•
Creating a linear equivalent circuit, LEC:
Suppose we have a device with three
terminals, X, Y, and Z, and that
we have expressions for the cur
rents into terminals X and Y in
terms of the voltages v
XZ
and v
YZ
:
Suppose we also have expressions for
the charge stores associated with
terminals X and Y:
We begin
with the static model for the terminal characteristics, and
linearize them about an bias point, Q, defined as a specific set of
v
XZ
and v
YZ
that we write, using our notation, as V
XZ
and V
YZ
For example, for the current into terminal X we have:
For sufficiently small (v
XZ
V
XZ
) and (v
YZ
V
YZ
), we have:
continued on the next page
Clif Fonstad, 10/03
Lecture 14
 Slide 4
Y
X
Z
q
X
(v
XZ
, v
XY
)
q
Y
(v
YZ
, v
YX
)
i
X
(v
XZ
, v
YZ
)
i
Y
(v
XZ
, v
YZ
)
i
X
(
v
XZ
,
v
YZ
)
and
i
Y
(
v
XZ
,
v
YZ
)
q
X
(
v
XZ
,
v
YZ
)
and
q
Y
(
v
XZ
,
v
YZ
)
i
X
(
v
XZ
,
v
YZ
)
=
i
X
(
V
XZ
,
V
YZ
)
+
∂
i
X
∂
v
XZ
Q
(
v
XZ

V
XZ
)
+
∂
i
X
∂
v
YZ
Q
(
v
YZ

V
YZ
)
+
higher order terms
i
X
(
v
XZ
,
v
YZ
)
i
X
(
V
XZ
,
V
YZ
)
+
∂
i
X
∂
v
XZ
Q
(
v
XZ

V
XZ
)
+
∂
i
X
∂
v
YZ
Q
(
v
YZ

V
YZ
)