Low-Power Low-Noise Pseudo-Open-Loop Preamplifier for Neural Interfaces

In this paper, we present a low-power, low-noise fully differential pseudo-open-loop preamplifier with programmable bandwidth for monitoring neural activities. The proposed pseudo-open-loop topology can achieve high-power-noise efficiency as well as high linearity and precise gain control over process. The proposed fully differential preamplifier can balance the common mode of the differential outputs without a commonmode feedback circuit, and bias the ac-coupled input transistors without an external reference. A current-ratio gain design can set a stable gain over process and bias current variations. A programmable embedded g
_m
- C low-pass filter (LPF) can be tuned by adjusting bias current, so that the proposed preamplifier can be configured to be used in recording single neuron spikes or field potentials (EEG, ECoG). The proposed amplifier is configured to consume 400 nA at 2.5-V power supply; the total chip area is 0.189 mm
²
. The measured thermal noise floor is 85 nV/√Hz and input-referred noise is 1.69 μV
_rms
from 0.3 Hz to 1 kHz when using a chopper stabilization technique to suppress 1/f noise. The fabricated preamplifier shows a noise efficiency factor of 2.43 in the fully differential topology.