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SiGe BiCMOS LNA’S AND TUNABLE ACTIVE FILTER FOR FUTURE WIDE-BAND
MULTI-PURPOSE ARRAY ANTENNAS
1
1
R. Malmqvist, and 2M. Hansson
Swedish Defence Research Agency FOI, Box 1165, SE-581 11 Linköping, Sweden
2
Linköping University, SE-581 83 Linköping, Sweden
[email protected], and [email protected]
SUMMARY
In this paper, we present three monolithical microwave integrated circuits (MMIC’s) that potentially
may be used in the receiver front-ends of future wide-band multi-purpose array antennas, for example.
Two low-noise amplifiers (LNA’s) and one tunable filter have been designed in a 0.35µm bipolar
complementary metal oxide semiconductor (BiCMOS) technology containing high frequency silicongermanium (SiGe) hetero-junction bipolar transistors (HBT’s). The use of BiCMOS technologies
based on SiGe HBT’s to enhance RF performance could enable RF functions to be integrated on the
same chip as complex digital functions. Firstly, a single-stage LNA is presented together with a twostage wide-band LNA. Simulated RF performance of these circuits seems promising in terms of values
of gain and noise figure achieved, respectively, over large bandwidths. Relatively wide-band input and
output impedance matching together with reasonably low values of power consumption are achieved
for these LNA’s. Finally, a 7.3-8.1GHz tunable active filter is also described.
INTRODUCTION
One of the future strategies suggested to improve the handling of today’s complex battlefield scenarios
is the development of adaptive multi-purpose phased array antennas that can handle radar,
communication and electronic warfare functions using a single wide-band RF system. A single wideband RF front-end solution could, compared to traditional solutions requiring separate systems for
realizing each sensor function, better accomplish desired sensor platform objectives in terms of high
survivability, low observability as well as low weight and cost. To be able to realize multi-purpose
array antennas in the future that are compact and cost-effective, integration methods that can be used
to reduce size and complexity of RF front-ends have to be developed. The technology chosen must be
able to meet requirements in terms of RF performance (e.g. low noise and high linearity) and should in
the same time allow a high production yield at a low cost. The use of BiCMOS technologies based on
silicon germanium (SiGe) hetero-junction bipolar transistors (HBT’s) to enhance RF performance
could enable RF functions to be integrated on the same chip as complex digital functions. A key
component in a microwave receiver chain is the low noise amplifier (LNA) since it affects the noise
and large-signal properties of the whole receiver. To obtain a low vulnerability to jamming signals due
to electronic warfare or electromagnetic interference (EMI), for example, is essential in modern radar
systems. One way to achieve this is to use a frequency hopping radar where the transmitter and the
receiver jump in a pseudo-random like way between different selected frequencies. To further reduce
the vulnerability to jamming signals adaptive methods and digital beamforming can be adopted [1].
Increased interest has recently been focused on the possibility of using frequency tunable narrow-band
active MMIC filters to reduce the vulnerable bandwidth of frequency hopping radar receivers [2].
Compared with using a fixed frequency bandpass filter, a tunable filter may also reduce the number of
down-converting stages required in an agile receiver by allowing a greater down-conversion step to be
made. Rejection of interfering signals that, for example, may occur at the receiver image frequency
should be high enough to minimize the effect of jamming. Typical requirements for receiver front-end
components (such as an LNA or a tunable active filter) of future wide-band multi-purpose array
antennas are summarized in Table 1. The specification is based on our experience in the area and on
assumed radar system requirements. To the best of our knowledge, relatively few papers have been
published on SiGe based wide-band LNA’s at X-band (8-12GHz) and above (see e.g. [3-4]).
Advanced SiGe HBT processes with values of the cut-off frequency and the maximum frequency of
oscillation (fT and fmax) in the order of 70-100GHz, respectively, were used in [3,4]. In this paper, we
present two LNA’s and one frequency tunable active filter intended for multi-purpose array antennas
working in the 2-18GHz range using a 0.35µm SiGe BiCMOS process with somewhat lower values of
fT and fmax (47 and 60GHz respectively). Circuit schematics, layout and simulated results are
summarized below. Simulations are performed using Cadence RF Spectre together with a foundryprovided design kit.
Gain (G)
≥ 10dB
Noise figure (NF)
< 3-5 dB
Input third order intercept point (IIP3)
≥ 0 dBm
Table 1: Typical requirements for receiver front-end components (such as an LNA or a tunable active
filter) in future wide-band multi-purpose array antennas.
CIRCUIT DESIGN, LAYOUT AND SIMULATED RESULTS
Single-stage X-band LNA and two-stage cascaded wide-band LNA
Figure 1a shows the schematic of a single-stage common-emitter (CE) based LNA designed with a
negative feedback applied between the base and the collector. This has the effect of stabilizing the
amplifier at the expense of somewhat reduced small signal gain (s21) and increased noise figure (NF).
A small-sized inductor is placed between the emitter and ground in order to improve the LNA noise
performance. Figure 1b shows simulated s-parameters of the single-stage LNA. As can be seen in Fig.
1b, s 21 is above 10dB between 2-9GHz. Amplifier gain is thereafter sharply rolled off approaching
5dB at 11GHz and 0dB at close to 13GHz. The input impedance matching (s11) is below -10dB from
6–11GHz and the output impedance matching (s 22) is below -10dB from 7.5-10.1GHz. The reverse
isolation (s12) is below -30dB. Noise simulations of the single-stage LNA reveal that NF is close to
3dB from 2-6GHz. NF is increased to 4dB at 9GHz and is lower than 5dB for frequencies up to
11GHz. The high roll off in gain at frequencies above 8 to 9GHz implies the lower part of the X-band
is the upper frequency limit for this amplifier. According to simulations, the input referred third order
intercept point (IIP3) equals –3dBm at 8GHz. The total DC power consumption (PDC) equals 7.5mW
drawn from a base bias voltage (VBB) of 1.1V and a collector bias voltage (VCC) of 2.0V.
VCC
Lchoke
Rf
Lout
Cf
Cblock
RFout
Lin
RFin
T1
Cblock
Cout
Rbias
Le
VBB
a)
b)
Fig. 1. Single-stage common-emitter LNA: a) circuit schematic b) simulated s-parameters.
Due to the mere fact that the single-stage LNA does not provide a sufficiently high gain at frequencies
above X-band we have also designed a two-stage cascaded CE based LNA (see Fig. 2a for circuit
schematic). In this design the first stage (stage 1) is designed for low noise and the second stage (stage
2) is designed for high gain. It is then possible to use a higher collector current (ICC) in the second
stage in order to reach a higher fT something that is needed to be able to improve the amplifier gain
and bandwidth. To be able to use the LNA in a wide frequency band an adequate input and output
impedance matching should be achieved over a large bandwidth. For this reason, the LNA has been
designed with on-chip wide-band input and output impedance matching networks (denoted IMN and
OMN, respectively, see Fig. 2a). Simulated s-parameters of the two-stage wide-band LNA are shown
in Fig. 2b. As can be seen, s 21 is above 10dB within a 10GHz wide frequency band (from 4-14GHz).
s11 is below –10dB in two frequency intervals (between 5-7.5GHz and 10.5-14GHz, respectively). s22
below –10dB is achieved between 6-10.5GHz and s 22 is below –9dB from 2-11GHz. The reverse
isolation (s12) is equal to –43dB or lower. Noise simulations of the LNA show that an NF below 5dB is
achieved over a more than 11GHz wide frequency band (from 1.5 to 12GHz). An NF higher than 3dB
and below 4dB is achieved from 2 to 9GHz. The simulated value of IIP3 at 10GHz equals –13dBm.
PDC equals 22.7mW (VBB1=1.1V, VCC1=2.0V, ICC1=3.6mA, VBB2=1.4, VCC2=2.0V and ICC2=7.6mA).
VCC2
VCC1
Lchoke2
Lf
Lchoke1
Ros
Lout
RFout
T2
Lin1
RFin
Lin2
T1
Cblock1
Cin
Cblock2
Cos
Cblock3
Rbias1
Cblock4
Rop
Rbias2
Cop
Le
VBB2
VBB1
IMN
OMN
Stage 2
Stage 1
a)
b)
Fig. 2. Two-stage cascaded common-emitter LNA: a) circuit schematic b) simulated s-parameters.
7.3-8.1GHz frequency tunable filter
A tunable X-band active filter based on a recursive filter topology was presented in [5] using a
gallium-arsenide (GaAs) high electron mobility transistor (HEMT) technology. In this topology a
single-stage LNA together with a passive (varactor tuned) delay network are placed between two
lumped 3dB couplers in a positive feedback arrangement that enables a relatively high filter selectivity
to be achieved. The schematic of a corresponding filter implemented in a 0.35µm SiGe BiCMOS
process is shown in Fig. 3a. The filter is tunable between 7.3-8.1GHz. Figure 3b shows simulated sparameters when the filter center frequency (fc) equals 7.3GHz and 8.1GHz, respectively. Simulated
results at 7.3GHz (and at 8.1GHz, respectively): s 21=7dB (7dB), s11=-8dB (-7dB), s22=-12dB (-6dB),
s12=-21 (-20dB), NF=7.1dB (7.3dB) and PDC=2.3mW (3.7mW). The relative 3dB filter bandwidth is
equal to approximately 5% (corresponding to a filter Q-factor of close to 20) at both frequencies.
10
s
5
Line inductance
0
VCC
-5
Varactor
Lchoke
L3dB
C3dB
Rf
Cdelay
C3dB
Cin
RFin
C3dB
T1
Lin
C3dB
Rbias1
L3dB
VBB
C3dB
-15
Cf
R3dB
-10
L3dB
Cblock
C3dB
21
R3dB
Ldelay R
bias2
Lout
Cout2
s
s
11
22
RFout
-20
C3dB
Vvar
C3dB
L3dB
Cout1
5
6
7
8
Frequency [GHz]
a)
b)
Fig. 3. Tunable recursive active filter: a) circuit schematic b) simulated s-parameters.
9
10
Simulated results
Single-stage LNA
Gain [dB]
≥10 (@f=2-9GHz)
Two-stage LNA
≥10 (@f=4-14GHz)
Filter (fc=7.3-8.1GHz)
7
NF [dB]
<4 (@1<f<9GHz)
<5 (@1<f<11GHz)
<4 (@2<f<9GHz)
<5 (@1.5<f<12GHz)
7
IIP3 [dBm]
-3
PDC [mW]
7.5
-13
22.7
N/A
2.3-3.7
Table 2: Summary of simulated RF performance for two different LNA’s and one active filter.
Simulated RF performance for the two LNA’s and the tunable active filter are summarized in Table 2.
A layout of these circuits (as well as some additional break out circuits) implemented in a 0.35µm
SiGe BiCMOS process is shown in Fig. 4. The total circuit area of the layout is equal to 4x3mm2.
Fig. 4. A layout containing several LNA’s, a tunable active filter and some break out circuits.
CONCLUSION
Three MMIC’s (two LNA’s and one tunable active filter) intended for the receiver front-ends of future
wide-band multi-purpose array antennas have been designed in a 0.35µm SiGe BiCMOS process.
According to simulations of the two LNA’s (a single-stage LNA and a two-stage cascaded LNA), RF
performance seems promising in terms of values of gain and noise figure achieved, respectively, over
wide frequency bands. Relatively wide-band input and output impedance matching together with
reasonably low values of power consumption are obtained for these LNA’s. In order to improve LNA
performance (to obtain a higher linearity over a large bandwidth, for example) or, alternatively, to
extend the usable bandwidth of the LNA’s more advanced processes with higher values of fT and fmax
are probably needed. Simulated results of the tunable filter imply a somewhat inadequate performance
with respect to filter gain and noise figure. To achieve a lower noise figure the active filter could be
re-optimized by using an unbalanced coupler (instead of using a 3dB coupler) at the filter input.
ACKNOWLEDGEMENTS
This work is financially supported by The Swedish Defence Material Administration (FMV) and by
The Swedish Armed Forces (FM).
REFERENCES
[1] L. Pettersson et al., "An experimental S-band digital beanforming antenna," IEEE AES Syst. Mag.,
Vol. 12, pp. 19-26, Nov. 1997.
[2] A. Gustafsson et al., “Tuneable S-band filter for on-chip receiver,” Proc. of 1998 Asia-Pacific
Microw. Conf., pp. 781-784.
[3] K. -B. Schad et al., “A Ku band SiGe low noise amplifier,” Silicon Monolithic Integrated Circuits
in RF Systems 2001 Dig., pp. 52-54.
[4] H. Knapp et al., “15 GHz wideband amplifier with 2.8 dB noise figure in SiGe bipolar
technology,” IEEE MTT-S 2001 Int. Microwave Symposium Dig., pp. 591-594.
[5] M. Danestig et al., “Recursive filters employing transmission type phase shifters and novel selfswitched time shifters for frequency tuning,” Proc. of 1998 Europ Microw. Conf., pp. 352-357.