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2004 RF AND MICROWAVE CONFER ENCE, OCTOBER 5 - 6, SUBANG, SELANGOR, MALAYSIA

Low Noise A mplifier Circuit Design for 5 GHz to 6 GHz

Mohd. Zoinol Abidin Abd Aziz, Jafri B. Din, Mohd. Kamal A. Rahim

Wireless Communication Center,Faculty of Electrical Engineering,

Universiti Teknologi Malaysia,81300Skudai, Johor, Malaysia.

Abstract--The development of wireless portableelectronics is moving towards smaller and lighterdevices. Although low noise amplifier (LNA)performance was extremely good nowadays, thedesign engineer still had to make some complexsystem trades. Many LNA were large, heavyand consumed a lot of power. The design of anLNA in Radio Frequency (RF) circuits requiresthe trade-off of many importance characteristicssuch as gain, noise figure (NF), stability, powerconsum ption and complex ity. This situationforces designers to make choices in the design ofRF circuits. The designed simulation process isdone using Advance Design System (ADS),while FR4 strip board is used for fabricationpurposed. A single stage LNA has successfullydesigned with 7.78 d B forward gain and 1.53 dBnoise figure, which stable along the UN11frequency band.1. I n t r oduc t i on

Based on S parameters of the transistorand certain performance requirements, asystematic procedure is developed for the designof LNA. To ensure the designed circuit fulfilsperformance requirement and could be install asa practical component in the future, one of themost popular standard followed by the marketproducts, which is developed by Institute ofElectrical and Electronic Engineering (IEEE), istaken as the major requirement that designedcircuit should achieve. In LNA design, themost important factors are low noise, moderategain, matching and stability. Besides thosefactors, power consumption and layout designsize also need to be considered in designedworks.

0-7803-8671-X/04/$20.00 02004 IEEE

2. DC Bias ingIn order to design a low noise device, thetransistor should be biased such that theminimum noise figure is as ow as possible. Thedevice width should be chosen so that theoptimum resistance is close to the drivingresistance which typically 50 R. The minimumnoise figure is independent of the device width.

I n order to keep low minimum noise figure, thecutoff frequency of the device should be muchhigher than the operating frequency [I].For this project, the DC biasing circuitas shown in Figure I above, has been choose asDC biasing network. Thus, a bipolar source isneeded to operate the transistor. Negativevoltages need to be applied at the gate terminal.The gate voltage is then adjusted for the desiredvalue of drain current [Z]. Transistor needbiasing point at Vd (drain voltage) =4 V and Id.(drain-source current) =40 mA. This biasingpoint is obtained by using a V (Gate voltage)range from -0.6 V to -0 .4 V as shown in I-Vcurves found in the datasheet [Z].

v g - - 2 vVd.5V VdhFigure 1: basic dc biasing network.

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In order to keep the DC source isolatedfrom the AC signals, radial stubs will beimplemented as shown in Figure 2. Radial stubhas low impedance at lower frequencies howeverit generates high impedance at a higherfrequency. The input impedance of radial stub ismore consistent and suitable for broadbandapplication. The effect of quarter-wavemicrostrip line is cancelled by a quarter-waveradial stub reactance [3][4][5].

Figure 2: DC biasing network with applicationof radial stubs.2.1 Single Stage Amplif ierA single stage microwave transistor amplifiercan be modeled by the circuit in Figure 3, wherea matching network is used both sides of thetransistor to transform the input and outputimpedance Za to the source and load impedanceZs nd ZL. he most useful gain definition foramplifier design is the transducer power gain,which accounts both source and load mismatch.Thus from 161, can be define separate effectivegain factors for the input (source) matchingnetwork, the transistor itself and the output(load) matching network as follow:

n ra ru r,Figure 3: The general transistor amplifier circuit.

Then the overall transducer gain is GT=GsGoGL.he effective gains from G s and GL aredue to the impedance matching of the transistorto the impedance%.

2 .2 St a b i li t y Cons i de r a t i onAnother important consideration inamplifier design is stability. In he circuit Figure

4,oscillation is possible if either the input oroutput port impedance has a negative real part.This would imply that lrinl 1 or Ir,J > I .These because of r;. and r,, depend on thesource and load matching network s. While, thestability of the amplifier depends on and rL spresented by the matching networks.

Figure 4: A lossless network matching networksarbitrary load impedance to a transmission line.Alternatively, it can be shown that theamplifier will be unconditionally stable if thefollowing necessary and sufficient conditions aremet:

1 - l&12 - P 2 2 I 2 +1AI2 (4)K =*ls,2s2,

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The cascode amplifiers are oflenapplied in higher frequency circuits because theeffective capacitance at the input is reduced.Besides, it provides a high reverse isolation andthus ensures stability. A high reverse isolationof LNA is important for the sak e of avoiding LOpower leakage through the LNA to the antennathus causing interference [7][8].3. M a t c h i n g N e t w o r k

The basic idea of impedance matching isillustrated in Figure 4, which shows animpedance matching network placed between aload imped ance and transmission line. Thematching network is ideally lossless to avoidunnecessary loss power and is usually designedso that looking into the matching network is ZThen reflections are eliminated on thetransmission line to the left of the matchingnetwork, although there will be reflectionsbetween matching network and the load.Impedance matching is important for themaximum power delivered to the load,As long as the load impedance, Z,, has somenonzero real part, a matching network canalways be found. Several types of matchingnetwork are available, however factors likescomplexity, bandwidth, implementation andadjustability need to be considered in thematching network selection. The quarterwavetransformer matching network is choose in thisdesigned as showed in Figure 5 .

4. N oi se F i gu r e S i m u l a t i on Re s u l tThe lowest noise figure is needed inorder to achieve the maximum gain. Figure 6shows the minimum noise figure plot. Thehighest Fm,,, .527 dB is obtained at frequency 6GHz. While lowest F,,

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7.78 dB gain and 1.509 dB noise figure atfrequency 5GHz to 6GHz.

7. Future WorkThe LNA have been designed by usingsingle stage m ethod. In the future, cascade stagedesign method can be implement, whichproduces higher gain and low powerconsumption. This method will increase theLNA gain with an acc eptable noise figure. Othermatching network such as series stub is alsosimple and easier to design. Different type oftransisto r, which has h igher forward gain andlower noise at the selected frequency if used, willyields better result. The LNA design also can beintegrate with WLAN transceiver later, which isunder development at WCC .

ReferencesE. Abou-Allam, T. Manku (1998). ALow Voltage Design Technique For LowNoise RF Integrated Circuits,Proceedings of the 1998 lEEElnternational Symposium on Circuits andSystems, ISCAS 98, Volume: 4,3 1 May-3 June 1998.373 - 77 .Agilent Technologies (2000).Application Note 1190 - Low NoiseAmplifier for 900 MHz using the AgilentATF-34143 Low Noise PHEMT, USA:Agilent Technologies. 1-8.Sorrento, R. and Roselli, L. (1992). ANew Simp le And Accurate Formula For

Microstrip Radial Stub, Microwave andGuided Wave Letters, IEEE, Volume: 2Issue: 12, December 1992.480 -482.[4] Giann ini, F.; Sorren tino, R.; Vrba, 1.(1984). Planar Circuit Analysis ofMicro strip Rad ial Stub, Micro waveSymposium DigesS MTT-S International,Volume: 84 Issue: 1, May 1984. 124 ~125.

[ 5] Yuan Ning; Liang Changhong; NieXiaochun. (1999). A New Kind ofPracticable Microstrip Stub.Computational Electromagnetic and It sApplications. Proceedings. (ICCEA 99)1999 International Conference on, 1999.398 -401.D.M. Pozar (2000). I Microwave and RFWireless System, United States ofAmerica: John Wiley and Sons Inc. 77-97,205-207.P. Sungkyung and K. Wonchan (2001).Design of A 1.8 GH z Low-noiseAmplifier For RF Front-end In A 0.8umCMOS Technology, IEEE Transactionson Consumer Electronics, Volume: 47Issue: I ,Feb20 01. 10-15.Kuei-Ann Wen, Wen-Shen Wuen, Guo-Wei Huang, Liang-Po Chen, Kuang-YuChen, Shen-Fong LIU, Zhe-Sheng Chen,Chun-Yen Chang (2000). CMOS RFIC:Application to Wireless TransceiverDesign, IEICE T rans. Electron, Volume:E83-C, 2 Feb 2000. 131- 142.[9] Agilent Technologies (2002). 08720-40392 - Users Guide: AgilentTechnologies 8722ES NetworkAnalyzer, USA: Agilent Technologies.

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Figure 5 : Input and oulpul matching network schem atic

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