OrCad Spice - plotting tangent line of curve

Discussion in 'Homework Help' started by sayeo87, Feb 9, 2008.

  1. sayeo87

    Thread Starter New Member

    Aug 30, 2007
    3
    0
    Hi, I'm having trouble plotting the tangent line on a curve (or the derivative evaluated at a point) in spice. I know how to plot the derivative of the entire curve using the d() function, but I don't know how to evaluate it at a point. Any help is much appreciated!
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,178
    1,799
    You use the definition of the derivative at a point
    Code ( (Unknown Language)):
    1.  
    2. f'(x) = (f(x+h)-f(x))/h
    3.  
    As the constant h approaches zero the approximation to the derivative becomes better and better.
     
  3. sayeo87

    Thread Starter New Member

    Aug 30, 2007
    3
    0
    OK. How do I enter that in the "Add trace" window though? For example, the name of my function f is IB(MPS3704). I can't do something like IB(MPS3704)(x+0.6). I thought the "@" operator would help, but an expression like IB(MPS3704)@50uA was invalid too. Essentially, if I could find out how to use the value of a function at a point, that would solve a lot of problems. Anybody know how to do this?
     
Loading...