A. Mediavilla

Extracting a bias-dependent large signal MESFET model from pulsed I/V measurements

In this paper a new large-signal metal semiconductor field effect transistor (MESFET) model suitable for applications to nonlinear microwave CAD has been developed and the different phenomena involved in the nonlinear behavior of the transistor have been studied. The importance of this work lies in the fact that multibias starting points (hot and cold device) for pulsed measurements are used to derive a single expression for I/sub ds/ that describes the dc as well as the small and large signal behavior of the transistor, while taking into account the quiescent point dependence. The algorithms of this new model can easily be incorporated into commercially available nonlinear simulators. The operating-point dependent current I/sub ds/ is modeled by two nonlinear sources: one of them is the dc characteristic nonlinear equation, and the other represents the differences between dc and pulsed characteristics at every bias point. A complete large-signal model is presented for a 10*140 /spl mu/m GaAs-MESFET chip (F20 process) from the GEC-MARCONI Foundry and a 16*250 /spl mu/m MESFET chip (DIOM process) from the Siemens Foundry. Comparisons have been made between simulations and measurements of pulsed characteristics at different operating points. There was very good agreement between the P/sub in//P/sub out/ measurements and the MDS simulations using the complete large signal model.

Characterizing the gate to source nonlinear capacitor role on FET IMD performance

This paper discusses the gate to source nonlinear capacitor contribution on small signal intermodulation distortion (IMD) performance of FET devices. The second and third order coefficients for the Cgs(Vgs) Taylor-series expansion, experimentally extracted with a simplified one-sided version of our previously proposed test set-up, are shown to be responsible for some detected differences on IMD behaviour at high frequencies.

Resistive FET mixer conversion loss and IMD optimization by selective drain bias

This paper describes a dedicated nonlinear MESFET model extraction technique, which was used to accurately characterize the devices channel resistance nonlinearity. Plotting Ids(Vgs,Vds) Taylor series expansion coefficients across V/sub GS/ and V/sub DS/ revealed not only the presence of important minimum conversion loss bias, but also of in-band IMD sweet spots that were then used to optimize a FET resistive mixer performance.

Characterization of thermal and frequency-dispersion effects in GaAs MESFET devices

New simple and accurate measurement procedures that enable the dispersion and thermal effects in GaAs MESFETs to be observed independently are presented in this paper. The results indicate that the differences observed between the static and pulsed characteristics of the device are not solely due to thermal effects, as is sometimes thought. Electrical and thermal measurements also show the GaAs MESFET to take a relatively long time before the effect of self-heating manifests itself on the IV characteristics of the device.

The Quijote CMB Experiment

We present the current status of the QUIJOTE (Q-U-I JOint TEnerife) CMB Experiment, a new instrument which will start operations early in 2009 at Teide Observatory with the aim of characterizing the polarization of the CMB and other processes of galactic and extragalactic emission in the frequency range 10–30GHz and at large angular scales. QUIJOTE will be a valuable complement at low frequencies for the PLANCK mission, and will have the required sensitivity to detect a primordial gravitational-wave component if the tensor-to-scalar ratio is larger than r = 0.05.

Very low-noise differential radiometer at 30 GHz for the PLANCK LFI

The PLANCK mission of the European Space Agency is devoted to produce sky maps of the cosmic microwave background radiation. The low-frequency instrument is a wide-band cryogenic microwave radiometer array operating at 30, 44, and 70 GHz. The design, test techniques, and performance of the complete differential radiometer at 30 GHz are presented. This elegant breadboard 30-GHz radiometer is composed of a front-end module (FEM) assembled at the Jodrell Bank Observatory, Cheshire, U.K., and a back-end module assembled at the Universidad de Cantabria, Cantabria, Spain, and Telecomunicacio/spl acute/, Universitat Polite/spl acute/cnica de Catalunya, Barcelona, Spain. The system noise temperature was excellent, mainly due to the very low noise performance of the FEM amplifiers, which achieved an average noise temperature of 9.4 K.

Octave Bandwidth Compact Turnstile-Based Orthomode Transducer

A 64% instantaneous bandwidth scalable turnstile-based orthomode transducer to be used in the so-called extended C-band satellite link is presented. The proposed structure overcomes the current practical bandwidth limitations by adding a single-step widening at the junction of the four output rectangular waveguides. This judicious modification, together with the use of reduced-height waveguides and E-plane bends and power combiners, enables to approach the theoretical structure bandwidth limit with a simple, scalable and compact design. The presented orthomode transducer architecture exhibits a return loss better than 25 dB, an isolation between rectangular ports better than 50 dB and a transmission loss less than 0.04 dB in the 3.6-7 GHz range, which represents state-of-the-art achievement in terms of bandwidth.

Empirical modeling of low-frequency dispersive effects due to traps and thermal phenomena in III-V FETs

An empirical approach is proposed which accounts for low-frequency dispersive phenomena due to surface state densities, deep level traps and device heating, in the modeling of the drain current response of III-V FETs. The model, which is based on mild assumptions justified both by theoretical considerations and experimental results, has been applied to GaAs MESFETs of different manufacturers. Experimental and simulation results that confirm the validity of the model are provided in the paper. >

High speed automated pulsed I/V measurement system

Thermal and trap effects in GaAs MESFET and HEMT devices can be accurately studied using Pulsed Gate and Drain measurement systems. Modelling methods based on static, pulsed I/V characteristics along with S parameters can be implemented into nonlinear simulators in order to obtain better agreement with the experiment. This work proposes a new compact instrumentation philosophy for Pulsed I/V measurements (PIVMS) that achieves 16bit resolution in 300ns pulse widths, avoiding the need for complex expensive external instrumentation and/or Hall effect current probes. The measurement system has been designed to meet requirements of high speed automated test systems, tacking about 20sec for extracting a complete set of bias points. Experimental verification shows the performance of this instrumentation setup.

The QUIJOTE-CMB experiment: studying the polarisation of the galactic and cosmological microwave emissions

The QUIJOTE (Q-U-I JOint Tenerife) CMB Experiment will operate at the Teide Observatory with the aim of characterizing the polarisation of the CMB and other processes of Galactic and extragalactic emission in the frequency range of 10-40GHz and at large and medium angular scales. The first of the two QUIJOTE telescopes and the first multi-frequency (10-30GHz) instrument are already built and have been tested in the laboratory. QUIJOTE-CMB will be a valuable complement at low frequencies for the Planck mission, and will have the required sensitivity to detect a primordial gravitational-wave component if the tensor-to-scalar ratio is larger than r = 0.05.