1,720,983 research outputs found
Modelling DC characteristics of GaAs MESFETs in a wide range of temperatures
No full textIn this paper, a new semiempirical DC thermal model of low- and high-power GaAs MESFETs is proposed. The model takes into account the effect of device negative output conductance and simulates external thermal effects modelling the dependence on temperature of the device threshold voltage and the maximum saturation drain-source current. A number of GaAs MESFETs, very different from a geometrical and technological point of view, have been characterized as a function of temperature and modelled by our model with high accuracy. The CPU extraction time results are moderate in any example. Results have been compared with the Rodriguez-Tellez model, showing improvements of accuracy better than 30 per cent. The model can be successfully used n MMIC CAD application
Collegamento di teleinformatica tra microcalcolatori e centro di calcolo esterno nel progetto di sistema ottici di telecomunicazioni
No full textDesign and Modelling of Photonic Band-Gap Resonance Cavity
No full textAn optimal design of Photonic Band-Gap (PBG) based resonance cavities has been carried out and
optimal design rules have been drawn by a very fast and accurate computer code, developed by the authors,
implementing a new model of one-dimensional finite-size PBG materials. The model also takes into account the
presence of defects; it allows to accurately determine the mode propagation constants, electromagnetic harmonics
and total field distribution, transmission and reflection coefficients, forward and backward power flow, guided and
radiated power and total losses due to radiation, Bragg scattering and out of plane scattering. The design of resonance
cavities advancing the state of the art of commercial Dense Wavelength Division Multiplexing (DWDM) filters is
performed. A great number of optical cavities have been designed and quickly simulated thanks to the fastness of
the code, allowing optimal design rules to be drawn
Amplificatori M. I. C. implicanti transistori ad arseniuro di gallio
No full textThe design criteria for broad-band MESFET microwave amplifiers, that is to say the equivalent circuit of the GaAs transistors used, the matching networks and the microstrip dispersion on alumina substrates, are examined. It is found that the unilateral equivalent circuit of the MESFET is valid up to 12 GHz and the same bandwidth is confirmed by noise parameters. The amplifier design is examined, solving the matching problems with lumped networks instead of distributed networks. Nevertheless, for high values of inductance or capacitance, distributed parameter networks must be employed. Therefore, the microstrip dispersion on alumina substrates is investigated, proposing a linear relation between the effective dielectric constant and the frequency. As an example, a two-stage amplifier with three matching networks in the band 8 divided by 12 GHz, obtaining a gain near 15 db and an input and output VSWR less than 2, is analyze
Analytic model for temperature-Dependent I-V characteristics and small-signal parameters of GaAs MESFETs
No full textIn this paper a 2-D I-V MESFET model coupled with a 3-D thermal model is presented. The temperature dependence of the velocity-electric field expression proposed by Chang et al. [1] has been considered so as to evaluate the device characteristics and small-signal parameters at the actual channel temperature. The effect of the device self-heating has been included by a coupled electrothermal simulation. The thermal dependence of all physical parameters involved both in the electric model and in the thermal model has been taken into account
Analytical investigation of the temperature dependence of GaAs FET equivalent circuit parameters
No full textIn this paper a 2-D I-V MESFET model coupled with a 3D thermal model is presented. The temperature dependence of the velocity-electric field expression proposed by Chang et al. has been considered so as to evaluate the device characteristics and small-signal parameters at the actual channel temperature. The effect of the device self-heating has been included by a coupled electrothermal simulation. The thermal dependence of all physical parameters involved both in the electric model and in the thermal model has been taken into account
A new technique for analysing light propagation in lithium niobate slab waveguides
No full textAn accurate method is proposed for evaluating the index dispersion and field distribution within a Ti: LiNbO3 slab waveguide. The derivation is based on analytical solutions of the wave equation. The propagation characteristics are obtained using Fuchs' theorem which allows the solution of the boundary-value problem, with the desired degree of accuracy, for any analytically expressed refractive-index profile, even in the cut-off regions. Only a few minutes of computer time are required to draw the dispersion curves and field distribution using a VAX system
Analytical modelling of multilayer structure electronic devices for electrothermal layout optimisation
No full textIn this paper, an analytical model for the electrothermal solution to the non-linear 3-D heat flow equation for multilayer structure electronic devices is proposed. Compared with previous models presented in literature, it is general and can be easily applied to a large variety of integrated devices, provided that their structure can be represented as an arbitrary number of superimposed layers with a 2-D embedded thermal source, so as to include the effect of the package. The proposed method is independent of the specific physical properties of the layers, hence GaAs MESFETs and HEMTs as well as silicon and silicon-on-insulator MOSFETs and heterostructure LASERs can be analysed. Moreover, it takes into account the dependence of the thermal conductivity of all the layers on the temperature; the heat equation is solved coupled with the device current-voltage relation in order to give physical consistence to the experimental evidence that a temperature increase causes a degradation of the electrical performances and that the electrical power is not uniformly distributed
An Analytical Approach for the Thermal and Electrical Design of Multilayer Structure Devices
No full textAn analytical method for the electrothermal design of multilayer structure integrated devices is presented. It can be easily applied to a large variety of devices and is independent of the specific physical properties of the layers, also accounting for the temperature dependence of the thermal conductivity
Theoretical Characterization of Multilayer Photonic Crystals having a 2D periodicity
No full textWe present a new, very accurate and fast model of Photonic Band-Gap (PBG) structure characterized by a two-dimensional (2D) periodic change of the refractive index and finite height, therefore named quasi 3D PBG.
The new model is based on the Floquet-Bloch formalism and allows to find all the propagation characteristics including the space harmonics and the total field distribution, the propagation constants, the guided and radiated power and modal loss induced by the 2D grating. A clear explanation of the physical phenomena occuring when a wave propagates inside the 2D periodic structure is presented, including the photonic bandgap formation and the radiation effects.
The approach does not require any theoretical approximation, and can be applied to study rigorously manner any PBG-based multilayer structures. We have applied the model to investigate several structures for both optical and microwave applications
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