A2 /22W 100 nV/rtHz Chopper-Stabilized Instrumentation Amplifier for Chronic Measurement of Neural

Abstract

This paper describes a prototype micropower instru- mentation amplifier intended for chronic sensing of neural field potentials (NFPs). NFPs represent the ensemble activity of thou- sands of neurons and code-useful information for both normal ac- tivity and disease states. NFPs are small—of the order of tens of V—and reside at low bandwidths that make them susceptible to excess noise. Therefore, to ensure the highest fidelity of signal measurement for diagnostic analysis, the amplifier is chopper-sta- bilized to eliminate /49 and popcorn noise. The circuit was pro- totyped in an 0.8 m CMOS process and consumes under 2.0 W from a 1.8 V supply. A noise floor of 0.98 Vrms was achieved over a bandwidth from 0.05 to 100 Hz; the noise-efficiency factor of 4.6 is one of the lowest published to date. A flexible on-chip high-pass filter is used to suppress front-end electrode offsets while main- taining relevant physiological data. The monolithic architect and micropower low-noise low-supply operation could help enable ap- plications ranging from neuroprosthetics to seizure monitors that require a small form factor and battery operation. Although the focus of this paper is on neurophysiological sensing, the circuit ar- chitecture can be applied generally to micropower sensor inter- faces that benefit from chopper stabilization.