Hi,
I'm currently doing a course on OP amps and I am trying to figure out this question. For the life of me I am not able to figure out the differential gain (Av diff) and the Common mode gain (Av cm). I feel like I have a good understanding of the 2 yet when i apply what I think I know the answer isn't even in the ball park. I was hoping you someone here could spend a bit of time and give me some feedback.
I've attached a picture of the problem in question. Av diff is 95.9 and Avcm is 8.18. I can't get those numbers.
What I thought:
Well I can find the current in that circuit by taking Vb1 / R1 + R3. I can then find all the drops across the 4 resistors and i found Vout to be .1818V. This is correct as it is the right answer. The part that eludes me is...av diff is Vout/v1  v2. V1 is Vy and V2 is Vx and I found values of 0.0999V and .08999V respectively. Yet my numbers dont seem to work so either i made a ciruit analysys mistake or I dont quite grasp the idea of Av diff and Av cm yet....
*apologies for the sideways image :S
I'm currently doing a course on OP amps and I am trying to figure out this question. For the life of me I am not able to figure out the differential gain (Av diff) and the Common mode gain (Av cm). I feel like I have a good understanding of the 2 yet when i apply what I think I know the answer isn't even in the ball park. I was hoping you someone here could spend a bit of time and give me some feedback.
I've attached a picture of the problem in question. Av diff is 95.9 and Avcm is 8.18. I can't get those numbers.
What I thought:
Well I can find the current in that circuit by taking Vb1 / R1 + R3. I can then find all the drops across the 4 resistors and i found Vout to be .1818V. This is correct as it is the right answer. The part that eludes me is...av diff is Vout/v1  v2. V1 is Vy and V2 is Vx and I found values of 0.0999V and .08999V respectively. Yet my numbers dont seem to work so either i made a ciruit analysys mistake or I dont quite grasp the idea of Av diff and Av cm yet....
*apologies for the sideways image :S
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