IEEE Microwave Magazine - May 2017 - 148

Opt
14.0 V
6.0 V

20.0 V
12.0 V
PDF

18.0 V
10.0 V

16.0 V
8.0 V

IMN

3f0
3f0

f0

IMN
2f0

Total Efficiency (%)

70
2f0
Combiner
Reference Plane

60
50
40
30
20
10
0
20

22

(a)

24

26 28 30 32 34
Output Power (dBm)

36

38

(b)

Figure 19. (a) A Chireix outphasing GaN MMIC PA, 3.8 mm # 3.2 mm, and an MMIC mounted in fixture. This MMIC
is designed to be modulated with a multilevel supply. (b) The measured phase sweeps for supply levels from 6-20 V in 2-V
increments at 9.7 GHz. The optimal trajectory is selected to maximize the total efficiency. In black is the PDF of a 6-dB PAR
quadrature phase-shift keying signal which can be used to calculate an average total efficiency of 48% for five and more
supply levels [43]. IMN: input matching network.

Supply modulation is not limited to the outputstage drain of a multistage PA. For example, it can be
shown that efficiency improves if the drain supplies of
both the driver and final stage PA are simultaneously
modulated. The addition of gate-supply modulation
has been discussed both in the context of Doherty PAs
and for improving the linearity of ET PAs. Finally,
another type of PA, referred to as harmonicallyinjected, where one of the PAs in Figure 2 is in class-A
mode while the other PA is at the second harmonic,
has been demonstrated to give high efficiency over a
range of output powers when assisted by supply modulation [44]. The interesting quality of harmonically
injected PAs is that they can be efficient and linear, at
the expense of the addition of a low-power harmonic
injection circuit.

Acknowledgments
I would like to thank all my graduate students and
post docs for the hard work and dedication that led
to the results shown in this article: Dr. David Sardin,
Dr. Scott Schafer, Dr. Michael Litchfield, Dr. Andrew
Zai, Michael Coffey, Maxwell Duffy, Dr. Gregor Lasser,
Dr. Tibault Reveyrand, Dr.  Michael Roberg (now at
Qorvo), and Dr. Asmita Dani (now at Infineon), as well
as Dr. Chuck Campbell at Qorvo and Prof. Dragan
Maksimovic and his students in the Colorado Power
Electronics Center. We are grateful for support from
the U.S. Office of Naval Research under the Defense
Advanced Research Projects Agency's Micro-Power
Conversion program and to Dr. Dan Greene and Dr.
Paul Maki for support and technical advice, as well as
the support of Boeing and Lockheed Martin.

148

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May 2017



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