Ldo Linear Regulator's Research And Design

With the high-speed development of the information era, the power technology becomes more and more important. In numerous Power, LDO (Low Dropout Voltage Regulator) has aroused greater attention because of its small area, high PSRR, low power dissipation, low noise and few off-chip components, etc. In addition, the transient response to input voltage and output load is faster. These advantages make LDO suitable for the domain concerning portable electronic products, industry and automobile, for example: the PDA, MP3, DC ,radiotelephony and DDR.Using CSMC CMOS 0.5um models, the paper analyzes and designs a novel LDO linear regulator, and it includes the second curvature compensation bandgap voltage reference, error amplifier, over thermal protect, limit current protect. Firstly, the author introduces the basic structure and operational principle of it, Secondly, according to the function and performance of LDO, the improved circuit, which is based on traditional LDO and the serial structure of power taransistors, achieves the capability of 2A source\sink and satisfies the stable supply voltage for DDR. The simulated result, which is 600us of start-up time, 1.25V of the output and 2.86mV of the output change, reflects this circuit has good transient response and the stable output. Considering the safety of power transistor, it also has thermal protect circuit and current limit protect circuit. The shutdown temperature is 169.4℃, and the hysterisis temperature is 40.8℃. Power transistors'currents are respectively limited by 2.86A and 2.66A. these suggest that LDO has high precision, fast response, good reliability, and the safety of the whole circuit under destructive environment or sudden short-circuit condition.All simulations of the paper are completed by Cadence-Spectre simulated tool. Comparing the simulated result with the pre-target, the DDR application is satisfied, which is providing the evidence for LDO design. In additional, its layout has also been designed by applying the foundry's technology.