Analog CMOS Integrated Circuit Design Set 2 - Courses - University ...

SM
Circuit Impedance - 1
• It is often useful to determine the impedance of a circuit seen from a
specific pair of terminals.
• The following is the recipe to do so:
1. Connect a voltage source, V X, to the port.
2. Suppress all independent sources.
3. Measure or calculate I X.
SM
V
R = X
I
EECE 488 – Set 2: Background
Circuit Impedance - 2
Example:
• Find the small-signal impedance of the following current
sources.
• We draw the small-signal model, which is the same for both
circuits, and connect a voltage source as shown below:
v
v
X
X
i =
+ g ⋅ v =
X
m GS
r
r
o
vX
R = = r
X
o
i
X
EECE 488 – Set 2: Background
SM 32
X
X
o
63
64