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Design of CMOS Millimeter-Wave and Terahertz Integrated Circuits with Metamaterials by Yang Shang, Hao Yu

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Chapter 7
Power Comb i n e r
7.1 Introduction
Power combining can improve output power and PAE at 60GHz [192, 193].
Numerous power c ombining techniques have been published for 60GHz CMOS
applications [194, 192, 193, 195, 196, 197]. The most straightforward method
is to use a Wilkinson power divider/combiner a s implemented in [194]. It has
the advantage of ea sy implementation, low loss, and good isolation between
ports. However, the required λ/4 transmission like (T-line) occupies a large
area. Two modified techniques are implemented in [193] and [192]. The first
one merges the power combining/dividing function into the existing matching
network, which is still bulky in area. The latter one, on the other hand, uses a
zero-degree power divider instead, which eliminates the resistor and only re-
quires equa l-length short T-line and is thus much more compact. However, to
achieve high output power, it still requires many branches to be combined with
a large power combiner area due to its 1D power combining nature. Another
widely explored device for power combining is Transformer. The distributed
active transformer (DAT) has been proven as an efficient method for power
combining [1 95, 1 96, 198]. However, the DAT topolog y limits the number of
combined transistors , which in turn limits the achievable output power. As
a res ult, to achieve high output power, either a larger DAT size needs to be
adopted or multiple branches need to be used, both of w hich degrade the
output power density due to its 1D power combining nature. One 2D power
combining is introduced in [199], where an electrical funnel” is constructed
by 2D T-line network, which still suffers from bulky size for impedance trans-
formation, low PAE and difficulty of matching.
T-line is commonly utilized in power combining to polog ies to provide
power transmission for the required impedance and phase transformation.
147

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