A low-power, high-bandwidth LDO voltage regulator with no external capacitor

Abstract

A low-dropout (LDO) voltage regulator for low-power applications is designed without an external capacitor for compensation. The regulator has two stages, the first a folded cascode amplifier and the second a large pass transistor acting as a common-source amplifier. To better explore the tradeoff between bandwidth and power supply rejection, transistor dimensions are modified to support three different bias current levels for the same topology. Tradeoffs involving phase margin and load capacitance are also explored. In simulation, the regulator provided an output of 1.3 V from an unregulated 1.8 V supply, using a 0.75 V reference. By exploiting the tradeoffs between PSRR, bandwidth, and power consumption, a PSRR between 40-60 dB is achieved with a bandwidth between 10 kHz-350 kHz while burning no more than 150 pA of current. The output voltage is stable for load currents between 18-174 mA.