The Experts below are selected from a list of 4719 Experts worldwide ranked by ideXlab platform

Michael E. Tobar - One of the best experts on this subject based on the ideXlab platform.

  • Current limitations of cryogenic Microwave oscillator frequency stability
    2014 IEEE International Frequency Control Symposium (FCS), 2014
    Co-Authors: Stephen R. Parker, Michael E. Tobar, Eugene Ivanov, John G. Hartnett
    Abstract:

    Cryogenic Microwave Oscillators built upon sapphire loaded cavity resonators exhibit excellent levels of frequency stability. Here we present an overview of the current understanding of the various processes and noise sources that limit this frequency stability performance and provide an outlook of future research.

  • Precise phase synchronization of a cryogenic Microwave oscillator
    The Review of scientific instruments, 2010
    Co-Authors: Eugene Ivanov, Michael E. Tobar, D. Mouneyrac, J.-m. Le Floch, Dominique Cros
    Abstract:

    We developed a novel technique for accurate phase synchronization of Microwave Oscillators based on sapphire dielectric resonators cooled to liquid nitrogen temperature. The achieved quality of phase synchronization (a few milliradians) enables the accurate measurements of extremely weak phase fluctuations expected from the next generation of ultralow phase noise Microwave Oscillators.

  • Accurate phase synchronization of a cryogenic Microwave oscillator
    2010 IEEE International Frequency Control Symposium, 2010
    Co-Authors: Eugene Ivanov, Michael E. Tobar, D. Mouneyrac, J.-m. Le Floch, Dominique Cros
    Abstract:

    We developed an effective technique for phase synchronization of a cryogenic Microwave oscillator. The achieved quality of phase synchronization is a few milliradians. It enables accurate measurements of extremely weak phase fluctuations expected from the next generation of frequency stabilized Microwave Oscillators based on the cryogenically cooled sapphire dielectric resonators.

  • Design and Performance of Low-Phase Noise Microwave Oscillators
    2007 IEEE International Frequency Control Symposium Joint with the 21st European Frequency and Time Forum, 2007
    Co-Authors: E.n. Ivanov, Michael E. Tobar
    Abstract:

    This work verifies that the X-band Microwave Oscillators with the phase noise spectral density approaching -157 dBc/Hz at 1 kHz offset frequency can be reproducibly constructed. Such a performance can be achieved by frequency locking a conventional loop oscillator to the room temperature stabilised sapphire dielectric resonator using the principles of Microwave circuit interferometry and operating the resonator at the elevated level of dissipated power. We discuss the noise mechanisms responsible for the flicker frequency fluctuations of the high power Microwave Oscillators with interferometric signal processing, as well as the technique for the high resolution noise measurements at Microwave frequencies.

  • Ultra-low-noise Microwave oscillator with advanced phase noise suppression system
    IEEE Microwave and Guided Wave Letters, 1996
    Co-Authors: Eugene Ivanov, Michael E. Tobar, R A Woode
    Abstract:

    An advanced phase noise reduction technique has been developed to improve the short-term frequency stability of Microwave Oscillators. The technique is based upon an ultrasensitive Microwave frequency discriminator with effective noise temperature close to its physical temperature. The phase noise spectral density of a 9 GHz Microwave loop oscillator incorporating such a discriminator has been measured as -120 dBc/Hz and -150 dBc/Mz at offset frequencies of 100 Hz and 1 kHz, respectively. This performance is at least 25 dB better than current state of the art. The developed phase noise reduction technique is quite general and can have valuable implications for the design of various low phase noise Microwave Oscillators.

Mabel Ponton - One of the best experts on this subject based on the ideXlab platform.

  • analysis of the transient dynamics of Microwave Oscillators
    IEEE Transactions on Microwave Theory and Techniques, 2019
    Co-Authors: Sergio Sancho, Franco Ramirez, Almudena Suarez, Mabel Ponton
    Abstract:

    A semianalytical method for the global prediction and understanding of the transient dynamics of oscillator circuits is presented. It covers both the linear and nonlinear transient stages, which are related with the circuit generalized eigenvalues, here introduced for the first time. The transient model relies on the application of the implicit function theorem to the harmonic-balance (HB) system, in order to derive a reduced-order nonlinear differential equation from a given observation node. This requires the extraction of a nonlinear admittance function, depending on the voltage excitation and oscillation frequency, which is done with a forcing auxiliary generator (AG). The linearization of this admittance function for each excitation amplitude provides a sequence of linear ordinary differential equations (ODEs), describing the system dynamics in the vicinity of each point of the transient trajectory, which can be reconstructed from the expression of the solution increment at each time step. The sequence of differential equations provides a set of generalized eigenvalues, responsible for the acceleration or deceleration of the oscillation growth and capable to detect spurious transient frequencies. The concept of escape time, or time required by the transient trajectory to go through a certain interval of amplitude values, is also introduced, for the first time to our knowledge. The method has been successfully applied to analyze the transient dynamics of several FET Oscillators, including dual-frequency Oscillators and switched Oscillators.

Sergio Sancho - One of the best experts on this subject based on the ideXlab platform.

  • analysis of the transient dynamics of Microwave Oscillators
    IEEE Transactions on Microwave Theory and Techniques, 2019
    Co-Authors: Sergio Sancho, Franco Ramirez, Almudena Suarez, Mabel Ponton
    Abstract:

    A semianalytical method for the global prediction and understanding of the transient dynamics of oscillator circuits is presented. It covers both the linear and nonlinear transient stages, which are related with the circuit generalized eigenvalues, here introduced for the first time. The transient model relies on the application of the implicit function theorem to the harmonic-balance (HB) system, in order to derive a reduced-order nonlinear differential equation from a given observation node. This requires the extraction of a nonlinear admittance function, depending on the voltage excitation and oscillation frequency, which is done with a forcing auxiliary generator (AG). The linearization of this admittance function for each excitation amplitude provides a sequence of linear ordinary differential equations (ODEs), describing the system dynamics in the vicinity of each point of the transient trajectory, which can be reconstructed from the expression of the solution increment at each time step. The sequence of differential equations provides a set of generalized eigenvalues, responsible for the acceleration or deceleration of the oscillation growth and capable to detect spurious transient frequencies. The concept of escape time, or time required by the transient trajectory to go through a certain interval of amplitude values, is also introduced, for the first time to our knowledge. The method has been successfully applied to analyze the transient dynamics of several FET Oscillators, including dual-frequency Oscillators and switched Oscillators.

  • growth rate function for the nonlinear analysis of the transient dynamics of Microwave Oscillators
    International Microwave Symposium, 2016
    Co-Authors: Almudena Suarez, Sergio Sancho, Franco Ramirez
    Abstract:

    In this paper, a new technique is presented for the analysis of the transient dynamics of Microwave Oscillators. The technique makes use of a nonlinear admittance function that can be identified in commercial Harmonic Balance software. This function is included in a time-frequency domain equation governing the transient dynamics. The equation provides the growth rate function of the first harmonic amplitude, which allows an exhaustive analysis of the transient speed from the neighborhood of the dc solution to the oscillation establishment, with no need for a numerical integration, as in time domain or envelope-transient methods. The technique has been applied to predict the length of the transient towards the oscillating state of a FET oscillator at 5 GHz.

  • General stabilization techniques for Microwave Oscillators
    IEEE Microwave and Wireless Components Letters, 2005
    Co-Authors: Sergio Sancho, Franco Ramirez, Almudena Suarez
    Abstract:

    A general stabilization technique is proposed to suppress undesired spurious oscillations in Microwave Oscillators. The purpose is to eliminate these oscillations while maintaining the oscillation frequency and amplitude of the originally-unstable solution. The main advantage of the technique is its wide generality of application, not restricted to low-frequency spurious oscillations. It has been tested on an unstable 18-GHz push-push oscillator that has been manufactured and measured, with very good agreement with the simulation results.

Olivier Llopis - One of the best experts on this subject based on the ideXlab platform.

  • High-Q Optical Resonators for Laser Stabilization in Microwave Photonics Oscillators
    2009
    Co-Authors: Pierrehenri Merrer, Olivier Llopis, A Bouchier, Houda Brahimi, Gilles Cibiel
    Abstract:

    High-Q optical resonators are interesting for Microwave Oscillators and laser stabilization. We present whispering gallery modes resonators and resonant fibre loops with measured optical quality factors higher than 10^9, and an application.

  • high q optical resonators for stabilization of high spectral purity Microwave Oscillators
    International Frequency Control Symposium, 2009
    Co-Authors: Pierrehenri Merrer, Olivier Llopis, A Bouchier, Houda Brahimi, Gilles Cibiel
    Abstract:

    Different high-Q optical resonators are presented in this communication. Our aim is to use them to develop compact high performances Microwave Oscillators. The optical quality factor of a quartz disk used as a whispering gallery modes resonator has been measured to be higher than 109. We also investigate the potentialities of high-Q fibre ring resonators. The performances of an optoelectronic oscillator at 10 GHz based on such a passive fibre ring resonator are presented here.

  • Optical techniques for Microwave frequency stabilization : resonant versus delay line approaches and related modelling problems
    2008
    Co-Authors: Pierrehenri Merrer, Houda Brahimi, Olivier Llopis
    Abstract:

    Optical techniques for Microwave Oscillators stabilization or Microwave sources phase noise measurement are discussed. The advantage in terms of Q factor of optical resonant devices goes with increased difficulties in the system stabilization. System modelling is also complex, because of the interaction of noise sources around three different frequencies : optical, Microwave and baseband.

  • High-frequency noise contribution to phase noise in Microwave Oscillators and amplifiers
    Noise in Devices and Circuits II, 2004
    Co-Authors: Gilles Cibiel, Laurent Escotte, Olivier Llopis, Michel Chaubet
    Abstract:

    Phase noise of Microwave free running sources has always been an important problem in various applications. This noise generates an increased bit error rate in a telecommunication link and degrades the sensitivity of a radar (particularly in the case of Doppler or FM-CW radar). Reducing this noise contribution is a difficult challenge for Microwave engineers and circuit designers. The main contributor to this noise is well known to be the Microwave transistor and finally an improvement of the oscillator phase noise will result from an optimization of the transistor phase noise. The 10 kHz to 1 MHz offset frequency range is the most important frequency range for many Microwave Oscillators applications. An improvement of the transistor (or oscillator) phase noise in this frequency range cannot be obtained without a good knowledge of the noise mechanisms involved in the device. In this frequency range, two different mechanisms may be at the origin of the phase noise. The first one involves the conversion to high frequencies of the transistor baseband noise (or 1/f noise) through the devices nonlinearities. The second one is due to the direct superposition of the transistor high frequency noise. This noise is simply added to the carrier, and this contribution may be described using the amplifier noise figure. In this paper, the evidence of the transistor high-frequency noise contribution in residual phase noise data is demonstrated. This behavior is observed in several bipolar devices in which the low-frequency noise contribution has been carefully minimized using an optimized bias network. Then, the phase noise behavior is correlated to nonlinear noise figure measurements. This study has been carried on numerous different Microwave transistors, including FET and bipolar devices. An increase of the noise figure with the Microwave signal level has been observed in each case.

  • analytic investigation of frequency sensitivity in Microwave Oscillators application to the computation of phase noise in a dielectric resonator oscillator
    Annales Des Télécommunications, 1996
    Co-Authors: Olivier Llopis, Jeanmarc Dienot, Jacques Verdier, R Plana, Michel Gayral, J Graffeuil
    Abstract:

    The conversion of low frequency noise into phase noise in Microwave Oscillators is studied through an analytical calculation of the pushing factor. This calculation is based on a simplified equivalent circuit for two types of active devices : field effect transistors (Fet) and heterojunction bipolar transistors (hbt). The preeminence in the conversion process of the gate- source capacitance in theFet and the base- emitter junction in thehbt is pointed out. Practical methods are proposed to reduce the phase noise in these circuits.

Franco Ramirez - One of the best experts on this subject based on the ideXlab platform.

  • analysis of the transient dynamics of Microwave Oscillators
    IEEE Transactions on Microwave Theory and Techniques, 2019
    Co-Authors: Sergio Sancho, Franco Ramirez, Almudena Suarez, Mabel Ponton
    Abstract:

    A semianalytical method for the global prediction and understanding of the transient dynamics of oscillator circuits is presented. It covers both the linear and nonlinear transient stages, which are related with the circuit generalized eigenvalues, here introduced for the first time. The transient model relies on the application of the implicit function theorem to the harmonic-balance (HB) system, in order to derive a reduced-order nonlinear differential equation from a given observation node. This requires the extraction of a nonlinear admittance function, depending on the voltage excitation and oscillation frequency, which is done with a forcing auxiliary generator (AG). The linearization of this admittance function for each excitation amplitude provides a sequence of linear ordinary differential equations (ODEs), describing the system dynamics in the vicinity of each point of the transient trajectory, which can be reconstructed from the expression of the solution increment at each time step. The sequence of differential equations provides a set of generalized eigenvalues, responsible for the acceleration or deceleration of the oscillation growth and capable to detect spurious transient frequencies. The concept of escape time, or time required by the transient trajectory to go through a certain interval of amplitude values, is also introduced, for the first time to our knowledge. The method has been successfully applied to analyze the transient dynamics of several FET Oscillators, including dual-frequency Oscillators and switched Oscillators.

  • growth rate function for the nonlinear analysis of the transient dynamics of Microwave Oscillators
    International Microwave Symposium, 2016
    Co-Authors: Almudena Suarez, Sergio Sancho, Franco Ramirez
    Abstract:

    In this paper, a new technique is presented for the analysis of the transient dynamics of Microwave Oscillators. The technique makes use of a nonlinear admittance function that can be identified in commercial Harmonic Balance software. This function is included in a time-frequency domain equation governing the transient dynamics. The equation provides the growth rate function of the first harmonic amplitude, which allows an exhaustive analysis of the transient speed from the neighborhood of the dc solution to the oscillation establishment, with no need for a numerical integration, as in time domain or envelope-transient methods. The technique has been applied to predict the length of the transient towards the oscillating state of a FET oscillator at 5 GHz.

  • General stabilization techniques for Microwave Oscillators
    IEEE Microwave and Wireless Components Letters, 2005
    Co-Authors: Sergio Sancho, Franco Ramirez, Almudena Suarez
    Abstract:

    A general stabilization technique is proposed to suppress undesired spurious oscillations in Microwave Oscillators. The purpose is to eliminate these oscillations while maintaining the oscillation frequency and amplitude of the originally-unstable solution. The main advantage of the technique is its wide generality of application, not restricted to low-frequency spurious oscillations. It has been tested on an unstable 18-GHz push-push oscillator that has been manufactured and measured, with very good agreement with the simulation results.

  • nonlinear optimization tools for the design of high efficiency Microwave Oscillators
    IEEE Microwave and Wireless Components Letters, 2004
    Co-Authors: S V Hoeye, Franco Ramirez, Almudena Suarez
    Abstract:

    A new systematic method is presented for the design of high-efficiency Microwave Oscillators. It is based on the control of the transistor output-voltage waveform, through the combined use of a nonperturbing auxiliary generator and a substitution generator. The nonperturbing generator sets the oscillation frequency at the desired value during the entire design process. The combination of the two generators allows obtaining a quasisquare output-voltage waveform, with optimum harmonic components to maximize the efficiency. Attention is paid to the stability and phase noise of the implemented oscillator, which are analyzed versus technological parameters. A 6-GHz oscillator has been designed using these techniques, with good experimental results.