Radio Frequency Integrated Circuit Design - Webs

Impedance Matching
S22 = b 2
a2 | a1 =0
91
(4.43)
S22 is the output reflection coefficient measured by applying a source at
the output and with the input terminated with Z o .
S12 = b 1
a2 | a1 =0
(4.44)
S12 is the reverse transmission coefficient measured with the input terminated
with Z o .
In addition to S parameters, there are many other parameter sets that can
be used to characterize a two-port network. Since engineers are used to thinking
in terms of voltages and currents, another popular set of parameters are the Z
and Y parameters shown in Figure 4.32.
�v 1
v2� =� Z 11 Z 12
Z 21 Z 22��i1 (4.45)
i2�
�i1 i2� =� Y11 Y12
Y21 Y22��v1 (4.46)
v2�
It is also useful to be able to translate from one set of these parameters
to the other. These relationships are well known and are summarized in Table
4.3.
Microwave transistors or amplifiers are often completely (and exclusively)
characterized with S parameters. For radio frequency integrated circuits, detailed
transistor models are typically used that allow the designer (with the help of
the simulator) to design circuits. The models and simulators can be used to
find S parameters, which can be used with the well-known microwave techniques
to find, for example, maximum gain, optimal noise figure, and stability. However,
the simulators, which use the models to generate the S parameters, can
be used directly to find maximum gain, optimal noise figure, and stability
Figure 4.32 General two-port system with input and output currents and voltages.