Log-domain circuits for auditory signal processing

The theory and practice of log-domain filter design has reached the point where it is possible to incorporate log-domain filter structures into large current-mode VLSI systems. We report on interface circuits used to implement a current-mode frontend filterbank and feature extractor for acoustic pattern recognition. These circuits maintain a log-domain structure, acting on the unexpanded filter output to execute such functions as peak-to-peak voltage measurement, full-wave rectification, smoothing, and normalization. A fabricated VLSI sixteen-channel filterbank feature extractor exhibits 40 dB resolution for short-term energy envelope measurements of class A log-domain second-order bandpass filter outputs.