Design and integrated circuit implementation for a programmable gm-C filter set for hearing aid applications

Abstract

This thesis pertains to the design and integrated circuit (IC) implementation of an analogue signal processor: a CMOS analogue programmable transconductance-C (gm-C) filter set for micropower low-voltage and small IC area applications. The specific application here is a digitally programmable analogue hearing aid where micropower dissipation, low voltage and compactness (in terms of IC area) are critical parameters. Current-art programmable filter sets in digitally programmable hearing aids employ sampled-data Switched-Capacitor (SC) filter technology. We propose a continuous-time gm-C alternative for two reasons. First, the different clocks of the SC filters and Class D amplifiers in current-art hearing aids often result in unacceptable 'beating' noise. Second, gm-C filters, being continuous-time, does not require anti-aliasing or reconstruction filters, and does not suffer from foldback noise aliased into the base band.