ULTRA-WIDEBAND LOW NOISE
AMPLIFIER USING A CASCODE
FEEDBACK TOPOLOGY
Jihak Jung, Taeyeoul Yun, and Jaehoon Choi
Department of Electrical and Computer Engineering
Hanyang University
17 Haengdang-dong, Seongdong-gu
Seoul, 133-791, Korea
Received 6 December 2005
ABSTRACT: An ultra-wideband (UWB) low-noise amplifier (LNA) that
consists of two cascode and shunt feedback stages is presented. The
measurement results show the maximum gain (S21) of 11.9 dB with the
3-dB band from 2 to 6.5 GHz and return losses (S11, S22) of less than
⫺7.8 dB from 2 to 11 GHz. In addition, the fabricated LNA achieves
the average noise figure (NF) of 4.5 dB from 2 to 10 GHz, which value
is much lower than previously reported state-of-the-art UWB amplifiers.
The input-referred 3rd-order intercept point (IIP3) and the input-referred
1-dB compression point (P1dB) of the LNA are achieved as 4 and ⫺5
dBm, respectively, while consuming 27 mW in the 0.18-␮m RF CMOS
process. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett
48: 1102–1104, 2006; Published online in Wiley InterScience (www.
interscience.wiley.com). DOI 10.1002/mop.21611
Key words: cascode; CMOS; low-noise amplifier; shunt feedback; ultra-wideband (UWB)
1. INTRODUCTION
Recently, considerable interest in ultra-wideband (UWB) technology has centered on its potential applicability for short-range,
high-speed wireless communications. In general, this technology
has several advantages such as low complexity, low cost, low
power consumption, and high data rate for wireless connectivity
among devices within or entering the personal operating space.
The UWB is thus a candidate of IEEE 802.15 Wireless Personal
Area Network (PAN) for short range and high rate connectivity
that complements other wireless technologies. According to the
proposed multiband orthogonal frequency division multiplexing
(OFDM) for IEEE 802.15.3a, the UWB system is assigned to
operate over 3.1–5 GHz or 3.1–10.6 GHz [1]. The low frequency
band from 3.1 to 5 GHz has been allocated for development of the
first generation of UWB systems.
In this paper, a broadband CMOS LNA is proposed with a
cascode feedback topology and broadband-matching techniques,
which meets requirements of multiband OFDM UWB systems in
noise and bandwidth simultaneously [2]. The design principles and
the measurement results of the implemented UWB LNA are described.
2. CIRCUIT DESIGN
As shown in Figure 1, the proposed CMOS LNA is composed of
two stages, designed with Agilent’s Advanced Design System
(ADS) based on Samsung’s 0.18-␮m RF CMOS technology. The
first stage consists of cascoded MOSFETs, input matching networks, and a shunt feedback. The cascode topology has significant
properties such as high gain, broad bandwidth, and high reverse
isolation [3]. The input matching network consisted of a source
degeneration inductance L s and a gate inductance L g reduces
signal reflections between the input impedance Z in and the source
resistance R s [4, 5]. In the proposed LNA, L s is achieved with a
transmission line. The resistive and capacitive shunt feedback (R f ,
C f ) are employed to produce the better stability, gain flatness, and
1102
Figure 1 Schematic of the proposed LNA
bandwidth. The large values of feedback resistors (700⍀–1100⍀)
also improve the input impedance matching, without affecting the
noise figure significantly [2].
The first stage’s transistor size and bias point should be optimized for low NF because both factors seriously affect the noise
performance, and also the first stage dominantly contributes to the
total NF. In the approach used, the transistor size is chosen to
obtain the least-noise figure at the desired drain current. The gate
optimum widths of M 1 and M 2 and the gate bias voltage V g1 for
the first stage [6] are finally designed at 160 ␮m and 0.8 V,
respectively. The input impedance at the resonant frequency ␻ o is
calculated from the following equations [3], assuming that the
feedback effect is very small:
Z in ⫽
冉 冊
␻ 02 ⫽
g mL s
⫽ ␻ TL s,
C gs
(1)
1
,
共L g ⫹ L s兲C gs
(2)
where g m is the transconductance, C gs the gate-source capacitance,
and ␻ T the unity-gain bandwidth, which are already decided by the
transistor size and bias point. To attain a good input impedance
matching, L s is appropriately chosen together with ␻ T from Eq.
(1). L g is determined by the resonance condition of Eq. (2).
Finally, Z in is close to R s , at 50⍀.
The second stage should consider the linearity performance
because the last stage is a prominent contributor to degrade the
linearity [7]. For a cascaded amplifier, the total input-referred
3rd-order intercept point (IIP 3,total ) is expressed as
␣ 12
␣ 12␤ 12
1
1
⬇
⫹
⫹
⫹···,
IIP 3,total IIP 3,1 IIP 3,2 IIP 3,3
(3)
where ␣1 and ␤1 are the linear gains for the first and second stages,
respectively. Eq. (3) shows that the last stage’s IIP 3 significantly
affects the total IIP 3 . Thus, the device size and bias condition of
the second stage are designed for the high gain and linearity
improvement with restricted power consumption. The gate width
of 80 and 160 ␮m are chosen for M 3 and M 4 , respectively. The
gate bias voltage V g2 of 0.85 V is chosen for M 3 .
The tank circuits of L t and C t are also designed to yield a flatter
and broader bandwidth. R o and C t bypass networks with the L t C t
tank are integrated with dc bias lines to ensure a better gain and
MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 48, No. 6, June 2006
DOI 10.1002/mop
Figure 2 Microphotograph of the fabricated LNA. [Color figure can be
viewed in the online issue, which is available at www.interscience.wiley.
com]
stability at a low frequency. It also affects the broadband output
matching. L c can improve the gain and NF of the amplifier at a
high frequency.
3. RESULTS AND DISCUSSIONS
The post-layout circuit simulation is performed using a Cadence
SpectreRF to include parasitic effects of the actual devices in the
CMOS process. When 1.8 V are supplied, a total dc-current
consumption of the proposed LNA is only 15 mA. Due to a high
sheet resistance of the poly gate of RF MOSFET, a multifinger
layout technology is adopted to reduce the noise from the gate
resistance and to improve its RF performance. A microphotograph
of the fabricated LNA is shown in Figure 2. Total chip size
including pads is 0.8 ⫻ 1.1 mm.
Figure 3 shows the measured S-parameter results. The measured S 11 of less than ⫺7.8 dB and S 22 of less than ⫺10 dB are
obtained over 2–11 GHz. This proves effectiveness of the broadband matching realized by the matching networks, shunt feedback,
and LC tanks. In addition, the fabricated LNA achieves the maximum S 21 of 11.9 dB with a 3-dB band from 2 to 6.5 GHz. The
excellent isolation S 12 of less than ⫺39 dB is obtained due to the
cascode topology.
Figure 3 Measured S-parameters (S 11 , S 22 , S 21 , and S 21 )
DOI 10.1002/mop
Figure 4 Measured and simulated noise figure (NF)
The measured and simulated NF is compared in Figure 4. The
measured average NF has 4.5 dB over 2–10 GHz, with the minimum NF (NF min ) of 4.1 dB. Discrepancy between the measurement and simulation in NF is mainly caused by inaccuracy of the
transistor’s noise model which will be improved. To observe the
nonlinear behavior, two-tone signals with equal power levels at 4.0
and 4.01 GHz are applied to LNA. Figure 5 indicates that the LNA
has IIP 3 of 4 dBm and P 1dB of ⫺5 dBm. These results demonstrate that the proposed UWB LNA achieves enough linearity even
with the low noise figure. Table 1 summarizes the measurement
results and compares them with previously reported works [8 –10].
The proposed CMOS LNA shows that the noise performance is
superior to others, especially at a high frequency.
4. CONCLUSION
In this paper, an ultra-wideband (UWB) LNA with cascode feedback and broadband matching techniques has been presented. The
circuit consisted of two stages, whereby design issues of noise and
linearity were almost separated into each stage; the first stage
contributed to optimize the low noise performance and the second
stage to improve the LNA’s linearity. According to measurement
results, the fabricated LNA has satisfied UWB system require-
Figure 5 Measured input-referred 3rd-order intercept point (IIP 3 ) and
1-dB compression point (P 1dB)
MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 48, No. 6, June 2006
1103
TABLE 1
Summary of LNA Performance and Comparison with Previously Published Designs
Ref.
BW3-dB
[GHz]
NF
[dB]
S 21
[dB]
S 11
[dB]
IIP 3
[dBm]
PDC
[mW]
[8]
2–4.6
2.3–6
9.8
⬍ ⫺9
⫺7
12.6
[9]
3–6
4.7–6.7
15.9
⬍ ⫺12
⫺5
59.4
[10]
2–5.9
4.7–8.5
16
⬍ ⫺3
—
38
This work
2–6.5
4.1–4.6
11.9
⬍ ⫺7.8
4
27
ments with a low-noise figure in the interesting band. Thus the
proposed LNA should be readily useful for UWB receiver systems.
ACKNOWLEDGMENTS
This research was supported by University IT Research Center
Project (INHA UWB-ITRC), Seoul, Korea.
REFERENCES
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bipolar LNA, IEEE Int Symp Circ Syst Dig 4 (2001), 842– 845.
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low-noise amplifier in 0.18-␮m CMOS technology, Electron Lett 39
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8. C.W. Kim, M.S. Kang, P.T. Anh, H.T. Kim, and S.G. Lee, An
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© 2006 Wiley Periodicals, Inc.
1104
Tech.
0.18-␮m
CMOS
0.18-␮m
CMOS
0.13-␮m
CMOS
0.18-␮m
CMOS
COUPLING AND POWER DISSIPATION
IN A COAXIALLY EXCITED TM01l MODE
CYLINDRICAL APPLICATOR WITH A
SPHERICAL LOAD
Vyacheslav V. Komarov1 and Vadim V. Yakovlev2
1
Department of Radio Engineering
Saratov State Technical University
Polytekhnicheskaya St. 77
Saratov 410054, Russia
2
Department of Mathematical Sciences
Worcester Polytechnic Institute
100 Institute Road
Worcester, MA 01609
Received 16 November 2005
ABSTRACT: This paper presents the results of 3D FDTD modeling of
a 915-MHz cylindrical structure with the TM01l mode excited by a coaxial line and intended for thermal processing of a spherical load (a
fruit). Energy coupling is shown to be insensitive to the fruit’s type and
temperature, but dependent on its size and location and the loop’s radius. The patterns of dissipated power are analyzed from the viewpoint
of heating uniformity. © 2006 Wiley Periodicals, Inc. Microwave Opt
Technol Lett 48: 1104 –1108, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21612
Key words: coaxial excitation; coupling; cylindrical cavity; FDTD
model; spherical load; TM01l mode
INTRODUCTION
Cylindrical single-mode applicators employing the TM01l mode
[1] find practical use in microwave power engineering for thermal
treatment of optical fibers [2], liquid media [3], food stuffs [4], and
other substances of axially symmetric geometry. Although underlying theoretical aspects of wave propagation in circular axially
loaded waveguides have been described in literature (for example,
[3– 6]), full-wave numerical analysis is essential for competent
design of practical devices [7]. Known examples of CAD of
cylindrical TM01l applicators include the models developed in
order to evaluate the occurrence of higher modes emerging in case
of high dielectric constant of the load [4], to take into account the
presence of other system elements (dielectric molds, metal irises,
etc.) [8], to calculate resonant characteristics of the applicator with
the inner stubs [9], and to address some other specific issues.
One of the most critical problems of the applicator design is its
efficient excitation. While the TM01l mode can be excited in a
cylindrical structure in different ways, corresponding computer
models have been reported only for a waveguide aperture excitation in multifeed applicators [4, 10]. A coaxial line ended in a
probe or a loop, a standard coupling element, has been also used in
practical applicators (for example, [1, 3, 9]), but this has been
MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 48, No. 6, June 2006
DOI 10.1002/mop