A 6-µW AC-Coupled, Two-Step Incremental ∆Σ ADC for High-Density Neural Recording

This paper proposes an AC-coupled two-step incremental ∆Σ analog-to-digital converter (ADC) neural recording analog front end (AFE). Compared to other neural recording AFEs, it achieves rail-to-rail electrode DC offset (EDO) rejection, low noise, small area, and ultra-low power consumption. Considering the weak amplitude of neural signals, a transconductance-capacitance (Gm-C) integrator combined with current reuse is employed. In addition, the two-step quantization design of the AFE also offers the benefits of low power consumption and compact size. Fabricated in a 180-nm CMOS process, the AFE consumes 6 µW, with an area of 0.02 mm
²
. Within a bandwidth of 1-10 kHz, the input reference noise is 6.02 µVrms, where the local field potentials (LFP, 1 Hz-1 kHz) noise is 5 µVrms and the action potential (AP, 300 Hz-10 kHz) noise is 3.86 µVrms. The maximum input range of AFE is approximately 21mVpp, and it can achieve a maximum effective number of bits (ENOB) of about 9.5 bits.