I have the following simple circuit to obtain characteristics of an N type MOSFET.

The gate voltage will be swept from 3 to 6 Volts while the drain voltage will be swept from 0 to 0.5 Volts to obtain ID VS VDS graph for different VGS values. The threshold voltage is calculated from the SAT condition with a different setup and the MOS will always be in triode region with these voltage sweep values.

I am asked to find "the most precise" Kn which is equal to ID/(VDS *( VGS-VT))(Dropping VDS2 for convenience). But what is meant by "the most precise" value?


1 Answer 1


Unless you measure \$Vt\$, you are approximating \$Kn\$. \$Vt\$ will vary device to device. To find a precise value for \$Kn\$, additional measurements must be taken.

  • \$\begingroup\$ VT is already calculated for that particular device as I stated. \$\endgroup\$ Nov 1, 2018 at 11:03
  • \$\begingroup\$ VT is Threshold Voltage not Thermal Voltage \$\endgroup\$
    – MIL-SPEC
    Nov 1, 2018 at 11:14
  • \$\begingroup\$ sorry about that mistake, I fixed it. But I wonder what is meant by "the most precise one"? Does a change in gate voltage affect the "precision" of Kn calculation? \$\endgroup\$ Nov 1, 2018 at 11:26
  • \$\begingroup\$ VT will vary due to doping concentration, and Kn will vary due to gate capacitance. I think the question is asking for a measurement of Kn with the least assumptions. \$\endgroup\$
    – MIL-SPEC
    Nov 1, 2018 at 11:51
  • 1
    \$\begingroup\$ It is probably related to gate capacitance which I totally overlooked so far. Thanks a lot for the answers. \$\endgroup\$ Nov 1, 2018 at 12:01

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