A 125$\mu$W 8kS/s Sub-pA Area-Efficient Current Sensing 45nm CMOS ADC for Biosensing

TL;DR

This paper introduces a highly area- and power-efficient 45nm CMOS ADC capable of sensing ultra-low sub-picoampere currents at 8kS/s, suitable for biosensing applications.

Contribution

It proposes a novel integrated TIA and Delta-Sigma modulator architecture that reduces noise and power consumption for ultra-low current sensing.

Findings

Achieved 125μW power consumption and 0.042mm² area.

Realized 81dB dynamic range at 8kS/s.

Successfully sensed sub-pA currents in biosensing contexts.

Abstract

This paper presents a 125$\mu$W, area efficient (0.042mm2) 81dB DR, 8kS/s current sensing ADC in 45nm CMOS capable of sensing sub-pA currents. Our approach combines the transimpedance amplifier (TIA) and ADC into a unified structure by folding a low-noise capacitive TIA into the first stage integrator of a 2nd order Delta-Sigma modulator. The dominant DAC feedback noise is mitigated by utilizing current scaling via slope modification by an integrator and differentiator pair.