tran simulation about op point problem

[mightyocean]

Hi, there
I am running a tran sim of an opamp in ADE, environment is set up as followed:
a small ac signal 100uV biased with a dc voltage is added at positive input, a same dc voltage is added at negative input. The single output's dc operating point is changing down slightly at the beginning of tran sim, then keep stable.
Maybe it's a simple question but my analysis ability is limited,so pls help me
thank you all

 

[LvW]

.............
a small ac signal 100uV biased with a dc voltage is added at positive input, a same dc voltage is added at negative input. The single output's dc operating point is changing down slightly at the beginning of tran sim, then keep stable.

Is there no feedback around your opamp ?

 

[mightyocean]

it's a two-stage opamp, feedback is between the output and the first stgae
you mean connect the negative node to the output?

 

[LvW]

it's a two-stage opamp, feedback is between the output and the first stgae
you mean connect the negative node to the output?

Yes, that´s what I mean.
What is the overall gain of your amplifier ?
Normally, an opamp has a very high gain (at least 80 dB) which makes negative feedback necessary in order to avoid output saturation due to offset voltages.

 

[mightyocean]

about 90dB. That means my tran sim configuration is wrong?
If connect it as a source follower, the output surely follows the input, then it won't get a ramp figure, is my understanding right?

 

[LvW]

about 90dB. That means my tran sim configuration is wrong?
If connect it as a source follower, the output surely follows the input, then it won't get a ramp figure, is my understanding right?

I have no information about your tran configuration (power supply, bias, feedback, input/output operaing point,....). Do you really speak about a "classical" opamp (because you mentioned "source follower") ?