Sharif Digital Repository

A technique to reduce close-in phase noise in CMOS LC voltage controlled oscillators is proposed. In CMOS differential LC oscillators, the up-conversion of flicker noise mainly determines the close-in phase noise. The flicker noise of the bias current is a major component contributing to the overall low frequency noise. In this paper, a switched biasing technique to suppress the flicker noise of the bias circuit is presented. A 1.8v 2.4GHz differential LC VCO is designed in a 0.18u CMOS technology using this technique. With the proposed switching technique, the close in phase noise is improved as much as 15dB at 500 kHz offset. The simulated phase noise at the offsets of 500 kHz and 1 MHz is... 

The flow-induced oscillation (FIO) of bluff bodies is commonly encountered in the fluid structure interaction (FSI) problems. In this study, we use an unstructured moving grid strategy and simulate the FIO of two rigid plates, which are elastically hinged at the two ends of a fixed flat plate in a cross-flow. We use a hybrid finite-element-volume (FEV) method in an arbitrary Lagrangian–Eulerian (ALE) framework to study FIO of the two hinged plates. The current simulations are carried out for wide ranges of flow Reynolds number (50–175), spring stiffness coefficient, and the two hinged plates’ moment of inertia magnitudes. The influences of these parameters are investigated on the magnitudes... 

A methodology for controlling three phase PFC Sepic converter is presented, and behavior of the system is evaluated. The converter is connected in delta at the input and parallel at the output side, and is controlled by variable hysteresis current control method. By this approach, the current drawn by each of the individual converters is controlled to be in phase with its own input voltage. Detailed design criteria for the power and control stages of the single-phase SEPIC converter are presented and effects of this method on THD are verified  

This paper presents a broadband low-loss quadrature-hybrid-based network that enhances the phase and the amplitude matching of quadrature signals. The performance of this network is investigated, and a detailed theoretical analysis is provided. Several stages of this network can be cascaded to generate broadband balanced quadrature signals. Each stage has a loss of 0.5 dB and enhances the image rejection ratio (IRR) by approximately 8 dB. Compared with the conventional polyphase quadrature signal generation methods, the proposed network enables lower insertion loss, wider bandwidth, and reduced sensitivity to process variations. To verify the theoretical analyses, two proof-of-concept... 

When a transparent plane-parallel plate is illuminated at a boundary region by a parallel monochromatic beam of light, Fresnel diffraction occurs because of the abrupt change in phase imposed by the finite change in refractive index at the plate boundary. The intensity of the diffraction fringes varies periodically with changes in the optical path difference of the light passing through the plate edge. The optical path difference depends on the incident angle of the light, the refractive index of the plate and surrounding medium, and the wavelength of the light. Plotting the intensity of the diffraction fringes versus optical path difference provides a general phase shift method for phase... 

Among the locomotion concepts employed in the microrobotics, friction-based locomotion principles are of considerable importance. In this study, the dynamic modelling of friction drive microrobots subjected to the tangential and normal excitations is investigated, which have the same frequency, but are shifted in phase. The motion equation of the microrobot reveals a strongly non-linear differential equation with discontinuity for which the elastic force term is proportional to a signum function. Using the homotopy perturbation method, simple expressions are derived for predicting average velocity of the slider. The obtained results are in good agreement with those achieved from numerical... 

In this paper, a modified method based on the frequency discriminator technique for measuring phase noise of microwave oscillators is presented. In the proposed method, the phase shifter is omitted. In contrast, a 90° hybrid with one more channel containing a phase detector, and a low-noise amplifier is added to the measurement setup. It can be said that an in-phase/quadrature phase-noise detection has been developed. With the proposed method, tuning of the variable phase shifter is not needed anymore. Therefore, the measurement is done automatically, and as a result, the measurement time is decreased. Another considerable advantage of this method is that the method is theoretically... 

This paper presents a technique for estimation of amplitude information from an interferometric time-domain optical coherence tomography (OCT) signal. The conventional estimation scheme is based on the in-phase and quadrate (IQ) demodulation concept. A disadvantage of this method is that the IQ components include a ripple whose frequency is the double of the interferometric signal frequency. The improved method of demodulation, presented in this paper, yields a more precise estimation of the amplitude information by fundamentally removing the ripple. Theoretical and experimental OCT signals are applied to both demodulation systems and the amplitude is computed. The detected signals from both... 

The prevention of combustion instability is unquestionably the greatest technical challenge and can be a significant cost driver in new engine development programs. In order to meet challenge, a predictive stability code is required. The main objective of this work is to develop a mechanistic engineering code for analysis of high frequency combustion instability in LRE. The developed MEchanistic Combustion Stability COmputer Program (MECSCOP), evaluates combustion stability using the transfer function approach, whereby the ability of the chamber to dissipate acoustic oscillations is compared to the oscillatory combustion driving mechanisms. The driving mechanisms are classified by the source... 

In the present paper, numerical simulation of thermal barrier coating system under thermo-mechanical loadings is performed, using the finite element method in ABAQUS software. The base material is Aluminum-silicon alloy, A356.0 which is widely used in automotive components such as diesel engine cylinder heads. Thermal barrier coatings (TBCs) are applied to combustion chamber in order to reduce fuel consumption and pollutions and also improve fatigue life of components. The roughness effect of coating layers on stress distribution of test specimens is investigated. Semi-ellipsoid roughness of the interfaces between substrate/bond coat and bond coat/top coat are simulated to get the stress... 

A new broadband frequency discriminator is introduced for demodulating the frequency modulated signals in the microwave frequency range. Direct demodulation with no need for tuning the center frequency of the resonance circuits is the most important advantage of the proposed technique. This technique uses the in-phase/quadrature demodulation, in some manner, without using any additional local oscillator for down conversion. Simulation of the proposed demodulator has been done with Advanced Design System software to evaluate and predict the system behavior. A setup based on the proposed method was designed and implemented in order to verify the accuracy of the theory. We tested the proposed... 

A multi-band frequency synthesizer for In-phase and Quadrature (I/Q) LO signal generation in Digital TV tuners is presented. Using divisor numbers other than powers of 2 (2 n ) for quadrature generation, reduces the required frequency range of the VCO, hence the number of VCO circuits, in multi-band frequency synthesizers. In the proposed synthesizer, VHF, UHF and L-band frequencies are covered with only one VCO. This is achieved by using a novel divide-by-3 circuit which produces precise I/Q LO signals. The VCO tuning range in this design is 2,400-3,632 MHz which is covered by a 6-bit switched-capacitor bank. A fast adaptive frequency calibration block selects the closest VCO frequency to... 

A single-stage structure is proposed for realizing a unity power factor three-phase isolated AC-DC converter for telecommunication power supply modules. This structure is composed by integrating a boost converter to the isolated threephase three-switch buck rectifier. Modified space vector modulation method is applied to the three-phase three-switch isolated unity power factor input buck rectifier based on the space vector modulation for non-isolated buck. The output boost switch operates during heavily unbalanced mains conditions. Input currents are sinusoidal and in phase with the input voltages even for heavily unbalanced input voltages, e.g. loss of one phase. The converter is modeled by... 

Induced Polarization (IP) is a non-intrusive geophysical method to monitor Dense Non-Aqueous Phase Liquid (DNAPL) contamination and remediation processes underground. In this study, an advanced numerical code simulating DNAPL flow and complex electrical resistivity is presented. The model was validated against existing IP results and image measurements that were carried out previously in a series of 2D tank experiment. Multiphase flow modeling in porous media is coupled with electrical current modeling to simulate the process of DNAPL migration and the associated IP response. This brings a broader view of the contamination in space and time compared to surface and borehole measurements,... 

This paper presents a phase-noise reduction technique for voltage-controlled oscillators (VCOs) using a harmonic tuned (HT) LC tank. The phase-noise suppression is achieved through almost rectangular-shaped VCO oscillating signal which effectively maximizes oscillating signal slope at zero crossing points resulting in-phase-noise degradation. In addition, by shortening down converted noise power around oscillating signal second harmonic, more phase-noise suppression has been achieved. A comprehensive analysis for frequency and amplitude deviations as high as 20% for third harmonic and its effect on output phase-noise suppression has been discussed. In the followings, a comprehensive analysis...