International audienceThis paper presents the application of the state space approach to analyze stability and robustness of multiloop linear low dropout (LDO) regulators. Because of the increasing complexity of the LDO architecture, the stability study consisting of an open-loop ac analysis is more and more difficult to apply. In this paper, we demonstrate how a state matrix decomposition of a system allows the stability analysis in closed loop to be performed where the open- loop ac analysis failed. Based on this technique, a methodology of design, a time response criterion, and a Monte Carlo analysis are proposed. The efficiency of this approach is illustrated comparing the classical open-loop ac study with the state matrix decomposition analysis of a complex innovative architecture LDO. The results are verified experimentally

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This paper presents a black box small-signal modeling of a low-dropout (LDO) voltage regulator. The small-signal model is derived for each part of the system around an operating point. Then, the closed-loop transfer-functions are obtained to build a five port network model of the LDO. The analytical solution is validated by simulation comparison with transistorlevel implementation of a PMOS LDO in a 90nm CMOS process from STMicroelectronics. Due to the hand calculation difficulty, we proposed an automated extraction flow based on the QZ algorithm. The flow is verified with the model extraction of a complex PMOS LDO, designed in a 55nm STMicroelectronics CMOS process.

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