Hi. I am trying to find out what R4 is for or what its job is. Can anyone help? Thank you.
This is a typical differential amp circuit that you have gain of -1 if you drive V1, gain of +1 if you drive V2. Remember the gain of the non inverted amp is R3/R1+1. In order to achieve gain of 1, you need to divid the V2 by 2 so when multiplied by 2, you get gain of 1. R4 form the divide network with R2.
I see, it is needed for a voltage divider. That makes sense. Thank you for your reply and sorry for my late reply.
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