As long as you have enough loop gain regulator works from dc point of view but think about mid band PSRR..

Hi supermoment,

If the size alone is your concern, you can keep the transistor in triode. However, it would increase the voltage swing at the gate which in-turn demands the design of the previous stage for higher voltage swings which may not possible. This situation is particularly worse when you have to supply highest load current at lowest supply voltage and at SS -40.

as raja.cedt pointed out, AC PSRR will get affected, because, if the transistor is in triode then vds will also control the current through the channel which will effect output voltage. This will happen at those frequencies where loop can no longer regulate the output voltage (happens roughly  beyond unity-gain frequencies of the loop).

Any comments are welcome.

Bye.

Hello,
Buffer based design is quite common in older days but with lower supply buffer might be ended up in sub-threshold region but this is also okay to some level, this will give better psrr by isolating Cgs from the opamp being driven, watch out buffer current it is not negligible.. Plz refer the following pap...

A Transient-Enhanced Low-Quiescent
Current Low-Dropout Regulator With
Buffer Impedance Attenuation

Thanks,
Raj!!!

hi
Thanks for your info.

What is the current method??

I also find that the offset is relatively large during no-load condition as the gain is lower because vg net of the pmos is relatively higher.

LDOs usually have a "ground current" that is a current that goes through the resistive divider that generates the feedback signal.

If you're having stability problems at startup or in a low-current state you can resolve this by increasing the current through the feedback divider resistors.  Obviously this reduces your efficiency but sometimes it is necessary.

Yes it is achievable across PVT.  It's a design issue.  You have to design you op amp so it is stable at no load current.  Simple as that.  Increasing the current through the divider is kind of a cheap way to help you op amp, but you may have to look into how your compensating it.

yes i know bleeder can solve the problem at the cause of power.
However in many papers, it claim low Q current which is <50uA current. Their efficiency is near to 99%. Is that true?

for example the Raja point out:
http://www.ece.ust.hk/public/activities/fyp/fyp07/poster_MP3-07.pdf
the Q current is only 55uA and efficiency is 99.9%