Analyzing the Results
In the previous section, you measured the drain current (Id) while performing
a synchronous sweep of the gate voltage (Vg) and drain voltage (Vd). And the
measurement results were drawn graphically on the screen.
In this section, you analyze the measurement results on the graph and search
threshold voltage (Vth) of the DUT.
The basic algorithm to search for the threshold voltage is:
1.
Assign gate voltage (Vg) to X-axis
,
p
Id
to Y1-axis, and
@
@V g
p
Id
to Y2-axis.
2.
Search for the maximum value of
@
@V g
p
Id
curve, which is also the point
where the gradient of
p
Id
curve is maximum.
3.
Draw a tangent line to the point where the gradient of
p
Id
curve is
maximum.
4. Read the X-coordinate value where the tangent line crosses the X-axis
.
This value is threshold value (Vth).
Vth
Tangent
17
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