- #1
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Homework Statement
http://i59.tinypic.com/1smqlu.png
I'm not sure how to calculate differential mode gain
Homework Equations
I know formuals for CMRR and Acm but not Adm
CMRR = | Adm/Acm |
Rb/Ra = (1-ε)Rd/Rc
Well let's see. You've used 1000 for R3 when the circuit says it's 24000. You've used 24000 for R4 when your circuit says it's 25000, and 25000 for R2 when your circuit gives it as 1000.So using:
Ad = 1/2[R3/(R1+R3)] [(R4 + R2)/R2 + R4/R2]
1/2[1000/(1000+1000)] * [(24000 + 25000)/1000 + 24000/25000] = 12.49
So it's exactly half of what the answer should be according to the answers up there? 24.98? Why does it have the 1/2 in front of it? Without it the answer would be 24.98 which would be correct...
Lucky you! I never had it so easy :)I remember my prof deriving this for us but he told us we don't need to know how to derive it?
I agree with your result. My calculation gives Ad=24.49My answer in post #5 seems to be off by .5. I can't spot anything that's wrong
You and your calculator must have a difference of opinion on the order operations implied by a given key sequence.Where did I mess up? I keep putting it in my calculator and getting it wrong haha
Yeah that was the issue, thank you :)Hmm. I think perhaps the given formula may have suffered from careless algebra. I derived the expression myself and used that, obtaining the correct result. The expression I arrived at was:
$$A_{dm} = \frac{1}{2} \left[ \left( \frac{R3}{R1 + R3} \right) \left( \frac{R2 + R4}{R2} \right) + \frac{R4}{R2} \right] $$