High Incremental Drain impedance (from the book The art of electronics)

[khatus]

Hello guys, I don't understand the meaning of this line

"The FET has a high incremental drain impedance, giving roughly constant current for VDS greater than a volt or two"

from field-effect transistors chapter of the book "The art of electronics".
Here what does it means by "high incremental drain impedance" Can anyone help me to understand it?

 

[KlausST]

Hi,


what exactly don´t you understand?

Do you understand "incremental impedance" generally?
If not: do internet search first .. then give a link to the document you work with..

Klaus

 

[danadakk]

Basically large Vds changes do not impact Idrain, in saturation region. So effectively the incremental R
of the drain to source is quite high. Hence the constant current source effect.