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TARGET.news 9/2006
The e-letter of the European Project TARGET - Top Amplifier Research Groups in a European Team
Topics
- TARGET Year 2 Review Meeting
- WP 2.2.B.1 "Front-End Sampler Group" has ended
- WP 2.2.B.2.1 "Thermal Measurement Techniques I" has ended
- Review of the 2nd TARGET Winter School on "Microwave Transistors: Materials and Devices"
- Review of the 1st TARGET Online Tutorial on "Device Modelling"
Events
- IEE - TARGET Workshop on "High Efficiency Power Amplifier Design for Next Generation Wireless Applications"
- TARGETs' 2006 event calendar
TOPICS
TARGET Year 2 Review Meeting
On March 23/24 TARGET’s Year 2 Review Meeting was held in Vienna and after a very positive Year 1 Review the project received even better marks this time!
The feedback was kept rather short as “the reviewers and I could not discern any major problems, something that you are probably aware of…” (which was the opening line of our project officer).
Again, the scientific achievements as well as TARGETs’ dissemination activities were lauded, and the steep increase in participation at the biggest international RF and microwave conferences in Europe, the US and Asia were appreciated. The project management that was found to be outstanding last year, still improved further.
The strategic integration will need to be further improved but the likelihood of the overall achievement is rated very high by our reviewers as it is anticipated that the aims of the project will be reached.
Finally, it should be mentioned that the change of project officers in the middle of the reporting period posed no problem at all as our new officer Andrej Litwin has a strong background in the RF scientific community which surely was a bonus. The continuity of success will certainly inspire us to carry on working hard and with full verve in order to achieve our aim of durable integration.
Our special thanks go to all TARGET members for their unbroken enthusiasm and effort that is the real motor behind our long running success!
Sue Raab, Gottfried Magerl
WP 2.2.B.1 "Front-End Sampler Group" has ended
The objective
After 18 months the work package WP.2.2.B.1 Front-End Sampler Group finished in December 2005. The partners were IRCOM from the University of Limoges, ELEC from the Vrije Universiteit Brussel and NMDG Engineering. The goal of the work package was to bring a critical group of institutes and companies together to define and launch a separate follow-up project to strengthen the position of Europe in sampler technology and to asses the importance of doing so.
Introduction
As well known, TARGET is aiming at advancing power amplifier technologies from transistor to systems through the mechanism of a Network of Excellence. The European research community continues to build up a very good reputation in power amplifier technologies, like transistor modelling, design, linearization etc. But the measuring aspect has always received marginal attention, except for very few institutes. Nevertheless, being able to measure physical phenomena is an important part of the progress. This is also true to evolve power amplifier technologies.
The complexity of signals, applied to power amplifiers, keeps growing with information carriers increasing in frequencies and with broader modulation bandwidths. On top, nonlinear behaviour cannot be avoided, creating all kinds of mixing products, including signals at lower frequencies. It is important to be able to measure what is going on at the level of the transistors, power amplifier modules and systems.
Why is sampler technology so important?
Sampler technology, complementing mixer technology, is considered as one of the keys to be able to measure signals with scattered frequency content (low frequency, carrier and modulation, harmonics etc.) before digitizing them. During power amplifier design one is confronted with modulated carriers, intermodulations, harmonics and induced low-frequency signals. A very high frequency one-shot digitizer would be ideal but does not exist yet. A mixer block converts high-frequency signals into low frequencies and as such allows only to captures parts of the frequency spectrum.
But using the aliasing principle, a sampler compresses high frequency spectral tones into a low-frequency band, maintaining phase coherence between the tones, whether they are low- or high frequency. Of course, there is no free lunch. The signals must consist of spectral tones and as such must be (pseudo-) periodic. When compressed, the spacing between the tones must be large enough to keep them separately and also all noise is down-converted. This imposes requirements on the signal and on the sampler front-end.
The realizations of the work package
A half-day tutorial was organized at EuMC 2005, explaining the principles and importance of the sampler technology. Additionally, applications in PA characterisation and design were presented: the use of harmonic measurements, the low-frequency signals in the bias circuit, stability analysis, use of conversion matrices and more.
To evaluate the characterisation needs for the next 5 years, an on-line survey was organized about the type of components, signals and the type of measurements and simulations that one feels important for the future. Amongst others, the outcome clearly showed a need for better characterisation tools where the time domain aspect plays an important role.
In the work package one partner did focus on the study of the sampler principles and implemented in simulation a sampler front-end to learn the different mechanisms. This was in preparation to launch a follow-up thesis project that aims at the realisation of a discrete sampler. Additionally this partner compared the advantages and disadvantages of different types of receiver front-ends (mixers, one-shot digitizer, time-equivalent sampling and sampling using synthesis) with the application to broadband modulation signals. Meanwhile the meaning of “phase” and “phase relations” was studied. Another partner focused on the application of the sampler technology in multi-port characterisation in general and for mixers specifically.
An important part of the work package was spent on discussions with different institutes and companies to define a follow-up project. Presently interested partners are identified and progress is being made towards a follow-up project.
Conclusion
During the work package awareness on front-end sampler technology was definitely created and a lot of knowledge has been built up while the potential in different characterisations of PAs was demonstrated.
The launch of a follow-up project was not realized, mainly due to the challenge to build up the interest to work on measurement science. But now the interested partners are identified and it will be very likely that the follow-up project will be launched before the end of 2006.
Marc Vanden Bossche
WP 2.2.B.2.1 "Thermal Measurement Techniques I" has ended
The increase in temperature due to self-heating effects strongly influences the performance and reliability of microwave devices and amplifiers. As a result fmax and power gain decrease with temperature. The temperature in Solid State Power Amplifiers (SS PA) can be modulated by signal envelope thus affecting the PA linearity, too.
The goal of WP 2.2.B.2.1 was to provide the TARGET consortium with tools and methods for thermal evaluation of devices and PA’s. An important objective was the comparison of several different thermal experimental techniques and the evaluation of their suitability for microwave devices. Another goal was to use the experiments for calibration and verification of proposed thermal simulation models.
The WP started in June 2004 and ended in December 2005. The task force consisted of Université de Limoges (IRCOM), Vienna University of Technology (TUW) and Université des Sciences et Technologies de Lille (USTL). Optical thermal imaging techniques like Transient Interferometric Mapping (TIM) and micro-Raman spectroscopy, and several variants of DC or pulsed electrical methods were applied. The optical techniques in their combination and complementarity provide µm spatial, ns time and high temperature resolution.
The work was focused on the investigation of self-heating effects in single or multifinger AlGaN/GaN high electron mobility transistors (HEMTs) and other GaN-based test structures. These are future candidates for high power HF applications. A backside version of the Raman method developed at USTL is useful for temperature evaluation in cases where top metallization like e.g. air-bridge structure prevents topside measurements. The measurements performed via Raman (USTL) and electrical DC techniques (TUW) show a nice consistency. The unique measurement technique TIM of TUW provided information on heat spreading dynamics in HEMTs in the 100ns time scale. A method has been developed for localization of power dissipation sources by TIM and for a transient temperature evaluation from source resistance drop. A thermal model has been developed to explain the transient thermal behaviour in the HEMT channel.
The combination of TIM and electrical measurements with the thermal simulation allows us to determine the thermal boundary resistance (TBR) between GaN and substrate. TBR is found to be a crucial parameter limiting the effective heat transfer from the channel region to the substrate. Its value is about two orders of magnitude higher than the theoretically predicted value indicating that the GaN/substrate interface still needs optimization. An electro-thermal simulation method based on Ritz-vector has been developed at IRCOM. The simulation results show an agreement with an alternative pulsed electrical thermal evaluation method based on forward current Schottky diode measurements.
The work was presented respectively published in an IEEE Transactions paper, several conference contributions and two TARGET workshops/tutorials. A researcher exchange has been performed between TUW and USTL. The work has been performed also in collaboration with Thales, Universities in Ulm and Darmstadt, FBH Berlin and Forth in Crete. In the follow-up WP 2.2.B.2.2 (started in June 2005) further microwave device types as well as PA’s shall be investigated both experimentally and by simulation, together with a new partner, Chalmers University of Technology.
Dionyz Pogany
Review of the 2nd TARGET Winter School on "Microwave Transistors: Materials and Devices"
The second TARGET Winter School about "Microwave Transistors: Materials and Devices", held on 21 - 24 February at the University of Jena, Germany, was finished very successfully.
The intensive, four-day course provided a thorough understanding of the essential background of RF transistor function and production methods. The following topics were covered in 12 talks given by international experts:
- Semiconductor materials
- RF devices
- CMOS, LDMOS
- Technology Power Amplifiers
- SiGe devices
- SiC Diodes
- Mixed signal devices
- HBTs, power HEMTs
29 students from 11 European countries attended the school. In the end seven students took part in a written exam about "Microwave transistors: materials and devices". Everybody who passed the test got 3 credit points.
In addition three interesting lab tours were organized, one of them to the "Zentrum für Mikro- und Nanotechnologien" at the Technical University of Ilmenau. The Winter School ended with a panel discussion about the future of RF transistors.
Wolfgang Richter
Review of the 1st TARGET Online Tutorial on "Device Modelling"
On 7 April 2006 the first TARGET Online Tutorial on Nonlinear Modelling was held. With 43 attendees this 3 hour event was a very successful start of the online series of TARGET tutorials. 4 presenters reported on their work and the results in the field of nonlinear device modelling for PA design where topics like modelling of memory effects, electro-thermal modelling, neural modelling and large signal vectorial measurement based modelling were stressed in detail.
In an online questionnaire at the end of the event attendees clearly indicated that they like the new idea of TARGET tutorials and highlighted that this is a convenient and time efficient way to meet and listen to scientific contributions without travelling. It was further indicated that the used tool (WebEx) could also be very beneficial for work package meetings.
Markus Mayer
EVENTS
IEE - TARGET Workshop on "High Efficiency Power Amplifier Design for Next Generation Wireless Applications"
THE CHALLENGES
Microwave Power Amplifiers is a key component of modern day mobile devices. Industry competition and growing consumer demand is driving research and development of microwave power amplifiers. The work TARGET has undertaken is at the epicentre of next generation mobile devices. There is a need to unite all the research bodies involved to discuss results.
KEY OBJECTIVE OF THIS SEMINAR
- Demonstrate results after 2 years activity
- Present advanced techniques in power amplifier design covering the main issues from semiconductor material to transmitter design
- Provide a unique networking opportunity for all the Research Centres involved in the R&D of Microwave Power Amplifiers
KEY SPEAKERS
Richard Ranson, [Chief Engineer, Filtronic]
Frank Schwierz, [TU Ilmenau, Germany]
Markus Mayer, [Vienna University of Technology, Austria]
Dominique Schreurs, [Catholic University of Leuven, Belgium]
Paolo Colantonio, [University of Rome – Tor Vergata, Italy]
Máirtín O'Droma, [University of Limerick, Ireland]
Albert Cesari, [LAAS – CNRS, France]
Konstantinos Vryssas, [School of Electrical and Computer Engineering, National Technical University of Athens]
Programme and registration is now available at: http://www.iee.org/events/target.cfm
For more information on this event please contact:
Alfred Mani
Professional Network Manager
amani@theiet.org
TARGETs' 2006 event calendar
| May 23 | TARGET - IET (IEE) Workshop | |
 | Cambridge, UK | Workshop on High Efficiency Power Amplifier Design for Next Generation Wireless Applications |
| May 25 | Workshop | |
| Cracow, Poland | TARGET/MIKON Workshop on GaN devices | |
| June 11-16 | IMS 2006 | |
| San Francisco, USA | ||
| June 13-15 | IMS Exhibition | |
| San Francisco, USA | TARGET booth | |
| July 24-28 | 3rd TARGET Summer School | |
| Castelldefels (Barcelona), Spain | Linear Amplifier Design & Wireless Systems | |
| Sept. 11-14 | EuMW 2006 | |
| Manchester, UK | 4 Workshops, TARGET focused session, LSNA Users' Forum | |
| Sept. 12-14 | EuMW Exhibition | |
| Manchester, UK | TARGET booth | |
| Oct. 16-17 | TARGET Days | |
| Frascati, Italy | 3 Tutorials | |
| Dec.12-15 | APMC 2006 | |
| Yokohama, Japan |
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Imprint
published by: ftw. Forschungszentrum Telekommunikation Wien Betriebs-GmbH, Donau-City-Straße 1, 1220 Vienna, Austria, Phone +43/1/5052830-0
responsible for content: Prof. Dr. Gottfried Magerl, Mag. Sue Raab
