4W GaAs MMIC Power Amplifier for PCS and W-CDMA

4W GaAs MMIC Power Amplifier for PCS and W-CDMA
4W GaAs MMIC Power Amplifier
for PCS and W-CDMA Base Station
Frédy König*, Haruo Shimizu**, Hidenori Takahashi**
Shigemi Miyazawa**, Jun Fukaya**.
* Fujitsu Microelectronics Europe Quantum Device Division, Network House, Maidenhead SL6 4FJ, UK.
**Fujitsu Quantum Devices Ltd., Yamanashi, 409-3883 Japan.
Abstract – A three stage amplifier has been
developed for PCS, EDGE and W-CDMA
applications. Using the MESFET GaAs process
of the Fujitsu foundry, we achieved a typical
30dB gain and 4 Watts output power. The input
matches for a 50ohm system and the output
used a pre-match circuit in order to increase its
low impedance. This amplifier has a frequency
range of 1.7Ghz to 2.3 Ghz.
I.
INTRODUCTION
The demand for Power Amplifiers for base station
EDGE or W-CDMA is increasing. High power
devices of 60-80 Watts or even higher are in
demand to satisfy the difficult requirement of the
new third generation (3G) Base Station. High
efficiency, good Adjacent Channel Power Ratio,
good Intermodulation product are the new key
words of this field. Also a need of a driver stage for
this high power devices is required. This driver
may be composed of a two or three stage amplifier
in order to get the power and gain required to drive
this High PA. The idea of having an MMIC is to
reduce the space and volume of the inside Base
Station. From the point of view of the Base Station
design it is also easier to introduce an MMIC in
order to integrate directly the three stage amplifier.
Using this MMIC may mean that only external
matching has to be adjusted which simplifies the
design and gives a shorter design time cycle of the
Base Station system. This MMIC has to be
designed in order to respect the condition of the 3G
system. Therefore the device has to be tested for its
Power, its Third Intercept Intermodulation Point,
its Adjacent Channel Power Ratio. The design of
this MMIC seems to be a long process but it is one
of the steps towards a new and more convenient
part for this new generation technology.
II.
TECHNOLOGY
The Metal-Semiconductor FET process used for
the MMIC is a well-established process of Fujitsu.
Due to this stable GaAs MESFET process, high
production of the MMIC can be easily provided for
a large volume needed for the 3G application. We
had to optimize some parameters such as the
thickness of the substrate, the unit gate width, the
total gate width, the gate to gate pitch in order to
get good performances with a compromise between
the Output Power, the Gain and the thermal
resistance of the circuit [1]. The package used for
the circuit is a ceramic package of internal size 4.5
x 4.5mm, leaving us only with little space for the
overall circuit, but it gives us a very compact
design.
III.
DESIGN
We designed a 4-Watt 3- stage amplifier MMIC
using the GaAs MESFET technology. The
bandwidth frequency is 1.7 to 2.3Ghz. This
frequency is mainly targeting the new mobile
frequency band. The input matching circuit was
matched for a 50 ohms impedance system. The
output matching was realized out of the MMIC
chip due to the compact size of the MMIC and also
due to the current limitation which occur at the last
stage of the chip. Therefore a Pre- matching
element has been inserted inside the VF package at
the output of the MMIC in order to lower the
output impedance of the circuit. The inter-matching
circuits have been designed in order to get the
bandwidth frequency required. Also the design has
been conceived in the view to get a good linearity,
as it should be used for multicarrier systems. The
16mm total gate width of the last stage amplifier
has been matched using parallel techniques similar
to the ref. [2]. With this technique the last stage
amplifier, which has a large total gate width, is
been considered as parallel amplifiers added
together.
IV.
TEST RESULTS
Layout and Matching circuits:
Output power results:
Figure1: MMIC Chip
Figure 3: Output power vs. Frequency
Figure2: VF Package with chip and pre-matching
.
In figure 1 and 2 we can see the size which have
been achieved. The overall chip size is 2.16 x
3.46mm. The Ceramic package gives us a compact
device of 8.33x 17.78mm. Inside the package a prematching circuit composed of bondwire and
Alumina substrate gives us higher impedance.
The fact to use an MMIC gives us a very small
device for a 30dB gain and 4 Watts output power
amplifier.
Figure 4: Output power vs. Input Power
The three stage amplifier has been tested inside a
test fixture tune for the 3G W-CDMA frequency
range 1.9 to 2.2Ghz. A 37dBm of P1dB has been
achieved at Vds=10V, Vgs= -5V
In figure 4 we see a good linearity, which is an
important point when using a multicarrier system
like the EDGE or W-CDMA.
Intermodulation and Adjacent Channel Power
performance:
In Figure 6 the data have been measured for
fo=2.14GHz , VDD=10V [PEP=17.8dBm] this
using a Signal Source W-CDMA of 15ch .
Additional important points for the 3G systems are
the IM3 and the ACPR. Also it must be
remembered that the device is usually back-off at 5
to 10dB depending on the application giving us an
ACPR of –47dBc and an IMD of <46dBc for 2 to
2.2Ghz at Pout(average)=26dBm.
V.
Figure 5: Intermodulation performance.
CONCLUSION
We have presented a compact 4 watt Power
Amplifier with a good linearity and ACPR and a
gain of approximately 30dB, which will give to the
designer of the Base Station a good and compact
driver stage, or a good PA for macro cell Base
Station.
VI.
ACKNOWLEDGEMENT
The authors would like to thank Dr. Tom Cantle for
his continuous encouragement and suggestion.
VII.
REFERENCES
[1] Chapter 2 by Y. Aoki and Y.Hirano “High
Power GaAs FET Amplifiers” John L.B. Walker.
[2] Short course on High Efficiency Power
Amplifier- Gallium Arsenide Applications
Symposium- Munich Oct 1999.
Figure 6: Adjacent Channel Power Ratio.
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