0
\$\begingroup\$

I came across the following appnote(slyt647) which analyses the two op-amp instrumentation amplifier topology.

The gain was found by finding individual gains for each op-amp and adding them in accordance to superposition. I have some hard time understading how \$G_{A1V-IN} \$ (eq 8) was calculated. Circuit Diagram

As far as I see it for \$G_{A1V-IN} \$ we have the following equivalent circuit:

schematic

And thus it seems to me that: $$G_{A1V-IN} = -\frac{R_R}{R_G} -\frac{R_R}{R_f}\cdot \left(1+\frac{R_R}{R_f || R_G} \right) $$

Did I go wrong somewhere ?

\$\endgroup\$
0
\$\begingroup\$

You're right, they ignored Rg in A2 gain. I tried to sum the currents in A1- node, I made the same mistake and I've got the same result.

\$\endgroup\$
  • \$\begingroup\$ Oops... Now i've fixed it. This doesn't really answer the question though. Why does the gain term in the appnote neglect this part ? \$\endgroup\$ – Mike May 14 '18 at 18:03

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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