Low frequency model (linear region).

Above some expressions were derived for component values of the small- signal equivalent diagram, assuming that the transistor is in saturation. For the transistor operating in the linear region similar expressions are now derived.

The drain-source current in the linear region is given by:
 
The transconductance is obtained by differentiating (3.8) with regard to V_GS:
 
and the back-bias transconductance is obtained by differentiating with regard to V_BS:
 
Finally, we can determine the output conductance by differentiating (3.8) with regard to V_DS, thus getting:
 
This constitutes a set of component values for the equivalent diagram i Figure 3.2, valid for the transistor operating in the linear region.