Design Of LDO Regulator Without External Capacitor

In recent years, with the rapid development of consumer electronics, the demand for chips of power management is becoming more and more. The traditional Low Drop-out Regulator (LDO) has been widely used in various electronic products. However, the external capacitance of LDO is very large. Therefore, LDO without external capacitor is developed.In order to solve this problem, LDO regulator without external capacitor is researched in depth in this paper.In general, the structure of LDO regulator without external capacitor includes Band-gap Reference, Error Amplifier, Damping Factor Control (DFC) circuit, Transient Enhanced Circuit, Feedback Network and Power Tube. The error amplifier is an important part of LDO, the first level with folded cascode amplifier can effectively improve the loop gain of system. The second level with the source follower of dynamic bias can improve the driving ability of capacity for the error amplifier and the response ability of circuit. Damping factor control is a kind of method of frequency compensation frequency of the loop is given, which includes an amplifier and a damping control of capacitor and effectively improves the phase margin of system. Because the transient response of LDO regulator without external capacitor will become worse, the transient enhanced circuit is increased in the system to ensure that the output of transient change for the circuit is stable in the mutant load conditions.This design and each module are simulated by Cadence based on SMIC 0.18um CMOS technology. The output voltage of LDO is stable and its value is 1.8V in the power supply voltage changes from 2V to 4V. In addition, the line regulation and load regulation rate is 1.83 mV/V and 0.0022 mV/mA. The phase margin of the circuit is from 57 degrees to 67 degrees when the load varies from 100uA to 50mA. In a word, the design in this paper meets requirements.