An Ultra Wide Band pHEMT Low Noise
Amplifier With Darlington Stage
Jinse Jung, Choon Sik Cho, Member, IEEE, Jae W. Lee, Member, IEEE, Jaeheung Kim, Member, IEEE
Abstract— A 2-stage Ultra Wide Band (UWB) low noise amplifier (LNA) with Darlington stage using 0.25 um GaAs pHEMT
technology is proposed. Ultra wide band operation is achieved by
using shunt feedback and Darlington stage. The LNA obtains an
average gain of 10 dB, input and output return losses less than
-6dB, and a noise figure of 0.4-2.5 dB at 4-10 GHz. The input
1 dB gain compression point (P1dB) is -2 dBm at 7 GHz. The,
proposed LNA was fabricated in 2×2 mm dimension.
Index Terms— UWB LNA, Darlington, GaAs pHEMT, P1dB.
I. I NTRODUCTION
In RF transceiver, UWB LNA is probably a basic component in the receiver part[1-3]. Since received RF signal
at the antenna must have the noise by scattering, diversity
path and lower message signal power, LNA has to achieve
its best performance in low noise figure, high gain and wide
bandwidth.
In this paper, LNA for UWB wireless system applications
was designed using pHEMT technology and focused on new
structure. The GaAs pseudomorphic High Electron Mobility
Transistor (pHEMT) with 0.25 um T-gate with heterojunction
between the channel layer is increasing attention for IC
applications due to its improved performance. Therefore, we
describe a pHEMT MMIC that employs a low-noise GaAs
pHEMT (2f100 model gate width is 2×50um, length is 0.25
um) that is composed of cascode LNA stage and directly
coupled to Darlington output circuit stage. The negative gate
bias voltage of pHEMT device has attracted its use in the LNA
and Darlington circuit design[4-5].
Darlington circuit as gain blocks and improving linear
characteristic has become a workhorse for wireless and wire
line applications. Key point of Darlington circuit is that it
offers multi-decade performance, can be implement in a small
size, and is simple to use with few external component[6-8].
This design also requires no passive matching network because
of the high input and output impedance characteristics[9-10].
The analysis of Darlington circuit and comparison between
general cascode LNA stage and the proposed LNA stage were
shown in Section II, Section III describes the design and
implementation of UWB LNA with Darlington circuit, and its
This work was supported in part by IDEC (IC Design Education Center),
Korea and in part by the Korea Science and Engineering Foundation (KOSEF)
under ERC program through the Intelligent Radio Engineering Center (IREC)
project at ICU, Republic of Korea.
Jin se Jung, Choon Sik Cho and Jae W. Lee are with the School of
Electronics, Telecommunication and Computer Engineering, Korea Aerospace
University, Goyang, Korea. (+82-2-300-0140; email: jjs123@kau.ac.kr,
cscho@kau.ac.kr, jwlee1@kau.ac.kr)
Jaeheung Kim is with Information and Communications University (ICU),
Daejeon, Korea.(email: jaeheung@icu.ac.kr)
simulation and measurement result were indicated in Section
IV. The conclusion was presented in Section V.
II. P RINCIPLES O F UWB LNA A ND DARLINGTON S TAGE
In the UWB LNA, to achieve wide-band input matching,
general topology uses common-source cascode structure. Fig.
1 (a) shows the cascode structure with a source degenerate
inductor that is used for classical noise matching technique for
the narrow band LNA. Fig. 1 (b) is a simple shunt feedback
cascode structure without degenerate inductor[4]. In this work,
we employ the cascode shunt feedback two stage LNA with
Darlington circuit for wideband matching.
Fig. 1. Basic cascode LNA circuit topology (a) general cascode structure
with inductor (b) cascode structure without degenerate inductor.
Fig. 2 shows the proposed Darlington feedback circuit
topology with pHEMT implementation. The negative turnon voltage of pHEMTs which can be as high as -0.5 -0.4 V at moderate current densities, enables bias of the
Darlington stage. Since Darlington stage has also high input
and output impedance, output matching of front stage(cascode
shunt feedback LNA stage) was easily compromised. We
employed the source inductor in Fig. 2 (a) which obtained high
gain, low-noise figure. Fig. 3 shows the increasing linearity in
the proposed circuit. The cascode shunt feedback LNA with
Darlington stage improves linearity compared to the general
cascode LNA with degenerate inductor.
III. D ESIGN A ND I MPLEMENTATION O F UWB LNA W ITH
DARLINGTON S TAGE
Fig. 4 shows the block diagram of the 2-stage pHEMT
UWB LNA with Darlington circuit. A pHEMT cascode preLNA is directly coupled to a pHEMT Darlington feedback
amplifier. The pHEMT transistor is a pseudomorphic GaAs
device nominally biased 25 mA of current when drain voltage
was 2V, and model internal structure was gate finger = 2, total
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Fig. 2.
The ac equivalent circuit of proposed Darlington topology.
Fig. 5.
Measured and simulated noise figures.
Fig. 5 shows the measured and simulated noise figure of
total LNA. In this case, maximum and minimum noise figures
of measured result were 2.5 dB and 0.3 dB, respectively and
the proposed LNA reaches the goal for the noise figure.
Fig. 3. Simulated IIP3 comparison between Fig. 1 (a) and the proposed LNA
with Darlington stage.
gate width = 100 um, unit gate width = 50 um, gate length =
0.25 um.
Fig. 4.
Fig. 6.
Measured and simulated gains.
Fig. 7.
Measured input loss.
Block diagram of UWB LNA with Darlington stage.
Darlington stage employed two pHEMT transistors with
source inductors for increasing the gain, IIP3 and output
impedance[7]. Since the source inductor of Darlington stage
obtains the higher output impedance than that of general
source resistor, there is no passive matching circuit, and
bandwidth of cascode stage is wider and linear.
IV. S IMULATION A ND M EASUREMENT R ESULT
The proposed 2-stage UWB LNA with Darlington stage was
simulated using CADENCE analog environment at 3 GHz to
12 GHz frequencies.
Fig. 6 and Fig. 7 show the gain and return loss of the
proposed LNA, where the average gain in the Fig. 6 was flat
as 10-12 dB within 3-10 GHz. Linearity of the amplifier was
shown by input P1 dB which indicated good performance. Fig.
8 shows that measured and simulated results of input P1 dB
are -2dB and 3dB at 7 GHz frequency. Finally, 2-stage UWB
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TABLE I
P ERFORMANCE C OMPARISON O F UWB LNA
Work
[11]
[2]
[12]
This work
freq
(GHz)
3-6
3-10
3-11
4-10
NF
(dB)
4.7-6.7
1.8-3.1
2.8-4.7
0.4-2.5
S21
(dB)
14-16
20.3
20
8-14
IIP3
(dB)
-5
2.1
-8
-
input
P1dB
-14
-2
design library and this work was supported by the IC Design
Education Center(IDEC).
technology
CMOS
SiGe HBT
BiCMOS
pHEMT
LNA with Darlington stage circuit layout was shown in the
Fig. 9.
Fig. 8. Measured and simulated input 1dB compression point at 7 GHz
frequency.
Fig. 9.
R EFERENCES
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Microphotograph of UWB LNA with Darlington stage.
V. C ONCLUSION
The measured results of the proposed 2-stage UWB LNA
with Darlington stage using the GaAs pHEMT technology
showed that the average gain of 10 dB was obtained at 4GHz
to 10GHz. In case of minimum NF, we obtained 0.4dB at
9GHz frequency. The input P1dB of proposed UWB LNA
using Darlington stage reaches -2dB performance at 7GHz
frequency. Therefore, 2-stage UWB LNA with Darlington
stage can be applied for wireless receiver circuits requiring
wide-band and high linear operation.
VI. ACKNOWLEDGEMENT
The authors would like to thank ETRI for the fabrication
of the LNA circuit, using GaAs pHEMT foundry service and
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