on FDDA converts the capacitance variations into voltage signal, achieves a noise of 32 dB SPL (sound pressure level) and an SNR of 72 dB, additionally it also performs single to differential conversion allowing for fully differential analog signal chain. The analog front-end consists of 40dB VGA and a power scalable continuous time sigma delta ADC, with 68dB SNR dissipating 67uW from a 1.2V supply. The ADC implements a self calibrating feedback DAC, for calibrating the 2 nd order non-linearity. The VGA and power scalable ADC is fabricated on 0.25 um CMOS TSMC process. The dual channels of the DHA are precisely matched and achieve about 0.5dB gain mismatch, resulting in greater than 5dB directivity index. This will enable a highly integrated and low power DHA. iii DEDICATION I dedicate this work to the continuous encouragement of my parents especially my father to complete this work. To my wife and children for their patience in enduring through this decade long process. iv ACKNOWLEDGMENTS I want to specially acknowledge the infinite patience shown by Sayfe Kiaei, for allowing me to complete this work. He continuously nudged and prodded me to complete and readily allowed me to work around my crazy life schedule. Without his patience, I would not have been able to complete this. I would also like to thank my sister-in-law Nida Tanveer for helping with MS WORD related questions.