TIDA035 October   2020

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
  4. 2Two-point Insulation Resistance Measurements
  5. 3Equation Verification by Simulation
  6. 4Op-amp Caused Error Analysis
    1. 4.1 Input offset voltage
    2. 4.2 Input bias current
    3. 4.3 Open-loop gain
  7. 5Summary
  8. 6References

4.3 Open-loop gain

The initial analysis is based on the assumption that the open-loop gain of operational amplifier approaches infinity. However, if considering the finite open-loop gain of the op-amp, it can be started directly from the definition of open-loop gain.

Equation 15. GUID-20201012-CA0I-XDPS-9HCP-GKTQ7VWC2N04-low.gif
Equation 16. GUID-20201012-CA0I-NJWG-R45B-RVJGW1Z3NRRB-low.gif

Then ISO_POS and ISO_NEG can be got including open-loop gain error respectively.

Equation 17. GUID-20201012-CA0I-JC2M-KLFG-HNRT58VM87HC-low.gif
Equation 18. GUID-20201012-CA0I-Q458-MLFQ-PKKM4PRMZFBD-low.gif

If AOL in Equation 17 and Equation 18 is infinite, Equation 17 is equivalent to Equation 2, as well as Equation 18 is equivalent to Equation 5.