How to improve LDO PSRR when using NMOS as passive device

[zxasqw123]

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

 

[rfzheng]

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

 

[zxasqw123]

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

 

[zxasqw123]

Re: LDO PSRR problem

i am still waiting for answer ,can anyone help me

 

[12qwas]

LDO PSRR problem

you can refer to the topic
hope it will help u