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# integrator circuit does not work properly.

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#### mohamis288

##### Full Member level 3
Hello,
I have designed an integrator as in the following:

but I do not know why in my simulation, output is like this:

output is saturated at 1.2 v (supply voltage).

Solution
Problem is your simulation setup. Integrator is running into saturation during initial transient solution. You need to apply initial conditions or skip initial transient solution.
Hi,

What do you expect? (This is a serious question, please answer it).

* Inverting input at 300mV
* non inverting input at 900mV
--> for sure it saturates at positive rail.

Klaus

Hi,

What do you expect? (This is a serious question, please answer it).

* Inverting input at 300mV
* non inverting input at 900mV
--> for sure it saturates at positive rail.

Klaus
well, because opamp is in a negative feedback loop, I expect output to go from 900m to 1.2 volt, with constant current (or with a constant slope line).

Problem is your simulation setup. Integrator is running into saturation during initial transient solution. You need to apply initial conditions or skip initial transient solution.

Problem is your simulation setup. Integrator is running into saturation during initial transient solution. You need to apply initial conditions or skip initial transient solution.
thank you for your answer. I think by "initial condition", you mean initial voltage for capacitor ,which I put it equal to zero. But output seems weird. here is my circuit:

output voltage would be like this:

voltage of "common" node is like this:

both of voltages are weird. "common" node voltage must be constant and output voltage must increase. So, do you know what is the problem?

I think your power supply (1.2V) is too low. Try to increase to see if the circuit starts to work. What about op-amp parameters ?

Hi,

Now you
* added some DC at the input
* and - even worse - you switched input polarity!

No wonder it does what you tell it to do....

Klaus

If your squarish block is an opamp, then two things (basically one):
1. Circuit is not working in negative feedback configuration
1a. if input pins name are correct, you are trying to make positive feedback loop
1b. with only capacitor in feedback, you have not established feedback loop in dc, thus operating point is wrong (output will go to rail whatever you do)

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