A 9.1–10.7 GHz 10-W, 40-dB Gain Four-Stage PHEMT MMIC Power Amplifier

Abstract

This letter presents a compact X-band high gain and high power four-stage AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor (PHEMT) monolithic microwave integrated circuit (MMIC) high power amplifier (PA). This amplifier is designed to fully match a 50-Omega input and output impedance. Based on 0.35-mum gate-length power PHEMT technology, this PA MMIC is fabricated on a 3-mil thick wafer. While operating under 8 V and 2700-mA dc bias condition, the characteristics of 40-dB small-signal gain, a 10-W continuous-wave saturation output power, and 33% power added efficiency at 9.7GHz can be achieved

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IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS, VOL. 17, NO. 2, FEBRUARY 2007151
A 9.1–10.7 GHz 10-W, 40-dB Gain Four-Stage
PHEMT MMIC Power Amplifier
Chen-Kuo Chu, Hou-Kuei Huang, Hong-Zhi Liu, Che-Hung Lin, Ching-Hsueh Chang, Chang-Luen Wu,
Chian-Sern Chang, and Yeong-Her Wang, Member, IEEE
Abstract—This letter presents a compact X-band high gain and
highpowerfour-stageAlGaAs/InGaAs/GaAspseudomorphichigh
electron mobility transistor (PHEMT) monolithic microwave inte-
gratedcircuit(MMIC)highpoweramplifier(PA).Thisamplifieris
designedto fullymatcha 50-? inputand outputimpedance. Based
on 0.35- mgate-lengthpowerPHEMTtechnology,this PAMMIC
is fabricated on a 3-mil thick wafer. While operating under 8 V
and 2700-mA dc bias condition, the characteristics of 40-dB small-
signal gain, a 10-W continuous-wave saturation output power, and
33% power added efficiency at 9.7 GHz can be achieved.
Index
(MMIC), power amplifier (PA), pseudomorphic high electron
mobility transistors (PHEMTs), X-band.
Terms—Monolithicmicrowave integratedcircuit
I. INTRODUCTION
P
AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility
transistors (PHEMTs) have the advantages of possessing high
power densities with high gain, which are ideal for applications
requiring high efficiency, high power, broadband operations,
and small dimensions such as active phase radars, future cel-
lular,localmultipointdistributionservice(LMDS),andsatellite
communications. The fabrication of the monolithic microwave
integrated circuits (MMICs) for PAs with multistage configu-
ration can further reduce the chip dimension and increase the
small-signal gain to reduce manufacturing cost.
Previously, several respectable PA achievements for X-band
have been reported [1]–[8]. These MMICs present the per-
formances with high power and high power added efficiency
(PAE); however, the small signal gain of these PAs are not
high enough for the phase array radar applications and the
chip dimensions are still too large. A comparison of the results
reported to date in X-band PAs is shown in Table I.
To have a high gain as well as high power MMIC to ease
the circuit design, a fully matched four-stage MMIC PA using
OWER AMPLIFIERS (PAs) are one of the most impor-
tant components in radar and communications systems.
Manuscript received July 17, 2006; revised November 6, 2006. This work
wassupported in partby the NationalScience CouncilofTaiwan, R.O.C.,under
ContractNSC 94-2215-E-006-001, theMOE ProgramforPromotingAcademic
ExcellenceofUniversitiesunderGrantA-91E-FA08-1-4,andthe Foundationof
Chen, Jieh-Chen Scholarship, Tainan, Taiwan.
C.-K. Chu, H.-K. Huang, H.-Z. Liu, C.-H. Lin, and Y.-H. Wang are with the
Institute of Microelectronics, Department of Electrical Engineering, Advanced
Optoelectronic Technology Center, National Cheng-Kung University, Tainan.
701, Taiwan, R.O.C. (e-mail: yhw@eembox.ncku.edu.tw).
C.-H.Chang,C.-L.Wu,andC.-S.ChangarewithTranscom,Inc.,Tainan741,
Taiwan, R.O.C.
Color versions of one or more of the figures in this letter are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/LMWC.2006.890346
AlGaAs/InGaAs/GaAs PHEMTs with 40-dB small-signal gain,
delivering10Wofsaturatedoutputpower
at 9.7 GHz is demonstrated.
with33%PAE
II. CIRCUIT DESIGN
The device model was deembedded from the two-port
rameters of the 1.2-mm PHEMT measured by a HP8510C
vector network analyzer. The extraction of the parasitic param-
eters was done by cold-field effect transistor (FET) method and
the intrinsic parameters by hot-FET method and from fitting
of the measured and simulated
technique [9], [10], the required optimum large-signal load
impedance
is composed of
drawing of the proposed X-band 10-W four-stage PA MMIC
is shown in Fig. 1. The models for 0.6, 1.5, 6, and 16.8 mm
PHEMT were scaled up from the 1.2-mm PHEMT model for
circuit simulation and optimization [8], [11], [12].
The photograph of the fabricated MMIC for the completed
amplifier is shown in Fig. 2. For each two-stage PA, the first
matching network designed is the output matching network
which is designed to transfer maximum output power from
the FET to a 50-
system. According to the Cripps technique
[9], [10], the required optimized large-signal load impedance
is composed of
calculated from the biased voltage
is designed to be half of the maximum channel current for
class A operation.
The output power matching network was designed to transfer
the
to 50. The power-matching network comprises
a double resonant circuit with
and an-section filter. The output matching network was de-
signed with a shunt inductance in series with a bypass capacitor
to provide a dc path, a low-pass -section transformer, and a se-
ries block capacitor. The inter-stage matching network was de-
signed to transfer
to the
mismatch loss. The power matching for the
that maximizes the output power is also considered. A gate re-
sistor is used in each stage in order to achieve a lossy match and
to improve circuit stability. Then the circuit stability is further
confirmed by the simulation of K and
Finally, the input network was designed to smooth the small
signal gain and to improve impedance match for a better input
returnloss.Then,thewidthofthemicrostriplinewassimplyde-
finedbythedesignruleandthecurrent-densitylimitation.Based
on these essential matching networks, an optimization and EM
simulation were performed to achieve the required circuit per-
formance and the minimized chip dimension.
-pa-
-parameters. In the Cripps
and . The schematic
and. The is
and currentwhere
at the center frequency
in order to minimize the
and
factor.
1531-1309/$25.00 © 2007 IEEE
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152IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS, VOL. 17, NO. 2, FEBRUARY 2007
TABLE I
COMPARISON OF THE X-BAND PA MMIC AND THE INTERNALLY MATCHED FET
Fig. 1. Schematic of the four-stage X-band 10-W PA MMIC.
Fig. 2. Photograph of the four-stage X-band 10-W PHEMT MMIC PA.
III. EXPERIMENTAL
The X-band MMICs were processed by conventional pho-
tolithography on an AlGaAs/InGaAs/GaAs PHEMT structure
prepared by molecular beam epitaxy. The fabrication includes
five major steps: 1) Device isolation. The etching of AlGaAs
and GaAs for the mesa was achieved by using an HF-based so-
lution. 2) Ohmiccontact. The Au/Ge/Niwas evaporated to form
the source and drain ohmic contacts and annealed at 420 C
for 40 s. 3) Schottky contact. The Ti/Pt/Au was then deposited
for the Schottky gate by lift-off processes. 4) Passivation. The
is used to protect the Schottky gate and improve the
breakdown performance. 5) Transmission line and interconnec-
tion. The air bridge was formed by Au plating, the thickness of
Fig. 3. Measured small signal gain, input/output return loss (dB) versus fre-
quency.
which is more than 2.5
0.35 m.ThegatewidthofthePHEMTforeachstageis0.6mm
, 1.5 mm, 6 mm
tively. The chip dimension of the fabricated MMIC, as depicted
in Fig. 2, is as small as 4.52 3 mm . In order to reach lower
thermal resistances and lower inductances, the thickness of the
GaAs substrate is thinned to 3-mil and the source port is di-
rectly grounded with via-holes. Typical dc characteristics of the
saturated drain current, transconductance, breakdown voltage
and pinch-off voltage are 300 mA/mm, 250 mS/mm, 18 V and
1.6 V, respectively.
m. The gate length of the PHEMT is
, and 16.8 mm, respec-
IV. RESULTS AND DISCUSSION
The bias conditions for the MMIC are
0.63 V and2700 mA including 65 mA for the first
stage, 163 mA for the second stage, 650 mA for the third stage
and 1822 mA for the power stage. The measured small signal
gain, input/output return loss (dB) versus frequency in a wide
frequency range are shown in Fig. 3. The small signal gain is
greater than 40 dB and the gain flatness is better than 1.0 dB,
while the input/output return loss is better than 5/10 dB in-
creasing from 9.1 to 10.7 GHz, respectively.
The continuous wave (CW) 2-dB output compression power
, output saturated power and PAE as a function of fre-
quency are shown in Figs. 4 and 5, respectively. From 9.1 to
8 V,
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CHU et al.: 9.1–10.7 GHZ 10-W, 40-DB GAIN FOUR-STAGE PHEMT MMIC PA153
Fig. 4. ?
PA.
and PAE versus frequency of the X-band 10-W PHEMT MMIC
Fig. 5. ?
PA.
and PAE versus frequency of the X-band 10-W PHEMT MMIC
Fig. 6. Output power and PAE as a function of input power at 9.7 GHz.
10.7 GHz, the
than 27%. At the same frequency, the
with PAE of more than 28%. The output power, gain, and PAE
as a function of input power measured at 9.7 GHz are shown in
Fig. 6. It can be observed that the
with PAE of 30.5%, and the
of 33%.
The temperature dependence of the gain and saturated output
power performances for the MMIC, ranging from
to
90 C, is also investigated. At 90 C, the corresponding
is more than 38.5 dBm with PAE of more
is more than 39 dBm
is 39.2 dBm (8.32 W)
is 40 dBm (10 W) with PAE
50C
gain/
36.7 dB/39.3 dBm, and 38.8 dB/38.6 dBm, respectively. At
C, the corresponding values are at 45.1 dB/40.2 dBm,
44.1 dB/40.6 dBm, and 45.5 dB/40.0 dBm. The signal gain
variation as a function temperature, ranging from
90 C, is as small as
0.051 dB/ C for four stage PA. The
saturation output power variation as a function temperature is
as small as
0.0095 dBm/ C, which is equal or even better
than the reported high PAs [7].
at 9.1, 9.7, and 10.7 GHz are 37.8 dB/38.9 dBm,
50 C to
V. CONCLUSION
In summary, a compact, high performance, four-stage 10-W
X-band PHEMT MMIC high PA has been presented. The char-
acteristics of this MMIC are as follows: a 40-dB small-signal
gain, better than 5/10-dB input/output return loss, a 10-W of
, and 33% of PAE at 9.7 GHz. In addition, the chip area can
be as small as 13.79 mm . The proposed high power and high
gain MMIC is suitable for phase radars, future cellular, LMDS,
and satellite communications.
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