Distributed Transformers for Broadband Monolithic Millimeter-Wave Integrated Power Amplifiers

254 Pages·2015·7.87 MB·English

Karlsruher Forschungsberichte aus dem Band
Institut für Hochfrequenztechnik und Elektronik
80
Kai-Philipp Walter Pahl
Distributed Transformers for
Broadband Monolithic Millimeter-
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Kai-Philipp Walter Pahl
Distributed Transformers for Broadband Monolithic
Millimeter-Wave Integrated Power Amplifiers
Karlsruher Forschungsberichte
aus dem Institut für Hochfrequenztechnik und Elektronik
Herausgeber: Prof. Dr.-Ing. Thomas Zwick
Band 80
Distributed Transformers for
Broadband Monolithic Millimeter-
Wave Integrated Power Amplifiers
by
Kai-Philipp Walter Pahl
Dissertation, Karlsruher Institut für Technologie (KIT)
Fakultät für Elektrotechnik und Informationstechnik, 2014
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Print on Demand 2015
ISSN 1868-4696
ISBN 978-3-7315-0409-2
DOI 10.5445/KSP/1000048002
Editor‘s Preface
The enormous technological progress accomplished over the last
decades facilitates the utilization of millimeter-wave frequencies for
mass products like auto motive radar, industrial sensors, high-speed
data communication links or medical applications. Besides novel and
cost-efficient packaging technologies, in particular semiconductor
technologies (e.g. SiGe, CMOS, GaAs, GaN, InP, etc.) with constantly
improving cut-off frequencies are essential for the realization of cost-
efficient and compact millimeter-wave modules. The dominant limita-
tion factor of all semiconductor technologies is the available output
power. The realization of faster semiconductor devices requires down
scaling, which on the other hand results in a reduced breakdown
voltage and finally less output power. While millimeter-wave ampli-
fiers based on GaN achieve an output power of about 1 W at 100
GHz, above 200 GHz barely more than 100 mW have been achieved
using InP technologies. Another issue is that amplifiers optimized for
maximum output power usually only provide a limited bandwidth,
which often is not sufficient for many communication, radar and also
measurement applications.
The key issue of having output power in conjunction with bandwidth
is addressed in Mr. Kai-Philipp Walter Pahl’s thesis. To design an am-
plifier that provides more output power than that of a single transistor
device, multiple transistors are put in parallel. However, the maximum
number of parallel devices that actually leads to an increased overall
output power is limited, since the loss of the distribution network
increases more than linearly with the number of transistors. The rea-
sons for this are the increasing transmission lines lengths, which are
necessary to separate the active devices and to provide the required
impedance transformation. The higher the number of parallel transi-
stors the higher the impedance ratio between the parallel transistors
and the single common port of the amplifier. In addition a high trans-
formation ratio results in a reduced bandwidth. One way to solve this
issue is to use magnetic transformers for simultaneous power distribu-
tion and impedance matching. A group around Hajimiri and Rutledge
first proposed such an approach in 2001. In his dissertation Mr. Pahl
has developed important scientific fundamentals for the development
of monolithic integrated broadband amplifiers based on distributed
transformers. By using a novel geometry of multiple distributed trans-
formers, optimized for an application at millimeter-wave frequencies,
he was able to demonstrate superior performance compared to the
standard circular geometry known from literature. In particular the
significantly improved design equations for efficiency optimized dis-
tributed transformers, which are based on an improved equivalent
circuit model, but also novel design equations for distributed transfor-
mers with maximum symmetrical bandwidth, were a huge contributi-
on to the scientific field and extended the state of the art significantly.
I am absolutely sure that this work will attract much interest from the
research community worldwide with many circuit realizations based
on. My personal wish for Mr. Pahl is that his creativity and great inno-
vative capacity will continue to earn him both scientific and economic
success.
Prof. Dr.-Ing. Thomas Zwick
– Director of the IHE –