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

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 μV_rms. The LNA consumes 0.1-8.2 μA at 1.8 V and was implemented in a 0.18 μm CMOS technology.