T. Fernandez

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.

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.

Nonlinearity estimation in power amplifiers based on undersampled temporal data

In this paper we apply undersampling techniques to capture the temporal input-output relationship of RF power amplifiers. This approach avoids the distortion introduced by the upconverter and downconverter stages. We develop polynomial models with memory from the available data and evaluate its performance estimating device parameters like Adjacent power Ratio (ACPR) and AM-AM curves. The estimated parameters show good agreement with the empirical ones.

Nonlinear dynamics of microwave synthesizers-stability and noise

The nonlinear dynamics of microwave synthesizers based on type-II third-order loops is analyzed in this paper. Instead of using standard simplified models, realistic models are considered for the loop filter, phase detector (PD), and voltage-controlled oscillator based on experimental characterization. The new models enable the simulation of incidental frequency modulation and the accurate prediction of the synthesizer operation ranges, including possible hysteresis phenomena. The stability of phase-locked solutions is analyzed, enabling the prediction of possible chaotic behavior. For an accurate determination of the output spectrum, a phase-noise simulation is also carried out, considering the noise contributions from the loop elements. The sidebands inherent to the synthesizer solution are taken into account for this analysis. The analysis strategy has been applied to a microwave synthesizer, operating in the 2-3 GHz band, with very good results. Two types of PDs are considered: the JK flip-flop PD and frequency mixer, comparing the resulting loop performance in terms of stability and phase noise.

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.

Smoothing the canonical piecewise-linear model: an efficient and derivable large-signal model for MESFET/HEMT transistors

In this paper we present the smoothed piecewise-linear (SPWL) model as a useful tool in the device modeling field. The SPWL model is an extension of the well-known canonical piecewise-linear model proposed by Chua, which substitutes the abrupt absolute value function for a smoothing function (the logarithm of hyperbolic cosine), thus providing the model with several interesting properties. In particular, this function makes the model derivable, which is important to predict the intermodulation distortion behavior. Moreover, it allows one to control the smoothness of the global model by means of a single smoothing parameter. The parameters of the model are adapted to fit the nonlinear function, while the smoothing parameter is selected according to derivative constraints. The applied learning algorithm is a second-order gradient method. The proposed SPWL model is successfully applied to model a microwave HEMT transistor under optical illumination using real measurements. The model receives as input the bias voltages of the transistor, the instantaneous voltages, and the optical power and provides the drain to source current. The performance and computational burden of the SPWL model is compared with an empirical model and with some neural networks-based alternatives.

Modelling of operating point non linear dependence of Ids characteristics from pulsed measurements in MESFET transistors

This paper presents a large signal MESFET model suitable for applications in nonlinear microwave CAD. The originality of this work lies in the fact that multibias starting points (hot and cold device) for pulsed measurements are used to derive a unique expression for Ids that describes the DC as well as the small and large signal behaviour of a device and it is capable of taking into account the quiescent point dependence. The algorithms of this new model are easily implemented into the commercially available nonlinear simulators. The Ids current is modelled by two nonlinear sources, one of them is a bias point dependent nonlinear equation and the other one represents the differences between DC and Pulsed characteristics at every bias point. Experimental pulsed characteristics and simulations, for a NE72084 packaged transistor, have been carried out, showing excellent agreement. Furthermore, a complete model of a 6*50 ¿m chip transistor has been obtained. Successful comparisons between MDS simulations using the extracted model and experimental power measurements of the transistor loaded by 50 Ohms at the input and output ports have been done.

CHARACTERIZATION AND MODELING OF SCHOTTKY DIODES UP TO 110 GHZ FOR USE IN BOTH FLIP-CHIP AND WIRE-BONDED ASSEMBLED ENVIRONMENTS

This paper presents a wideband model, from Direct Current (DC) to W band, for a single Anode Schottky Diode based on a commercial VDI chip. Difierent measurements have been performed to obtain a complete large-signal equivalent circuit model suitable for the device under consideration up to 110GHz, and for its integration in planar circuits. The modeling has been done using a combination of DC measurements, capacitance measurements, and RF scattering measurements. The test structure for on-wafer S- parameter characterization has been developed to obtain an equivalent circuit for Coplanar to Microstrip (CPW-Microstrip) transitions, then verifled with 3D Electromagnetic (EM) tools and flnally used to de- embed device measurements from empirical data results in W band. 3D EM simulation of the diodes was used to initialize the parasitic parameters. Those signiflcant extrinsic elements were combined with the intrinsic elements. The results show that the proposed method is suitable to determine parameters of the diode model with an excellent flt with measurements. Using this model, the simulated performance for a number of diode structures has given accurate predictions up to 110GHz. Some anomalous phenomena such as parasitic resistance dependence on frequency have been found.

Optically controlled 2.4GHz MMIC amplifier

In this paper a 2.4GHz MMIC amplifier for mobile applications is used to demonstrate the significant control that can be achieved in the amplifiers performance using optical illumination. The results presented show a 15dB variation in the amplifiers S21 figure and a 6 to 10dB variation in the input and output return loss when the incident optical power is varied.

Nonlinear Modeling of Trapping and Thermal Effects on GaAs and GaN Mesfet/HEMT Devices

A novel nonlinear model for MESFET/HEMT devices is presented. The model can be applied to low power (GaAs) and high power (GaN) devices with equal success. The model provides accurate simulation of the static (DC) and dynamic (Pulsed) I-V characteristics of the device over a wide bias and ambient temperature range (from i70 - C to +70 - C) without the need of an additional electro-thermal sub-circuit. This is an important issue in high power GaN HEMT devices where self-heating and current collapse due to traps is a more serious problem. The parameter extraction strategy of the new model is simple to implement. The robustness of the model when performing harmonic balance simulation makes it suitable for RF and microwave designers. Experimental results presented demonstrate the accuracy of the model when simulating both the small-signal and large- signal behavior of the device over a wide range of frequency, bias and ambient temperature operating points. The model described has been implemented in the Advanced Design System (ADS) simulator to validate the proposed approach without convergence problems.