0
\$\begingroup\$

I want to use this circuit to generate a triangle wave from 100mv to 10v and an inverted wave from -100mv to -10v on triangle_inv. For my split rail supply, i'm using the VG1 circuit from this page virtual ground circuit

wave generator

It works correctly generating the positive wave, however the wave on triangle_inv is centered on 0v. It's inverted like it's supposed to be, but where's the offset coming from?

scope trace

\$\endgroup\$
5
  • 1
    \$\begingroup\$ Try connecting pin 5 to ground through a 5k resistor instead of directly. If that mostly solves the problem, then the answer to your question is "offset current". \$\endgroup\$
    – The Photon
    Feb 24, 2020 at 2:22
  • 4
    \$\begingroup\$ What does the green '~' symbol mean on the scope display after "CH2"? \$\endgroup\$ Feb 24, 2020 at 2:25
  • \$\begingroup\$ Research "op amp nonidealities and limitations," and in particular the topics of input offset voltage, input offset current, and input bias current. IMO, Mateo Aboy, on his YouTube channel, does a pretty good job of introducing these three effects: youtu.be/JiMhJJLplkQ and youtu.be/1tUaDghBmuc. Also, the LM324 is not a precision op amp, so you can and should expect a slight DC offset at the output. \$\endgroup\$ Feb 24, 2020 at 5:01
  • \$\begingroup\$ @Bruce Abbott nice catch \$\endgroup\$
    – user156429
    Feb 24, 2020 at 21:48
  • \$\begingroup\$ @Bruce Abbot. Ac coupling facepalm . Turns out the waveform was correct, but my scope got rid of the dc offset because i had it set up wrong \$\endgroup\$ Feb 25, 2020 at 3:14

1 Answer 1

2
\$\begingroup\$

I had channel 2 on AC coupling. My circuit was actually outputting the right waveform but my scope was lying to me. Facepalm

\$\endgroup\$

Your Answer

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

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