Hello, I would like to know if its possible to measure the resistance from an IV curve. For a linear curve, its the slope which is straight forward. but for a non linear, for example a schottky diode type curve or exponential curve?
I am currently performing an experiment and I want to find the resistance from just the IV curves and eventually the conductivity (R=rho.l/A) or is there any specific formula for the measurement?
You must first understand the concept of static and dynamic resistance.
The static resistance is V/I. It is constant if the I V curve is linear. If not it depends from the operating point of the component which is the couple
(I, V)at the operating point.
The dynamic resistance is the slope delta V / Delta I at the operating point. It depends from the operating point. If the curve is linear, static and dynamic resistances are the same.
If you mean the series resititnace of the diode, you can fit the exponential with the diode equation, substrat the fit from the data and be left with the series resistance. It is usually a bit messy but if you play around with the fit it might work.
I fully agree with Jean-Georges Gasser remark. I would like to add the following.
From Jeans remark you would know that for non linear curve the static resistance and dynamic resistance is not the same and it is the dynamic resistance which gives the accurate resistance of a non-linear curve. But where in the curve I will select the point (I,V) where I can do the dynamic resistance or differential resistance computation? This is how you approach this bias point. For Schottky diode or p-n junction diode, there is a small exponential non linear increase from moderate I-V values and for very high I-V biases, the curve is almost so exponential that its asymptote is a line. Extend this line on the x-axis intercept. The line will be almost tangential to one or two points or close to it in the curved region of the curve defined by low I-V bias points. You select a 1-2 few bias points in the curved region that is more or less touched by the tangential line created from the asymptote of the high exponential region of the I-V curve. They you would perform dynamic resistance on these bias points including the slope of the asymptote line and finally make an average. This should be accurate enough. If your I is y-axis and V is x-axis which is how these curves are ideally plotted, then the slope is differential conductance and inverse of this value is differential resistance.
If my answer helps you for your question, please recommend my answer.
Sincerely,
Dr. Nabil Shovon Ashraf.
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