2011 International Conference on Advancements in Information Technology
With workshop of ICBMG 2011
IPCSIT vol.20 (2011) © (2011) IACSIT Press, Singapore
A Novel Design of 1.5 GHz Low-Noise RF Amplifiers in L-BAND for
Orthogonal Frequency Division Multiplexing
Sharmila G.
+
and Govindan E.G.
Department of Electronics and Communication Engineering, Sri Venkateswara College Of Engineering,
Pennalur, Sriperumbudur-602105.
Abstract. Communication plays very important role in day-to-day life of people. Due to fast growing age,
multi carrier communication is preferred over single carrier waves for better transmission. The RF power
amplifier in OFDM transmitters plays a major role in amplifying the required high frequency RF signal
without distortions and other impairments which would decrease the usefulness of the signal. For narrowband
& wideband operation, one may construct simple amplifiers whose noise figure and power gain are close to
the theoretical optima allowed within an explicit power constraint.This paper introduces the design of a 1.5
GHz unconditionally stable Low-Noise RF amplifier in L-Band using Agilent’s Advance Design Systems
Software. The proposed design aims to provide an optimal gain of 12.715 dB with low Noise Figure (NF) of
1.768 dB in wideband.
Keywords: Orthogonal Frequency Division Multiplexing, Low-Noise Figure, Wideband.
1. Introduction
Wireless communication and its applications have travelled through rapid growth in recent years.
Cellular systems, WLANS, Bluetooth as well as WPANs have undergone numerous generations of evolution
in the swift development in wireless communication [1]. The radio frequency (RF) front-end electronics
plays an important part in high level integration of radio solutions. The low noise amplifier is one of the most
critical building blocks in modern integrated radio frequency solutions. The front-end low noise amplifiers
have been widely used in many applications including wireless personal communication systems, Orthogonal
Frequency Division Multiplexing.
This paper presents a circuit topology of the Bipolar Junction Transistor Low Noise Amplifier (BJTLNA) operating at 1.5 GHz. The circuit is constructed using AT41435 Low-Noise BJT Device. The design
proposes tradeoffs between gain, noise and blocking performances [2]. Agilent's ADS software in RF and
microwave simulation of circuit and system has unique advantages. Some of them are friendly interface,
model base of integrity, RF performance simulation and optimization of convenience. This paper just uses
Agilent's ADS software for designing the Low-Noise amplifier used in IEEE 802.11b and describes in detail
the methods involved in the design and simulation of Low Noise Amplifier. In Section 2, we have analyzed
the basic suitability of the device for the construction of the circuit at the desired frequency range of 1.5 GHz.
In the Section 3, we have analyzed and discussed the design methodology of Input Matching Network for
obtaining the optimum impedance matching. Then, we design the output matching network using
Microstrip-Lines in Section 4. In Section 5, we discuss the overall schematic and optimum Gain measurement
at Low-Noise Figure of 1.768 dB.The simulation results and future prospects of the design are presented in
Section 6.
2. Device Characterization
+
Corresponding author. Tel.: 9444709665.
E-mail address: rupinisharmila@gmail.com.
176
The design of Low-Noise Amplifier involves Device Characterization (DC Analysis), Biasing condition,
Stability analysis, Design of Input and Output Matching Network, Performance Optimization and Impedance
Matching. The first stage in the design process is to pick a suitable device that will give us plenty of gainmargin to allow for noise mismatching.
2.1
DC Analysis
The BJT Device used in this paper is AT-41435 biased to operate at Vce = 8V, Ic = 10 mA. The value Ibb is
calculated as 120 µA at the operating point using Ib=Ic/β as given in Fig 1. denoting the VI-Characteristic
Curve of the Device [5].
Device I-V Curves
18
16
DC.IC.i, mA
14
12
m5
10
8
6
4
2
0
-2
0
2
4
6
8
VCE
m5
VCE= 8.000
DC.IC.i=0.010
IBB=0.000120
Fig. 1: Voltage-Current Characteristics of BJT AT41435 Device
2.2
Stability Analysis:
Stability Analysis is performed to verify the immunity of the device against oscillations and the stability
factor K at required specification of 1.5 GHz is evaluated as 1.098.The optimum Noise Figure value for the
device is given by 1.571 dB. The necessary and sufficient conditions for unconditional stability are:
K > 1, |∆| < 1
(1)
(2)
where
&
(3)
The value of K obtained using the theoretical analysis is 1.1 and the value obtained using ADS is 1.098
which shows K > 1 and the value of |∆| obtained using theoretical analysis is 0.14 and the value obtained using
ADS is 0.123 as shown in Fig 2. K > 1, |∆| < 1 shows the device is unconditionally stable. Thus, the Device
Characterization helps us to choose the proper device meeting our specification.
0.22
mag_delta
0.20
m1
freq=1.500GHz
mag_delta=0.123
0.18
0.16
0.14
m1
0.12
0.10
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0
freq, GHz
1.2
m4
1.0
StabFact1
mag_delta
0.8
m5
freq= 1.500GHz
mag_delta=0.123
0.6
0.4
m5
0.2
m4
freq= 1.500GHz
StabFact1=1.098
0.0
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0
f req, GHz
Fig. 2: Stability Analysis of AT41435 Device – Rollett’s Factor K and Delta Function ∆
177
The general block diagram of RF Low-Noise Amplifier is given by Fig 3. The Block Diagram consists of
Input Matching Network, Output Matching Network and Biasing Network and impedance matching between
the same.
Fig. 3: Topology of Microwave Amplifier showing Input and Output Matching Network
The need for matching networks arises because, in amplifiers in order to deliver maximum power to a
load or to perform in a certain desired way, must be terminated properly at both the input and output ports.
The input matching network is designed to transform the generator impedance (50Ω) to the source impedance
Zs and the output matching network transforms the 50Ω termination to the load impedance ZL. The value of
unilateral Transducer Gain GTUmax is theoretically calculated as 15.12 dB where
0.38∟176◦,
0.48∟32◦ and simulated results are as shown in Fig 4.
Fig. 4: Evaluation of Maximum Unilateral Transducer Gain for AT41435 Device
3. Design of Input Matching Network
The input matching network can be designed to match the large signal input impedance of the RF power
device with the 50Ω source impedance. Therefore, the large signal input impedance of the RF transistor
should be estimated at the nominal input power, operating frequency, and bias voltages with the existence of
the load and output matching networks. The input matching network improves the net input power delivered
to the RF device. The amplifier circuit was simulated again after adding the input matching circuit using
ADS as shown in Fig 5. to improve the performance characteristics of the amplifier. This design has
presented and discussed the main guidelines for synthesizing the input matching circuits for the LNA RF
amplifier to achieve the improved performance.
178
Fig 5. Schematic Representation of Input Matching Network for Low-Noise RF Amplifier
If we use alumina with r = 9.6 and H = 25 mils to build the amplifier we find that a characteristics
impedance of 50Ω is obtained with W= 39.78 mils and ff = 6.64.The microstrip length in the 50Ω Alumina
microstrip line is λ = 0.3984 λ0 where f=1.5GHz.The value of S(2,1) is obtained as 11.71 dB and noise figure
value is given as 1.866 dB as given in Fig 6.
m1
freq=1.500GHz
dB(S(2,1))=11.71
12.6
12.4
freq
dB(S(2,1))
12.0
m1
11.8
S(2,1)
1.450 GHz
1.460 GHz
1.470 GHz
1.480 GHz
1.490 GHz
1.500 GHz
1.510 GHz
1.520 GHz
1.530 GHz
1.540 GHz
1.550 GHz
12.2
11.6
12.289 / -51.375
12.173 / -52.336
12.057 / -53.291
11.942 / -54.239
11.826 / -55.180
11.710 / -56.115
11.635 / -57.037
11.561 / -57.955
11.486 / -58.868
11.411 / -59.777
11.337 / -60.681
11.4
1.44
1.46
1.48
1.50
1.52
1.54
1.56
freq, GHz
m2
freq=1.500GHz
nf(2)=1.866
freq
2.00
nf(2)
1.724
1.749
1.776
1.804
1.834
1.866
1.899
1.934
1.971
2.009
2.049
1.95
1.90
nf(2)
1.450 GHz
1.460 GHz
1.470 GHz
1.480 GHz
1.490 GHz
1.500 GHz
1.510 GHz
1.520 GHz
1.530 GHz
1.540 GHz
1.550 GHz
m2
1.85
1.80
1.75
1.70
1.44
1.46
1.48
1.50
1.52
1.54
1.56
freq, GHz
Fig. 6: Simulation Results for Input Matching Network
4. Design of Output Matching Network
The output matching network for the LNA is designed to transform the impedance of 50Ω to the load
impedance ZL or to the load reflection coefficient. The output matching network for the Low-Noise
Amplifier operating at 1.5 GHz is designed using ADS as shown in Fig 7. The value of S(2,1) is given by
14.37 dB and noise figure is given by 1.51 dB as shown in Fig 8.
179
Fig. 7: Schematic Representation of Output Matching Network for Low-Noise RF Amplifier
S(2,1)
freq
1.450
1.460
1.470
1.480
1.490
1.500
1.510
1.520
1.530
1.540
1.550
GHz
GHz
GHz
GHz
GHz
GHz
GHz
GHz
GHz
GHz
GHz
nf(2)
freq
5.431
5.394
5.356
5.316
5.276
5.235
5.216
5.197
5.176
5.154
5.131
/
/
/
/
/
/
/
/
/
/
/
-43.001
-44.406
-45.820
-47.244
-48.678
-50.120
-51.525
-52.939
-54.362
-55.793
-57.233
1.450
1.460
1.470
1.480
1.490
1.500
1.510
1.520
1.530
1.540
1.550
GHz
GHz
GHz
GHz
GHz
GHz
GHz
GHz
GHz
GHz
GHz
1.538
1.544
1.551
1.557
1.564
1.571
1.578
1.584
1.592
1.599
1.606
m2
f req=1.500GHz
nf (2)=1.571
m1
f req=1.500GHz
dB(S(2,1))=14.378
1.61
14.7
1.60
14.6
1.58
nf(2)
dB(S(2,1))
1.59
14.5
m1
14.4
m2
1.57
1.56
1.55
14.3
1.54
14.2
1.44
1.46
1.48
1.50
1.52
1.54
1.56
1.53
1.44
freq , GHz
1.46
1.48
1.50
1.52
1.54
1.56
freq , GHz
Fig. 8: Simulation Results of Output Matching Network for 1.5 GHz LNA
5. Performance Optimization of Low-Noise Amplifier
The input and output matching network combined with the active biasing network of the BJT-LNA is
designed using ADS and impedance matching is performed to obtain the optimum gain of 12.715 dB and
gain ripple of 1.02dB with noise figure of 1.768 dB. The simulated results are given by Fig 9.
m3
freq= 1.500GHz
dB(S(2,2))=-34.262
m2
freq= 1.500GHz
nf(2)=1.768
1.95
13.2
1.90
13.0
1.85
m1
12.8
-25
1.80
12.6
1.75
12.4
1.70
12.2
-20
dB(S(2,2))
13.4
nf(2)
dB(S(2,1))
m1
freq= 1.500GHz
dB(S(2,1))=12.715
m2
1.46
1.48
1.50
1.52
1.54
1.56
m3
-35
-40
1.65
1.44
-30
-45
1.44
1.46
1.48
freq, GHz
1.50
1.52
1.54
1.56
freq, GHz
1.44
1.46
1.48
1.50
1.52
freq, GHz
Fig. 9: Simulation Results of Low-Noise Amplifier at 1.5 GHz
An LNA design presents a great challenge because of its simultaneous requirement for high gain, low
noise figure, good input and output matching and unconditional stability at the lowest current draw from the
amplifier [3]. Although gain, noise figure, stability, linearity and input and output match are all equally
important, each of these parameters are independent and rarely work. Typically, the proposed LNA requires:
180
1.54
1.56
• Low supply voltage, High gain, Low noise figure
• Low current consumption, hence ultra-low power consumption
• Unconditionally stable, Good Input return loss
• High isolation, Low cost
Most of these conditions can be met by carefully selecting a transistor, choosing the right component
values and understanding parameter trade-offs. Low noise figure and good input match can be
simultaneously obtained using feedback configurations. High gain apart from producing inter-modulation
distortion, can lead to instability. Unconditional stability requires a certain gain reduction.
6. Simulation Results and Future Prospects
The designed LNA requires a 15V supply voltage. The circuit is designed and simulated using Advanced
Design System Software from Agilent Technologies. At l.5 GHz, the proposed BJT-LNA has a low noise
figure (NF) of 1.768 dB and optimum gain of 12.715 for wideband as shown in Fig 10.
S(2,1)
0.0000 Hz
10.00 MHz
20.00 MHz
30.00 MHz
40.00 MHz
50.00 MHz
60.00 MHz
70.00 MHz
80.00 MHz
90.00 MHz
100.0 MHz
110.0 MHz
120.0 MHz
130.0 MHz
140.0 MHz
150.0 MHz
160.0 MHz
170.0 MHz
180.0 MHz
190.0 MHz
200.0 MHz
210.0 MHz
220.0 MHz
230.0 MHz
240.0 MHz
250.0 MHz
260.0 MHz
270.0 MHz
280.0 MHz
290.0 MHz
28.162 / 169.250
27.829 / 166.322
27.488 / 163.401
27.141 / 160.488
26.790 / 157.583
26.433 / 154.687
26.072 / 151.801
25.708 / 148.926
25.342 / 146.062
24.973 / 143.210
24.603 / 140.371
24.231 / 137.543
23.860 / 134.729
23.489 / 131.927
23.118 / 129.138
22.748 / 126.362
22.380 / 123.598
22.014 / 120.847
21.650 / 118.109
21.289 / 115.382
20.931 / 112.667
20.575 / 109.963
20.223 / 107.270
19.875 / 104.587
19.530 / 101.913
19.189 / 99.249
18.851 / 96.593
18.518 / 93.944
18.188 / 91.303
17.862 / 88.668
m3
f req=1.500GHz
dB(S(2,1))=12.715
40
m3
20
0
dB(S(2,1))
freq
-20
-40
-60
-80
0
1
2
3
4
5
6
7
8
9
freq, GHz
Fig. 10: Simulation Results of Wide-Band Low-Noise RF Amplifier
Table 1. presents the summary of Simulation Results of 1.5 GHz Low-Noise Amplifier.
Table 1. Simulation Results of 1.5 GHz Low-Noise Amplifier
PARAMETER
VALUE
RF Frequency
1.5 GHz
Power Supply
15 V
Noise Figure
1.7 dB
Gain
12.715 dB
S11
-2.97 dB
The amplifier can be further modified and improved to form Two-Stage Amplifier for achieving better
gain. When a two stage amplifier is to be designed, the source and load must be matched to the conjugate of
the output reflection coefficient of the first stage and input reflection coefficient of the second stage. The
impedance to be presented to the output of the first stage is transferred to the impedance to be presented for
the second stage directly to minimize the length of the transmission line. Thus, there are many design
challenges involved while designing the two-stage amplifier design.
7. Conclusion
The design proposed is efficiently used in the Wireless Communication applications for amplifying the
Wideband RF signals at 1.5 GHz with better gain of 12.715 dB and Low Noise Figure of 1.768 dB. The
design of RFIC remains a huge challenge due to strong constraints in power consumption and noise. Thus,
bipolar junction transistors were the first solid-state active device to provide better practical gain and low
noise figure at microwave frequencies.
181
10
8. References
[1] Golmie, N., Chevrollier, N., Rebala. Bluetooth and WLAN coexistence: challenges and solutions. In: IEEE
Wireless Communication, Volume 10, Issue 6, pp.22-29, Dec. 2003.
[2] D. K. Shaeffer and T. H. Lee. A 1.5-V, 1.5-GHz CMOS low noise amplifier. In: IEEE J.Solid-State Circuits,
Vol. 32, pp: 745-759, May 1997.
[3] S.F.W.M. Hatta. Design of an RF BJT-Low Noise Amplifier at 1 GHz. In: ICSE2006 Proc. 2006, Kuala Lumpur.
[4] Guillermo Gonzalez, Microwave Transistor Amplifiers - Analysis and Design. 2nd Edition, 1996.
[5] Anurag Bhargava, S. Deepak Ram Prasath, V. Periyasamy, S. Raju, V. Abhaikumar. RF Circuit Design Cook
Book, 2008.
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