how to do simulate frequency characteristic of OP?

[wolf001]

Usually I simulate the open loop gain of OP as below figure.How can I simulate the open gain of the back OP? Thanks.

 

[paladinzlp]

You can find the DC working point, then set input ac=1, then you can simulation the frequency characteristics of OP-AMP,
You can also plus a RC filer where the feedback's
point (the RC's W-3db is low such as R=1G C=100u)

 

[paladinzlp]

The frequency include gain(s), phase(s), psrr(s) CMRR(s) and so on.

 

[wolf001]

The OP include both of positive and negtive feedback,So the point to insert the ac input is hard to choose.When I put the ac input at the base of output transistor,the loop will be stable.But when I do tran simulation(add the VPWL as VCC),I find the oscillation at the output.So I think this ac simulation is not accurate.