15-10-2012, 10:34 AM
5.65 GHz High-Efficiency GaN HEMT Power Amplifier With Harmonics Treatment up to Fourth Order
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Abstract
A high-efficiency GaN HEMT power amplifier with
harmonics treatment up to the fourth order has been developed at
the 5.8 GHz band. The harmonics treatment was applied by considering
the influence of feedback and shunt capacitance in the GaN
HEMT, to reduce the average power consumption in a GaNHEMT
including parasitic elements. The fabricated GaN HEMT amplifier
delivered a maximum power-added efficiency of 79% and a
maximum drain efficiency of 90% at 5.65 GHz, and the saturated
output power was 33.3 dBm. This value represents state-of-the-art
C-band performance efficiency.
INTRODUCTION
I N advanced wireless communication systems such as
cellular phones or satellite communication systems, a
microwave power amplifier (PA) with high efficiency and high
linearity is required. In recent years, high-efficiency microwave
PAs are also required for wireless power transmission applications.
Many types of amplifiers have been reported to improve
efficiency at the microwave range, such as class-F [1], class-E
[2], class-E/F [3], class-J [4], etc. We have also developed
class-F amplifiers at 5.8 GHz [5] for the microwave wireless
power transmission system. Among these technologies, the
class-E and J technologies require an additional shunt capacitor
at the output side of a transistor so that the dissipation power at
the transistor is cancelled. However, since the capacitor has a
self-resonance frequency, the dissipation power cancellation at
higher-order harmonics is not easy; the order is usually up to the
third [6]. About 4% efficiency improvement is estimated when
the treated order of the harmonic is upped into the fourth from
the third, in an mathematical analysis [7].
AMPLIFIER WITH HARMONICS TREATMENT
Fig. 2 shows a fabricated GaN HEMT amplifier. An Agilent
EE_HEMT large signal model including parasitic elements for
the AlGaN/GaN HEMT [5] is also shown. To terminate with reactance
for the second- to fourth-order harmonics at the output
side of the transistor, a microstrip line with four open stubs including
matching for the fundamental frequency was used. In
addition, to consider the influence of feedback in the transistor
via drain-gate capacitance, the second harmonic is treated at the
input microstrip circuit. The stub positions were adjusted to obtain
maximum efficiency in simulation at 5.65 GHz, by using an
Agilent ADS 2009 Update1. In this simulation, electromagnetic
(EM) simulation results for the input and output circuits were
used. In the input circuit, a size of more than
was obtained from the adjustment. The input and output circuits
were made with alumina ceramics substrates. For the microstrip
lines, with a thickness of 3 was used. dc bias circuits
were not included in this module.
CONCLUSION
A high-efficiency GaN HEMT PA with harmonics treatment
up to the fourth order was developed at the 5.8 GHz band for
microwave wireless power transmission systems. In the simulation,
the drain-gate feedback capacitance was effective at
reducing the total average power consumption. The fabricated
GaN HEMT amplifier treated up to the fourth-order harmonic
delivered a maximum PAE of 79% and a maximum of 90%
at 5.65 GHz, and the saturated output power was 33.3 dBm.