Hey guys trying to work out the input offset current for an opamp schematic used in a practical. Please see attached pdf.
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Your circuit has positive feedback. I don't think that is what you intended.Hey guys trying to work out the input offset current for an opamp schematic used in a practical. Please see attached pdf.
RonH are you aware that you are a superstar?! As a second year engineering student I hang my head in shame at how easy you made that look!Check this out...
EDIT: This does not include amplifier offset voltage.
Did you actually look at how the equation was derived?I disagree.
Ronh, I think you have calculated Ibp and not Ioff.
Ioff should equal [Vo/(10^9)]-Ibn
Isn't there another tiny error?You're right. I forgot to account for Ibn flowing through R2. The error is generally miniscule, but it's an error nonetheless. I will edit the annotated schematic.
You are correct, of course. I went back and looked at my attachment and was stunned to see it was not what I thought I had posted. It is corrected now, I hope.Isn't there another tiny error?
Your 5th equation down is:
Vout = (Vx/100 - Ibn)*100k
Shouldn't this be:
Vout-Vx = (Vx/100 - Ibn)*100k
because the current in R2 is (Vx-Vout)/100k, not -Vout/100k
This leads to a slight change in your equation 8, which becomes:
Vout = 1.001e9*Ioffset - 1e5*Ibn
Look at the attachment again. I still had errors. I thought I had replaced the erroneous drawing yesterday. I should be correct now.Thanks to both of you again!