I have a set of data points which represent the IV characteristics of a diode. I'm confused on how to get the threshold voltage (x intercept) of that diode. Any suggestions and ideas are welcomed. Illustration:
or essentially I = a * exp(b * V) + c, then the intersection of the slope line depends on where the slope is evaluated. This is because the exponential function f( x) = e x has the special property that its derivative is the function itself, f′( x) = e x = f( x). So, do you want the slope at the last x that you have provided in your text file? If so, the slope is pretty easy to compute analytically. It's slope = a * b * exp(b * V). So use fitnlm() to figure out a, b, and c (using attached demo), then plug in a, b, and V to get the slope at that point. Then, knowing the slope and using the point-slope version of the equation for a line passing through that right-most point, you can get the equation of the line, then set that equal to 0 and solve for V.
Let me know if you want a fully worked out solution.