I'm building this circuit in Multisim. The amplifier's input is grounded, but I'm supposed to see that the output is not zero because of an input offset error. I'm clearly missing something since I don't see how I'm supposed to drive this circuit when the input is grounded. Where do I attach my AC voltage source?amplifier

Thank you.


The point of the exercise is to show that with no input signal that there will be a non-zero voltage on the output.

Where do I attach my AC voltage source?

You don't.

Just read the voltage at PR1.

  • \$\begingroup\$ Alright, thank you for your help. \$\endgroup\$ – corgiworld Apr 8 '20 at 22:14
  • \$\begingroup\$ You're welcome. Don't forget to come back after a day or two and accept an answer if your question has bien answered and you can your any others that are useful. \$\endgroup\$ – Transistor Apr 9 '20 at 6:08

That's fairly straightforward.

Ground the left side of R1. Drive the + input with an AC waveform of, let's say, 100 Hz with an amplitude of 1 uV and zero DC level.

The output should be an AC waveform with an amplitude of about 1 mV. However, look at the DC level of the output. If there is no offset, the DC component will be zero.

It won't. It will be the input offset voltage times 1000.

  • \$\begingroup\$ Okay, I think this makes sense. Thanks. \$\endgroup\$ – corgiworld Apr 8 '20 at 22:14
  • \$\begingroup\$ Why do we need the AC waveform? Aren't we just showing that the bias currents are producing a DC offset? \$\endgroup\$ – Transistor Apr 8 '20 at 22:19
  • \$\begingroup\$ @Transistor - You are absolutely correct. However, he seemed to have a fixation on AC analysis, and I figured this was quicker workaround than trying to properly educate him. \$\endgroup\$ – WhatRoughBeast Apr 9 '20 at 17:23

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