Abstract-Auditory filter models have a history of over a hundred years, with explicit bio-mimetic inspiration at many stages along the way. From passive analogue electric delay line models, through digital filter models, active analogue VLSI models, and abstract filter shape models, these filters have both represented and driven the state of progress in auditory research. Today, we are able to represent a wide range of linear and nonlinear aspects of the psychophysics and physiology of hearing with a rather simple and elegant set of circuits or computations that have a clear connection to underlying hydrodynamics and with parameters calibrated to human performance data. A key part of the progress in getting to this stage has been the experimental clarification of the nature of cochlear nonlinearities, and the modelling work to map these experimental results into the domain of circuits and systems. No matter how these models are built into machine-hearing systems, their bio-mimetic roots will remain key to their performance. In this paper we review some of these models, explain their advantages and disadvantages and present possible ways of implementing them. As an example, a continuous-time analogue CMOS implementation of the One Zero Gammatone Filter (OZGF) is presented together with its automatic gain control that models its level-dependent nonlinear behaviour.

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This paper outlines the design and simulated performance of a novel, current-mode, companding, Class-AB, Sinh lossy integrator. Prior Sinh filter designs utilize current conveyor-like blocks which incorporate both Nand P-type devices in alternate cascode arrangement to process the splitted phases of the input. However, if these blocks were to be designed in weak inversion CMOS, the bulks of all the devices involved should be connected to their respective sources for accurate exponential/logarithmic conformity, which dictates the use of a triple-well process. Triple-well processes, apart from the fact that are not always available, have increased parasitics compared to twin-well ones, making the design and optimization of these already complicated filters a rather difficult one. In this paper, we present a new Sinh lossy integrator circuit that uses (either Nor) P-type devices rendering it to be practically realizable in any standard twin-well process. The circuit has been designed in 0.35µm AMS CMOS process with all simulation results obtained from Cadence Design Frame-work®. The resulting lossy integrator exhibits a simulated input dynamic range greater than 120dB with only one integrating capacitor, while dissipating 0.3µWs of power.

The scope of this paper is to evaluate the potential of Sinh filters synthesized by exploiting the exponential V-I relation of weakly inverted MOS devices. We report quiescent power consumption, tunability and linearity simulation results for: (a) a lowpass biquad, (b) a bandpass biquad and (c) a third-order Butterworth lowpass CMOS Sinh filter response using the 0.35µm AMS process parameters. Frey's state-variable mapping procedure is followed. Key synthesis and performance limitations are identified.

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