Design of an Output-Capacitorless LDO Regulator with Adaptive Power Transistors

Abstract

This paper presents a bandgap reference and an output-capacitorless LDO regulator with adaptive power transistors. The bandgap reference consists of a current reference circuit, a bipolar transistor and proportional-to-absolute-temperature (PTAT) voltage generators. The proposed LDO improves load transient and light load efficiency by permitting the regulator to transform itself between 2-stage and 3-stage topologies, depending on the load current condition. Cadence simulation with SMIC 0.18 μm process shows that the bandgap reference generates a reference voltage 569 mV and the quiescent current is only 0.23 μA, the proposed LDO generates an output voltage 1 V, the quiescent current is 0.88 μA (including bandgap reference) at no-load condition, the undershoot /overshoot voltage is 187 mV/152 mV and the settling time is 5 μs as load current suddenly changes from 0 to 100 mA, or vice versa.