0
\$\begingroup\$

I am currently writing a lab report for an introductory lab in electrical engineering on the subject of op-amps. One question that I'm stuck at is

With the op-amp operating in its linear regime, what voltage would you expect at the negative (inverting) input terminal, with respect to ground? How does this compare with your measurement of \$V_n\$?

I think the goal is to test the idealness of an inverting op-amp with the data that I have here: Op-amp idealness

The op-amp circuit:

schematic

simulate this circuit – Schematic created using CircuitLab

Supply voltages:
\$V_{cc+}=15.664\$ V
\$V_{cc-}=-15.143\$ V

I was taught that the golden rule of an ideal inverting op-amp is \$V_n=V_p\$. But what is \$V_p\$? It can't be the input voltage because of the golden rule. How do I answer those questions with the given data?

\$\endgroup\$
3
  • 6
    \$\begingroup\$ Was there a schematic with the question? It would be very useful. \$\endgroup\$
    – Transistor
    Feb 8, 2020 at 22:27
  • \$\begingroup\$ @Transistor Yes, I just added it. \$\endgroup\$
    – Sckizel
    Feb 8, 2020 at 23:20
  • \$\begingroup\$ "But what is Vp?" By inspection, voltage Vp--the voltage at the op amp's non-inverting input--is zero volts. (NB: Ground potential is zero volts, and the op amp's non-inverting input is connected directly to ground potential.) \$\endgroup\$ Feb 9, 2020 at 1:24

1 Answer 1

0
\$\begingroup\$

If you read the datasheet, Vp-Vn = Vio (input offset voltage), which should be close to ~3mV as the spec says. Ideally, you may think it should be zero.

Ip and In is the input bias current, Iib, which should be ~30pA. Your measurement seems to high, but your equipment may not go that sensitive.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.