2014 First International Conference on Computational Systems and Communications (ICCSC) | 17-18 December 2014 | Trivandrum
Design and Simulation of Low Noise Amplifier for RF front end at L band Jolly Rajendran
Rakesh Peter
Department of Electronics and Communication Engineering Amrita School of Engineering Amrita Vishwa Vidyapeetham, Coimbatore 641112 Email:
[email protected]
Centre of Excellence in Computational Engineering and Networking Amrita School of Engineering Amrita Vishwa Vidyapeetham, Coimbatore 641112 Email:
[email protected]
Abstract—In this paper, the design and evaluation of a low noise amplifier, that operates in the L-band, is being discussed. The amplifier was fabricated on FR-4 substrate. ATF-58143 Low Noise Enhancement Mode Pseudomorphic High Electron Mobility Transistor [HEMT] is used. The designed LNA is found to have a gain of 13 dB. The return loss is below -10 dB.
I.
I NTRODUCTION
Dual-polarized L-band radar has many applications like estimation of soil moisture[1]. The signal from antenna of L band radar is fed to a Low Noise Amplifier. This paper explores the design of low noise amplifier [LNA] for L band radar. Design of low noise amplifier is vital as it affects the overall performance of the RF front end. It is the first component in any RF receiver. The LNA consists of three stages viz the input matching network, the amplifier itself and the output matching network[2]-[3]. The block diagram of LNA is shown in Figure 7. The design goal is to have a reasonable gain over the desired frequency band with lowest possible noise figure. II.
Fig. 1.
DC analysis
Fig. 2.
Q point
D ESIGN
A. Selection of transistor In the design, ATF-58143 from Avago Technologies was used. ATF-58143 is a low noise enhancement mode pseudomorphic high electron mobility transistor (HEMT). It has a high dynamic range, and comes in a 4-lead SC-70 (SOT-343) surface mount plastic package[4]. Since it has a high gain, high linearity and low noise characteristics, it is an ideal candidate for low noise amplifier. The ideal frequency range for amplifier operation is 450 MHz to 6 GHz for the particular transistor. The S parameters of the transistor in the L band was studied. B. DC biasing The Q point was first fixed by dc analysis. The simulation set up for dc analysis is shown in Figure 1. The Q point is shown in Figure 2. The Q point is fixed so that the transistor remains in the active region. The Q point selected is somewhere on middle of the load line. Inductors are added to block AC. c 978-1-4799-6013-2/14/$31.00 2014 IEEE.
C. Checking the stability criteria The VDS at Q point is 3 V and IDS is 50 mA. S parameter of the transistor is then obtained from which K and Δ are calculated from standard expressions: K=
2
2
1 − |S11 | − |S22 | + |Δ| 2 |S12 S21 |
2
(1)
86
2014 First International Conference on Computational Systems and Communications (ICCSC) | 17-18 December 2014 | Trivandrum
Fig. 3.
Fig. 5.
Input impedance matching
Fig. 6.
Output impedance matching
Variation of k with frequency in L band
of the transmission lines are optimized to achieve matching. Optimization goal[5] is set to minimize the input reflection coefficient S11. Since the goal is to make S11 as small as possible, the maximum and minimum limit was chosen as -30 dB. Random optimizer was chosen. The simulation set up for input impedance matching is shown in Figure 3.
Fig. 4.
Variation of delta with frequency in L band
|Δ| = |S11 S22 − S12 S21 |
2
(2)
For an unconditionally stability, the two conditions viz. K > 1and Δ < 1, should be satisfied. The plot of K and Δ are shown in Figure 3 and Figure 4 . K is greater than 1 and Δ < 1 over the desired frequency range. D. Designing Matching Network The next step in the design is to design a proper matching network. The input impedance and output impedance of the transistor has to be matched to source and load impedance (assumed to be 50 Ohms). 1) Input matching network: The input impedance from data sheet[4] is found to be 28.2 + j9.4Ω. It is matched to source impedance which is assumed to be 50 Ohms. This is achieved by placing stub at input side. The length and width
2) Output matching network: Similarly output impedance is matched to load impedance (assumed as 50 Ohms). The output impedance from data sheet is found to be 51−j3.3Ω. It is matched to load impedance. This is achieved by placing stub at the output side. The length and width of the transmission lines are optimized to achieve matching. Optimization goal[5] is set to minimize output reflection coefficient, S22. As the goal is to make S22 as small as possible, the maximum and minimum limit was chosen as -30 dB. The S parameter set up for output impedance matching is shown in Figure 4. E. Gain Thus both source and load mismatch is eliminated to improve the transducer power gain. The overall transducer gain is given by the standard expression: G T = GS GO GL
(3)
where GS is the gain associated with input matching network and GL is the gain associated with the output matching network. GS , the gain associated with input matching network is given by the standard expression: GS =
1 − |ΓS |
2
|1 − ΓS Γin |
(4)
2
87
2014 First International Conference on Computational Systems and Communications (ICCSC) | 17-18 December 2014 | Trivandrum
Fig. 7.
Fig. 8.
Fig. 9.
LNA block diagram
Fig. 10.
Variation of S parameters of LNA in L band
Fig. 11.
Variation of S parameters of LNA in L band
AC analysis simulation set up
Input voltage vs. Output voltage (AC analysis)
III.
GL , the gain associated with the output matching network is given by the standard expression: GL =
1 − |ΓL |
2
|1 − S22 ΓL |
2
(5)
The general block diagram of the designed LNA is shown in Figure 5.
R ESULTS AND A NALYSIS
The simulation results of ac analysis is shown in Figure 7. The input and output voltage waveforms are given in Figure 7. The amplifier is found to have a gain of 13 dB in the desired frequency range. The simulation results of S parameter is shown in Figure 8 and Figure 9. It is observed that an isolation of -30 dB is achieved in the desired frequency range. The gain varies from 13 dB to 20 dB in the frequency range. The return loss is below -10 dB. IV.
F. AC analysis After achieving matching, ac analysis is performed. The ac simulation set up is shown in Figure 6. DC blocking capacitors are added at the input side and output side. AC signal is then applied. The input and output voltage signals are then compared.
C ONCLUSION
In this paper a low noise amplifier circuit for L band radar front end has been designed The amplifier characteristics for the frequency range 0.9 GHz to 1.5 GHz was studied. Simulation was performed. The designed LNA has forward gain of 13 dB and is unconditionally stable for the frequency range 0.9 GHz to 1.5 GHz. 88
2014 First International Conference on Computational Systems and Communications (ICCSC) | 17-18 December 2014 | Trivandrum
R EFERENCES [1]
Xinyi Shen., Kebiao Mao., Qiming Qin., Yang Hong., Guifu Zhang., “Bare Surface Soil Moisture Estimation Using Double-Angle and DualPolarization L-Band Radar Data,” Geoscience and Remote Sensing, IEEE Transactions on, Vol. 51, No. 7, 3931–3942, July 2013. [2] B. Jung Jang., I. Bok Yom., S. Pal Lee., “V Band MMIC Low Noise Amplifier Design Based on Distributed Active Device Model,”Proceedings of APMC2001, IEEE, 25-28, 2001. [3] Sungkyung Park., Wonchan Kim., “Design of a 1.8 GHz low-noise amplifier for RF front-end in a 0.8,” Consumer Electronics, IEEE Transactions on, vol. 47, no. 0098, 2001. [4] Avago Technologies ATF-58143 datasheet, Low Noise Enhancement Mode Pseudomorphic HEMT in a Surface Mount Plastic Package , http://www.avagotech.com/docs/AV02-0672EN [5] Mohd. Zoinol Abidin Abd Aziz., Jafri B. Din., Mohd. Karnal A. Rahim., “Low Noise Amplifier Circuit Design for 5 GHz to 6 GHz,” 2004 RF and Microwave conference, October 5-6, Subang, Selangor, Malaysia Agilents Advanced Design System 2009, www.agilent.co.
89
