In this paper we present a contribution to create a VHDL-AMS
radio-frequency component library. Currently, integrated circuit
technology tends to integrate in a sole chip not only mixed signal but
also mixed technology systems, going to a more general definition of
the so called Systems On Chip. A library of RF models would be useful
to model, in a same framework, circuits and systems of different
physical domains, including RF, which will certainly optimise design
process of such systems.
Generally, VHDL-AMS, the analogue and mixed signal extension to IEEE
standard VHDL does not include specific formulation for RF devices or
systems modeling, as it does not support distributed parameters for
simulation or description purposes. However, RF devices can be
modeled by means of more general VHDL-AMS resources, like sentences
including algebraic and trigonometric relations.
Recently, neuromodeling methods of microwave devices have been developed. These methods are suitable for the model generation of novel devices. They allow fast and accurate simulations and optimizations. However, the development of libraries makes these methods to be a formidable task, since they require massive input-output data provided by an electromagnetic simulator or measurements and repeated artificial neural network (ANN) training. This paper presents a strategy reducing the cost of library development with the advantages of the neuromodeling methods: high accuracy, large range of geometrical and material parameters and reduced CPU time. The library models are developed from a set of base prior knowledge input (PKI) models, which take into account the characteristics common to all the models in the library, and high-level ANNs which give the library model outputs from base PKI models. This technique is illustrated for a microwave multiconductor tunable phase shifter using anisotropic substrates. Closed-form relationships have been developed and are presented in this paper. The results show good agreement with the expected ones.
Two broadband methods for simultaneously measuring the complex values of the permittivity and permeability of film-shaped materials are presented. The complex properties of these materials are calculated from S-parameter measurements of coplanar or microstrip cells propagating the quasi-TEM dominant mode. The S-parameter measurements are easy to be implement. They are carried out from a network analyzer and on-wafer systems allowing different sizes of cell and covering 0.05-40 GHz. In the case of the coplanar, the dispersion is very low for a cell shape such as h>W+2S. Thus, a fast extraction method of the coplanar substrate properties ((epsilon) r,(mu) r ) has been developed from analytical relationships. It is faster than the microstrip extraction method, which requires a numerical method for a rigorous analysis of the microstrip cell in order to take into account the quasi-TEM mode dispersion. Measured (epsilon) r and (mu) r data for several materials are presented in the 0.05 GHz to 40 GHz frequency range. These methods show good agreement between measured and predicted values.
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