ABSTRACT
Low-dropout (LDO) regulators, which provide fast-transient response and good power supply ripple rejection, are indispensable in system-on-a-chip designs. Conventional analog LDO regulators can perform excellent in normal supply voltages, while the digital LDO regulators recently become very popular for its low-voltage operation, good large-signal performance and process-scaling characteristics. This chapter addresses the design considerations, circuit techniques of LDO regulator, and discusses the recent advancements on both analog and digital LDO regulators. An LDO is basically a linear amplifier that has large output current capability. The chapter summarizes the pros and cons of designing the dominant pole at the output node or the internal node. It introduces the fast-transient circuit techniques for both analog and digital LDOs. The analog LDOs give excellent performances at nominal supply voltages, while digital LDOs find their applications in low-voltage scenarios.
