  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.
