how to reduce the quiescent current of the output stage?

[ttnknathan]

in this fugure,if the output stage drives a low value resistance,so the scale of pmos and nmos is very big.But big scale of mos transistor deduces big quiescent.how to reduce it?Optimizing the ratio of the scale of the nmos and pmos? Or modifying the scale of M21 and M24 ?Maybe someone can suggest me another circuit to control the quiescent current?
thanks

 

[tsanlee]

Your circuit is biased in saturation region,so this bias (quiescent ) cuurrent is necessary.

Can you modify your output stage or OPA structure in your application ?

 

[Vamsi Mocherla]

Well you seem to have a class AB configuration at the output stage. Hence the current requirement will actually depend on the load you are driving, which I guess is fixed. So, there is nothing much you can do about it. The CLASS AB buffers need to have the size to provide the amount of quiscient current

 

[dumbfrog]

check this paper out
zero point to download

 

[ttnknathan]

Thanks to Tranlee and Vamsi Mocherla.You are right! In order to drive low resistance,so the scale is very big!But the bigger is ,the better the performance!I think the scale is adjustive! So,I wonder that I may optimize the ratio between the scale of the two output transistors!(I think this is the key pont,for the sttucture is decided) By the way,in this case ,the gate vovltage of the two is campatible with their threshold and just to be sure of the low current!
There I hesistate that if I modify M21 and M24 to reduce the gate voltage of the output transistor, the current in the output satge will be handreds uA,the full stability will not be guaranteed especial for the technical corner!
Thanks to dumbfrog, in this figure,M21 and M24 are just for the current control.In such case ,the Mos's must be in saturation regime!I think in this case the gate voltage of the output transistors is limited if low current is needed!

Thanks to all!
If I don't alter the structure,So,how to optimize it?

 

[andy2000a]

another method is close this output stage when no
input signal , but you should reduce output stage when Turn_on "noise" -> if use in earphone Amp .