why does negative feedback do not work?

[mohamis288]

Hello,

here is my circuit which is implementing negative feedback. the input is just a sine wave with DC level of 300m V and amplitude of 200m V:

our opamp is ideal. But when I simulate it, opamp negative lead represents the following plot:

it is weird. why? I expect ot to be constant all over the simulation time. it seems so that sine generator is connected to opamp negative lead. How can I avoid this to happen?

 

[dick_freebird]

Your circuit is an integrator, so any DC error will make the output
center-point drift. That error can / does include Vio.

 

[mohamis288]

Your circuit is an integrator, so any DC error will make the output
center-point drift. That error can / does include Vio.

You know I want to use this integrator in my dual slope ADC. so, I should solve this problem in a way. I want negative lead to be constant. Is there any solution?

 

[FvM]

No stable operation point without some negative DC feedback. You can make a lossy integrator my placing a high-ohmic resistor parallel to capacitor.

 

[barry]

Why do you want your negative lead to be constant?

 

[dick_freebird]

In a sampling machine, reset switches are a possibility.