A Switched-Capacitor Front-End for Velocity-Selective ENG Recording

Multi-electrode cuffs (MECs) have been proposed as a means for extracting additional information about the velocity and direction of nerve signals from multi-electrode recordings. This paper discusses certain aspects of the implementation of a system for velocity selective recording (VSR) where multiple neural signals are matched and summed to identify excited axon populations in terms of velocity. The approach outlined in the paper involves the replacement of the digital signal processing stages of a standard delay-matched VSR system with analogue switched-capacitor (SC) delay lines which promises significant savings in both size and power consumption. The system specifications are derived and two circuits, each composed of low-noise preamplifiers connecting to a 2nd rank SC gain stage, are evaluated. One of the systems provides a single-ended SC stage whereas the other system is fully differential. Both approaches are shown to provide the low-noise, low-power operation, practically identical channel gains and sample delay range required for VSR. Measured results obtained from chips fabricated in 0.8 μm CMOS technology are reported.