Search for: circuit-oscillations
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    Optimised analytic designed 2.5 GHz CMOS VCO

    , Article Electronics Letters ; Volume 39, Issue 16 , 2003 , Pages 1160-1162 ; 00135194 (ISSN) Dehghani, R ; Atarodi, S. M ; Sharif University of Technology
    An analytic method for prediction of oscillation amplitude and supply current of differential CMOS oscillators is presented. The validity of this method has been verified by designing an LC CMOS oscillator in a 0.24 μm CMOS technology. The predictions are in good agreement with simulation results over a wide range of supply voltage  

    An analytical approach in calculation of noise spectrum in microwave oscillators based on harmonic balance

    , Article IEEE Transactions on Microwave Theory and Techniques ; Volume 48, Issue 5 , 2000 , Pages 822-831 ; 00189480 (ISSN) Mehrshahi, E ; Farzaneh, F ; Sharif University of Technology
    In this paper, a novel method for nonlinear analysis of noise in microwave oscillators is presented. Based on harmonic balance, the method is general from the point-of-view of circuit topology, noise sources spectral distribution, and their cross correlation. In this method, the effects such as frequency conversion and frequency modulation are considered simultaneously in a unified treatment. Relatively precise estimations for the output signal spectral density of an oscillator is practically obtained. © 2000 IEEE  

    Output power variations in two mutually coupled microwave oscillators and the effect of non-linear reactance on the locking bandwidth

    , Article IEE Proceedings: Microwaves, Antennas and Propagation ; Volume 150, Issue 2 , 2003 , Pages 61-66 ; 13502417 (ISSN) Banai, A ; Farzaneh, F ; Sharif University of Technology
    The locking of two mutually coupled microwave oscillators is considered. The common frequency of oscillation is obtained both without and in the presence of a non-linear reactance. The effect of the non-linear reactance on the locking bandwidth is studied. It is shown analytically that, unlike the common injection locked oscillator case, the locking bandwidth can be either increased or decreased by the non-linearity. The variations in amplitude of oscillations is investigated. It is demonstrated that the total power delivered by the active devices decreases in interinjection locked oscillators  

    Approximation behavior of Van der Pol equation: Large and small nonlinearity parameter

    , Article IMECS 2011 - International MultiConference of Engineers and Computer Scientists 2011, 16 March 2011 through 18 March 2011 ; Volume 2 , March , 2011 , Pages 1539-1544 ; 9789881925121 (ISBN) Azarkhalili, B ; Moghadas, P ; Rasouli, M ; Sharif University of Technology
    The labels mathematician, engineer, and physicist have all been used in reference to Balthazar van der Pol. The van der Pol oscillator, which we study in this paper, is a model developed by him to describe the behavior of nonlinear vacuum tube circuits in the relatively early days of the development of electronics technology. Our study in this paper will be based entirely on numerical solutions. The rigorous foundations for the analysis (e.g., the proof that the equation has a limit cycle solution which is a global attractor) date back to the work of Lienard in 1928, with later more general analysis by Levinson and others  

    Static feedback versus fractionality of the electrical elements in the Van der Pol circuit

    , Article Nonlinear Dynamics ; Volume 72, Issue 1-2 , 2013 , Pages 365-375 ; 0924090X (ISSN) Tavakoli Kakhki, M ; Tavazoei, M. S ; Sharif University of Technology
    In this paper, it is shown that by benefiting from a static feedback control signal it is possible to reduce the effect of fractionality of the electrical capacitors on the amplitude of the oscillations produced by a Van der Pol circuit. The averaging method is used in this paper for the behavior analysis of the approximated responses of the under study circuits. Numerical simulation results are presented to confirm the effectiveness of the proposed control technique  

    Interaction of the dynamics of doubly fed wind generators with power system electromechanical oscillations

    , Article IET Renewable Power Generation ; Volume 7, Issue 2 , March , 2013 , Pages 89-97 ; 17521416 (ISSN) Jafarian, M ; Ranjbar, A. M ; Sharif University of Technology
    The interaction of the dynamics of doubly fed wind generators with the electromechanical mode of nearby synchronous generators (SGs) can affect the small signal stability of power systems with high penetration levels of wind power. In this study, a novel approach is developed to investigate these interactions and their impact on the damping of power system oscillations. In this approach it is not necessary to model the dynamic behaviour of system SGs and only the frequencies of system oscillations are important. This approach is based on the sensitivity of SGs electromechanical eigenvalue with respect to variations in the Jacobian matrix of power system. By applying this approach to a test... 

    The impact of wind farms with doubly fed induction generators on power system electromechanical oscillations

    , Article Renewable Energy ; Volume 50 , 2013 , Pages 780-785 ; 09601481 (ISSN) Jafarian, M ; Ranjbar, A. M ; Sharif University of Technology
    Introduction of large amounts of new wind generation can affect the small signal stability of power systems with three mechanisms: displacing synchronous generators (SGs); reducing SGs power generation; and the dynamics of wind farms (WFs) interacting with the electromechanical mode of SGs. In this paper a novel approach is developed to investigate the impact of the latter mechanism on existing power systems oscillations. In this approach, the dynamic behavior of grid connected WFs is studied independent of the dynamic behavior of system SGs. This approach helps to identify the conditions in which the dynamics of WFs may interact with the electromechanical mode of SGs. Also it helps to... 

    A homotopy analysis method for limit cycle of the van der Pol oscillator with delayed amplitude limiting

    , Article Applied Mathematics and Computation ; Volume 217, Issue 22 , July , 2011 , Pages 9404-9411 ; 00963003 (ISSN) Eigoli, A. K ; Khodabakhsh, M ; Sharif University of Technology
    In this work, a powerful analytical method, called Liao's homotopy analysis method is used to study the limit cycle of a two-dimensional nonlinear dynamical system, namely the van der Pol oscillator with delayed amplitude limiting. It is shown that the solutions are valid for a wide range of variation of the system parameters. Comparison of the obtained solutions with those achieved by numerical solutions and by other perturbation techniques shows that the utilized method is effective and convenient to solve this type of problems with the desired order of approximation  

    A non-stationary analysis of low-frequency electromechanical oscillations based on a refined margenau-hill distribution

    , Article IEEE Transactions on Power Systems ; Volume 31, Issue 2 , 2016 , Pages 1567-1578 ; 08858950 (ISSN) Hatami, M ; Farrokhifard, M ; Parniani, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc 
    This paper focuses on the use of quadratic time-frequency distributions (QTFDs) to characterize the temporal variation of low-frequency electromechanical oscillations (LFEOs) using ringdown data. A refined Margenau-Hill distribution (MHD) and a procedure to extract the instantaneous frequencies and damping factors as well as initial phase angles of system low-frequency modes when the analyzed signal is multi-component are proposed. The refinement process enjoys a fast-converging iterative algorithm and without loss of generality it can be applied to other QTFDs for using in other applications. A non-stationary synthetic signal as well as simulated ringdown data of a 5-area, 16-machine power... 

    Improving hardware Trojan detection using scan chain based ring oscillators

    , Article Microprocessors and Microsystems ; Volume 63 , 2018 , Pages 55-65 ; 01419331 (ISSN) Asadi Kouhanjani, M. R ; Jahangir, A. H ; Sharif University of Technology
    Elsevier B.V  2018
    In recent years, the security of integrated circuits (ICs) has received more attention as usage of ICs made by untrustworthy foundries has increased in safety-critical systems [1]. In this paper, we introduce a novel approach for fingerprinting the delay of functional paths in a sequential circuit that have millions of transistors, like processors. We present a method for inserting Ring Oscillators (ROs) into scan chain for measuring the delay of each functional path inside the chip. Using the proposed method, the payload part of Trojans will be detected according to their size and cell types. Our method can be used by power-based Trojan detection approaches for finding the trigger part of... 

    The direct piece-wise affine modeling of llc resonant converter

    , Article 45th Annual Conference of the IEEE Industrial Electronics Society, IECON 2019, 14 October 2019 through 17 October 2019 ; Volume 2019-October , 2019 , Pages 2062-2067 ; 9781728148786 (ISBN) Barzkar, A ; Tahami, F ; Molla Ahmadian, H ; Sharif University of Technology
    IEEE Computer Society  2019
    Resonant converters are hard nonlinear systems which are comprised of both continuous and discontinuous nonlinearities. Many nonlinear modeling approaches lead to a very awkward, unsystematic stability analysis and controller design. Hence, stability analysis and stabilizing controller design of the popular LLC resonant converter still remain challenging as direct consequences of the absence of a "systematic modeling". In this paper, the LLC resonant converter is modeled in the form of Piece-Wise Affine (PWA) systems and a Direct Piece-Wise Affine (DPWA) model of the DC-DC LLC resonant converter is proposed. No dynamic is omitted in the modeling approach, and accordingly, the proposed... 

    A state observer and a synchronization method for heart pacemakers

    , Article Journal of Applied Sciences ; Volume 8, Issue 18 , 2008 , Pages 3175-3182 ; 18125654 (ISSN) Gholizade Narm, H ; Azemi, A ; Khademi, M ; Karimi Ghartemani, M ; Sharif University of Technology
    In this study a synchronization method is developed to prevent the blocking arrhythmias which are caused by lack of synchronization between the two major heart pacemakers called the Sino-Atrial (SA) node and Atrio-Ventricullar (AV) node. Such pacemakers can be modeled by the Van der Pol oscillators. Feedback linearization method is used in synchronization. Since all states are not always available, they are estimated by a new observer in this research. To design the observer, first we introduce a robust observer for a unique Van der Pol oscillator. The robustness of proposed observer is obtained using gain and phase margins test. The observer variables are such that the error dynamical... 

    Extended phase compensation design of power system stabilizer for Bisotoun power plant

    , Article IFAC Proceedings Volumes (IFAC-PapersOnline) ; Volume 5, Issue PART 1 , 2006 , Pages 279-284 ; 14746670 (ISSN); 9783902661081 (ISBN) Zafarabadi, G ; Parniani, M ; Rasouli, M ; Ansarimehr, P ; Sharif University of Technology
    IFAC Secretariat  2006
    In this paper, performance of power system stabilizer (PSS) of a large thermal power plant, as tuned by the manufacturer, is investigated. Then, the stabilizer is redesigned based on extended phase compensation of the exciter input - electrical torque transfer function and root locus analysis; and its effect on local, interplant and inter-area electromechanical oscillations is thoroughly analyzed. As Bisotoun PSS has a special structure with two inputs, frequency and power, its performance is compared with power-speed PSS. The effect of PSS with existing and new tunings on transient stability is also studied. Simulation results are verified by experimental test records. Copyright © 2006 IFAC... 

    Stabilisation of multi-loop amplifiers using circuit-based two-port models stability analysis

    , Article IET Circuits, Devices and Systems ; Volume 15, Issue 6 , 2021 , Pages 553-559 ; 1751858X (ISSN) Pasdar, A ; Meghdadi, M ; Medi, A ; Sharif University of Technology
    John Wiley and Sons Inc  2021
    This article applies a systematic approach based on the normalized determinant function (NDF) theory to analyse stability in multi-loop circuits and to design the required stabilization network. Presenting several provisions, the return ratios are extracted by employing immittance or hybrid matrices (Z, Y, G or H) of active two ports. Using these matrices, instead of the S-parameters, facilitates the selection of an appropriate stabilizer network. As a practical case, a non-uniform distributed amplifier (NDA) is designed and inspected for potential instabilities. The presented procedure detects instability associated with one of the NDA circuit's loops, and an appropriate stabilization... 

    Analysis of a fractional order Van der Pol-like oscillator via describing function method

    , Article Nonlinear Dynamics ; Volume 61, Issue 1-2 , 2010 , Pages 265-274 ; 0924090X (ISSN) Attari, M ; Haeri, M ; Tavazoei, M. S ; Sharif University of Technology
    In this paper, the behavior of a fractional order Van der Pol-like oscillator is investigated using a describing function method. A parametric function for the boundary between oscillatory and nonoscillatory regions of this system is extracted. The analytical results are evaluated by numerical simulations which demonstrate sufficient reliability of the proposed analyzing method  

    Phase noise degradation of varactor and BJT frequency multipliers in the presence of parametric instability

    , Article IET Microwaves, Antennas and Propagation ; Volume 4, Issue 3 , 2010 , Pages 408-419 ; 17518725 (ISSN) Ahmadi, A ; Banai, A ; Farzaneh, F ; Sharif University of Technology
    Varactor and bipolar junction transistor (BJT) frequency multipliers are a class of non-linear circuits that show parametric instability when the input drive is varied. If parametric oscillations are present in the circuit, output phase noise of the multiplier degrades remarkably in some specific driving levels. Phase noise analysis is performed by the conversion matrix method using generalised nodal analysis. The conversion method predicts the phase noise degradation precisely because it encompasses the effect of the noise sources that are modulated by the large signal drive. The added phase noise of a varactor and a BJT frequency doubler with subharmonic oscillation is calculated and the... 

    Low-order dynamic equivalent estimation of power systems using data of phasor measurement units

    , Article International Journal of Electrical Power and Energy Systems ; Volume 74 , 2016 , Pages 134-141 ; 01420615 (ISSN) Shiroei, M ; Mohammadi Ivatloo, B ; Parniani, M ; Sharif University of Technology
    Elsevier Ltd 
    This paper utilizes data measured by phasor measurement units (PMUs) to extract a low-order dynamic equivalent model for power system stability studies. The estimated model is a 2-order model for synchronous machines. This model has the advantage of simplicity of classical model and considerably reduces the oversimplifying error of classical model. This method offers an alternative approach to analytical model reduction techniques based on the detailed system models. The proposed method uses the synchronized bus voltage and current phasors measured by PMUs. Using post disturbance data, electrical and mechanical parameters of the equivalent generator are estimated sequentially. Furthermore, a... 

    Ultra-low power frequency-shift keying demodulator based on injection-locking ring oscillator without using phase locked loop for wireless body area networks

    , Article Electronics Letters ; Volume 53, Issue 16 , 2017 , Pages 1148-1150 ; 00135194 (ISSN) Sattari, R ; Safarian, A ; Sharif University of Technology
    An ultra-low power frequency-shift keying (FSK) demodulator based on injection-locking ring oscillator for wireless body area networks is presented. The proposed system uses the power-efficient injectionlocking ring oscillator (ILRO) to replace the LC oscillator which occupies much more area on chip with higher power consumption. In addition, through the ILRO, the frequency modulated input signal is converted to a full swing rectangular signal, which can be directly demodulated by a chain of down-conversion passive mixers, lowpass filters and a comparator. Power efficiency and simplicity of the proposed structure eliminate conventional FSK demodulator based on power-hungry phase locked... 

    Hybrid control of the dc-dc SRC operating below resonance

    , Article IET Power Electronics ; Volume 10, Issue 1 , 2017 , Pages 1-9 ; 17554535 (ISSN) Afshang, H ; Tahami, F ; Molla Ahmadian, H ; Sharif University of Technology
    Institution of Engineering and Technology  2017
    Control and stabilisation of the resonant converters are essential problems in power electronics. The conventional model of the dc-dc series resonant converter (SRC) is derived using the sinusoidal approximation and generalised averaging followed by linearisation about an operating point. This model involves considerable approximation and is not applicable for large variation of load and supply voltage. The authors have already proposed a direct piece-wise affine (DPWA) modelling and control approach for the SRC that operates above resonant frequency. However, the DPWA technique is not applicable to an SRC that operates below resonance because of the presence of harmonics. In this study, a... 

    Using fractional-order integrator to control chaos in single-input chaotic systems

    , Article Nonlinear Dynamics ; Volume 55, Issue 1-2 , 2009 , Pages 179-190 ; 0924090X (ISSN) Tavazoei, M. S ; Haeri, M ; Bolouki, S ; Siami, M ; Sharif University of Technology
    This paper deals with a fractional calculus based control strategy for chaos suppression in the 3D chaotic systems. It is assumed that the structure of the controlled chaotic system has only one control input. In the proposed strategy, the controller has three tuneable parameters and the control input is constructed as fractional-order integration of a linear combination of linearized model states. The tuning procedure is based on the stability theorems in the incommensurate fractional-order systems. To evaluate the performance of the proposed controller, the design method is applied to suppress chaotic oscillations in a 3D chaotic oscillator and in the Chen chaotic system. © 2008 Springer...