Thesis (MScIng)--Stellenbosch University, 2008. / ENGLISH ABSTRACT: Modern communication systems demand efficient, linear power amplifiers. The amplifiers are
often operated in the backed-off power levels at which linear amplifiers such as class B amplifier
are particularly inefficient. The Doherty amplifier provides an improvement as it increases efficiency
at backed of power levels. Doherty amplifiers consists of two amplifiers, a carrier amplifier
and a peaking amplifier, of which the output is combined in a novel way. Implementation of
the Doherty amplifier with transistors is not ideal. One of the main problems is the insufficient
current production of the peaking amplifier at peak envelope power (PEP) if it is implemented
as a class C amplifier. A suggested solution to this problem is a bias adaption system that
controls the peaking amplifier gate voltage dynamically depending on the input power levels.
The design and evaluation of such a adaptive Doherty amplifier is the main goal of this thesis.
A classical Doherty amplifier with and an uneven Doherty amplifier with unequal power division
between the carrier and peaking amplifiers are also evaluated and compared with the adaptive
Doherty amplifier.
The amplifiers are designed using a 10 W LDMOS FET device, the MRF282. The adaptive
Doherty amplifier and the uneven Doherty amplifier show significant improvements in efficiency
and output power over the even Doherty amplifier. At PEP the adaptive Doherty delivers 42.4
dBm at 39.75 % power added efficiency (PAE), the uneven Doherty amplifier 41.9 dBm at 40.75
% PAE and the even Doherty amplifier 40.8 dBm at 38.6 % PAE. At 3dB backed-off input power
the adaptive Doherty amplifier has an efficiency of 34.3%, compared to 34.9 5% for the uneven
Doherty amplifier and 29.75 % for the even Doherty amplifier. / AFRIKAANSE OPSOMMING: Moderne kommunikasie stelsels vereis effektiewe, linieêre drywing versterkers. Die versterkers
word dikwels in laer drywings vlakke bedryf waar linieêre versterkers soos ’n klas B versterker
besondere lae effektiwiteit het. Die Doherty versterker bied ’n uitweg omdat dit verbeterde
effektiwiteit by lae drywings vlakke bied. ’n Doherty versterker bestaan uit twee versterkers, die
hoof versterker en die aanvullende versterker, waarvan die uittrees met ’n spesiale kombinasie
netwerk bymekaar gevoeg word. Die implementasie van Doherty versterkers met transistors is
nie ideaal nie. Een van die hoof probleme is die onvoldoende stroom wat deur die aanvullings
versterker gebied word by piek omhulsel drywing (POD). ’n Oplossing vir die probleem is om ’n
aanpassings sisteem te gebruik wat die aanvullende versterker se hekspanning dinamies beheer
afhangende van die intree drywings vlakke. Die ontwerp en evaluasie van so ’n aanpassings
Doherty versterker is die hoof doel van hierdie tesis. ’n Klassieke Doherty versterke met gelyke
drywings verdeling en ’n ongelyke Doherty versterker wat gebruik maak van ongelyke drywings
verdeling tussen die hoof-en aanvullende versterkers is ook gevalueer en vergelyk met die aanpassings
Doherty versterker.
Die versterkers was ontwerp met ’n 10 W LDMOS FET, die MRF282. Die aanpassings Doherty
versterker en die ongelyke Doherty versterker het aanmerklike verbeteringe in effektiwiteit en
uittree drywing gebring in vergelyking met die ewe Doherty versterker. By POD het die aanpassings
versterker 42.4 dBm teen 39.75 % drywing toegevoegde effektiwiteit (DTE) gelewer, die
ongelyke Doherty versterker 41.9 dBm teen 40.75 % DTE, en die ewe Doherty versterker 40.8
dBm teen 38.6 DTE. By ’n intree drywingsvlak 3 dB laer as POD het die aanpassings Doherty
versterker ’n effektiwiteit van 34.3 % getoon, in vergelyking met die onewe Doherty versterker
se 34.9 % en die ewe Doherty versterker se 29.75 % DTE.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/20445 |
| Date | 03 1900 |
| Creators | Jansen, Roelof |
| Contributors | Van Niekerk, C., Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xx, 101 leaves : ill. |
| Rights | Stellenbosch University |
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