fundamentals of engineering supplied-reference handbook - Ventech!

186
ELECTRICAL AND COMPUTER ENGINEERING (continued)
Enhancement MOSFET (Low and Medium Frequency)
Schematic Symbol Mathematical Relationships Small-Signal (AC) Equivalent Circuit
Cutoff Region: vGS < Vt
iD = 0
Triode Region: vGS > Vt and vGD > Vt
iD = K [2vDS (vGS – Vt) – vDS 2 ]
Saturation Region: vGS > Vt and vGD < Vt
iD = K (vGS – Vt) 2
where
K = conductivity factor
Vt = threshold voltage
Same as for N-channel with current directions
and voltage polarities reversed.
gm = 2K(vGS – Vt) in saturation region
where
∂v
rd
=
∂i
ds
d
Q
point
Same as for N-channel.