How to improve LDO PSRR when using NMOS as passive device

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if we use a NMOS as pass device ,is it useful to improve PSRR by adding a bypass CAP ,
another question, to compensation more easily we often add a buffer to increase the second NON dominant pole ,and somone says adding a buffer can improve PSRR ,can anyone explain why
thanks in advance
 

LDO PSRR problem

you should know that if your LDO want to go into dropout region, the dirve voltage of the NMOS should higher than vin and vout than a VTH ,how can you boost such high drive voltage??

but if the pass element is PMOS ,the drive voltage is zero will case the LDO went into dropout region
 

Re: LDO PSRR problem

yeah ,i know this ,i mean if i have a charge pump to imprvoe my gate voltage ,then dropout voltage is no longer a problem ,my concern is if using a NMOS as a pass device ,how can i improve PSRR ?
i think by adding a bypass cap can not improve PSRR
 

Re: LDO PSRR problem

i am still waiting for answer ,can anyone help me
 

LDO PSRR problem

you can refer to the topic
hope it will help u
 

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