# Small signal approximation diode model

hello all im new here so i dont know if this is the correct place for this topic so sorry for any inconvenience caused.

this is my question:
Use the small-signal model of the diode to predict the output voltages for the input voltages given. Plot a graph of | vout(t) | based on the small signal model.

Input Voltage 1 = 0.65 + 0.04cos(2*pi*200*t) V
Input Voltage 2 = 0.68 + 0.01cos(2*pi*200*t) V
0 ≤ t ≤ 20ms

i know vout = -Is*R*exp(vin/Vt)

How would you solve this? what basically is the small signal model? is it like a formula that I have to substitute these values in? And for the graph what goes on the x-axis and what goes on the y-axis?

I've got a diagram of the circuit if it helps for you to see:
http://www.flickr.com/photos/24949707@N07/3430348460/ [Broken]

Thank You.

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## Answers and Replies

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Redbelly98
Staff Emeritus
Science Advisor
Homework Helper
Welcome to Physics Forums ... and sorry about the delayed response.

This explains the small-signal model for diodes:
http://en.wikipedia.org/wiki/Diode_modelling#Small-signal_modelling

For Input 1 you'll need to figure out:
• The diode current when Vdiode = 0.65V
• dI/dV for the diode, when Vdiode = 0.65V

Use that information to get a linear relation between I and V, that is the small-signal model for the diode.