Area-Efficient Low-Cost Low-Dropout Regulators Using MOS Capacitors

Traditional design of low-dropout regulators offer the use of metal-insulator-metal (MIM) compensation capacitors to prevent instability in the absence of load capacitor 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 changed according to the value of load current. The idea has been applied to stabilize a 1.2V, 100mA low-dropout regulator in a 0.18 mu m CMOS n-well process. Using the proposed technique, the regulator meets stability with a small 100pF MOS output capacitor and no ESR.