ATTS: Active Load Pull System for ... - Maury Microwave

MAURY MICROWAVECORPORATIONProgettazione ad Alta FrequenzaPAFATTS: Active Load Pull System forCharacterization of Power DevicesA MAURY-PAF Joint Venture ProductBy Surinder Bali, Member, IEEE,and Professor Andrea Ferrero, Member, IEEE*MT925C - ATTS Head Assembly UnitsModel MT925B/C/D25 January 2001MT925B - ATTS Switch UnitUS and InternationalPatents Pending.IntroductionMT925C - ATTS Loop UnitThis document discusses some of the reasons forusing an Active Load Pull System in applicationswhich have certain primary engineering requirements.These requirements include the need to:• Pre-match the device under test (DUT) due tohigher magnitude of the DUT gamma• Maintain independent control of harmonics inphase and magnitude• Determine the DUT input reflectioncoefficient• Ensure the accuracy of the measured dataCurrently, there are two commercially offered hybridsolutions that meet these requirements—one, apassive system, and the other, an active system. Thepassive solution includes the use of harmonic tunerswhich incorporate resonant cavities. The two maindisadvantages of such tuners is their inability to tune*Professor Andrea Ferrero, Politecnico di Torino, Torino, Italythe frequency and magnitude of gamma and theirrelatively high insertion loss. The active solutionincludes an active module and has the tunerconnected in a loop which incorporates twocirculators. This configuration overcomes theinsertion loss problem, but is subject to oscillationsof the active loops without the flexibility of a vectornetwork analyzer (VNA) measuring system.This application note discusses the main advantagesof active load pull systems with emphasis on one inparticular; the Active Tuning Test Set (ATTS).Developed jointly by Maury Microwave Corporationand Progettazione ad Alta Frequenza (PAF). TheMaury/PAF ATTS uses a traditional VNA witha switching technology to sample the four DUTsignals. Optionally, a four-sample receiver can beused to speed up measurement. The system also hasthe option of using a time domain receiver (i.e.,Agilent’s Microwave Transition Analyzer, MTA) to2900 Inland Empire Blvd. • Ontario, California 91764-4804Tel: 909-987-4715 • Fax: 909-987-1112 • http://www.maurymw.comCopyright© 2000 Maury Microwave Inc., all rights reserved.application note 5C-046SPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICEPage 1 of 11

MAURY MICROWAVECORPORATIONload pull system based on active loops and a singleVNA (see “Large-Signal 2nd Harmonic On-WaferMesfet Characterization” 6 ). This system is the fatherof the current active load pull systems offered byPAF. The innovations they introduced were:1. Tuning the VNA (8510) at harmonic frequencyto measure the harmonic load and harmonicpower level.2. Use of a new on-wafer calibration for vectorerror correction of power (up to the on-waferreference plane) without disconnecting the probeand without an on-wafer power meter.3. The first harmonic active loop based on multipleloop configuration.• In 1992, using basically the same system at higherfrequency, Brian Hughes, Andrea Ferrero, and AlexCognata developed the first active harmonic systemable to reach millimeter wave frequencies (50 GHz).(See “Accurate On-Wafer Power and HarmonicMeasurements of MM-Wave Amplifiers andDevices” 7 .) This system is in use at Hewlett-PackardTechnological Division in Santa Rosa, California,and is still one of very few active load pull systemscapable of operating up to 50 GHz.In 1993, the on-wafer calibration math was firstpublished by Andrea Ferrero, Umberto Pisani andFerdinando Sanpietro (see “Small and Large SignalProgettazione ad Alta Frequenza17 July 2000PAFDevice Characterization Made Easier and Fasterwith an Integrated Test System” 8 ).It should be noted that all the work presented up tothis point was mainly research work and, althoughthe measurement system was fully automatic, theload movement was still manual.• In April of 1994, a definitive step-by-step methodfor effective active load pull systems was presentedby Andrea Ferrero, Ferdinando Sanpietro, UmbertoPisani, and Claudio Beccari (see “Novel Hardwareand Software Solutions for a Complete Linear andNonlinear Microwave Device Characterization” 9 ).In this method, the VNA directly controls the loadmovement, thus reaching a much higher speed of51 loads/100 ms. A then-new fitting procedure,especially designed for load pull systems, wasproposed.• At the IEEE Instrumentation and MeasurementTechnology Conference in 1996, a more accuratevariation of thru-reflect-load (TRL) calibration wasintroduced by Pisani and Ferrero. This technique isused in the current WINDOWS® NT softwareversion of PoliPull2000. Developed by Politecnicodi Torino, Italy, the PoliPull2000 software drivesPAF's Active Load Pull System, and allows for thecalibration of load pull and S-parameter measurementswith a unified and simple standardsequence (see “A Unified Calibration Algorithm forScattering and Load Pull Measurement” 10 ).7B. Hughes, A. Ferrero, and A. Cognata, “Accurate On-Wafer Power and Harmonic Measurements ofMM-Wave Amplifiers and Devices,” Digest, 1992 IEEE MTT-S International Microwave Symposium,Jun 1992, pp 1019–1022.8A. Ferrero, U. Pisani, and F. Sanpietro, “Small and Large Signal Device Characterization Made Easierand Faster with an Integrated Test System,” IMTC ‘93, Irvine, Jun 1993.9A. Ferrero, F. Sanpietro, U. Pisani, and Claudio Beccari, ”Novel Hardware and Software Solutions for aComplete Linear and Nonlinear Microwave Device Characterization,” IEEE Transactions On MicrowaveTheory And Techniques, Vol. MTT-22, No. 12, Dec 1974, pp 1146–1152.10U. Pisani and A. Ferrero, “A Unified Calibration Algorithm for Scattering and Load Pull Measurement,”Proceedings, IEEE Instrumentation and Measurement Technology Conference, Jun 1996, pp 1250–1253.11G. Madonna and A. Ferrero, “Simple Technique for Measuring Source Reflection Coefficient whileCharacterizing Active Devices,” Submitted for publication to IEEE Transactions On Microwave Theory AndTechniques, Nov 1999.2900 Inland Empire Blvd. • Ontario, California 91764-4804Tel: 909-987-4715 • Fax: 909-987-1112 • http://www.maurymw.comCopyright© 2000 Maury Microwave Inc., all rights reserved.application note 5C-046SPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICEPage 3 of 11

17 July 2000• In November of 1999, GianLuigi Madonna andAndrea Ferrero introduced a new real-timetechnique for obtaining the vector-correctedmeasurements of source impedance (see “SimpleTechnique for Measuring Source ReflectionCoefficient while Characterizing Active Devices” 11 ).This technique (available in PoliPull2000, version3) measures the source impedance without pumpingthe device from the back, as was previouslynecessary.Key Points of the Active Load PullSystem (ATTS)The remainder of this application note will discussthe key features of active load pull, with the focus onMaury/PAF active loop technology. These are:1. VECTOR ERROR CORRECTION guarantees anoverall accuracy level which is not comparablewith passive systems. The accuracy of a VNAbasedactive load pull system is of the sameorder of magnitude as that achieved in normalS-parameter measurements. (Both rely on thesame receiver and use the same error model.)2. ABSOLUTE POWER ACCURACY is higher withthe ATTS than with passive power meter-basedsystems. The VNA acts as a very narrow bandreceiver, without integration of harmonic powercontent, as occurs with passive systems. Poweris computed through a vector error correctionthus assuring better accuracy.3. SYSTEM CALIBRATION IS UNAFFECTED bychanges in the measurement setup outside thereflectometer plane, which means that the usercan change source or even load type withouthaving to remake the calibration.4. REAL TIME CAPABILITY means measured datainstantaneously reflects every change in the DUTas it occurs. In traditional passive systems, allvariables must be fixed in advance and deembeddingprocedures must be applied beforemeasurements are made.5. VNAs YIELD ADDITIONAL INFORMATION inan active load pull system, which is notcommonly available in passive systems. Forexample, the ratio of b2/a1 is measured inmagnitude and phase thus giving an accuratemeasurement of the AM/PM conversion effect.6. THE DUT INPUT REFLECTION COEFFICIENT isalso measured in real time in the active system.This yields fundamental inter-stage designinformation, such as conjugate matching sourceimpedance and changes in the DUT inputimpedance versus Load or Input Power.7. INCREASED EFFICIENCY results from therelatively high operating speed of the VNA,allowing active systems to operate considerablyfaster than passive systems, thus reducing thetime required to complete measurements.8. OBTAINABLE GAMMA IS SUPERIOR to thatachieved by other commercially availablesystems. A primary advantage of this system isthat Gamma is unaffected by the insertion loss ofprobes, fixtures, or any other device betweenthe tuner port and the DUT.9. PRE-MATCHING THE DEVICE IS UNNECESSARYsince the system attains a maximum Gamma of“unity.” In a passive system, pre-matchingtechniques are used to improve the reflectioncoefficient in some Smith Chart areas.However, these techniques are frequencydependent and require difficult tuner calibration.10. INDEPENDENT TUNABILITY OF HARMONICSis possible with this system (as with activeharmonic tuning systems). The active loops areeasily tuned to different frequencies and processthe various harmonic components of the signalso that no interference occurs betweenfundamental and harmonic loads. In a passivesystem, the permuted circuit adversely affectsthe harmonic capability of the harmonic tuner.With the active system, users are free to move onthe overall Smith Chart across each harmonic ina complete independent way.11. INSERTION LOSS IS MINIMAL becauseadditional instruments are not needed forharmonic applications. In passive systems, asmore harmonics are required (and, therefore,more passive harmonic tuners are added) moreinsertion loss is introduced into the setup. This,reduces the load reflection coefficient that canbe obtained at the DUT reference plane.5C-046 application noteSPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICEPage 4 of 112900 Inland Empire Blvd. • Ontario, California 91764-4804Tel: 909-987-4715 • Fax: 909-987-1112 • http://www.maurymw.com

MAURY MICROWAVECORPORATION12. NO “BOTTLENECK” EFFECT with this activeload pull system. Passive harmonic systemscommonly suffer from a “bottleneck” effect,generated near the Smith Chart edge, whichdrastically limits their effectiveness as harmonicinvestigation tools.13. EXCELLENT MEASUREMENT FREQUENCYFLEXIBILITY means the user simply changes themeasurement on the VNA to retune the load(i.e., change the YIG filter center frequency).Technical Description of Basic PAFSystems FeaturesACTIVE LOOPThe active load loop is the main feature of eachsystem. It is based on a high quality pin diodeattenuator, a tunable broadband YIG filter, and avariable mechanical phase shifter hosted inside ATTSunits, plus a power amplifier and a directional couplerwhich are generally external.Progettazione ad Alta Frequenza17 July 2000PAFA factor known as the “loop oscillation problem” isthe main reason users fear active loop systems. Afterseveral years of research to improve active loopperformance with regard to all the possible origins ofoscillations, we can affirm that Maury/PAF has thecorrect technology to keep the active loop absolutelystable up to higher reflection coefficients, irrespectiveof the DUT output Gamma. This has resulted in acareful proprietary design of the active loop and anultra fine electronic control of the YIG filter.Ideally, the system functions by simply forcing abackward wave, proportional to the incoming one,in order to compensate for all losses from the DUTreference plane and the loop coupler section. Theloop can be used to generate up to the unity reflectioncoefficient as a load or source tuner and has a typicalbroadband coverage (in GHz) of 0.5-4.5, 2-18, 18-40, 33-50, depending on the application. More thanone loop can be combined to provide harmonic loadcontrol as shown in figure 1. Each loop has a narrowband YIG filter inside which enables independentcontrol of the load at various frequencies.Figure 1. Harmonic Active Load Pull Setup using the ATTS Active Loop Technique2900 Inland Empire Blvd. • Ontario, California 91764-4804Tel: 909-987-4715 • Fax: 909-987-1112 • http://www.maurymw.comCopyright© 2000 Maury Microwave Inc., all rights reserved.application note 5C-046SPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICEPage 5 of 11

17 July 2000Measurement SystemThe system is based on a tradional VNA with aswitching technology to sample the four DUT signals.Optionally, a four-sample receiver can be used tospeed up the measurement. The system can also actas a time domain receiver (like the Agilent TransitionAnalyzer) for sampling time domain waveformes.Figure 2 shows a possible configuration of the ATTSwith two loops, but up to four loops can be combinedto provide independent harmonic control. Load pulldata are taken in real time and the vector errorcorrected as would be the case in an S-parametermeasurement system. The increased complexity ofthis system (compared to the traditional passive loadpull system) adds many advantages such astremendous degree of flexibility, real time measurementcapability, vector measurements and anaccurate calibration.CalibrationActive load pull systems are calibrated using atechnique similar to that used for calibrating ordinaryVNAs. It differs from passive load pull systemcalibration in that it is based on the insertion ofstandards in real time at the DUT reference planerather than on a pre-calibration of the tuner at all thetuner positions with de-embedding of fixtures, probes,etc. The user inserts typical two port standards (thruline-short)at the DUT reference planes and coaxialstandards at the output load plane. The errorcoefficients are computed from real time measurementsof the standard parameters using a modelalmost identical to that used for ordinary S-parametermeasurement.The system automatically acquires the followingquantities in real time at both the fundamental andharmonic frequencies.1. Load Reflection Coefficient2. Output Power3. Input Power4. Input Reflection Coefficient*5. Source Reflection Coefficient6. Gain7. Bias Data8. AM/PM Conversion Data (b2/a1 Waves inMagnitude and Phase)*9. Power Added Efficiency (PAE)10. IMD and ACPR Measurements (Requires anAdditional Spectrum Analyzer.)*Some data (e.g., DUT input reflection coefficient orAM/PM conversion data) are not available withpassive load pull systems, but are available withMaury/PAF or other VNA-based systems.Figure 2. Active Load Pull Setup using a VNA-Based System5C-046 application noteSPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICEPage 6 of 112900 Inland Empire Blvd. • Ontario, California 91764-4804Tel: 909-987-4715 • Fax: 909-987-1112 • http://www.maurymw.com

MAURY MICROWAVECORPORATIONMeasurement ExamplesFigures 3 through 7 (below and following) are someexamples of measurement results obtained with thePAF system. The data were taken at differentProgettazione ad Alta Frequenza17 July 2000PAFfrequencies from different devices made by fourdifferent manufacturers.Figure 3. IM3 contours at 18.0 GHz with POUT = 18 dBmFigure 4. PAE contours at 1 dB compression point, f = 18.0 GHz2900 Inland Empire Blvd. • Ontario, California 91764-4804Tel: 909-987-4715 • Fax: 909-987-1112 • http://www.maurymw.comCopyright© 2000 Maury Microwave Inc., all rights reserved.application note 5C-046SPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICEPage 7 of 11

17 July 2000Figure 5. PAE versus harmonic loading f1 = 4.0 GHz, f2 = 8.0 GHzFigure 6. Power Sweep at best load for POUT5C-046 application noteSPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICEPage 8 of 112900 Inland Empire Blvd. • Ontario, California 91764-4804Tel: 909-987-4715 • Fax: 909-987-1112 • http://www.maurymw.com

MAURY MICROWAVECORPORATIONProgettazione ad Alta Frequenza17 July 2000PAFFigure 7. Example of a power sweep with constant load and corresponding measured Gamma-In(see the absolute stability of the load).MT925C - ATTS Head Assembly UnitsMT925B - ATTS Switch UnitMT925C - ATTS Loop Unit2900 Inland Empire Blvd. • Ontario, California 91764-4804Tel: 909-987-4715 • Fax: 909-987-1112 • http://www.maurymw.comCopyright© 2000 Maury Microwave Inc., all rights reserved.application note 5C-046SPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICEPage 9 of 11

17 July 2000ATTS – ACTIVE LOAD PULL SYSTEM SETUPTwo-loop ATTSFour-loop ATTS5C-046 application noteSPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICEPage 10 of 112900 Inland Empire Blvd. • Ontario, California 91764-4804Tel: 909-987-4715 • Fax: 909-987-1112 • http://www.maurymw.com

MAURY MICROWAVECORPORATIONConclusions• Load pull measurement is an effective designtechnique for optimizing the performance of poweramplifiers in terms of their output power, powerefficiency, linearity, etc.• Active systems provide highly accurate characterizationsin real time, at higher matching ranges,and with independent control of harmonics andgamma-In capability• Passive systems are more economical but providereduced matching range at high frequenciesReferences1. A. Ferrero and U. Pisani, ”Large Signal 2ndHarmonic On-Wafer Mesfet Characterization,”36th ARFTG Conference Digest, Monterey,November 19902. A. Ferrero, B. Hughes and A. Cognata, ”Accurateon-wafer power and harmonic measurements ofmm-wave amplifiers and devices,” IEEE MTT-SDigest, pp. 1019-1022, Albuquerque 1992.3. A. Ferrero, U. Pisani and F. Sanpietro, ”Smalland Large Signal device characterization madeeasier and faster with an integrated test system,”IMTC ’93, Irvine, June 1993.4. A. Ferrero and U. Pisani, ”An improvedcalibration technique for on-wafer large signaltransistor characterization,” IEEE Trans. onInstrumentation and Measurements, Vol. IM-42,No. 2, April 1993.5. A. Ferrero, U. Pisani and F. Sanpietro, ”Anintegrated high speed microwave test set forlinear and non-linear device characterization,”Asia Pacific Microwave Conference, 18-21October, Taiwan, 1993.6 A. Ferrero, U. Pisani and F. Sanpietro, ”NovelHardware and Software Solutions for a CompleteLinear and Non-linear Microwave DeviceCharacterisation," IEEE Trans. on Instrumentationand Measurements, Vol. 43, No. 2, April 19947. A. Ferrero, U. Pisani and GianLuigi Madonna,"Recent Technological Advances For ModularActive Harmonic Load-Pull MeasurementSystems," International Conference GAAS 1999.Progettazione ad Alta Frequenza177 July 2000The AuthorsPAFSurinder Bali holdsa B.S. degree in Electricaland Electronic Engineeringfrom Leeds Universityand a M.S. degree fromUniversity College London,England . He joined G.E.C.Research Centre, Chelmsford,UK, as a Research Scientistworking on components andsubsystems for frequenciesup to 110 GHz. He later joined Raytheon Systems, inHarlow, UK, as a Principal Engineer. He later worked forCastle Microwave (UK) and Focus Microwaves, Inc.(Canada) as a Technical Sales Manager. He joined MauryMicrowave Corp. in January (2000) and currently serves asMaury’s International Sales Manager, which includesresponsibility for the Maury Automated Tuner System(ATS) and the Maury/PAF ATTS.Andrea Ferrero holds aB.S. degree (1987) andPh.D. (1992) in ElectronicEngineering from Politecnicodi Torino, Italy. In1988 he joined Aeritalia asa microwave consultant. In1991, he began a periodof research at Hewlett-Packard’s Microwave TechnologyDivision, in SantaRosa, California. He iscurrently a Professor in theElectronics Department ofPolitecnico di Torino. In parallel, he is a technicalsupervisor of PAF, Progettazione ad Alta Frequenza (acompany he helped establish in 1996), where he worksprimarily with Active Load Pull Systems development andprovides technical support in the field of devicecharacterization techniques. In 1998 PAF launched itsfirst commercially available Active Load Pull System(ATTS), and in June, 2000, began a joint venture withMaury Microwave to manufacture and market the ATTSworldwide. Professor Ferrero is the author of more than 50papers on microwave measurement techniques.Contact Informationa. Surinder Bali: Tel: 909-987-4715 ext. 226;Fax: 909-987-1112; or e-mail: sbali@maurymw.comb. Prof. Andrea Ferrero: e-mail: andreapierenrico.ferrero@tin.it2900 Inland Empire Blvd. • Ontario, California 91764-4804Tel: 909-987-4715 • Fax: 909-987-1112 • http://www.maurymw.comCopyright© 2000 Maury Microwave Inc., all rights reserved.application note 5C-046SPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICEPage 11 of 11