fundamentals of engineering supplied-reference handbook - Ventech!

184
ELECTRICAL AND COMPUTER ENGINEERING (continued)
N-Channel Junction Field Effect Transistors (JFETs)
and Depletion MOSFETs (Low and Medium Frequency)
Schematic Symbol Mathematical Relationships Small-Signal (AC) Equivalent Circuit
SIMPLIFIED SYMBOL
Cutoff Region: vGS < Vp
iD = 0
Triode Region: vGS > Vp and vGD > Vp
iD = (IDSS/Vp 2 )[2vDS (vGS – Vp) – vDS 2 ]
Saturation Region: vGS > Vp and vGD < Vp
iD = IDSS (1 – vGS/Vp) 2
where
IDSS = drain current with vGS = 0 (in the
saturation region)
= KVp 2 ,
K = conductivity factor, and
Vp = pinch-off voltage.
2
g =
m
where
r
d
∂v
=
∂i
ds
d
I
V
DSS
p
I
Q
point
D
in saturation region