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Wideband Characterization of Power Amplifiers Using Undersampling
KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
Center for RF Measurement Technology, Univeristy of Gävle.
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2009 (English)In: 2009 IEEE MTT-S International Microwave Symposium Digest, 2009, 1365-1368 p.Conference paper, Published paper (Refereed)
Abstract [en]

In this paper a radio frequency power amplifier is measured and characterized by the use of undersampling based on the generalized Zhu-Frank sampling theorem. A test system has been designed allowing the bandwidth of the stimuli signal to be 100 MHz in the characterization process. That would not be possible with any vector signal analyzer on the market. One of the more challenging problem within the proposed concept is the model validation process. Here, two different techniques for model validation are proposed, the multitone and the spectrum scan validation methods.

Place, publisher, year, edition, pages
2009. 1365-1368 p.
Series
IEEE MTT-S International Microwave Symposium, ISSN 0149-645X ; Vols 1-3
Keyword [en]
Communication system performance, modeling, nonlinear systems, power amplifiers, radio transmitters
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-11674DOI: 10.1109/MWSYM.2009.5165959ISI: 000273507400343Scopus ID: 2-s2.0-70450273349ISBN: 978-1-4244-2803-8 (print)OAI: oai:DiVA.org:kth-11674DiVA: diva2:279199
Conference
2009 IEEE MTT-S International Microwave Symposium, IMS 2009; Boston, MA; United States; 7 June 2009 through 12 June 2009
Note

QC 20150713

Available from: 2009-12-02 Created: 2009-12-02 Last updated: 2015-07-13Bibliographically approved
In thesis
1. On Radio Frequency Behavioral Modeling: Measurement Techniques, Devices and Validation Aspects
Open this publication in new window or tab >>On Radio Frequency Behavioral Modeling: Measurement Techniques, Devices and Validation Aspects
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [sv]

Effektförstärkare för radiofrekvensapplikationer utgör fortfarande ett av de största problemen i trådlösa kommunikationssystem. Detta beror på att dessa förstärkare är ickelinjära, har låg energieffektivitet och ger mycket distortioner. Bättre verktyg för att förstå och korrigera dessa beteenden är nödvändiga. Ett sådant verktyg är beteendemodellering. En beteendemodell kan ses som en svart låda med insignal(er) och utsignal(er). In detta fall är dessa signaler samplade basbandssignaler och den svarta lådan är en matematisk relation mellan en insignal och en utsignal.

Avhandlingen behandlar några krav för beteendemodellering av nämnda system genom att presentera metoder för utvärdering och förbättring av modellernas prestanda. Detta åstadkoms genom att betrakta ett frekvensviktat felkriterium. Ett högpresterande mätsystem är också nödvändigt för experimenten. Prestandan hos det tillgängliga systemet jämförs med prestandan hos ett allmänt erkänt mätsystem, en s.k. storsignalsnätverksanalysator, genom att betrakta prestandan hos beteendemodellerna som extraheras och valideras med data från respektive mätsystem. Resultatet visar att det existerande mätsystemet har god prestanda.

Ett stort problem vid beteendemodellering är att kunna sampla med tillräckligt hög hastighet. Genom att använda Zhu-Franks generaliserade samplingsteorem vid beteendemodellering kan en del av detta problem undvikas. Teoremet medför att man kan sampla med en väsentligt lägre samlingsfrekvens än vad Nyquistteoremet säger. Modeller extraheras och prestandan utvärderas genom att använda kriteriet normalized mean square error (NMSE).

För stabil prediktion och korrektion av utsignalen måste robustheten hos de använda modellerna verifieras. En sådan studie som berör robustheten mot variationer i lastimpedansen har genomförts. Prestandan på direkta modeller försämras med 7 dB mätt som adjacent channel error power ratio (ACEPR). Prestanda på inversmodellen, implementerad som digital predistortion, försämras med upp till 13 dB mätt som adjacent channel power ratio (ACPR).

Abstract [en]

Radio frequency (RF) power amplifiers (PA) are still the most troublesomepart of a wireless system due to their inherent nonlinearity, low powerefficiency and high distortions. Better tools are needed to understand and correct the undesirable behavior. Some of these tools are behavioral models. A behavioral model is often thought of as a black box with some inputs andsome outputs. In the case here these inputs are sampled signals which meansthat the modeling amounts to finding a mathematical relationship betweenthe input signal(s) and the output signal(s).

This thesis considers some requirements for behavioral modeling of said systems by presenting methods for general performance evaluation and improvement by considering a frequency weighted error criterion.

A high performance measurement system is also needed. The performance of the available system is compared to the performance of a well recognized system, the largesignal network analyzer (LSNA). The results show that the existing measurementsystem can extract behavioral models with the same performance as the LSNA and can give lower performance validation errors.

Still the need for higher bandwidths drives the measurement systems to the limits, especially the digital parts. By utilizing the so called Zhu-Frank generalized sampling theorem, behavioral modeling of a PA is done by using data acquired at a sampling rate lower than the Nyquist rate. Models of a PA are extracted and the performance is evaluated using the normalized meansquare error (NMSE) criterion. For prediction and correction of the output signals the stability of the models regarding changes must be investigated. One such study considering controlled variations on the output load of the PA is done and both the predictive and corrective capabilities of the models are evaluated. The predictive capability gets up to 7 dB worse measured as adjacent channel error powerratio (ACEPR) and the corrective, as digital predistortion, gets up to 13 dB worse measured as adjacent channel power ratio (ACPR).

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. vi, 65 p.
Series
Trita-EE, ISSN 1653-5146 ; 2009:056
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-11678 (URN)978-91-7415-526-6 (ISBN)
Presentation
2009-12-10, Hörsal 99131, Högskolan i Gävle, Kungsbäcksvägen 47, Gävle, 10:00 (English)
Opponent
Supervisors
Available from: 2009-12-09 Created: 2009-12-02 Last updated: 2010-10-15Bibliographically approved
2. Enhancing Radio Frequency System Performance by Digital Signal Processing
Open this publication in new window or tab >>Enhancing Radio Frequency System Performance by Digital Signal Processing
2010 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis measurement systems for the purpose ofcharacterization of radio frequency power amplifiers are studied.Methods to increase the speed, accuracy, bandwidth, as well as toreduce the sampling requirements and testing cost are presented. Amethod intended for signal shaping with respect to peak-to-averageratio reduction and its effects-improvements on the radio frequencyfront-end performance is investigated.

A time domain measurement system intended for fast and accuratemeasurements and characterization of radio frequency poweramplifiers is discussed. An automated, fast and accurate techniquefor power and frequency sweep measurements is presented.Multidimensional representation of measured figure of merits isevaluated for its importance on the production-testing phase ofpower amplifiers.

A technique to extend the digital bandwidth of a measurement systemis discussed. It is based on the Zhu-Frank generalized samplingtheorem which decreases the requirements on the sampling rate of themeasurement system. Its application for power amplifiers behavioralmodeling is discussed and evaluated experimentally.

A general method for designing multitone for the purpose ofout-of-band characterization of nonlinear radio frequency modulesusing harmonic sampling is presented. It has an application with thevalidation of power amplifiers behavioral models in theirout-of-band frequency spectral support when extracted fromundersampled data.

A method for unfolding the frequency spectrum of undersampledwideband signals is presented. It is of high relevance tostate-of-the-art radio frequency measurement systems which capturerepetitive waveform based on a sampling rate that violates theNyquist constraint. The method is presented in a compact form, iteliminates ambiguities caused by folded frequency spectra standingoutside the Nyquist band, and is relevant for calibration matters.

A convex optimization reduction-based method of peaks-to-averageratio of orthogonal frequency division multiplexing signals ispresented and experimentally validated for a wireless local areanetwork system. Improvements on the radio frequency power amplifierlevel are investigated with respect to power added efficiency,output power, in-band and out-of-band errors. The influence of thepower distribution in the excitation signal on power amplifierperformance was evaluated.

Place, publisher, year, edition, pages
SE-100 44 Stockholm, Sweden: Signal Processing, School of Eletrical Engineering, Royal Institute of Technology, 2010. ix, 9 p.
Series
Trita-EE, ISSN 1653-5146 ; 2010:030
Identifiers
urn:nbn:se:kth:diva-24536 (URN)
Presentation
2010-08-20, 99:132, Kungsbäcksvägen 47 Gävle, SE-801 76, University of Gävle, 10:15 (English)
Opponent
Supervisors
Projects
KKS
Note
QC 20101001Available from: 2010-10-01 Created: 2010-09-14 Last updated: 2010-10-01Bibliographically approved

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Citation style
  • apa
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