Energy efficient front-ends and systems

Team : X. Begaud, E.Bergeault, J.C. Cousin, B.Huyart, A. Khy, A.C. Lepage

Fundings : European Project (CELTIC/Spectra), ANR (Smartvision), FUI System@TIC (CONRAHD/OPTIMUM),  Telecom Foundation funding (Projet DEMODU)

Mixer down converter 35-45 GHz

MMIC design for RF front-end Our research activity has been focused on the design of demodulator dedicated to software defined radio applications. Two three-phase demodulators using MMIC technology have been designed in the 1-24 GHz bandwidth and Q band (33-45 GHz). This demodulator architecture shows a better rejection of adjacent channels than classical IQ structure but requires one more Low Frequency (LF) outputs. In order to reduce the number of LF components, a new design based on theoretical study of symmetry was tested and patented. The reduction of the number of RF and LF components involved is our goal to make the front-end energy efficient. Another way is the insertion of an Automatic Matching Impedance Circuit (AMIC) between the antenna and the power amplifier (PAs) to keep the best operating conditions for the PAs. Indeed compact antennas are sensitive to their variable electromagnetic environment. First studies were conducted on the design of a compact antenna and a variable matching circuit. As the Three Phase Demodulator (TPD) may act as a mismatch detector, the next step will be to design of the AMIC including the TPD and the variable matching circuit.

Power probes and PAs Our researchs in fundamental metrology with the LNE have yielded significant results for the realization of original RF power sensors that could be used as reference power standards instead of conventional bolometer mounts. This work aims to study the feasibility of a calculable HF power standard. A calibrating procedure is no more necessary with a calculable power standard since it is only based on physical and mathematical principles. A power standard has been realized in coplanar (CPW) technology up to 8 GHz. Probe measurements techniques of MMIC components have been also investigated with the LNE over a wide frequency band (few kHz-40 GHz). We have studied and defined the traceability and the accuracy of the Line-Attenuator-Reflect calibration technique up to millimeter wave frequencies. An original calibration kit has been realized on GaAs substrate. The power amplifier is one of the most critical circuits responsible for the major fraction of the system’s power consumption and distortion. Consequently, the optimization of the power amplifier requires a trade-off between output power, efficiency and spectral. It is then important to provide large signal measurements under conditions that are similar to those used in real operating modes under complex modulated signals. We have realized different measurement systems for different frequency bands. Since 2009, our efforts have focused on the design and implementation of a load-pull and source-pull measurement setup in the 40-60 GHz frequency band. Numerical predistortion techniques have been also used to fight the degradation of the RF signal. The originality of our setup concerns the generation of modulated signals up to 1GS/s in the 40-60 GHz frequency band realized by means of an Arbitrary Wave Generator to provide high data rate modulation schemes with an intermediate frequency carrier taken in the [1 5 GHz] frequency range. This signal is up-converted in the [40 60 GHz] frequency band by means of a double side band mixer.

Radio communications channel sounding Two channel sounders have been designed and realized for non stationary MIMO channel in the Wi-Fi and UWB frequency bands. Our studies have been focused on the simultaneous determination of the angles of departure and arrival of transmitted and received signals and the measurement of arrival time. Comparisons between measurement and models were made from a 3D ray tracing. Another aspect of channel sounding has been led with Orange Labs to estimate the contribution of relays in a multi link propagation channel modeling for the 4G systems. To this end, a multi link measurement campaign with relays has been carried out in realistic urban environments. These have allowed to assess the relaying aspects and to focus on the path loss models developed for the 4G systems, the shadow fading correlation and the impact of the relay antenna height. A particular attention has been paid for the Base station-Relay Station link which had not been studied yet.

RF front-end for Radar The team was involved in the French ANR Smartvision, dealing with the development of a smart corridor or electronic gate dedicated to scan people without physical searches insecure area as airports, embassies and so. In this project, we have participated to the design of the RF front-end of a 77 GHz bi-static radar. This radar is mounted at 30 cm from the center of a rotative disk turning at 1500 rpm (rounds per minute). This bi-static radar includes the Transmitter (Tx) and the Receiver (Rx) and 2 antennas linked respectively to Tx and Rx. Tx provides a Continuous Wave source as a sinus signal at 77 GHz. Rx is an IQ demodulator allowing to compare the Doppler response of a scanned body to reference Doppler responses given by the presence of hazardous objects (gun, explosive and so).

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