Low-cost area-efficient low-dropout regulators using MOSFET capacitors

Traditional design of low-dropout regulators offers the use of metal-insulator-metal (MIM) compensation capacitors to avoid instability in the absence of output capacitance with equivalent series resistance (ESR). In addition to area efficiency achieved by replacing these capacitors with MOS transistors, the location of implanted transfer function poles and zeros are adaptively varied according to the value of load current. This idea has been applied to stabilize a 1.2V, 100mA low-dropout regulator in an industrial 0.18 mu m CMOS n-well process. Using the proposed technique, the regulator meets stability with a small 100 pF MOSFET output capacitor and no ESR.