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Intermodulation of passive RF mixers

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Français - Anglais

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General information

Reference : UPR8001-CHRVIA-001
Workplace : TOULOUSE
Date of publication : Wednesday, February 05, 2020
Scientific Responsible name : Christophe Viallon
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 October 2020
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly

Description of the thesis topic

The performance of microwave circuits in terms of intermodulation is not always correctly estimated by current microwave CAD softwares. The problem exists especially with radio equipment handling a large number of carriers, as in satellites, or when the transmission must be maintained despite the presence of a strong interferer. The two-carrier intermodulation measurements of this equipment, generally limited in dynamic range (70 dB typ.), hide the problem, but it remains very present. Under small-signal condition, the performance extrapolated from measurements and simulations carried out at higher levels can thus be too optimistic and may lead to a non-optimal system dimensioning concerning the linearity / consumption ratio.
The thesis aims to study intermodulation phenomena in passive mixers built around field effect transistors. For these circuits, the intermodulation measurement with two carriers reveals, at low level, a non-integer slope of between 2 and 3 dB/dB for third-order intermodulation where conventional values of 3 dB/dB are observed in most microwave circuits. This characteristic leads to rethink the way in which the cold-biased transistor is modeled in CAD softwares.
The experimental part of the proposed work will use a simple integrated mixer designed for the project and using MOS transistors for which we have a founder model. A second demonstrator based on GaN technology could also be designed and then evaluated. The non-linear modeling work will be carried on based both on the static measurements of the transistor and on the RF intermodulation measurements of the mixer. An experimental test setup developed for the project, which it may be improved regarding sensitivity, will be used for two-carrier intermodulation measurements of the circuit.
This thesis is based on the complementary skills of the MOST team at LAAS (C. Viallon) and the TeSA laboratory (J. Sombrin). The subject is part of a collaboration initiated in 2018 between these two laboratories and CNES agency. It has a strong theoretical character through the development of a mathematical model to be implemented in an electrical simulator, a design phase of the demonstrator and an experimental part through the use and the optimization of a high-dynamic intermodulation measurement setup developed for this project.

Work Context

The Laboratory of Analysis and Architecture of Systems (LAAS) is a CNRS research unit linked with the Institute for Engineering and Systems Sciences (INSIS) and the Institute of Information Sciences and their interactions (INS2I).
LAAS' research activities fall within the domain of Information Sciences and Technologies and address complex systems (artificial and sometimes natural) generally heterogeneous, and at different scales, to devise theories, methodologies and tools for modeling, designing and controlling them.

Research, innovation and transfer are tied. The lab has a history of strong relationships with industry and works in a large number of collaborative projects with inteThe systems considered in our research are of different kinds: integrated systems, embedded systems with real time and safety requirements, distributed systems, mobile systems, autonomous and robotics systems, micro and nano systems, biological systems. They fall in various application domains such as aeronautics and space, telecommunications, transports, production, services, security and defense, energy management, healthcare, environment and sustainable development.rnational, national and regional industries of all size.

Constraints and risks

As a final year student in a master's or engineering school with a specialization in microelectronics and RF circuit design, you know microwave CAD tools (i.e. Cadence virtuoso, Keysight ADS, AWR Microwave Office) and you want to contribute to academic research on a very specific subject. Curious and motivated, you like new technologies, you have good assimilation skills and you know how to be rigorous and autonomous.

The candidate must be of French or European Community nationality

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