Estimation of Threshold voltage and MOSFET Transconductance
engineering
Description
Part I – Estimation of Threshold voltage and MOSFET Transconductance (kn)
Connect two separate power supplies to the Drain and Gate of your MOSFET. Apply a large VDS voltage (5V).
Connect the Source to ground and use the ammeter to measure the drain current (between the VDD source and the drain of the transistor).
Adjust the Gate voltage until the current is approximately equal to 20mA. Remember that if VGS < Vt, then the transistor will be in the cutoff region and “no” current will flow.
Record the gate voltage (VGS1).
Increase VDD until the drain current is approximately equal to 80mA (~4 times the original ID)
Record the gate voltage (VGS2).
Using the data from steps 3, 4, 5, 6 and
ID = 0.5 kn (VGS1 – Vt)2 4ID = 0.5 kn (VGS2 – Vt)2
you can estimate the Threshold Voltage (use exact values for ID, 4ID, VGS1 and VGS2).
Then, using your data and your estimate of Vt, you can find kn.
