Op-Amp Applications: Current-to-Voltage Converter with Finite Rs and Aod Gain

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Discussion Overview

The discussion revolves around the concept of input resistance in a current-to-voltage converter circuit, specifically considering the effects of finite output resistance (Rs) of the current source and finite open-loop gain (Aod) of the operational amplifier (op-amp). The focus is on deriving the expression for input resistance.

Discussion Character

  • Homework-related
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant presents the equation for input resistance as Rin = RF/(1+Aod) but does not provide context or derivation.
  • Another participant questions the relevance of the equation provided and asks for a more general definition of input resistance.
  • Some participants argue that there is no relevant equation beyond the one given, suggesting the task is simply to find the expression for input resistance.
  • A participant emphasizes the need to refer to textbooks or lecture notes for the definition of input resistance, indicating that understanding this definition is crucial for solving the problem.
  • Another participant points out that the provided equation is not a definition but rather the equation to be derived.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the definition of input resistance or the relevance of the equation provided. The discussion reflects differing views on how to approach the problem and what constitutes a valid definition.

Contextual Notes

There is an indication that participants may be missing a foundational understanding of input resistance, as the discussion highlights the need for a general definition rather than specific equations. The conversation also suggests that assumptions about the problem's context may not be fully articulated.

kahei
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Homework Statement



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

Homework Equations



Rin = RF/(1+Aod)

The Attempt at a Solution



Rin = RF / (1+Aod)
 

Attachments

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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?
 
There is no relevant equation.
The question is just find the expression of the input resistance.
 
What is the defining equation for input resistance?
 
Show that the input resistance Rin is given by Rin = RF/(1+Aod).
 
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?
 
the picture which attached in the first post shows the input resistance.
 
You need to look in your textbook 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 textbook 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:

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