Field-dependent mobility effects in the excess noise of junction-gate field-effect transistors

According to Sah's theory (1964) of excess noise in junction-gate field effect transistors the equivalent saturated diode current Ieq of the drain noise should vary as Vd
^5/2
below saturation (where Vd is the drain to source voltage) and rapidly turn over into its saturated value at saturation. Experimentally, one finds in many units that Ieqa ries as Vd
^5/2
at low currents, roughly as Vd
^3/2
at intermediate currents and that IeQ gradually turns over into its saturated value at saturation. We shall see that this behavior can be explained by field-dependent mobility effects.