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In this paper we present a coherent set of tools allowing an accurate and predictive design of low phase noise oscillators. Advanced phase noise modelling techniques in non linear microwave devices must be supported by a proven combination of the following : - Electrical modeling of low-frequency noise of semiconductor devices, oriented to circuit CAD . The local noise sources will be either cyclostationary noise sources or quasistationary noise sources. - Theoretically-based design rules are needed in order to define the most appropriate circuit architecture in function of the main characteristics to be optimized. For phase noise evaluation in feedback oscillators, the modified Leeson formula is a useful tool. Finally, results obtained with a 2 GHz HBT push-push VCO based on this methodology are presented.

This paper presents a theoretical and experimental analysis of the phase conversion phenomena in a power PHEMT transistor. Relationships between the linearity of the device and the intrinsic gate-source capacitance CGS, gate-drain capacitance CGD ,transconductance GM as well as the load impedance ZL ,are explained. A judicious choice of the transistor’s operating conditions allows to reduce thephaseconversion AM/PM. In the case of PHEMT devices, the behaviors of CGS,CGD,GM elements and ZL value induce internal compensation phenomena between the intrinsic non-linearities.

A versatile pulsed I(V) and 40 GHz pulsed S parameters measurement system of microwave transistors is described Capability of discrimination between thermal and trapping effects with a pulse set-up is demonstrated A method to measure electrically the thermal resistance and capacitance of transistors with a pulse set-up is proposed Finally, it is explained how to derive transistor nonlinear characteristics from these measurements for modeling purposes.

Stability analysis of MMICs becomes a preoccupation of engineers for the design of power amplifiers as well as of oscillators. In this paper it is shown that the classical approach of linear stability analysis fails in the case of unstable unloaded circuits. Nyquist based methods are proposed to circumvent this problem. A method relying on the general Harmonic Balance formulation is proposed, which enables the linear and non linear stability analysis. Examples of global stability analysis based on the resolution of the bifurcation equations are given. Finally an open loop method is proposed which allows to design analog frequency dividers with the aid of standard CAD packages.

Recently, a new configuration has been proposed for the design of MMIC frequency dividers [1]. Following this method, a MMIC broadband analog frequency divider in the millimetric range has been designed and manufactured for applications in mobile communication systems. Nonlinear simulations of the device have been performed, showing the ability of H.B techniques to handle such complicated functions. Finally, comparisons between calculated and measured results have been performed, exhibiting a good agreement.

The design of optimized non-linear microwave circuits remains a difficult task although commercial CAD tools come to maturity. The aim of our paper is to provide some insights on different aspects encountered by designers confronted with the problem of modelling and simulation of non-linear circuits.