Abstract

Low-dropout regulators (LDO) are required in many applications because, compared to switching converters, these regulators are inherently low noise and offer a simple solution with lower costs. Applications exist where even the lowest noise LDO cannot meet the desired noise specification, such as high-performance RF circuitry, laser current drivers, and so forth. Placing LDOs in parallel can potentially lower the noise even further when the correct parallel LDO architecture is chosen. This document provides a comprehensive analysis on the noise reduction of recent parallel LDOs using ballast resistors. The ballast resistor technique is compared against two other parallel LDO techniques, (1) using op-amps and an additional feedback loop to parallel the LDOs, and (2) using current mirrors formed from matched BJTs to parallel the LDOs.