Drain Current
In deriving the current components the following assumptions are made
- Constant mobility assumed
- Uniformly doped channel
Considering Fig 13.4
we get
 Electron drift velocity 
Put  and W(x) expression together and integrate from source  to drain 
 for 
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For small drain voltage
Expand in a taylor series and retian 1 st two terms
This represents the 1-V characteristics of linear region given  as  is made more and more negative i.e,  decreases.
Finally  , transistor to turn off.
Turn off voltage or threshold voltage. 
 Transconductance for small  in linear region.
 in saturation region.
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Drain current in saturation region.
Independent of 
Short channel MESFETs  depends on E.
In the above equation the value of V G should be placed with sign.
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