RF Electronics Chapter 9: Impedance Matching of Power Amplifiers Page 311
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
impedance 50 now being the same as (R
l
- R
device
) used in the Pi network. So instead
of R
l
, the value R
l
- R
device
is used in the equations. However if the source or load
impedance of the matching network has a reactive part, then the Pi network equations no
longer apply. For simplicity in the following example, the capacitance C1 in figure 9.5 is
the same as C1 in figure 9.1. The impedances of C
2
and L
1
are tuned to obtain a correct
device match at the correct frequency, using variables Xcct and Xlct, in figures 9.7 and
9.8. These variables can be tuned manually, or they can be tuned by optimisation.
Example 9.1: 100 MHz, 25 W Amplifier
To illustrate the design process, the above equations are applied to an MRFE6VS25N [3],
1.8-2000 MHz, 25 W, 50V, laterally-diffused metal-oxide semiconductor
(LDMOS) FET
to obtain a suitable match. This FET is suitable for wide variety of applications handling
a wide variety of modulated signals from FM to OFDM. For this example, the LDMOS
FET is used to obtain a 25W output in the FM 88-108 MHz band.
Figure 9.6. Part of datasheet showing large signal input and output impedances [3].
RF Electronics: Design and Simulation
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