# Integrator (Op amp) Simulation OrCAD

I'm working on in a integrator op amp and actually i make the desing in a breadboard and is working but in time of simulation is like there is not voltage in the output of the op amp. I don't understand what this error is. Im working with a frequency of 1kHz and a gain of 1.

Figure 1. Integrator Schematic.

Figure 2. Schematic Graph. Figure 3. Integrator Ideal Graph (Texas Instruments). enter link description here

• @Sparky256 I'm actually change the R2 value at 100k but if my frequency is 1kHz the period T have to be 1/1kHz and that is 1ms Commented Oct 7, 2018 at 4:09

There are multiple issues.

R2 should be 100000K, you've got it at 100m$$\\Omega\$$. MEG may work in PSPICE. SPICE was originally developed in the mid-1970s using FORTRAN and does not distinguish case.

TD, TR and TF should not have the 's' after them.

Your supply voltages are too low. You need at least +/-5V but also keep in mind that the offset voltage of the LF353 can be as much as 13mV so your DC output voltage will be 1000 times that or +/-13V. You can set an initial condition on C1 of 0V. Use the .ic directive. Setting the initial condition will not keep it from eventually drifting, but you're probably not going to simulate that long. You may see a slight positive or negative slope to the simulation results depending on the Vos in the model.

Your calculation of C1 is off by around 4 orders of magnitude (it will be between 1 and 2 nF, please calculate it carefully).

C = $$\\frac{I}{dv/dt}\$$

You have a mistake. R2 should be 100K, not 100M, which would give you a gain of 1,000 at a frequency of .001 HZ. Maybe the simulator is working ok but 1,000000 times too slow with a 1,000 times too much gain. For a gain of -1, R1 = R2.

+/- 2.5 volts is not enough to power most JFET op-amps with bipolar power supplies. There minimum is usually +/-6 volts. I have confirmed with another program that 100K * 1.59uF resonates at 1KHZ.

• Thanks a lot for your solution a really aprecciated. Commented Oct 7, 2018 at 18:14

As someone already pointed out, it doesn't destinguish between uppercase and lowercase, so M is actually milli. You have to use MEG, i.e R2 should be 100MEG.