A Biomimetic, 4.5 \muW, 120+ dB, Log-Domain Cochlea Channel With AGC

• Published in: IEEE journal of solid-state circuits 2009-03, Vol.44 (3), p.1006-1022
• Main Authors: Katsiamis, A.G., Drakakis, E.M., Lyon, R.F.
• Format: Article
• Language: English
• Subjects: auditory processing; Automatic gain control; Biomimetics; bionic ear; Circuit synthesis; cochlea; companding; Dynamic range; gammatone; log-domain; low-power; Nonlinear filters; Passband; Robustness; Semiconductor device modeling; Signal synthesis; Tail; Transfer functions
• ISSN: 0018-9200; 1558-173X
• DOI: 10.1109/JSSC.2008.2011039

This paper deals with the design and performance evaluation of a new analog CMOS cochlea channel of increased biorealism. The design implements a recently proposed transfer function, namely the One-Zero Gammatone filter (or OZGF), which provides a robust foundation for modeling a variety of auditory data such as realistic passband asymmetry, linear low-frequency tail and level-dependent gain. Moreover, the OZGF is attractive because it can be implemented efficiently in any technological medium-analog or digital-using standard building blocks. The channel was synthesized using novel, low-power, class-AB, log-domain, biquadratic filters employing MOS transistors operating in their weak inversion regime. Furthermore, the paper details the design of a new low-power automatic gain control circuit that adapts the gain of the channel according to the input signal strength, thereby extending significantly its input dynamic range. We evaluate the performance of a fourth-order OZGF channel (equivalent to an 8th-order cascaded filter structure) through both detailed simulations and measurements from a fabricated chip using the commercially available 0.35 mum AMS CMOS process. The whole system is tuned at 3 kHz, dissipates a mere 4.46 muW of static power, accommodates 124 dB (at < 5% THD) of input dynamic range at the center frequency and is set to provide up to 70 dB of amplification for small signals.