An Ultralow-Power Fast-Transient Capacitor-Free Low-Dropout Regulator With Assistant Push-Pull Output Stage

A low-voltage low-dropout (LDO) regulator that converts an input of 1 V to an output of 0.85–0.5 V, with 90-nm CMOS technology is proposed. A simple symmetric operational transconductance amplifier is used as the error amplifier (EA), with a current splitting technique adopted to boost the gain. This also enhances the closed-loop bandwidth of the LDO regulator. In the rail-to-rail output stage of the EA, a power noise cancellation mechanism is formed, minimizing the size of the power MOS transistor. Furthermore, a fast responding transient accelerator is designed through the reuse of parts of the EA. These advantages allow the proposed LDO regulator to operate over a wide range of operating conditions while achieving 99.94% current efficiency, a 28mV output variation for a 0–100mA load transient, and a power supply rejection of roughly 50 dB over 0–100kHz. The area of the proposed LDO regulator is only 0.0041 mm2, because of the compact architecture.