# Gain of differential amplifier

Discussion in 'Homework Help' started by gonzasvydd, Nov 30, 2014.

1. ### gonzasvydd Thread Starter New Member

Nov 30, 2014
4
0
For the circuit below, R1 = 12 KΩ, R2 = 1 KΩ. Determine the gain, G.

I have done the following:

G=(Va-Vb)/(V2-V1)
V-=V+=V2
V+=V2
I1=V2/R2
V1=(V2/R2)*R1

Va=V2((R1/R2)+1)
Va=(13)(V2)

now for trying to do the second part for V1 and Vb I am stuck.

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2. ### WBahn Moderator

Mar 31, 2012
18,094
4,920
You need to define your variables. You use V- and V+. But those are not on your diagram and since you have two op-amps it is ambiguous which voltages you are referring to. You also use I1 but define neither where that current is or what direction it is flowing in.

Label all nodes that are not already unambiguously labeled and then any currents you refer to annotate them on the diagram. Doing this not only aid in communicating your thoughts and intentions to others (including the grader!), but they will help you think more coherently about the problem, too.

3. ### ericgibbs AAC Fanatic!

Jan 29, 2010
2,605
396
hi,
Look at this clip from a datasheet, it should give you a hint on how to solve the problem.
E

• ###### AAesp02.gif
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