A 0.3 V High-Efficiency Bulk-Driven Rail-to-Rail OTA with High Gain-Bandwidth for Wearable Applications

This paper presents a high-efficiency, nW-level operational transconductance amplifier (OTA) capable of operating at 0.3 V with rail-to-rail input and output. The design utilizes a bulk-driven technique in the input stage to extend the common-mode input range under ultra-low-voltage conditions. A simplified intermediate stage ensures reliable MOS operation at ultra-low-voltage levels while reducing power consumption, and a modified Class-AB controlled output stage facilitates rail-to-rail output and enhances current efficiency. Fabricated using SMIC 0.18 μm technology and operating at a 0.3 V supply, the OTA achieves a DC gain of 63.07 dB, phase margin of 61.5°, a gain-bandwidth product of 37.68 kHz, and a slew rate of 21.85 V/ms while consuming only 123 nW with a 60 pF load. The design also demonstrates superior small-signal figures of merit (12.25 MHz·pF/μW) and large-signal figures of merit (10.66 V/μs·pF/μW) compared to state-of-the-art low-voltage OTAs. These results indicate that the proposed amplifier offers a balanced solution of low power consumption, wide bandwidth, and high slew rate, making it well-suited for energy-constrained applications such as portable electronics, IoT sensors, and biomedical devices.