SUMMARYThe 'Quite universal circuit simulator ' (Qucs) is an open source circuit simulator supporting Verilog-A compact model standardization. This paper describes a number of compact semiconductor device and circuit macromodelling techniques that have been implemented in recent Qucs releases, stressing those techniques that are not found in SPICE 2g6 or 3f5. It also introduces a novel hierarchical approach to Verilog-A compact model and circuit macromodel construction based on non-linear equation-defined devices, linear-controlled sources and noise generators embedded in subcircuits. To illustrate the new approach, the properties and models of a number of components with electrical and non-electrical characteristics are described. These models demonstrate how recent trends in open source simulation technology use embedded equations as integral elements in component and physical process models.

SUMMARYRecent trends in compact device modelling and circuit simulation suggest a growing movement towards standardization of Verilog-A as a vehicle for semiconductor device specification and model interchange among commercial and open source simulators. This paper introduces a nonlinear equation-defined device (EDD) characterized by current, voltage and charge equations with a similar syntax to Verilog-A. The EDD has been implemented in Qucs and used extensively as a central feature in an interactive modelling system that allows straightforward prototyping of compact device models prior to translation into Verilog-A. To illustrate the properties and the use of the Qucs EDD a number of examples centred on well-known SPICE models are described.

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Characterization of the frequency response of coherent radiometric receivers is a key element in estimating the flux of astrophysical emissions, since the measured signal depends on the convolution of the source spectral emission with the instrument band shape. Laboratory Radio Frequency (RF) measurements of the instrument bandpass often require complex test setups and are subject to a number of systematic effects driven by thermal issues and impedance matching, particularly if cryogenic operation is involved. In this paper we present an approach to modeling radiometers bandpasses by integrating simulations and RF measurements of individual components. This method is based on QUCS (Quasi Universal Circuit Simulator), an open-source circuit simulator, which gives the flexibility of choosing among the available devices, implementing new analytical software models or using measured S-parameters. Therefore an independent estimate of the instrument bandpass is achieved using standard individual component measurements and validated analytical simulations. In order to automate the process of preparing input data, running simulations and exporting results we developed the Python package python-qucs and released it under GNU Public License . We discuss, as working cases, bandpass response modeling of the COFE and PLANCK Low Frequency Instrument (LFI) radiometers and compare results obtained with QUCS and with a commercial circuit simulator software. The main purpose of bandpass modeling in COFE is to optimize component matching, while in LFI they represent the best estimation of frequency response, since end-to-end measurements were strongly affected by systematic effects.-1 -arXiv:1011.6363v2 [astro-ph.IM]