CHAPTER 5 - Amplifier Design
214
This allows us to increase the gain of the transistor by a factor of
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|
A
conjugate match at the input allows us to improve the gain as much as possible by means of the
input matching network. In general however we may decide not to maximise this gain and apply
some selective mismatch in order to achieve a specific value of Gain. We can think of our input
matching network as a gain dial, which may increase the gain by a factor of
whose maximum
value is
. This is shown in Figure 5.3-8.
Figure 5.3-8 Gain tuning by means of input matching network with unilateral device
The analytical expression for is shown below
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It
is apparent that this expression is maximum when
i.e. when a conjugate match is
achieved.
A similar argument applies for the output. If we design a matching network which
transforms the load impedance into the conjugate of the output impedance of the transistor we can
improve the gain by a factor of
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G
0
Transistor
+
Bias
Z
0
Z
0
S
12
S
21
S
11
S
22
Input
matching
network
G
S
S
G
0
G
S
Conquer Radio Frequency
214 www.cadence.com/go/awr
