A. Tazon

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

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.<<ETX>>

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.

Miniaturized Microstrip Patch Antenna with Defected Ground Structure

The aim of this work is to miniaturize a microstrip patch antenna resonating at 3 GHz. For this purpose, defected ground structure (DGS) has been employed to shift the resonance frequency of an initial microstrip antenna from 5.7 GHz to 3 GHz by disturbing the antennas current distribution. The proposed DGS is incorporated in the ground plane under the patch antenna to improve its performances. Finally, a miniaturization up to 50%, with respect to the conventional microstrip antenna, is successfully accomplished. A prototype of the antenna was fabricated with the FR4 substrate and tested. The measurements results were in good agreement with simulation results.

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.

A nonlinear MESFET model for intermodulation analysis using a generalized radial basis function network

Abstract In this paper we use a generalized radial basis function (GRBF) network to model the intermodulation properties of microwave GaAs MESFET transistors under dynamic operation. The proposed model receives as input the bias voltages of the transistor and provides as output the derivatives of the drain-to-source current, which are responsible for the intermodulation properties. The GRBF network is a generalization of the RBF network, which allows different variances for each dimension of the input space. This modification allows to take advantage of the soft nonlinear dependence of the output derivatives with the drain-to-source bias voltage. The learning algorithm chooses the GRBF centers one by one in order to minimize the output error. After selecting each new center from the training set, the centers and variances of the global network are optimized by applying gradient descent techniques. Finally, the amplitudes are obtained by solving a least-squares problem. The effectiveness of the proposed GRBF model is validated through load-pull intermodulation prediction based on the experimental nonlinear characterization of an NE72084 MESFET device.

Accurately modeling the drain to source current in recessed gate P-HEMT devices

In this work, a continuous nonlinear model for the I/sub ds/ current source in recessed gate pseudomorphic HEMT heterostructures is proposed. A careful characterization of the DC, pulsed, and small-signal nonlinear distortion behaviour of this predominant nonlinearity has been employed in order to extract the model parameters. Being able to reproduce the current-voltage (I-V) behaviour as well as the higher order derivatives of the transconductance and output conductance, the equation is valid for an accurate control of the critical nonlinear distortion phenomena in HEMT applications. Comparisons between measured and simulated results prove its validity under both static and dynamic conditions for either large- or small-signal operation.