Nonvolatile Correction of &-offsets and Instabilities in Cochlear Filters

We present a feedback circuit that performs nonvolatile correction of instabilities and resonant-gain offsets (&-offsets) in individual cochlear filters. The subthreshold CMOS circuit adapts using analog floating-gate technology. We present experimental data from a working chip that illustrates the performance of the circuit. We discuss how to extend our work to do very long-term gain control in the silicon cochlea. Positive-feedback circuits, such as our cochlear filters, are very sensitive to parameter variations. This potential problem becomes an advantage in our corrective feedback loop where the hypersensitivity behaves merely like high loop gain.