Specifications

3-2 Agilent 4155B/4156B Quick Start Guide, Edition 2
Analyzing the Results
In the previous chapter, 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 chapter, 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, ÖId
to Y1-axis, and ¶ÖId / ¶Vg to Y2-axis.
2. Search for the maximum value of ¶ÖId
/ ¶Vg curve, which is also the point
where the gradient of ÖId
curve is maximum.
3. Draw a tangent line to the point where the gradient of ÖId
curve is maximum.
4. Read the X-coordinate value where the tangent line crosses the X-axis. This
value is threshold value (Vth).