(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

Assume the op amp is ideal.

Design the circuit such that Vo = Va + 2Vb + 3Vc

3. The attempt at a solution

Not sure how to go about this one.

I started with

[itex]\frac{V_a}{R_a}+\frac{V_b}{15k}+\frac{V_c}{R_c} = 0[/itex] since the op amp is ideal, the sum of the currents going into the non-inverting input must be 0.

From here I haven't got any ideas how to proceed. But what is the voltage at the inputs? I'm assuming it's zero because Vn/20k = 0 : Vn = 0

EDIT: Alright I found Ra to be 30k, Rc to be 10k. Now I have to find the currents ia, ib, and ic, when Va=.5, Vb=.7, and Vc=1.2. Shouldn't that just be Va/Ra =ia? I know one of them must be negative since the total current flowing in must be 0, but how do I know which one?

I found Vo =5.5 at those values for Ra,Rb,Va,Vb,Vc.

Ok.... I figured it out. I guess sometimes it just helps to type it out on a forum haha. For anyone wondering, Vo=6Vn (by KCL at the negative terminal). Since Vo = 5.5, then Vn = .9166...

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# Homework Help: Op Amp : Design the circuit such that

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