High-PSR Capacitorless LDO with Adaptive Circuit for Varying Loads

Abstract

A capacitorless low-drop-out (LDO) regulator with an NMOS pass transistor-based adaptive network to achieve high and constant power-supply rejection (PSR) for varying loads is presented. The proposed LDO does not require an external capacitor making it suitable for System-on-Chip (SoC) applications. The low-frequency PSR of the LDO varies with load current as the transconductance and output conductance of the power transistor depend on the load current. The proposed LDO is capable of maintaining a constant and high PSR for varying loads by using an adaptive network. The NMOS pass transistor in the adaptive network tracks the power-supply noise through the power transistor and bypasses this noise current through it to the ground. This helps to avoid the flow of this noise current through the load and thus the circuit can achieve high and constant PSR for varying loads. The LDO with adaptive network achieves very high power-supply rejections of [Formula: see text][Formula: see text]dB at low frequencies and [Formula: see text][Formula: see text]dB at 1[Formula: see text]MHz, for a load current of 4[Formula: see text]mA. This LDO is implemented in 0.18-[Formula: see text]m CMOS technology and consumes 1.35-mW quiescent power over the range of 1–10[Formula: see text]mA of the load current.