A body-driven, 1.8 nW, 75 dB gain, single stage OTA, for ULV and ULP applications

In this work,a novel bulk-driven OTA capable to operate with a supply voltage as low as 400mV is presented. The proposed single stage topology results in an increased differential gain of about 75dB, while guaranteeing a very low power consumption in the range of 1.8nW. The amplifier exploits a body-driven input stage with a current-mirror-based differential to single-ended converter. The gain of the OTA is boosted thanks to the adoption of a cascode configuration and of a positive feedback loop, which allows to increase the output resistance without adding additional current branches. The CMRR is also improved thanks to the adoption of a replica bias loop which takes track of common-mode voltage variations to adjust the common-mode current, resulting in a CMRR higher than 85dB. The circuit has been designed considering a 180nm CMOS technology from TSMC, and post-layout simulations in the Cadence Virtuoso environment have shown an excellent resilience of the proposed OTA to PVT variations.