# Sine Wave Input for Op Amp Integrator but Output Looks Weird

The input is in sine form (AC input) but the output (in blue color) is the straight line. So what is wrong with my schematic in LT Spice this time? I thought I should've got output in sine form if I have input in sine form

• It's probably computing a DC solution for the starting condition. Try turning that off in the simulation control panel. If you're going to do it by forcing initial conditions, you should force both the $V_-$ pin and the output pin of the op-amp to zero. – TimWescott Apr 23 '19 at 18:39
• There's a reason practical integrators usually have a resistor in parallel with the capacitor. – Hearth Apr 23 '19 at 18:52
• It's just the learning curve for a simulator with many options for trace display and intitial condition is one of them. – Tony Stewart EE75 Apr 23 '19 at 19:49

You have a 159.15Hz sine wave. The integral of $$\A \sin(2\pi ft)\$$ is $$\ \frac{-A}{2 \pi f} \cos(2\pi ft)\$$. You have an on transient which might be dying away slowly, and then your sine wave might be sitting on top of that, and is just too small to see on this y-scale. Try nuking your initial conditions, and try looking at the response 100s or so later to see if they print better.