Picowatt-Power Analog Gain Stages in Super-Cutoff Region With Purely-Harvested Demonstration

In this work, gain stages with power down to the sub-pW/stage range are introduced to enable always-on mm-scale systems based on either pure harvesting across all practical environmental conditions, or micro-battery with near-shelf life lifetime (e.g., 20 years). The proposed circuit techniques suppress the need for supply voltage regulation, allowing direct harvesting (i.e., no intermediate dc–dc conversion). A CMOS 180-nm fully differential operational transconductance amplifier (OTA) is shown to consume 0.43–1.26 pW at 0.4–0.6 V as voltage harvested across all practical conditions from 2.16-mm2 solar cell down to 1 lux. The OTA shows 0.8-mV input offset and 18-
$\mu \text{V}$
input-referred noise. As an example of its application, a pW-power human grip/touch detection system for always-on event monitoring is demonstrated at light-harvesting down to moonlight.