rds in VGS < VT (depletion)

[harry456]

In the linear region a rds can be descript by rds = 1/(mu Cox W/L (VGS-VTH)). In a mos-cap VDS is equal to zero but what's the value for rds when VGS<VTH oder VGS<0?

 

[erikl]

In the linear region a rds can be descript by rds = 1/(mu Cox W/L (VGS-VTH)). In a mos-cap VDS is equal to zero but what's the value for rds when VGS<VTH oder VGS<0?

In such cases you obviously can't use this equation. Instead use

rds = VDS/(mu Cox W/L) = VDS/Id

For VDS -> 0 --> rds -> ∞