Showing papers by "Giorgio Vannini published in 2005"

Accurate pHEMT nonlinear modeling in the presence of low-frequency dispersive effects

Abstract: Low-frequency (LF) dispersive phenomena due to device self-heating and/or the presence of "traps" (i.e., surface state densities and bulk spurious energy levels) must be taken into account in the large-signal dynamic modeling of III-V field-effect transistors when accurate performance predictions are pursued, since these effects cause important deviations between direct current (dc) and dynamic drain current characteristics. In this paper, a new model for the accurate characterization of these phenomena above their cutoff frequencies is presented, which is able to fully exploit, in the identification phase, large-signal current-voltage (I-V) measurements carried out under quasi-sinusoidal regime using a recently proposed setup. Detailed experimental results for model validation under LF small- and large-signal operating conditions are provided. Furthermore, the I-V model proposed has been embedded into a microwave large-signal pseudomorphic high electron-mobility transistor (pHEMT) model in order to point out the strong influence of LF modeling on the degree of accuracy achievable under millimeter-wave nonlinear operation. Large-signal experimental validation at microwave frequencies is provided for the model proposed, by showing the excellent intermodulation distortion (IMD) predictions obtained with different loads despite the very low power level of IMD products involved. Details on the millimeter-wave IMD measurement setup are also provided. Finally, IMD measurements and simulations on a Ka-band highly linear power amplifier, designed by Ericsson using the Triquint GaAs 0.25-/spl mu/m pHEMT process, are shown for further model validation.

Improvement of PHEMT Intermodulation Prediction Through the Accurate Modelling of Low-Frequency Dispersion Effects

Abstract: Large-signal dynamic modelling of III-V FETs cannot be simply based on dc i/v characteristics, when accurate performance prediction is needed. In fact, dispersive phenomena due to self-heating and/or traps (surface state densities and deep level traps) must be taken into account since they cause important deviations in the dynamic drain current. In this paper, a recently proposed large-signal i/v measurement setup is exploited to extract an empirical model for low-frequency dispersive phenomena in microwave electron devices. This i/v model is then embedded into a microwave large-signal PHEMT model. Eventually, a Ka-band highly linear power amplifier, designed by Ericsson using the Triquint GaAs 0.25µm PHEMT process, is used for model validation. Excellent intermodulation distortion predictions are obtained with different loads despite the extremely low power level of IMD products involved. This entitles the proposed model to be also used in the PA design process instead of conventional loadpull techniques whenever the high-linearity specifications play a major role.

A Ku band monolithic power amplifier for TT&C applications

Abstract: The paper describes the design of a 38 dBm monolithic power amplifier at Ku band. The amplifier has to be used as the final stage of the downlink transmitter of a TTC therefore performances have to be matched imposing the devices to work at de-rated conditions respect to the process maximum ratings. In this perspective, the device channel temperature becomes a very tight design objective and has to be carefully controlled by means of a thermal simulator. The paper describes the three dimensional thermal model built to predict the devices thermal behavior in the environment of a finite difference thermal simulator. The design of the circuit is also described from the specifications to the final layout.

A preliminary study of different metrics for the validation of device and behavioral models

Abstract: In integrated circuit and/or system design using CAD tools, model accuracy has obviously a direct impact on the quality of the final performance prediction. One of the most common ways to evaluate the quality of a model has always been the visual inspection of the comparison between simulations and measurements; the highest quality is assigned to the model that returns the set of curves closer to the measured ones. Unfortunately a large number of variables (bias, frequency, power level, large signal regime, etc.) may be of concern and, in such a case, it can be quite hard to decide which is the best model for a targeted application. Therefore, the problem of accuracy evaluation can be addressed by defining suitable "metrics", i.e., numerical formulae which return, possibly, dimensionless quantity as performance indexes for a model in term of best fitting between simulations and measurements. In this work several metrics have been studied from the model validation point of view. In particular, different metrics for DC characteristics, scattering parameters as well as large signal performance have been tested for HBT and NMOS transistor models, and for WCDMA base station LDMOS power amplifier models. Dis/Advantages of the proposed metrics and possible solutions/improvements are discussed.

Accurate modeling of electron device I/V characteristics through a simplified large‐signal measurement setup

Abstract: Low-frequency dispersive phenomena due to self-heating and/or “traps” (that is, surface-state densities and deep-level traps) cause important dynamic deviations in the I/V characteristics of III-V devices and they must be taken into account when an accurate large-signal dynamic model is needed. To this end, different low-frequency dispersive I/V models have been proposed by the research community and, quite often, a characterization based on pulsed I/V measurement systems has been suggested as the most appropriate for the identification of model parameters. Unfortunately, besides requiring special-purpose setups, pulsed characterization may suffer from some drawbacks, as discussed in this article. As an alternative, a simple large-signal measurement setup is presented here, which is based on low-frequency sinusoidal excitations and can be easily implemented by means of conventional general-purpose laboratory instrumentation. The proposed setup is successfully adopted in this article to identify the dispersive I/V characteristics of a GaAs PHEMT large-signal model providing excellent prediction of intermodulation distortion at Ka-band frequencies. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005.

A new technique for thermal resistance measurement in power electron devices

Abstract: A simple technique is proposed for the thermal resistance measurement of electron devices. The new approach is based on the standard measurements which are normally carried out for the electrical characterization of power devices, without requiring special-purpose instrumentation and/or physics-based temperature-dependent electrical device models. Experimental results, which confirm the validity of the new method, are provided.

Comparison of electron device models based on operation-specific metrics

Abstract: In the context of the European Union TARGET Network of Excellence (NoE) a specific interest has been oriented to the comparison of different electron device models in order to choose the most suitable for a particular application (eg highly linear amplifiers, low phase noise oscillators) To this purpose different metrics have been defined to compare the models behavior under different operating conditions (ie dc, ac small-and large-signal) In this paper we apply different metrics proposed under the TARGET NoE in order to compare two models, the nonlinear discrete convolution (NDC) model, based on a table-based black-box approach, and the EEHEMT1 model, based on the classic equivalent circuit approach The goal is to provide a set of practical criteria for carrying on reliable model comparisons

TX system-level analysis by behavioral modeling of RF building blocks: the IEEE802.11a and IEEE802.15.3a case studies

Abstract: The paper highlights some of the newest results achieved in the framework of the transmitter modeling for wideband access transmitters work package within the IST-EU network of excellence TARGET. Two cases of study have been considered to discuss the outcome, namely the IEEE 802.11a WLAN and the IEEE 802.15.3a UWB. A specific discussion about the subsystem modeling requirements in terms of key parameters allow the construction of subsystem models capable of numerical efficiency and accuracy. The subsequent insertion of such subsystem behavioral models allows fast and accurate co-simulations of complete transmitters for the performance investigation.

A simple non-quasi-static non-linear model of electron devices

Abstract: A technology-independent, non-quasi-static non-linear model of electron devices capable of accurate predictions at microwave and millimetre waves is proposed in this paper. The model is based on the definition of a quasi-static associated device, which is controlled by means of equivalent voltages. In particular, in the paper it is shown how to define and experimentally identify suitable voltage-controlled voltage sources, which modify the original domain of applied voltages and create a suitable control environment for the purely-quasi-static associated device. The advantage of this approach is that conventional purely quasi-static models can still be adopted even at very high frequencies, if suitable equivalent voltages are applied. Preliminary experimental validation of the approach is provided in the paper by means of a GaAs PHEMT.

Small-signal operation-based simplified verification of nonlinear models for millimeter-wave electron devices

Abstract: Large-signal modeling of electron devices for nonlinear MMIC design is a fundamental topic for the microwave community. Many different nonlinear modeling approaches have been proposed in the last years, and quite often circuit designers suffer from the lack of reliable comparison criteria, on the basis of which identify what model, between those available, could be the most suitable for the desired application. Moreover, similar strategies are needed even from the research groups, whose activity is devoted to the model identification and extraction, in order to quantify the degree of accuracy achievable by the modeling approach adopted. In this paper an approach to verify large-signal model accuracy will be discussed, which is simply based on the comparison between de-embedded measurements and model predictions of Y-parameters versus the bias voltages at the intrinsic device ports.

Accurate modeling of electron device I/V characteristics through a simplified large-signal measurement setup: Research Articles

Abstract: Low-frequency dispersive phenomena due to self-heating and/or “traps” (that is, surface-state densities and deep-level traps) cause important dynamic deviations in the I/V characteristics of III-V devices and they must be taken into account when an accurate large-signal dynamic model is needed. To this end, different low-frequency dispersive I/V models have been proposed by the research community and, quite often, a characterization based on pulsed I/V measurement systems has been suggested as the most appropriate for the identification of model parameters. Unfortunately, besides requiring special-purpose setups, pulsed characterization may suffer from some drawbacks, as discussed in this article. As an alternative, a simple large-signal measurement setup is presented here, which is based on low-frequency sinusoidal excitations and can be easily implemented by means of conventional general-purpose laboratory instrumentation. The proposed setup is successfully adopted in this article to identify the dispersive I/V characteristics of a GaAs PHEMT large-signal model providing excellent prediction of intermodulation distortion at Ka-band frequencies. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005.

Simplified validation of non-linear models for micro- and millimeter-wave electron devices

Abstract: Large-signal modelling of electron devices for nonlinear MMIC design is a fundamental topic for the microwave community Many different non-linear modelling approaches have been proposed in the last years, and quite often circuit designers suffer from the lack of reliable comparison criteria to identify which model (between those available) could be the most suitable for the desired application Moreover, similar strategies are needed even from the research groups, whose activity is devoted to the model identification and extraction, in order to quantify the degree of accuracy achievable by the modelling approach adopted In this paper an approach to verify large-signal model accuracy will be discussed, which is simply based on the comparison between de-embedded measurements and model predictions of Y-parameters versus the bias voltages at the intrinsic device ports

Implementation of non-conventional nonlinear models for electron devices in commercial CAD tools

Abstract: In nowadays CAD environments for integrated microwave circuit design, dedicated tools for the implementation of user defined component models are becoming more and more important. These tools are mainly oriented to the definition of equivalent circuit models. However, the need for more accurate prediction of nonlinear electron device performance pushes the modelling community towards the research of new, often non-conventional, modelling approaches (e.g., frequency-domain, behavioural, integral models, look-up-table based, state-space based, etc.). In such a context, the model implementation tools usually available may result not sufficiently flexible. The paper provides useful hints and points out the main limitations which can be encountered in the implementation of non-conventional electron device models. As an example, the implementation of a nonlinear discrete convolution model is considered by using three different advanced tools: the model wizard of AWR Microwave Office, the model development kit and Verilog-A language of Agilent ADS.