Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Differential Op Amp Gain Problem

  1. Jul 4, 2005 #1

    I have a problem I am trying to work out on simple Op Amps gain, and I am having trouble trying to prove what the gain is. I know what the gain is supposed to be (see below), but I am stumped as to how to actually go about proving it. When I try to setup the Kirchoff node equations I get a really ugly polynomial.

    I can put the design into a spice deck and prove it, but I want to understand the design from an analytical point of view.

    Gain = 2*R2/R1 * (1 + R2/Rg)(V2-V1) (GAIN FOR THE OP AMP in the attached jpg file)

    Now looking at the above equation it is obvious if you eliminate resistor Rg, the equation becomes a simple differential amplifier gain, which I can easily solve and prove. However when you add the positive feedback from the output, you get a different Beta for the loop gain that is hard to figure out.


    Attached Files:

  2. jcsd
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?