A Hybrid-Mode Operational Transconductance Amplifier for an Adaptively Biased Low Dropout Regulator

Abstract

This paper presents a hybrid-mode, operational transconductance amplifier (HM-OTA) to improve the dynamic response of an adaptively biased low dropout regulator (AB-LDR) while maintaining a low quiescent current. Using the proposed HMOTA in the AB-LDR, we can achieve higher dc gain and wider loop bandwidth compared to a conventional current-mode OTA (CM-OTA). Additionally, the proposed HM-OTA provides a high discharging slew-rate at the gate of the PMOS power transistor during a low-to-high load step. So, the proposed HM-OTA helps to achieve a good dc load regulation as well as a reduced undershoot during load transient. At the same time, the regulator requires a small value of the output capacitor for achieving the loop stability compared to the conventional differential-mode OTA (DM-OTA). The conventional CM-OTA and the DM-OTA turn out to be special cases of the proposed HM-OTA that does not occupy extra space in silicon or consume additional power to realize. The AB-LDR using the proposed HM-OTA has been implemented in 0.18-μm CMOS technology. The regulator consumes a quiescent current of 1.6-μA at the no-load condition with a transient variation of 24 mV at V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> = 1.2 V for 0-50 mA of load step with a 1-μF output capacitor.