A 6 mW Low Noise Amplifier for 3.1-10.6 GHz UWB Application
Varish Diddi #1, Kumar Vaibhav Srivastava #2 , Animesh Biswas #3
#
Department of Electrical Engineering, Indian Institute of Technology, Kanpur
India
1
varish.bvb@gmail.com
2
kvs@iitk.ac.in
3
abiswas@iitk.ac.in
Abstract — This paper presents a single stage low-noise
amplifier (LNA) using cascode topology for low-power UWB
applications. Resistive feedback is used to obtain large
bandwidth. The LNA achieves peak gain of 11.8 dB and noise
figure varying from1.72 – 3.62 dB within the band of 3.1 – 10.6
GHz. The LNA uses supply of 2 V while consuming only 6 mW
of dc power. The technology used for design is 0.25 µm IHP SiGe
BiCMOS which employs Heterojunction Bipolar Transistor
(HBT). The output 1 dB compression point and input IP3 for
LNA are -23 dBm and -12.48 dBm respectively.
smaller areas as compared to filter usage [13]. The design
uses cascode topology to achieve high gain, enhanced
isolation and improved stability [14].
In this paper we present LNA for UWB application
employing 0.25 µm SiGe BiCMOS technology. Section II
details the design procedure involved. Section III presents the
simulation results.
II. LOW-NOISE AMPLIFIER DESIGN
Index Terms — Low-power LNA, Ultra-wideband (UWB),
SiGe BiCMOS, Heterojunction Bipolar Transistor (HBT).
I. INTRODUCTION
Ultra-wideband (UWB) communication systems have
recently received significant attention due to the potential of
transmitting data at very high rates over large band of
frequencies. UWB technology may be used in imaging
systems, ground and vehicular penetrating radars and many
other applications. Such applications need low-noise
amplifiers which have high gain and low noise figure over a
large band of 3.1 – 10.6 GHz. III-V compound semiconductor
technologies are dominant in such applications due to their
inherent low-noise characteristics at high frequencies. Such
technologies are AlGaAs-GaAs Heterojunction Bipolar
Transistors (HBTs), InAlAs-InGaAs HBTs, InGaP-GaAs
HBTs, AlGaN-GaN High Electron Mobility Transistors
(HEMTs) [1]-[5]. But the high performance designs on Si
CMOS and SiGe BiCMOS have also been achieved [6]-[9].
These designs are advantageous from integration and
economical point of view.
SiGe BiCMOS technology uses SiGe HBT in combination
with Si CMOS device. SiGe HBT is the first bandgap
engineered device realized in silicon. This technology
provides a unique opportunity for Si-based radio frequency
system on chip solutions [10]. The cut-off frequency (ft ) and
maximum oscillation frequency (fmax) of SiGe HBT have
reached the range of 300 GHz [11]-[12]. Thus its role in RF
applications is justified.
Literature presents two methods of UWB LNA design. One
uses an appropriate filter at input to obtain large bandwidth
[7]-[8]. The other which is usually considered inferior uses
resistive feedback to enhance the bandwidth. The resistor
used adds directly to the noise figure (NF) of LNA but
choosing it cautiously can lead to implementation occupying
The cascode topology, shown in Fig. 1 used for design
consists of a transconductor (Q1) which is operating in
common emitter (CE) mode and cascode (Q2) device
operating in common base (CB) mode. The cascode topology
has voltage gain given by:
Av   g m ro 
(1)
where gm is transconductance of Q1, ro is output resistance of
Q2 and β is current gain of Q2 [14]. The gain of cascode is β
times larger than the gain obtained from single-transistor CE
amplifier.
For LNA design the cascode circuit is biased and then input
and output matching is done. First optimum collector current
density (Jc,opt) is chosen and then device size is decided. Jc,opt
is decided based on gain and noise performance. The device
size is chosen so that the optimum input resistance (Rs,opt)
equals source resistance (Rs) [15]. The Jc,opt along with device
size decides the bias current. But in this design the power is
constrained to 6 mW. With the supply of 2 V the bias current
is already fixed to 3 mA. So the collector current density and
device size have to be simultaneously optimized [16].
The simultaneous optimization of Jc,opt and device size
involves varying the device size for constant current which is
3 mA in this case at the mid-band frequency of 7 GHz. The
variation of cut-off frequency (ft) and optimum input
resistance or real part of optimum input impedance (Re{Zopt})
at 7 GHz with device size normalized to 0.21×6.72 µm2 is
shown in Fig. 2. The variation of minimum noise figure
(NFmin) and real part of optimum input impedance
(Re{Zopt}) at 7 GHz with device size is shown in Fig. 3.
From Fig. 2 we observe that as the device size increases the
cut-off frequency (ft) decreases because the collector current
density (Jc) decreases. From Fig. 3 we observe that for a
particular device size the minimum noise figure (NFmin )
reaches minimum. The device has to be so chosen that the
978-1-61284-091-8/11/$26.00 ©2011 IEEE
optimum input resistance (Re{Zopt}) equals 50 Ω. This
ensures noise matching [15].
The next step of design is input and output matching. Input
matching is achieved by use of degeneration inductor (Le)
and base inductor (Lb) as shown in Fig. 1 [17]. The values are
calculated as below:
Le 
Lb 
where
t=2
Rs
t
(2)
1
 Le
 2 Cbe
(3)
ft and Cbe is base-emitter capacitance of Q1.
The output matching is achieved by buffer appropriately
designed. Thus LNA is both simultaneously noise and
impedance matched. The feedback resistance (Rf) is chosen,
by simulations, to get wideband gain. The designed
component values for UWB LNA are given in table 1.
Fig. 1 Cascode LNA for UWB application
TABLE I
LIST OF COMPONENT VALUES FOR UWB LNA
Fig. 2 Plot of cut-off frequency and optimum input resistance versus device
size normalized to 0.21×6.72 µm2 at 7 GHz
Components
Cb
Cf
Cout
Lb
Le
LL
Rb
Rf
RL
Q1
Q2
Values
3 pF
2 pF
2 pF
1.2 nH
100 pH
3 nH
20 kΩ
800 Ω
100 Ω
0.21×26.88 µm2
0.21×26.88 µm2
III. SIMULATION RESULTS
The LNA designed achieves a peak gain of 11.8 dB. The
gain performance of UWB LNA is shown in Fig. 4. The noise
figure (NF) of LNA varies from 1.72 dB – 3.16 dB. The noise
performance of UWB LNA is shown in Fig. 5. The input
reflection co-efficient (S11), output reflection co-efficient
(S22) and reverse isolation (S12) of LNA are shown in Fig. 6.
The Rollet’s stability factor (kf) and parameter delta ( ) are
needed in investigating the stability of LNA in the operating
band of 3.1 GHz – 10.6 GHz. They are defined as below:
2
kf 
Fig. 3 Plot of minimum noise figure and optimum input resistance versus
device size normalized to 0.21×6.72 µm2 at 7 GHz
2
1  S11  S 22  
2 S 21S12
2
(4)
  S11 S 22  S12 S21
(5)
If kf is greater than unity and is lesser than unity then
LNA is stable [18]. The plots of kf and given in Fig. 7 and
Fig. 8 respectively, confirm that LNA is stable in its operating
region.
Fig. 7 Plot of Rollet’s stability factor for UWB LNA versus frequency
Fig. 4 Plot of gain of UWB LNA versus frequency
Fig. 8 Plot of parameter delta ( ) of UWB LNA versus frequency
Fig. 5 Plot of noise figure of UWB LNA versus frequency
IV. CONCLUSION
A ultra-wideband LNA employing cascode topology was
designed on IHP 0.25 µm SiGe BiCMOS node. With the
power constraint of 6 mW LNA exhibited a peak gain of 11.8
dB and noise figure between 1.72 dB – 3.16 dB.
ACKNOWLEDGEMENT
Authors would like to thank Prof. S. Qureshi of Electrical
Engineering departing of IIT Kanpur for providing laboratory
facilities and IHP microelectronics, Germany for providing
process design kit.
Fig. 6 Plot of input reflection co-efficient (S11 ), output reflection (S22) and
reverse isolation (S12 ) of UWB LNA versus frequency
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