RF Electronics Chapter 9: Impedance Matching of Power Amplifiers Page 309
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
Bandpass L Network
Figure 9.3. Bandpass L matching network.
The bandpass L network is often used as test circuit by semiconductor manufacturers. It
incorporates a DC block (C1), to allow biasing to be set up for the input of transistors and
to prevent any DC supply from appearing on the output of an amplifier stage. Normally
C1 and C2 are adjustable, making it very easy to tune the amplifier for either a peak of
output for an output-matching network or for the best input match for an input matching
network.
The equations for the band pass L network are as follows:
D C
QR X
1
where R
D
+ jX
D
is the device impedance Eqn. 9.13
d l
d
l C
R R
R
R X
2
Eqn. 9.14
2
1 2
C
L D
C L
X
R R
X X
Eqn. 9.15
The device reactance X
D
is incorporated in either C
2
for capacitive device impedances or
into L
2
for inductive device impedances. In the equations of figures 9.7 and 9.8, this is
incorporated by having X
pd
= X
d
and X
md
= 0 if X
d
> 0 and having X
pd
= 0 and X
md
= X
d
if X
d
< 0. This will ensure the lowest Q of the network and thus the widest bandwidth.
This network can only be used if
R
D
< R
L
, since the parts under the square root sign
Bandpass T Network
Figure 9.4. Bandpass T matching network.
RF Electronics: Design and Simulation
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