# Op-amp with capacitor showing output voltage of 2.98 V despite 0 input voltage

I am having trouble with my circuit as shown above. The capacitor has zero initial values. Why is the output voltage shifted by 3V?

The original purpose of the circuit is to implement a PI controller. I have graphed the inverse Laplace transform of the output voltage and the difference between the theoretical computation and simulation is a shift of 3V.

• Here is a great video showing and explaining a better circuit for real, non-ideal use: youtu.be/pX0gnFnjiQI?t=988 Sep 22 at 5:59

• That's the right approach. You are giving a path for the DC so you should find two things: 1. There is a small output offset of $I_{BIAS} \times R_f$ and you've affected the DC and low-frequency response of your integrator as now you have created a high-pass filter. Sep 22 at 7:05