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|Title: ||Broadband distributed type Doherty amplifier|
|Other Titles: ||Kuan pin fen bu shi Duohedi fang da qi|
|Authors: ||Leung, Tik Shun (梁狄信)|
|Department: ||Department of Electronic Engineering|
|Degree: ||Master of Philosophy|
|Issue Date: ||2008|
|Publisher: ||City University of Hong Kong|
|Subjects: ||Broadband amplifiers.|
|Notes: ||CityU Call Number: TK7871.58.B74 L48 2008|
x, 93 leaves : ill. 30 cm.
Thesis (M.Phil.)--City University of Hong Kong, 2008.
Includes bibliographical references.
|Abstract: ||Distributed amplifiers (DAs) provide broadband amplification due to its transmission
line type characteristics, formed by the active device’s capacitance and interconnected
inductances. Although DAs has flat gain over its operating frequencies band, the
power added efficiency (PAE) of DAs is low particular at higher frequencies. The
low-PAE disadvantage of DAs is mainly caused by the presence of a dummy load,
which absorbs the backward traveling wave, at the output artificial transmission line.
The dummy load consumes significant power and hence reduces the PAE.
While the Doherty amplifiers, which consist of a carrier amplifier and a peaking
amplifier, offers higher PAE over a wide dynamic range using load modulation, it
however, can only operate in narrow bandwidths due to the presence of a power
splitter and quarter-wave transmission line. Therefore, the work presented here aims
to combine the benefit of DAs and Doherty amplifiers for use in current wireless
communication systems offering wide bandwidth, small size and low cost benefits.
An unequal bias distributed amplifier (UBDA) is proposed for the improvement in
the PAE of the conventional distributed amplifier. A higher efficiency bias technique
is applied by biasing the first gain cell with the highest current while the other two gain cells are biased at a smaller current. By applying the proposed bias technique,
the inefficient use of a dummy load at the output artificial transmission line can be
eliminated without affecting the bandwidth. The proposed UBDA provides a
maximum power added efficiency of 27.8% which is 16.8% higher than that of the
Finally, a broadband distributed type Doherty amplifier (DDA) is proposed. The
proposed DDA offers an operating frequency band from 0.8GHz to 2.6GHz. While
having the same broadband characteristic as that of the DAs, the proposed DDA also
has the high efficiency characteristic found in Doherty amplifiers. The proposed DDA
provides a significant PAE improvement over the optimized conventional distributed
amplifiers. Maximum PAE improvement occurs at 2.2GHz with a measured output
power of 19.4dBm and a PAE of 41.3%, which is 32% higher than that of the
optimized conventional distributed amplifier.|
|Online Catalog Link: ||http://lib.cityu.edu.hk/record=b2340787|
|Appears in Collections:||EE - Master of Philosophy |
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