Given an unknown MOS n-channel depletion-mode transistor wired to a variable positive voltage source, determine the transistor's transconductance parameter K and its pinch-off voltage Vp. If we load the circuit (V = +15V and RL = 220 Ohms) and measure the voltage at a test point Vo. We know that the transistor exhibits the transfer characteristic:
iD = 1/2*K*(Vgs - Vp)^2
as long as the transistor is in-saturation, that is as long as,
Vds > Vgs - Vp
The output voltage Vo is given by
Vo = 15 - RL*iD
The Scientist model for this system is shown below.
By inspection of the data we see that 0.1 and -1 are reasonable starting values for K and Vp respectively.
We perform a least squares fit calculation and find the following.