A 0.3-V 8.5-uA Bulk-Driven OTA

A bulk-driven operational transconductance amplifier (OTA) suitable for ultralow-power and ultralow-voltage applications is described. The amplifier exploits local positive feedback in the first stage to increase its transconductance. The OTA entails a single Miller capacitor for frequency compensation, thus saving area occupation and improving frequency performance. As a distinctive feature of the proposed solution, the OTA is stable for capacitive loads higher than 5 pF. Implemented in a 65-nm standard CMOS technology, the proposed solution occupies an area of 10.6 $\cdot$ 10 $^{-3}$ mm $^{2}$ and is powered from 0.3 V, with a total quiescent current equal to 8.5 $\mu $ A. Experimental measurements show a gain–bandwidth (GBW) product of 1.65 MHz (0.81 MHz) with a phase margin (PM) equal to 70 $^{\circ}$ (71 $^{\circ})$ when driving a 50-pF (150-pF) load, featuring the best figures of merit compared to other multistage sub-1-V OTAs in the literature.