Analysis and Design of Voltage Controlled Current Source for LDO Frequency Compensation

Abstract

Using voltage controlled current source (VCCS) instead of electrical series resistance (ESR) of load capacitor to create a zero is a novel LDO frequency compensation scheme. This paper analyzes this compensation scheme, and reveals that the VCCS circuit conduces to the improvements of transient response and PSR performance of LDO. A new area compact VCCS circuit that has a nearly ideal performance in wide frequency spectrum up to 5MHzis also presented. Using VCCS, a LDO with 300mV dropout, 2.5V output voltage and l00mA output current is designed in 0.5μm CMOS technology with pretty frequency performance, transient response and PSR performance. The total on-chip capacitor employed in this LDO is less than 1pF.