0.4-V nW-Power High-Gain Bulk-Driven Two-Stage OTA With Self-Cascode Composite Transistors and Intrinsic Current-Buffer Miller Compensation

This paper presents a 0.4-V bulk-driven two-stage operational transconductance amplifier (OTA) achieving an exceptionally high voltage gain exceeding 120 dB without requiring additional bias voltages. This is accomplished using a self-cascode composite transistor configuration. Common-mode and power-supply rejection ratios ( CMRR and PSRR, respectively) exceeding 90 dB are achieved through input stage optimization. An intrinsic current-buffer Miller compensation technique is also employed to enhance frequency performance. Compared to state-of-the-art designs, the proposed OTA exhibits superior performance in terms of gain-bandwidth trade-off, settling time, PSRR, and robustness against variations. This is demonstrated through extensive measurements across corner wafers and temperature within the range of -20∘C to 100∘C (unavailable in prior art).