Homework Help: Op-Amp Applications

1. Sep 13, 2009

kahei

1. The problem statement, all variables and given/known data

A current-to-voltage converter
The current source has a finite output resistances Rs, and the op-amp has a finite open-loop differential gain Aod. Show that the input resistance is given by

2. Relevant equations

Rin = RF/(1+Aod)

3. The attempt at a solution

Rin = RF / (1+Aod)
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

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• Op-Amp Applications.bmp
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2. Sep 13, 2009

Redbelly98

Staff Emeritus
Welcome to Physics Forums.

Well, you haven't really shown what equations are relevant here, just giving the one from the problem statement. So, what equation is used to find the input resistance?

3. Sep 14, 2009

kahei

There is no relevant equation.
The question is just find the expression of the input resistance.

4. Sep 14, 2009

Redbelly98

Staff Emeritus
What is the defining equation for input resistance?

5. Sep 14, 2009

kahei

Show that the input resistance Rin is given by Rin = RF/(1+Aod).

6. Sep 14, 2009

Redbelly98

Staff Emeritus
That is not the defining equation, it's the equation you are trying to derive.

How does your textbook or lecture notes define input resistance?

7. Sep 14, 2009

kahei

the picture which attached in the first post shows the input resistance.

8. Sep 14, 2009

Redbelly98

Staff Emeritus
You need to look in your text book and lecture notes to see how input resistance is defined. I mean the basic, general definition, not just some equation or figure that is specific to this problem only.

At Physics Forums, we help with homework by giving hints and pointing you in the right direction. As I indicated, you need to find the definition of input resistance in order to solve this problem. The fact that you have been assigned this problem means that it (definition of input resistance) should be available to you, either in your text book or in your class lecture notes.

I repeat, you need to look up what that definition is. Nothing you have posted here, so far, is the definition of input resistance.

I hope this is clear to you. Sorry if I sound too blunt.

Last edited: Sep 14, 2009