# Op-amp linear inverting circuit question

I'm trying to implement a linear inverting circuit using NI Multisim. I'm using a 1 Hz sine wave with a 1 V amplitude as input.

According to my circuit, the gain should be:

$$A_v = \frac{-R_2}{R_1}=-10$$

My input is:

My output is a bit concerning though. The positive half wave amplifies properly, but the negative half wave doesn't. The inverting property is working, but the gain in the negative half wave isn't proper. Here is my output (red is the output and cyan is the input signal):

I have taken the scale for the input signal to be 1 V/Div and for the output signal to be 5 V/Div, so it should take up 2 divisions to be 10 V. The positive half cycle is fine, but the negative half cycle isn't properly showing the amplification. Why is this? Even if I switch R2 to 5 kΩ, I still get a similar kind of behaviour of the negative half cycle. Here it is:

Why is only the negative cycle affected?

• I have not used Multisim recently so not sure what it expects: is the op amp supposed to fall back to some kind of implicit power supply when the supply pins aren't connected? I don't see you actually connecting the op amp's supply pins to any sort of power supply, so I'd expect it to be malfunctioning. Nov 1, 2022 at 17:30
• @nanofarad Our lab assistant told that Multisim Opamp automatically takes power? He said that connecting a power supply isnt always necessary? Nov 1, 2022 at 17:31
• @nanofarad But if the supply was the problem, why is it giving such behavior only in negative half cycle? Also, if the Gain were -0.1 instead of -10, it seems to be working Nov 1, 2022 at 17:32
• "Multisim Opamp automatically takes power" - may apply to a different device model, such as a generic op amp macro. e.g. cadence has an ideal op amp for quick simulations that doesn't require power, but if I wanted my PDK's op amp or another "real" op amp I'd have to be sure to power it. "why is it giving such behavior only in negative half cycle?" - Like many circuits, the LM741 has an internally asymmetric construction. If it is indeed missing its power supply (meaning its internal transistors are not properly biased), it may be doing wacky things internally only during one half cycle. Nov 1, 2022 at 17:38
• Since you didn't connect the power rails it appears the model is assuming a positive rail but ground for the negative rail. Perhaps it felt it would be presumptuous to assume a bipolar supply. Nov 1, 2022 at 18:09