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Theses

Développement d'un outil logiciel industriel d'aide à la conception des oscillateurs à quartz

Abstract : For long time crystal crystal oscillator was designed on the basic of empirical methods or approximate or inappropriate modelling techniques. Although these methods help to produce stable oscillators, their design procedure remains tedious and circuit oscillator behaviour is not always obtained with an optimal accuracy. ADOQ software (Dipolar Analysis of crystal Oscillators) was developed to remedy the limitations of these methods. This tool is based on the dipolar analysis which consists in modelling a crystal oscillator by taking in to account the amplifier nonlinearities separately from quartz resonator. This separation overcomes the expensive computing time imposed by the high—Q factor of the quartz résonator. The nonlinear behaviour of the amplifier can be determined in open loop by using transient analysis carried out by using an electric SPICE—like simulator. The nonlinear equivalent impedance of the amplifier can be obtained by processing the results provided by this simulator. The simulator's results allows us to determine accurately the nonlinear equivalent impedance of the amplifier, i.e. its impedance vs the frequency and amplitude. Then, the analysis consists in seeking the closed loop solution by using a series of open loop dipolar analyses and an itérative algorithm. This method leads to an accurate calculation of the operating conditions of the oscillator: frequency, resonator amplitude, drive level in steady—state operation, transient as well as state and amplitude and phase noise spectra. ADOQ allow us to determine characteristic sensitivity of the oscillator to the variations of the component value. The dipolar method requires to calculate the steady—state nonlinear amplifier impedance as a function of the harmonic current source amplitude. Although the separation of the resonator from the amplifier allows noticeable decrease of the computer time, the SPICE—like simulator transient analysis still needs a large computer time to reach the steady—state. Other analysis methods used in some industrial simulators allow to find the steady—state of a nonlinear circuit more quickly: harmonic—balance or shooting—method are among them. On the other hand, models used by SPICE are limited by component libraries provided by the vendor of the tool or the component manufacturer. A large part of this thesis consists in exploiting the Cadence CAD tool to increase the performances in terms of computing (SpectreRF) and facilites in terms of component models (Dracula) to optimize the ADOQ software. Tests and simulations have been performed and the results obtained evidence the achived improvements as well as their limits. KEY WORDS— Quartz oscillator, dipolar analysis, shooting-method, periodic steady
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Submitted on : Friday, June 23, 2006 - 12:58:03 AM
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  • HAL Id : tel-00081366, version 1

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Farid Chirouf. Développement d'un outil logiciel industriel d'aide à la conception des oscillateurs à quartz. Autre. Université de Franche-Comté, 2005. Français. ⟨tel-00081366⟩

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