# Homework Help: Op Amp Design #2

1. Mar 6, 2014

### Maylis

1. The problem statement, all variables and given/known data
Design a circuit containing a single op amp that can perform the following operation: Vo = 3*10^4(i2-i1), where i2 and i1 are input current sources

2. Relevant equations

3. The attempt at a solution
Where I'm at right now, I am just using the equation for a difference amplifier gains, but I have more unknowns than equations, so I don't know what to do.

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2. Mar 7, 2014

### Staff: Mentor

Hi Maylis. Could I suggest that you post images as unadorned jpeg (or png, etc) files, so those using basic tablets (and costly data plans) are still able to participate?

3. Mar 7, 2014

### Maylis

Alright, here is a .png

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4. Mar 7, 2014

### rude man

Your diagram labeling does not agree with your equations.

Big hint: since the inputs are current you need a total of only 2 resistors.

5. Mar 7, 2014

### Maylis

Oh I see, I need to change the label of R2 and R3. Either way my problem persists. The equation should be correct now with that change, as well as making it R3*i2 in my second stop

Last edited: Mar 7, 2014
6. Mar 7, 2014

### Maylis

Okay, I source transformed, corrected the labeling, and this is what I came up with.

Edit: my bad, I was saying that no current goes through R1 and R3, which cant be possible since there is a potential difference between Vn/Vp and the resistors. Now the equations are even messier. Where do you get the fact that I only need 2 resistors from? I am following the template for a difference amplifier as given in the textbook and I redrew as my original image, pre-source transform

#### Attached Files:

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• ###### 5.7 attempt 3.jpg
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Last edited: Mar 7, 2014
7. Mar 7, 2014

### Staff: Mentor

See if you can get it to work without R1 and R3.

8. Mar 7, 2014

### rude man

And RL.

And BTW the pdf file is a lot easier to read, for me anyway.

If the new tablets, iPads etc etc can't even read pdf files any more I am more po'd than ever that xp is disappearing ... we are dumbing-down at an ever-increasing rate ... :grumpy: