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COVER STORY|

Flexible Software-defined Test Instruments

Today’s rapidly changing development environments demand flexibility in all aspects

of design. The next generation of software-defined test instruments are a key element in cost control, time to market, design flexibility

and standards evolution.|By Greg Jue

There are many challenges inaddressing instrumentationneeds for emerging communi-cations signal formats. Time-to-market pressure drives R&Ddevelopment to begin beforethe wireless standards havebeen finalized. This, in turn,

drives demand for early R&D test instru-mentation solutions for the given wire-less standard, while providing the flexi-bility to accommodate changes in the sig-nal format as the standard evolves.

Similarly, the custom/proprietarynature of aerospace/defense applica-tions requires instrumentation solu-tions to generate and analyze cus-tom/proprietary signals. Typically, thismight be provided in the form of cus-tom test equipment designed for a par-ticular application. While custom testequipment may provide a unique solu-tion, it may also be limited in terms offlexibility to adapt to changes in thesignal format. Additionally, it may beexpensive to develop initially, andtime-consuming and expensive to mod-ify for different signal formats orapplications. For these reasons, it may

be desirable to use off-the-shelf testequipment and leverage the flexibilityof software to create and analyze thecustom/proprietary signals.

This article demonstrates a novelapproach for providing flexible soft-

ware-defined instrumentation solutionsusing the design software runninginside the test equipment to addressemerging communications signal for-mats and aerospace/defense R&Dapplications. Several examples are

GLOSSARY OF ACRONYMS

ADS — Advanced Design System

ARB — Arbitrary Waveform Generator

BER — Bit Error Rate

DUT — Device Under Test

EDA — Electronic Design Automation

EVM — Error Vector Magnitude

I/Q — In-phase and Quadrature

IP — Intellectual Property

OFDM — Orthogonal Frequency DivisionMultiplexing

POD — Probability Of Detection

R&D — Research and Development

UWB — Ultra-Wideband

Illustration by Roy Scott

Figure 1. Conceptual design and verification flow using design software inside of instruments.

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Software-defined Instrumentation Applications

Using the design software or similarsoftware inside the instruments allowsdesigners to create software-definedinstrument applications and also offersmany benefits in terms of a design andverification flow.

Typically, a design and verificationflow begins with an EDA solution used toput together the system and circuitdesigns. At this stage of the design flow,test equipment is not yet involved since itis still a design-only phase. Simulationsignal sources and signal measurementsare used in the software to begin designingthe system and circuits. For emerging

shown with the design software runninginside an ARB, to provide a flexible sig-nal source capability, and runninginside an oscilloscope, to provide aflexible signal analysis capability.Specifically, an emerging communica-tions signal format example is shownfor an UWB EVM measurement. Inaddition, an aerospace/defense examplealso is shown for a linear FM chirpedradar POD measurement. While quitedifferent, both examples will utilize thesame off-the-shelf test equipment setupand leverage the flexibility of thedesign software running inside theinstrumentation to provide the uniqueapplication solution.

communications signal format applica-tions (like UWB), these signal sources andmeasurements could be available as pre-defined simulation test benches, which arepre-configured to perform key simulationmeasurements such as EVM and BER. Foraerospace/defense applications, nativebehavioral models in the software couldbe used as building blocks to constructcustom/proprietary simulation signalsources and measurements so that the sys-tem and circuit design phase can begin.

When the design phase is complete andDUT hardware returns from fabrication,early R&D verification testing can begin.If off-the-shelf instrumentation solutionsare not readily available for the givenemerging communications signal format,then the software can be combined withtest instrumentation to provide an earlyR&D test solution. Likewise, for aero-space/defense applications, custom/pro-prietary signals may not be offered as off-the-shelf test solutions. In these instances,it may also be useful to combine the soft-ware with test instrumentation to createcustom R&D test solutions.

There have been numerous publica-tions written on concepts like Connected

Solutions to extend the instrumentation’sfunctionality for R&D applications.1-11

Most of the work-to-date has been imple-mented in the form of an external PC(such as a laptop) connected to the testinstrumentation to perform the signalgeneration and signal analysis. This hasenabled measurements such as codedBER to be performed for R&D applica-tions by extending the instruments’ capa-bility with the software.

However, once the Connected Solutionhas been created, the designer might takethis a step further by installing the designsoftware inside the instrument solution.This is somewhat dependent on theinstrument platform, and whether it cansupport installing and running the designsoftware or similar software. After thesoftware is installed on the instrument, itmight also be configured to run the meas-urement automatically by pressing a but-ton on the instrument’s front panel or bypressing a button in the instrument’sapplication software. This effectively cre-ates a software-defined instrument, usingthe design software to define the signalsource and measurement.

Thus, a design and verification flowfrom a pure design phase to an R&D testphase might conceptually look likeFigure 1. The signal analyzer might beused to generate the test signal in addi-tion to analyzing the measured signal byusing the instrument links available in thedesign software.

Note that this flow helps to bridge thedesign and test phases for a more seamlesstransition, leveraging IP developed in thedesign phase directly into the test phase byusing design software inside the instru-mentation. This IP can be in the form ofsignal sources and measurements foremerging communications signal formats,custom/proprietary signal sources andmeasurements for aerospace/defense, oreven simulated system and circuit design IPmodeled in the design software. Bridgingthe gap between the design and the testphase helps eliminate duplication in creat-ing IP for the design phase and then laterre-creating similar IP for the test phase. Inaddition, because design software is flexi-ble, it can be modified to accommodatechanges as an emerging signal formatevolves or to model different signal scenar-ios for aerospace/defense applications,such as interferers or jammers.

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Figure 2. Software-defined instrument conceptual flow diagram.

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examples shown in this article, a cable con-nects the vector signal generator’s output tothe oscilloscope’s input (no DUT).

The actual test setup is shown in Figure 3, with the wide bandwidth ARB inthe upper right-hand corner, the high fre-quency vector signal generator with widebandwidth I/Q inputs in the lower left-hand corner, and the high-speed oscillo-scope in the upper left-hand corner. Ahigh-frequency spectrum analyzer is alsoshown in the lower right-hand corner,which was used to measure the spectralflatness of the OFDM UWB spectrum.

The wide-bandwidth ARB utilizes anembedded controller, which was used toinstall the design software for I/Q signalgeneration directly in the ARB.

The high-speed oscilloscope also hasthe design software installed on it to pro-vide the software-defined UWB EVMmeasurement. The EVM measurementcan be initiated by either pressing a but-ton on the front panel of the oscilloscopeor by pressing a button on a vector signalanalyzer software application running inthe oscilloscope as shown in Figure 4.

The next section examines an emerg-ing communications signal format exam-ple and an aerospace/defense examplethat both use the capability describedabove. While these two examples arequite different, they both use the sameoff-the-shelf test equipment setup, withthe design software providing the uniqueapplication solution capability.

Emerging Communications Signal Example: UWB

This first example illustrates how thiscapability can be used to address theneeds of an emerging communicationssignal format.11 To create the software-defined instrumentation solution to usefor early R&D verification testing, thedesign software is combined with a wide-bandwidth ARB, a high-frequency vectorsignal generator with wideband I/Qinputs and a high-speed oscilloscope. Thebasic flow is shown in Figure 2.

To generate the OFDM UWB test sig-nal, the design software is used to createsimulated UWB I/Q data. The resultingI/Q data is then downloaded to the widebandwidth ARB. The I/Q waveforms arethen input into the wideband I/Q inputsof the high frequency vector signal gen-erator and modulated onto the carrier.Note that frequency-hopping is disabledfor this example.

The design software, combined withthe wide-bandwidth ARB and signalgenerator, represents the software-defined OFDM UWB signal source thatcould be used for DUT testing.

For the OFDM UWB EVM measure-ment, the vector signal generator’s outputis captured by the high-speed oscilloscopeand transferred into the design softwarefor the EVM measurement post-process-ing. The oscilloscope with the design soft-ware represents the software-definedOFDM UWB signal analyzer that couldbe used for DUT testing. Note that for the

The test setup and measurement canbe configured for either an RF EVM orfor a baseband I/Q EVM measurement.

Note: It is important to realize that thiscapability is not a real-time measurement,since it relies on the measured data to becaptured and transferred into the designsoftware, and the simulation measurementto be completed in the instrument.

Aerospace/Defense Example: LFM Chirped Radar

To illustrate the flexibility of usingsoftware for the signal generation andsignal analysis, the same instrumentationtest setup is used to create and analyze acustom linear FM chirped radar signal.The conceptual signal flow is the same asthat shown in Figure 2 and the test setupis the same as Figure 3.

To create the software-defined radarsignal source, the simulation schematic inFigure 5 is simulated on the wide-band-width ARB’s embedded controller. 12

The custom baseband linear FMchirped radar source is shown at the farleft of the simulation signal source

schematic. It is constructed with nativebehavioral models in the design software.The models are then used as buildingblocks to define and create the signal.

To perform the custom software-defined radar signal analysis, the radarsystem, including the transmit/receiveswitch, path models, target model, receiv-er and chirp post-processor, is simulatedinside the high-speed oscilloscope.

The measured signal from the vectorsignal generator’s output is captured withthe oscilloscope and then read into thedesign software for simulation post-pro-cessing. It is passed through a simulatedtransmit/receive switch and propagationpath model. A target model simulates theeffective radar cross-section, and thereflected signal is passed through a returnpropagation path model and input into asimulated receiver for down-conversionand post-processing. A custom POD sim-ulation measurement is then performed tocalculate the POD, which is dependent onboth the target distance and the effectiveradar cross-section of the target. The sim-ulated target distance and target’s effectiveradar cross-section can be varied while thesimulation is running on the oscilloscope.

Figure 7. Software-defined radar measure-ment with the oscilloscope.

Figure 3. Software-defined instrument testsetup.

Figure 4. Software-defined UWB EVM meas-urement.

Figure 5. The design software schematic: software-defined custom radar signal source usingwide-bandwidth ARB.

Figure 6. The design software schematic: software-defined custom radar analysis using anoscilloscope.

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instrumentation solutions using thedesign software running inside the testequipment to address emerging commu-nications signal formats andaerospace/defense R&D applications. AnOFDM UWB EVM measurement wasshown as an emerging communicationssignal format example. Using the sameequipment setup, the software-definedsignal source and signal analyzer wasreconfigured for a linear FM chirpedradar example to illustrate an aerospace/

Again, it is important to note that this isnot a real-time measurement.

The custom software-defined radarmeasurement on the high-speed oscillo-scope is shown in Figure 7. Note that themeasurement being displayed is from aprerecorded measured signal.

SummaryThe early prototype work shown in

this article illustrates a novel approachfor providing flexible software-defined

defense application.Using the design software inside the

test instrumentation to create software-defined instruments offers the benefit ofleveraging IP from the design phasedirectly into instruments to help bridgethe gap between design and test, whileproviding flexibility to address emergingcommunications signal formats and aero-space/defense R&D applications

AcknowledgmentsThe author would like to recognize TakahisaYamaguchi, Kengo Tanaka and Mikio Morishita ofAgilent Technologies for their contributions to theUWB example. The author would also like to recognize David Leissof Agilent Technologies for his contributions to theradar example.

About the AuthorGreg Jue is a communications system application spe-cialist with Agilent EEsof EDA. He is the product manag-er for the design software 3GPP W-CDMA designlibrary, and has helped to pioneer combining designand test solutions at Agilent Technologies as an applica-tions technical lead. He has authored numerous arti-cles, presentations and application notes, including thepopular Application Note 1394 on Connected Solutions,and most recently co-authored the new Logic AnalyzerConnected Solutions Application Note 1471. Greg creat-ed the the design software 3GPP W-CDMA course andthe design software Communications System Designcourse, and has taught numerous RF circuit design,communication system design and 3GPP W-CDMAdesign courses using the design software. Before join-ing Agilent in 1995, he worked on system design forthe Deep Space Network at the Jet PropulsionLaboratory/Caltech University.

WD&D

References and Additional Reading1. G. Jue, “Accelerating the Design

and Verification Process,” RF DesignMagazine, Aug. 2004. http://rfde-sign.com/mag/radio_accelerating_design_verification/

2. G. Jue and S. Ferguson, “RF AndDigital Tests Unite Against BER,”Wireless Systems Design Magazine,Nov. 2004,http://www.wsdmag.com/Articles/ArticleID/9272/9272.html

3. “RF/IF-To-Digital ConnectedSolutions Bit Error Rate Using theAdvanced Design System,” Agilent

Technologies, Application NoteNumber 1471, http://literature.agi-lent.com/litweb/pdf/5989-0024EN.pdf

4. “Connected Simulation and TestSolutions Using the AdvancedDesign System,” AgilentTechnologies, Application NoteNumber 1394, http://literature.agi-lent.com/litweb/pdf/5988-6044EN.pdf

5. J. Dunsmore, G. Jue and J. Kikuchi,“A Measurement-Based BehavioralModel for I/Q RF Modulators,”Microwave Journal, Dec. 2002, pp.82-88, http://www.mwjournal.com/default.asp?journalid=1&func=arti-cles&page=0212m44&year=2002&month=12

6. G. Jue, “3GPP W-CDMA Systems:Design and Test,” IEEE MicrowaveMagazine, June 2002, pp 56-64,http://ieeexplore.ieee.org/iel5/6668/21676/01004052.pdf?isNumber=21676&prod=JNL&arnum-ber=1004052&arSt=56&ared=64&arAuthor=Jue%2C+G

7. B. Zarlingo, K. Kalbasi and G. Jue,“Flexible DigitalDemodulation/Integrating SimulationSoftware with MeasurementHardware,” IEEE Autotestcon 2002.

8. G. Jue, M. Iglesias, “W-CDMASystem Design and Verification withEDA and Test Equipment,”NetSeminar™ http://www.netsemi-nar.com/nss/showSeminar?sem_num=614, April 2002

9. A. Amini, “Advanced WLANReceiver Testing eSeminar,”http://eesof.tm.agilent.com/news/news400.html#wlan_e_seminar

10.C. Ajluni, “Offering Merges Designand Test,” Wireless Systems Designcover feature, October 2002,http://www.wsdmag.com/Issues/IssueID/239/239.html

11.P. Cain, “Make UltrawidebandOFDM Transmitter Measurements,”Microwaves & RF Magazine, May2005, http://www.mwrf.com/Articles/Index.cfm?ArticleID=10313

12.D. Leiss, “Combined Virtual andPhysical Hardware PerformanceAnalysis,” IEEE Autotestcon 2002,http://eesof.tm.agilent.com/pdf/leiss0210.pdf

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