Questions about opamp output stage

[Lantis]

I got some question about opamp output stage.
1.
Is it necessary to have large current in the output stage?
why?
2.
Should i add a miller compensation cap between input stage and output stage?
just as in two-stage opamp?

3. The main purpose of the output stage is provide low output resistance, isn't it?

Thanks!

 

[willyboy19]

Re: OPAMP Output stage?

Here are some remarks I have:

1) The output stage does NOT necessarily need to have large current, it really depends on your OTA topology. You can bias the output stage with relatively small DC current if you have a class AB output stage. If you have a class A output stage, however, you may have to burn more current to keep your two stage OTA stable.

2) Miller compensation is always needed when you do have a two stage OTA.

3) The main purpose of having a dedicated output stage is to drive resistive load, as you understands. Thus, it is not always necessary to have an output stage in the system. You need to figure out this soon enough before doing any opamp design.

 

[ppenday]

Re: OPAMP Output stage?

yes its better to have output stage with more current so that it can handle low resistance next stages.