Bulk-Driven vs. Gate-Driven OTAs in Deep-Subthreshold ULV Operation: Analytical and Robustness Comparison in Self-Cascode Architectures

This work presents a comprehensive analytical and simulation-based comparison between bulk-driven (BD) and gate-driven (GD) operational transconductance amplifiers (OTAs) operating in the deep-subthreshold ultra-low-voltage regime. While BD techniques are traditionally considered unsuitable for high-performance analog design due to their lower transconductance efficiency, this study demonstrates that, when combined with self-cascode structures, BD architectures achieve competitive intrinsic gain, enhanced input common-mode range, and improved slew rate efficiency under nanoampere bias conditions. To support these claims, closed-form analytical derivations, dynamic analysis, and comprehensive Monte Carlo and PVT simulations are provided to quantify robustness and mismatch sensitivity. The results establish a systematic framework for evaluating BD versus GD architectures under identical technology and power constraints, offering practical design guidelines and optimized self-cascoded topologies for next-generation energy-autonomous systems.