In order to observe the I-V characteristic of a diode, we need to be able to plot the current
through the diode as a function of the voltage across the diode.
The oscilloscope only measures voltages. However, it can plot one
voltage as a function of another voltage. Consider the circuit shown in
Figure 
.
In this circuit, 
and is therefore linearly proportional to I.
When the LED conducts current in the forward direction, the voltage drop
across it will be in the vicinity of 1.4-1.6 V. If the voltage across the
diode is significantly greater than the voltage across the 10 
resistor,
then 
.
In order to observe the I-V characteristic, we will observe 
as a function of
, with the understanding that the shape of the I-V
characteristic is identical to the 
characteristic because
is proportional to I and 
.
