My school task was to simulate a 4BIT DAC converter in multisim. Im supposed to simulate the circuit when the switches are on/off and measure the output on the op amp.

I think the circuit works fine but I dont quite understand why the voltage is negative. I checked the poles and tried to invert reinvert it but nothing works. Is it standard for it to be negative? Or?

If my circuit is built wrongly please tell me how to fix it

Thank you very much

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  • 1
    \$\begingroup\$ Since the opamp is in an inverting configuration (as it should be, to get a "virtual earth" at the DAC output) this is all as it should be. \$\endgroup\$ Oct 24 '20 at 18:50
  • \$\begingroup\$ you want to know how to fix what? ... you have not said anything about any problems \$\endgroup\$
    – jsotola
    Oct 24 '20 at 19:08

As you're using an inverting amplifier, this is kind of expected – in fact, not only kind of. This is your design intent - inverting the voltage.

If you don't want inverted voltage, don't use an inverting amplifier configuration for your opamp, but a non-inverting one (there's gazillions of things on the internet about opamp configurations, do your own research. Even Wikipedia has a page on opamp applications).

  • \$\begingroup\$ Okay, I understand, thanks for your explanation \$\endgroup\$ Oct 25 '20 at 5:53

U2A is wired as an inverting amplifier so the positive current from the ADC network is converted to a negative voltage. To produce a positive output reverse the polarity of V1.

  • \$\begingroup\$ Yea I got it, thanks \$\endgroup\$ Oct 25 '20 at 5:53

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