Editing JFET (section)

=== Linear ohmic region ===
The current in N-JFET due to a small voltage ''V''<sub>DS</sub> (that is, in the ''linear'' or ''ohmic''<ref>{{cite web |title=What is the Ohmic Region of a FET Transistor |url=http://www.learningaboutelectronics.com/Articles/What-is-the-ohmic-region-of-a-FET-transistor |access-date=2020-12-13 |website=www.learningaboutelectronics.com |quote=ohmic region ... also called the linear region}}</ref> or ''triode region''<ref name=":2" />) is given by treating the channel as a rectangular bar of material of [[electrical conductivity]] <math>q N_d \mu_n</math>:<ref name="kumar">{{cite book |author=Balbir Kumar and Shail B. Jain |title=Electronic Devices and Circuits |date=2013 |publisher=PHI Learning Pvt. Ltd. |isbn=9788120348448 |pages=342–345 |url=https://books.google.com/books?id=jr5nAgAAQBAJ&pg=PA343}}</ref> 
: <math>I_\text{D} = \frac{bW}{L} q N_d \mu_n V_\text{DS},</math>
where
: ''I''<sub>D</sub> = drain–source current,
: ''b'' = channel thickness for a given gate voltage,
: ''W'' = channel width,
: ''L'' = channel length,
: ''q'' = electron charge = 1.6{{e|−19}} C,
: ''μ<sub>n</sub>'' = [[electron mobility]],
: ''N<sub>d</sub>'' = n-type doping (donor) concentration,
: ''V''<sub>P</sub> = pinch-off voltage.

Then the drain current in the ''linear region'' can be approximated as

: <math>I_\text{D} = \frac{bW}{L} q N_d \mu_n V_\text{DS} = \frac{aW}{L} q N_d \mu_n \left(1 - \sqrt{\frac{V_\text{GS}}{V_\text{P}}}\right) V_\text{DS}.</math>

In terms of <math>I_\text{DSS}</math>, the drain current can be expressed as{{cn|date=February 2014}}

: <math>I_\text{D} = \frac{2 I_\text{DSS}}{V_\text{P}^2} \left(V_\text{GS} - V_\text{P} - \frac{V_\text{DS}}{2}\right) V_\text{DS}.</math>