Mohamed Chaibi

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.

Modelling of temperature and dispersion effects in MESFET and HEMT transistors

In this paper, an accurate technique to model temperature, bias, and frequency dispersion effects in MESFET and HEMT transistors is presented. The approach is based on a single drain to source current source I ds nonlinear model. Pulsed I/V characteristics measurements are used to model bias and frequency dispersion effects while temperature is directly implemented in the I ds equation. Model parameters extraction strategy is simple, being based just on a few measurements. The approach validity is verified by comparing the simulated and measured I/V characteristics of the device tested under continuous and pulsed excitation. Large-signal simulation results show that the model can efficiently predict the output power under different bias and temperature conditions.

A new technique to evaluate the complex permittivity of a homogeneous dielectric material using rectangular waveguide

This paper presents a simple waveguide measurement technique to evaluate the complex permittivity of a homogenous dielectric material. The dielectric sample is loaded in the transmission line rectangular waveguide WR90. The S-parameters of the waveguide are measured by Network analyzer and calculated as a function of the complex permittivity using theory of transmissions lines. Using the MatLab Optimization Tools simple MatLab scripts are written to search for complex permittivity of a dielectric material so as to match the measured and calculated values of S-parameters. The complex permittivity of Teflon and Nylon at the X-band frequencies are then determined.