A mixed-signal analogue front-end for brain-implantable neural interfaces using a digital fixed-point IIR filter and bulk offset cancellation

Abstract

Advances in miniaturised implantable neural electronics have paved the way for therapeutic brain-computer interfaces with clinical potential for movement disorders, epilepsy, and broader neurological applications. This paper presents a mixed-signal analogue front end (AFE) designed to record simultaneously both extracellular action potentials (EAPs) and local field potentials (LFPs). The feedforward path integrates a low-noise amplifier (LNA) and a successive-approximation-register (SAR) analogue-to-digital converter (ADC), while the feedback path employs a fixed-point infinite-impulse-response (IIR) Chebyshev Type II low-pass filter to suppress sub-mHz components via bulk-voltage control of the LNA input differential pair using two R-2R pseudo-resistor digital-to-analogue converters (DACs). The proposed AFE employs a low-power (LP) mode and an offset-cancellation high-performance (HP) mode. The proposed AFE achieves 40.55 dB gain and supports neural recording from 0.1 Hz to 5.705 / 9.66 kHz (LP / HP), with typical input-referred noise of 3.9 / 6.615 uVrms in the LFP band and 11.42 / 11.11 uVrms in the EAP band (LP / HP). Its typical power per channel is 5.44 uW (LP) and 11.35 uW (HP), while it occupies 0.198 mm2.