A 0.01 mm2 fully-differential 2-stage amplifier with reference-free CMFB using an architecture-switching-scheme for bandwidth variation

Abstract

This work presents an area-efficient fully-differential 2-stage amplifier as analog pre-amplifier for active neural recording probes. It features an architecture-switching-scheme to reduce the overhead of unused feedback elements in variable-bandwidth-systems, as well as a double-differential self-defining common mode feedback to minimize the biasing overhead. Its area including all feedback elements measures 9,977 μm2, which is more than 2x smaller than previously published neural readout bandpass LNAs. It offers a switchable lower (1 or 140 Hz) and tunable upper (0.24-49 kHz) cut-off frequency with a gain of 26-32 dB and an input noise down to 11.9 μVrms. The LNA consumes 0.1-8.2 μA at 1.8 V and was implemented in a 0.18 μm CMOS technology.