CCD correlators for auditory models

Surface-channel charge-coupled devices (CCDs) provide a mechanism for analog signal delay that can be built using an ordinary double-poly CMOS digital process, such as offered by Orbit through MOSIS. This technique has been applied to implement the correlation processing needed in auditory models of the sort proposed by J.C.R. Licklider (1951) for monaural pitch perception and sound separation. The resulting chips take analog audio in and produce analog video out (moving pictures of the correlogram representation of the sound) in real time. These chips present a variety of interesting analog and digital design challenges, which are addressed here. The first working experimental chips show real-time correlograms with 84 cochlea taps and 70 CCD delay stages per tap. There remains at least one unanticipated and as yet not understood problem with these circuits, resulting in a serious skew in the displayed correlation levels. Several circuit improvements are planned for the next generation of experimental chips