# Op-amp wrong output

I have imported a Spice model of an op-amp from the link below and tried to plot the same outputs, but I am getting different results.

Link to the Spice model I used and the desired plot: https://www.eng.auburn.edu/~strouce/analogbc/opamp2.htm

Circuit I am using:

Output plots I am getting:

Edit: added a negative feedback and still getting the wrong results

• You need some amount of negative feedback - otherwise, the circuit has no fixed bias point at the linear portion of the transfer curve. This is due to the huge open-loop gain of the opamp.
– LvW
Jul 29, 2022 at 7:27
• After looking at the netlist at the end I can see that the non-inverting terminal is connected to an AC source (Vin 17 0 AC 1 DC 0 sin(0 1 1Mhz) and the inverting terminal is connected to a resistor (R1 18 0 0) but the value of resistance here is given as 0. Also I did run simulation with a negative feedback but still didn't get the wanted results.
– user316666
Jul 29, 2022 at 8:06
• Anshul show us the circuit with feedback.
– LvW
Jul 29, 2022 at 8:10
• added in an edit section of original question
– user316666
Jul 29, 2022 at 8:20
• When you run ac simulations, you must always look at the operating bias point. It tells you if the dc levels are within the expected ballpark or not. Here, OrCAD should let you display the bias points and we could see if they are correct or not. If the op-amp is stuck to the upper or lower rail, then something is wrong. I would first simulate the raw netlist given in the page and check results are correct. Then, redo the exercise with the included .LIB and see it is still correct. If all is ok but OrCAD keeps giving wrong results, then the symbol pinout might be the issue. Jul 29, 2022 at 8:22

For finding the open-loop curve, you should use "special" feedback.
For reference, Example with a "classic" op-amp.

For closed-loop, with one resistor your feedback is ok.
Probably, "operating point" check in your simulator.

NB: your generator amplitude voltage too high in TRAN analysis.

You can do also a DC Analysis if you want see the "characteristic" curve (Vout versus Vin).
See the "open-loop gain" under "slope" in the picture.

After "import" of the Spice file (free simulator microcap v12), I have this picture which seems "ok".
As pointed out by @Verbal Kint, probably pinout issue.