Proceedings of International Conference on Microwave - 08

A 18 - 40GHz Monolithic GaAs pHEMT Low NoiseAmplifier

T.Padmaja1, R. s. N'Gongo2

, Pummy Ratna1, P.S.Vasu1

, J.Subhash Babu1, V.S.R.Kirtyl

IAstra Microelectronic Technologies Ltd (AMTL), (MMIC Division of AMPL), Hyderabad­500069,India, 2 J&R Microwave Solutions Ltd., 31 Chemin du Boulodrome, 31200

Toulouse, France.E-mail: padmajat@astramtl.com;kirtV@astramtl.com

Abstract - This paper describes the design and measuredperformance of 18-40GHz MMIC Low noise amplifierdeveloped for mm-wave point to point, SATCOM, LMDS,VSAT and EW applications. A two stage amplifier hasbeen designed and developed on 4-001 thick InGaAspHEMT with a mature gate length of O.15pm low noiseprocess from the foundry, namely, WIN SemiconductorCorp., Taiwan. Two lange couplers were incorporated atthe RF input & output of the two stage amplifier. Thisbalanced topology enhanced the electrical specificationslike stability, return losses and the output power. Rigoroussensitivity checks and electromagnetic simulations werecarried at the design stage to ensure proper designcentering. The measured data shows better than 3.6 dB ofnoise figure with an associated gain of 11 ± O.5dB gainflatness. Excellent input/output return losses better than15dB and IdB compression more than 6dBm has beenachieved over the entire frequency band of 18 -40GHz. Thechip features a size of2.4mm x 2.1mm.Index Terms- Pseudomorphic High Electron MobilityTransistor (pHEMT), Low noise amplifier (LNA),Monolithic microwave integrated circuit (MMIC), andNoise figure (NF).

1. INTRODUCTION

The low noise amplifier is the key component inany front end receive chain, which dictates the dynamicrange of the receiver. Hence low cost and highperformance millimeter wave MMIC LNAs are requiredfor many system applications. More over marketpressures upon cost, size, functionality and powerconsumption make MMICs an attractive design solutionfor many applications. Furthermore, with systems andapplications evolving in the mm-wave spectrum, theinherent capabilities of MMICs make them the onlyrealistic choice. Low noise requirements in themillimeter wave frequencies are aggressive; also thebandwidth coverage in the commercially available chipsis limited, thereby encouraging the design of this wideband amplifier.

II. DESIGN DETAILS

The functional schematic diagram of the amplifieris shown in figure 1. Series feed back has been used tostabilize the device unconditionally over a widefrequency range of 0.1 to 50GHz. In the desiredfrequency band, sufficiently larger feedback forstabilizing can lead to reduction in the gainperformance, so resistive loading on the drain has been

978-1-4244-2690-4444/08/$25.00©2008 IEEE 309

used to stabilize the device. In order to obtain a low NFwith sufficient gain series inductive feedback is used oneither side of the device. Very low frequency stability istaken care by the resistors near the gate by providingDC return path for the device. A total gate periphery of400Jlm has been chosen to be the optimum size to meetall the specified requirements. The gain variations werecontrolled by input, interstage and output matchingnetworks. Input and output matching for the LNA weredictated by the Lange coupler characteristics. The LNAfeatures a self bias technique, with a typical drainvoltage of 4V consuming total drain current of 55 mAo

The broad band amplifier has been designed usingbalanced configuration approach for its advantages oversingle ended amplifier (1) improvement of 1 dBcompression point by 3 dB, (2) inherent 50 ohminput/output matching due to the coupler presence and(3) redundancy i.e. if one of amplifiers fails, thebalanced amplifier unit will still operate with reducedpower gain [1], [2].

LangeCoupler

Fig 1. Schematic diagram ofbalanced amplifierBalanced configuration helps in the improvement of

the gain flatness with relatively higher noise figure dueto the added coupler loss. To extract the bestperformance from this topology, 0.15Jlm pHEMTtechnology has been selected which offer low NFmin inthe operating band.

The balanced amplifier employs two Langecouplers. The Lange coupler was carefully designoptimized and EM simulated using SONNET EMSimulator. The designed coupler was centered at 32GHz covering a coupling bandwidth from 17 - 42GHzwith amplitude of -3.3 ± 0.8 dB. The isolated ports ofthe Lange coupler were terminated by on-chip 50 ohm

Proceedings of International Conference on Microwave - 08

resistors. The Lange coupler layout is as shown below infigure 2.

An Industry standard EDA tool AWR'sMicrowave Office (MWO) has been used for schematiclevel simulation .All the parasitics i.e. bond wires,external capacitors, impedance of interconnected linehave been considered in the simulation.

Input Return Loss

Frequency(GHz)

22 24 26 28 30 32

Frequency(GHz)

1 1 1 1 1 1 1 1 1 1- -t - -1- - -t - -1- - + - -1- - +- - -1- - r - -; - -

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18 20 22 24 26 28 30 32 34 36 38 40Frequency(GHz)

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- -I - -1- - -+ - -1- - + - -1- - +- - -1- - I- - -I - -1 I 1 1 1 1 1 1 I 1

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-30

-35

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E 12m~10m

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Fig.6 Measured performance of4 stage amplifiermodule

-30

-35

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18 20 22 24

3.6

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,1

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." ..~ ." ..~ ." ..~ -- -i .. .~ .. .~ .. +... -~ .. ~ ... +..-I 1 , 1 1 1 I 1 1 I

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1 I 1 I 1 1 I 11 , 1 , I 1 I I -Measured

2.0 +----+----+-+---+----+-+---+--i-+--+-----f

18 20 22 24 26 28 30 32 34 36 38 40

Frequency(GHz)

PIdB Vs Frequency

Noise Figure

-5

-10

-15iii"~20N

~-25

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310

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18 20 22 24 26 28 30 32 34 36 38 40Fre uen GHz

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t----------ll!l--------f$Ei

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IV. MEASURED PERFORMANCE

III. FABRICATION

The MMIC has been fabricated using 0.15JlmInGaAs pHEMT process available with WINSemiconductors, Taiwan. The chip features a size of2.4mm x 2.1 mm is as shown in figure 3 below.

The RF Characterization of the amplifier wasevaluated by using an on-wafer prober. Both DC and RFMeasurement characteristics show a good correlationwith the simulation in all respects i.e. small signal andlarge signal parameters. Comparison of measured andsimulated performances of S parameters, NF and PldBare shown in figure 4 below respectively.

Gain

Fig 2. Coupler layoutExtensive electromagnetic analysis has been carried

out to take in to account the effect of transmission linediscontinuities (especially for unusual geometries andfor those elements having a very critical influence onoverall performance), on-chip coupling using SONNETelectromagnetic design tool compatible with Microwaveoffice tool.

Proceedings of International Conference on Microwave - 08

A high gain module with 36 dB gain was realizedby cascading 4 stages. The slope obtained was betterthan ± 1.7 dB and return losses better than 12 dB. Thephotograph of module is as shown in figure 5 below andmeasured results are shown in figure 6. This MMIC isalso been used successfully in EDLVA applications.

V. CONCLUSION

A 18-40GHz balanced amplifier has beensuccessfully designed, fabricated and measured. With achip size of 2.4 mm x 2.1mm, this two-stage LNAachieved a small signal gain of 11 dB between 18 to40GHz, and a minimum of 3.6dB noise figure at19GHz. The device has all biasing, decoupling, inputand output matching networks on chip thus offering asimple and low cost amplifier solution. The chip isunique in offering a low noise figure. Simulated and

311

measured results compare very favorably over the entirefrequency band of interest.

ACKNOWLEDGMENT

Authors wish to thank Mr. B. MalIa Reddy, MD forthe approval in publishing this work and Mr. R.Ramanan for his encouragement throughout. We alsothank Mr. B.Raveendar for his support in the design andthe entire Assembly and Testing team of ASTRA fortheir technical support.

REFERENCES

[1] Application note ANO 108 Astra MicroelectronicTechnologies limited. (AMTL)

[2] Sanghyun Seo, Dimitris Pavlidis and Jeong-Sun Moon,"A Wideband Balanced AIGaN/GaN HEMT MMIC LowNoise Amplifier for Transceiver front-ends", 13th GASSSymposium-Paris, 2005, pp.225-228