The 23rd International Technical Conference on Circuits/Systems,
Computers and Communications (ITC-CSCC 2008)
Miniaturized active balun MMIC employing active device
Young-Bae Park1, Se-Ho Kim1, Han-Nah Joh1, Young Yun1*, Kyu-Ho Park2,
and Kwang-Ho Ahn2
1
Radio Communication Engineering, Korea Maritime University, Korea
#1, Dongsam-dong, Youngdo-gu, Busan 606.791, Korea
2
Korea Electronics Technology Institute, Korea
#68, Yatap-dong, Bundang-gu, Seongnam-si, Gyeonggi-do , Korea
E-mail: 1*yunyoung@hhu.ac.kr
Abstract: In this paper, miniaturized active
baluns employing active device were proposed.
The miniaturized active baluns were fabricated
employing InGaP/GaAs HBT (heterojunction
bipolar transistor) on GaAs substrate for MMIC
applications, and especially a composite structure
employing common-emitter (CE) and commoncollector (CC) circuits was used for 90° power
coupling. The size of the active balun for power
coupling was about 1.9 % of conventional passive
branch-line coupler. The active baluns for power
coupling showed good RF performances
comparable to passive branch-line couplers.
2. Design of active balun employing
active device
Figure 1 and 2 show a schematic circuit of the
active baluns employing InGaP/GaAs HBT.
Concretely, figure 1 and 2 show active balun for
power coupling and splitting, respectively. As
shown in Fig. 1, a composite structure employing
common-emitter (CE) and common-collector
(CC) circuits were used, and the output ports of
the CE and CC circuits were connected to each
other. To couple two input signals with 90° phase
difference, a coupling circuit was connected at
output port.
1. Introduction
Passive 90° power coupling and splitting
circuits have been used for signal mixing at
intermediate frequency (IF) output port of image
rejection mixer [1]~[25]. Until know, a passive
branch-line coupler has mainly been employed for
90° power coupling and splitting [1]. However,
the passive branch-line coupler occupies a very
large area in RF circuit. For example, if the
passive branch-line coupler is fabricated on a
GaAs substrate with a thickness of 100 ȝm for a
signal mixing of 2.4 GHz IF signals, the size will
be about 10.92 mm × 10.45 mm. Therefore, the
passive branch-line coupler circuit can’t be
integrated on MMIC (monolithic microwave
integrated circuit) due to their very large size [2].
To reduce the size of the passive branch-line
coupler circuit, it has to be fabricated employing
an active device.
In this work, for an integration of the active
balun circuits on MMIC, miniaturized active
balun circuits employing InGaP/GaAs HBT
(heterojunction bipolar transistor) were proposed.
G
G
Fig. 1. A circuit structure of active balun for
power coupling
885
GHz to 12.7 GHz.
Fig. 2. A circuit structure of active balun for
power splitting
G
Fig. 3. A photograph of the active balun
employing InGaP/GaAs HBT for power coupling
The coupling circuit was designed in order that
the output gain (S31) of CE circuit is equal to
output gain (S32) of CC circuit. The phase control
circuit was properly designed for a 90° phase
coupling of two input signals.
3. Measurement of active balun
employing InGaP/GaAs HBT
Figure 3 and 4 show the active baluns
employing InGaP/GaAs HBT for power coupling
and splitting, respectively, which were fabricated
on GaAs MMIC. As shown in Fig. 3, the size of
the fabricated active balun for power coupling is
2.05 mm u 1.05 mm, which is 1.9% of the size of
a conventional passive branch-line coupler (if
passive branch-line coupler with an operation
frequency of 2.4 GHz is fabricated on GaAs
MMIC, its size is 10.92 mm u 10.45 mm). As
shown in Fig. 4, the size of the active balun for
power splitting is 1.67 mm u 0.87 mm, which is
31.6% of a conventional passive branch-line
coupler (if passive branch-line coupler with an
operation frequency of 12 GHz is fabricated on
GaAs MMIC, its size is 2.11 mm u 2.18 mm).
Figure 5 shows a measured phase difference
between S31 and S32 of active balun for power
coupling. As shown in this figure, a phase
difference characteristic of -90 ± 2.5q is observed
from 2.3 GHz to 2.5GHz. The output gain
characteristics (S31 and S32) of the active balun for
power coupling was about 10 dB at 2.4 GHz.
Concretely, the proposed active balun for power
coupling showed a gain of 10 ± 1 dB from 2.3
GHz to 2.5 GHz. Figure 6 shows a measured
phase difference between S21 and S31 of active
balun for power splitting. As shown in this figure,
a phase difference characteristic of -90 ± 3.0q is
observed from 11.8 GHz to 12.1 GHz. An output
gain (S21 and S31) of about 10 dB was observed at
12 GHz. Concretely, the proposed active balun for
splitting shows a gain of 10 ± 1 dB from 11.5
Fig. 4. A photograph of the active balun
employing InGaP/GaAs HBT for power splitting
Fig. 5. Measured phase difference between S31
and S32 of active balun for power coupling
Fig. 6. Measured phase difference between S21
and S31 of active balun for power splitting
886
InGaP/GaAs HBT (heterojunction bipolar
transistor) on GaAs substrate for MMIC
applications, and especially used a composite
structure employing common-emitter (CE) and
common-collector (CC) circuits for 90° power
coupling. The size of the active balun for power
coupling was about 1.9 % of conventional passive
branch-line coupler. Form the active baluns, we
could observe good RF performances comparable
to passive branch-line couplers.
Acknowledgment
Fig. 7. Measured return loss characteristics of
active balun for power coupling
This work was supported by ETRI SoC Industry
Promotion Center & Human Resource
Development Project for IT SoC Architect. This
work was also supported by KETI, Korea.
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In this paper, we propose miniaturized active
baluns employing active device. We fabricated the
miniaturized
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employing
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