Neural Signal Quantization Circuits

Abstract

Integrated neural implant interface with the brain using biocompatible electrodes provides high yield cell recordings, large channel counts, and access to spike data and/or field potentials with high signal-to-noise ratio. By increasing the number of recording electrodes, spatially broad analysis can be performed that can provide insights into how and why neuronal ensembles synchronize their activity. In this chapter, we present several A/D converter realizations in voltage-, current- and time-domain, respectively, suitable for multichannel neural signal-processing. The voltage-domain SAR A/D converter combines the functionalities of programmable-gain stage and analog to digital conversion, occupies an area of 0.028 mm2, and consumes 1.1 μW of power at 100 kS/s sampling rate. The current-mode successive approximation A/D converter is realized in a 65 nm CMOS technology, and consumes less than 367 nW at 40 kS/s, corresponding to a figure of merit of 14 fJ/conversion-step, while operating from a 1 V supply. A time-based, programmable-gain A/D converter allows for an easily scalable, and power-efficient, implantable, biomedical recording system. The time-domain converter circuit is realized in a 90 nm CMOS technology, operates at 640 kS/s, occupies an area of 0.022 mm2, and consumes less than 2.7 μW corresponding to a figure of merit of 6.2 fJ/conversion-step.