An analog VLSI cochlea with new transconductance amplifiers and nonlinear gain control

We show data from a working 45-stage analog VLSI cochlea, built on a 2.2 mm/spl times/2.2 mm tiny chip. The novel architectural features in this cochlea are: (1) The use of a wide-linear-range low-noise subthreshold transconductance amplifier. (2) The use of "fuse-like" nonlinear positive-feedback amplification in the second-order cochlear filter. Several new circuit techniques used in the design are described here. The fuse nonlinearity shuts off the positive-feedback amplification at large signal levels instead of merely saturating it, like in prior designs, and leads to increased adaptation and improved large-signal stability in the filter. The fuse filter implements a functional model of gain control due to outer hair cells in the biological cochlea. We present data for travelling-wave patterns in our silicon cochlea that reproduce linear and nonlinear effects in the biological cochlea.