A Multi-Point Sensitivity Approach for Stability Analysis of Multi-Loop LDOs

This work presents a multi-point sensitivity approach for stability analysis in multi-loop low-dropout regulators (LDOs) without a common touching point (CTP). By probing closed-loop sensitivity at multiple locations, the approach estimates the overall stability margin from the worst-case result and identifies the stability-dominant loop and its critical frequency without explicitly extracting and recombining sub-loops. The approach is validated through three LDO examples and applied to a 40-nm CMOS SSF-based multi-loop LDO. Measurements confirm that the SSF-based LDO achieves stable transient behavior and improves dynamic reference behavior in a 12-bit 50-MS/s SAR ADC, demonstrating the practical utility of the proposed approach for design-oriented stability analysis.