Design and Characterization of a Wideband p-HEMT Low Noise Amplifier

Arpit Kumar, Student Member, IEEE and Nagendra Prasad Pathak, Member, IEEE Radio Frequency Integrated Circuits (RFIC) Laboratory

Department of Electronics and Communication Engineering Indian Institute of Technology Roorkee-India-247667

arpitkumarmittal2009@gmail.com, nagppfec@iitr.ac.in

Abstract—This paper reports a pseudomorphic high electron mobility transistor (HEMT) wide band low noise amplifier (LNA) for WLAN, vehicle communication systems and point to point communication applications. The LNA had been designed by using a single ATF36163 transistor. A wide band bias network has been designed and verified over the desired frequency range. The fabricated prototype of the proposed LNA has a gain of 2.5 dB with a noise figure (NF) of 1.3 dB over the frequency range of 5-6 GHz. The designed amplifier has bandwidth of 1 GHz over the frequency range from 5-6 GHz.

Keywords— bias network; gain; p-HEMT, matching; noise figure; wide band;

I. INTRODUCTION In the recent years the development of wireless automotive

networks [1-2] came into picture due to ever escalating fame of wireless local area networks (WLANs) and their spread over a wide range of applications. The network systems, part of the intelligent transportation systems (ITS), that provide wireless access to vehicular environment are known as WAVE systems [3]. IEEE 802.11p, an IEEE WAVE standard [4], is the IEEE standard developed for this cause. This technology defines how vehicle-to-vehicle (V2V) communication and vehicle-to-infrastructure (V2I) communication can be realized. To support the WLAN as well as the V2V application, traditionally, two independent radios were required. This approach increases the overall circuit cost, power consumption and the size of the circuit. The need of multifunctional radios had come in picture to cope with this ever growing need. The multifunctional radio supports different transmission standards with a single circuitry. A low noise amplifier (LNA) has a prime role to play in the radio as it governs the sensitivity of the received signal at the receiver side. Independent efforts had been initiated to design and develop LNA at WLAN bands [5], for V2V communication [6] and point to point communication [7]. In the present work, an effort has been initiated to design and develop a LNA which will operate from 5GHz to 6GHz band using a standard hybrid microstrip integrated technology (HMIC) process and a HEMT.

The rest of the paper is organized as: Section II describes the design of wideband bias network and the matching network configuration. The results and allied analysis had been provided in Section III. The paper is concluded in Section IV.

II. GEOMETRY OF THE PROPOSED LNA The proposed wideband LNA is comprehended by using simple microstrip line network and a transistor. Fig.2 shows the geometry of the proposed LNA.

Fig. 1. Proposed wideband LNA.

A. The wideband Bias Network A wideband bias network had been designed to operate

over the 5 to 6 GHz band. The drain and gate bias network had been implemented by using the concept of stepped impedance resonator. The bias network consists of three quarter wavelength transmission lines of different characteristic impedances at the desired band. Fig.2. depicts the proposed wideband bias network. The dimensions of the proposed bias network are given in the Table I.

/4Z1

/4Z1

/4Z2

Fig. 2. Proposed wideband bias network.

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TABLE I. DIAMENSIONS OF BIAS NETWORK

Impedance Length( mm) Width(mm)

Z1=20 6.806 12.88

Z2=120 7.9 0.44

Fig. 3 shows the S11 and S21 characteristics of the proposed bias network. It has been evidenced from Fig. 3 that the proposed bias network has a very large rejection to RF over the desired range of operation.

Fig. 3. S-Parameter analysis of proposed wideband bias network.

The stability analysis of the proposed LNA had been carried out with the proposed bias network and ATF36163 transistor. A resistance of 47 had been added in series with the drain terminal of the transistor for stability purpose. It was found that the proposed LNA was unconditionally stable with these arrangements. The stability analysis [7] has been provided in Table II.

TABLE II. STABILITY ANALYSIS

Frequency (GHz) S11 S21 K B1

5.25 0.918/170.9 o 0.136/-76.6o 1.42 3.122

5.9 0.890/132.6 o 0.151/-109.5 o 1.35 3.18

6 0.885/127.42 o 0.152/-114.3 o 1.32 3.26

Based on the stability analysis, the bias points for the proposed amplifier had been decided. Table III provides operating bias point of the ATF36163 transistor.

TABLE III. BIAS POINTS

Symbol Parameter Value

VDS Operational drain to source voltage 2.75 V

VGS Operational gate to source voltage -0.2 V

IDS Operational drain to source current 7 mA

B. The matching Network After the stability analysis, the design of the matching

network for the load and source side had been initiated. It was desired to have a wideband matching network. The function of the matching network is to convert the impedance looking into source and load side into 50 ohm. The source and load impedances were selected after drawing constant noise figure and constant gain circles at the desired frequencies. The impedances were chosen such that the noise figure of the LNA is low and gain is high. The matching network had been realized by the simple 50 transmission lines as shown in Fig.4.Table IV provides load and source impedances chosen for the design purpose.

ZL

L1

L2

Z0

Z050

Fig. 4. The matching network.

TABLE IV. DESIGN IMPEDANCE(S)

Impedance Matching Impedance Value(in )

Source (Zs) 26.831-j*25.405

Load (ZL) 51.625+j*14

In the matching network, the first transmission line is in

series with the load impedance and second transmission line is an open circuited stub. The first transmission line is used to convert the real part of the complex impedance to 50 ohm and according to that condition its imaginary part will also change. Then open circuited stub is used to cancel out the imaginary part of the impedance which finally leads to match the complex impedance to 50 ohm. Based on the impedances achieved, the dimensions of the matching network had been calculated. Table V provides the optimized dimensions of the matching network. The width had been kept stable in corresponding 50 for the ease of fabrication process.

TABLE V. DIAMENSIONS OF THE MATCHING NETWORK

Impedance Matching Width(mm) L1(mm) L2(mm)

Source

3.58 0 .1 3

Load 5 5.2

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III. RESULTS AND ANALYSIS The LNA was realized using hybrid microstrip integrated

technology (HMIC). The entire surface mount device was mounted on the commercial NH9320 substrate which is a Poly- Tera-Fluoro- Ethylene (PTFE)/glass/ceramic dielectric. The substrate is characterized by the dielectric constant of 3.2 and the substrate height is 1.524mm. The active device used in the designing of the LNA is ATF36163. The fabrication was carried out with the photolithography technique. Fig. 5 shows the fabricated prototype of proposed wideband LNA.

Fig. 5. Fabricated prototype of the proposed wideband LNA.

The designed impedance matching had bandwidth of more than 1 GHz. The return loss (S11), gain (S21) and noise figure of the LNA has been shown in the Fig. 6 to 8 respectively. It is clear that the gain is constant over the desired frequency range and is about 2.5 dB. The simulated noise figure over the desired frequency range is 1.3 dB. The return loss over the desired frequency range is -4 dB. The performance measurements of the LNA had been carried out using a vector network (Agilent PNA-X N5247A).

Fig. 6. S11 characteristics of the proposed wideband LNA.

The drift in the simulation and measurement characteristics can be credited to the limitations of the fabrication facilities and the unavailability of accurate S-parameters of ATF-36163. The entire design and simulation and prototyping of the LNA had been carried out by using ADS model of the transistor.

This may be the highest cause of a delta between the simulation and measurement of S11characteristics. A wide band response was evidenced from the simulated as well as measured insertion loss characteristics. Fig. 7 shows the insertion loss characteristics for the proposed LNA. Further the NF characteristics of the proposed LNA are within the permissible limits [8].

Fig. 7. S21 characteristics of the proposed wideband LNA.

Fig. 8 shows the simulated NF characteristics of the proposed LNA. Over the entire desired band of operation , it has a NF of around 1.3dB .

Fig. 8. NF characteristics of the proposed wideband LNA.

IV. CONCLUSIONS The paper reports a wideband LNA to operate over a range

of 5 to 6 GHz band. A fabricated prototype had been tested and analyzed. A wideband DC bias network had been designed to operate for the desired wideband operation. The measured and simulated results are having a good approximation. The proposed LNA has a fair gain and noise figure over the entire operating band. This LNA is well suited for the applications like WLAN (5.2GHz), intelligent transportation system (5.9GHz) and point to point communication (6GHz).

2014 International Conference on Advances in Computing,Communications and Informatics (ICACCI) 787

ACKNOWLEDGMENT This work has been partially supported by CSIR India through its research grant No.22 (0622)/1 3/EMR-11.

REFERENCES

[1] P. Papadimitratos, A. Fortelle, K. Evenssen, R. Brignolo, and S.Cosenza, “Vehicular communication systems: enabling technologies,applications, and future outlook on intelligent transportation,” IEEE Commun. Mag., vol. 47, pp. 84–95, Nov. 2009.

[2] J. Luo, and J.-P. Hubaux, “A survey of inter-vehicle communication,” EPFL, Lausanne, Switzerland, Tech. Rep. IC/2004/24, 2004.

[3] R. A. Uzcategui, and G. Acosta-Marum, “WAVE: A tutorial,” IEEECommun. Mag., vol. 47, pp. 126–133, May 2009.

[4] Draft Amendment to Standard for Information Technology -Telecommunications and Information Exchange between Systems -Local and Metropolitan Area Networks - Specific Requirements – Part 11: Wireless LAN Medium Access Control (MAC) and Physical layer (PHY) Specifications - Amendment 7: Wireless Access in Vehicular Environment, IEEE Std. 802.11p/D3.0, 2007.

[5] Brijesh Iyer and N.P.Pathak, “A concurrent dual-band LNA for noninvasive vital sign detection system,” Microwave and Optical Technology Letters, vol. 56,no.2, pp. 391-394, Feb 2014.

[6] H.Sahoolizadeh, A.Kordalivand, and Z.Heidari, "Design and Simulation of Low Noise Amplifier Circuit for 5 GHz to 6 GHz," World Academy of Science, Engineering and Technology Vol:3,pp.91-94, 2009.

[7] G. Gonzalez, Microwave Transistors Amplifiers Analysis and Design, Prentice Hall, New Jersey, 1997.

[8] D.M.Pozar, Microwave Engineering-3rd Edition,Wiley India Pvt. Limited, 2007.

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