Conclusion - Linear CMOS RF Power Amplifiers for Wireless Applications - page 123

for which the performance metric was the IMD3 for a 2-tone test. It was also shown
that the dynamic supply PA can be envisaged for application in WLAN. For this
purpose, the EVM obtained from OFDM measurements at 2.4 GHz was used.
8.2.2 Frequency-Tunable Capability
The main contribution of Chaps. 5 to 7 of this topic is the demonstration of the use
of coupled inductors in a tunable matching network for RF power amplifiers. In the
peripheral work that sustains this research, some other minor contributions can also
be found. In particular, we demonstrated empirically the property of π -matching
networks allowing the variation of only the inductance to keep the transformation
factor constant at different frequencies. A comparative study of the available tech-
niques that could be used in the implementation of the tunable RF power amplifier
was also carried out.
8.2.3 Impedance Matching
Besides the contributions on efficiency enhancement and frequency tunability, in
Chap. 10 (Appendix B) a novel procedure for impedance matching for application
in the characterization of printed-circuit RF amplifiers is presented. This procedure
was developed during the characterization of the power amplifiers described in this
topic.
8.3 Future Work
8.3.1 Efficienc Enhancement
Chapter 4 showed that the system that we implemented has some flaws that should
be solved for a practical implementation. A first work that should be done is de-
signing the system with the objective of employing it in an integrated CMOS trans-
mitter and not as a stand-alone RF power amplifier. The benefit of doing this is
twofold: first, it is a step toward a possible commercial product; second, it obviates
the need of analog envelope detection and processing, which would facilitate the
characterization of the dynamic supply CMOS RF PA and reveal its true limitations
concerning efficiency and linearity for a target application.
A second work that could be done concerns the application in WLAN and con-
sists of designing a higher-order filter to better attenuate the switching signal at the
output of the modulator while passing the high bandwidth OFDM envelope signal.
The feasibility of such a filter should be studied to determine its specifications for a
cutoff frequency of 20 MHz with a switching signal compatible with the global de-
lay of the modulator. It seems that improving the modulator delay from its current