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I am attempting to calculate the total error in an op amp (OPA2333 to be specific) that is used in a voltage sensing circuit. If I use the OPA2333 model in my SPICE circuit, are the errors already accounted for when I run a sim? Or do I need to calculate the errors separately and model it into the circuit?

And by errors, I am referring to things like the following:

  • Input offset voltage
  • Input offset current
  • CMRR
  • PSRR
  • Gain error

enter image description here

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    \$\begingroup\$ I can't say specifically for the OPA2333, but SPICE simulation usually has typical parameters, not worst case. \$\endgroup\$
    – user4574
    Jun 21 at 17:29
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    \$\begingroup\$ Just added a picture of the circuit. The output of this circuit is what goes into the ADC. \$\endgroup\$
    – flamezdude
    Jun 21 at 17:38
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    \$\begingroup\$ @flamezdude Do not forget the worst case for your resistor values. For example, here I'm using a simple program I wrote that allows me to calculate any two remaining values, given others, and takes into account resistor tolerances. I just populated it with 10 k values and a few other details. Take a look at the report there at the bottom, showing the variation. This is just three resistors tied to a shared node. \$\endgroup\$
    – jonk
    Jun 21 at 17:52
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    \$\begingroup\$ @flamezdude Also watch this video which leads up to using Monte Carlo simulations in LTspice. \$\endgroup\$
    – jonk
    Jun 21 at 19:04
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    \$\begingroup\$ I uploaded my current version of the circuit that accounts for variations in resistor & power supply tolerances. It is still not clear to me what parameters, if any, in the op amps I should change to get worst case. \$\endgroup\$
    – flamezdude
    Jun 21 at 19:28

1 Answer 1

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You would need to compute worst case and specify the environmental range and R & IC component tolerances. Then apply the worst case parameters for Vos, Ib, Ios, CMRR, PSSR, and apply the worst case resistor tolerances for the above along with cable impedance mismatch for CMRR and thus Vcm input then Vdm input and resulting SNR and gain error.

What are your expectations or requirements, acceptance critieria or Specs?

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