I. SILICON COCHLEAE
SILICON (Si) cochleae emulate cochlear processing of sound stimuli in very-large scale integrated (VLSI) systems, attempting to match the biological cochlea's sound sensitivity, frequency selectivity, and dynamic range. The effort to build artificial cochleae in Si has been largely motivated by their potential applications in hearing aids, cochlear implants, and other portable devices that demand real-time, low-power signal processing for speech recognition; these requirements favor subthreshold analog VLSI designs [1]. Furthermore, analog VLSI is amenable to cochlea-like distributed processing due to its compact computational elements, large numbers of which can be integrated in a small area of Si. However, digital outputs are easier to interface with higher level processing, whether performed by other neuromorphic chips or implemented in computer software. Thus, a mixed-mode approach, where the cochlea's analog outputs are converted to digital pulses-a function performed by the auditory nerve (AN)-is most attractive.