
599Microwave Transistors
In the linear region, V
d
≪ (|V
g
| +
ψ
0
); thus, the expression of drain current
reduces to
I
I V
V
V
V
d
p d
p
g
p
= −
+
1
0
1 2
| |
/
ψ
(14.23)
Drain conductance: The drain conductance (g
d
) is given by
g
I
V
I
V
V
V
d
d
d
V
g
p
p
g
p
=
∂
∂
= −
+
=constant
1
0
1 2
| |
/
ψ
(14.24)
Transconductance: The transconductance (g
m
) is expressed by
g
I
V
I V
V
V
V
m
d
g
V
p d
p
p
g
=
∂
∂
= −
+
2
1
2
0
1 2
| |
/
ψ
(14.25)
Drain saturation current: The drain current gets saturated at the pinch-off
voltage, thus by putting V
p
= V
d
+ |V
g
| +
ψ
0
, the expression for the drain satu-
ration current (I
d
) becomes
I I
V
V
V
V
d p
g
p
g
p
= −
+
+
+
1
3
2
3
0 0
1