CHAPTER 4 - Impedance Matching
188
Figure 4.4-9 Normalised conductance circles and susceptance lines form the Admittance Smith chart grid
This looks remarkably similar to the impedance chart shown in Figure 4.4-5 but DO NOT BE
FOOLED! The zero point here represents a point with 0 conductance i.e. infinite resistance. The point
in the same location in Figure 4.4-5, which is also labelled 0, indicates a point of zero resistance!
Similarly, the point on the admittance chart labelled , represents infinite conductance and hence
zero resistance. The point at the same location on the impedance chart instead represents a point
with infinite resistance!
The other crucial difference is that on an admittance chart the top half is capacitive, since
capacitors are characterised by positive susceptances, and the bottom half is inductive, since
inductors are characterised by negative susceptances. This is shown in Figure 4.4-10.
Figure 4.4-10 Capacitive and inductive halves of the Admittance Smith chart
ͲǤʹͷ ʹ Ͳ ͳ
ͲǤͷ
ͳ
ǦͲǤͷ
Ǧͳ
Conquer Radio Frequency
188 www.cadence.com/go/awr
