A question on decrease output impendence of EA of LDO

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fanrong

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Hi ,every one :
In LDO design , to increase the second pole ( the pole at the output node
of error amplifier) , the EA 's last stage is a buffer stage . So the pole
w= Ro*Cpass will be small ) .
But sometimes , the pole is still too low .
My question is , is there any other ways to decrease the output impendance
of the EA ? Does negative feedback will do ?
 

for a buffer without negative feedback, the minimum output resistance is about the reciprocal of the transcondance, so if you need to get a smaller output resistance, all you need to do is to increase the transcondance(Eg:increase the current and the width-length ratio,sometimes using nmos rather pmos due to mobility).

it's theoretically that you could obtain a very low output resistance by negative feedback, but it's very complicated, sometimes, the negative feedback doesn't work ideally at high frequency.
 

Thank you for your help , youyonggen_1 !
 

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