Sharif Digital Repository

Recently, a class of fractional multi-frequency oscillators, constructed based on using n integrators and n half-order ones, has been introduced, whose steady-state responses contain sinusoidal components with 0.5 (3 n- 1 ) number of selectable frequencies. In this paper, the structure of the introduced multi-frequency oscillator is modified such that, notwithstanding the frequency content preservation, the number of its involved integrators is reduced. With no effect on the frequency content of the generated oscillations, this modification causes that the circuitry implementation of the considered class of multi-frequency oscillators can be done with a less number of energy storage... 

Extensive wind tunnel tests have been conducted to study the unsteady aerodynamic behavior of a standard dynamics model, SDM, oscillating in plunge mode. The unsteady aerodynamic behavior of various missile and aircraft configurations under pitching motion has been studied so far. However up to now, there is little or no result on the plunging behavior of an aircraft or missile as a whole and the present experiments can be considered as one of the first attempts to study the compressible flowfield over an aircraft undergoing plunging motion. The experiments involved measuring the normal force and pitching moment of the model oscillating in plunge at Mach numbers of 0.4, 0.6 and 1.5 and... 

Modified two-phase latch and flip-flop are introduced to implement a linear phase-detector (LPD) for 1/N-rate clock recovery applications. This technique greatly simplifies the required circuitry of the LPD and makes it suitable for higher speed applications while consuming less power compared to the conventional techniques  

This paper deals with investigating the maximum number of frequencies generated by an oscillator in the case that a half number of integrators in the conventional dynamic structure of this oscillator are replaced by fractional integrators with an identical order. First, an upper bound for the maximum number of frequencies, which can exist in a steady state response of the oscillator, with respect to the number of integrators, is obtained. Then, on the basis of the recent advances in the field of determinant-based representations of bivariate polynomials, a lower bound is found for the maximum number of sinusoidal components in the steady state oscillations generated by the oscillator. A... 

In this paper, we propose a new voltage controlled oscillator (VCO) with a high oscillation frequency yet low power consumption. The oscillator which is a single stage circuit has a low phase noise due to reduced noise sources. To evaluate the performance parameters, the oscillator was simulated in a 0.18-μm standard CMOS process. The results show that the oscillation frequency of VCO may vary between 4.66-5.9 GHz. Also, the phase noise of the VCO at oscillation frequency of 5.6 GHz is -99.7 dBc at 1 MHz offset frequency. Also, the power consumption was 4.8 mW at the same oscillation frequency. © 2007 IEEE  

This paper presents a new architecture for VCO-based Continuous Time Delta Sigma Modulators. This approach is based on the differential configuration for the quantizer while maintains its inherent dynamic element matching property. Consuming no additional power and area compared to the conventional scheme, this architecture can eliminate the even orders of harmonic distortion and achieve higher linearity. Theoretical analysis for signal to quantization noise, power and area consumption and mismatch effect is provided. To illustrate the effectiveness of the new architecture in continuous time modulators, a modulator with 640 MHz sampling rate utilizing the mentioned quantizer is simulated in... 

An analysis of resonant modes in ladder networks is performed using difference equations. Linear and loop configurations are studied and analytical relations are derived for the mode distributions and resonant frequencies of these networks, having arbitrary elements. Furthermore, it is shown that a) Modes with an exponential distribution along network nodes may exist in some cases and b) The mode distributions in loop networks are independent of network elements. Finally, a simple criterion is obtained for a loop structure to control the spacing between resonant frequencies. © Sharif University of Technology, April 2008  

Recently, several high-order accurate methods have been developed for solving nonlinear equations governing in the high-frequency oscillations of a fluid column. If we assume that the value of Reynolds and Prandtl numbers are high enough then it is possible to neglect the effect of Stokes Layer and it has been previously shown that the calculated pressure profile obtained by solving three-dimensional axisymmetric compressible NS (Navier-Stokes) equations is in good agreement with one-dimensional adiabatic model of Ilinskii. For this particular flow which is the typical of engineering flows inside acoustical compressors, it is clear that high-resolution simulation of NS equations in higher... 

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... 

In this paper a self-oscillating mixer is presented fundamental signal generated by the oscillator subcircuit in the mixing process. The oscillator core consumes 3mA of current from a 1.8 V DC supply and results in an output power of -0.867 dBm per oscillator, and a measured phase noise of -91, -102 and -108 dBc/Hz at 100 KHz, 600 KHz and 1 MHz from the carrier, respectively. In the mixing process the proposed mixer achieved IIP3 of 0 dBm with conversation gain of 1.93 dB. The circuit was designed and simulated in 0.18-μm CMOS technology by ADS2010  

Studies show that High frequency oscillations (HFOs) can be used as a reliable biomarker of epileptogenic zone, thus many algorithms have been proposed to detect HFOs. Among the wide variety of HFOs, fast ripples (FRs) are important transient oscillations occurring in the frequency band ranging from 250 Hz to 600 Hz. The automatic detection of FRs can be degenerated by the presence of some 'pulse-like' events (commonly, the component of interictal epileptic spikes) associated with an increase of the signal energy in the high frequency bands, exactly as in the case of real FRs. The goal of this study is to propose a new method for automatic detection of fast ripples by using Hidden Markov... 

This paper presents a low voltage low noise open loop automatic amplitude control method for voltage-controlled oscillators (VCO's). In this method a feedback mechanism keeps the VCO at its optimum amplitude over temperature and process variations and then the loop is broken to avoid noise injection form the control circuitry to the VCO. The loop does not add extra noise to the VCO. Based on the proposed method, a low voltage low noise LC-VCO was designed for a low phase noise application in TSMC 0.18 micron RFCMOS technology. Simulations show considerable improvement in the phase noise with the application of the proposed method  

This paper presents the design and implementation of a low power, low voltage, continuous time delta sigma modulator for audio band in 90 nm CMOS technology. A VCO-based integrator and quantizer are used. Inherent dynamic element matching (DEM) of the quantizer eliminates the need for explicit DEM logic which results in a short excess-delay and power saving. Simulation results show that the modulator achieves 78 dB SNDR and 87 dB SNR in a 20 kHz input bandwidth and dissipates 106 μW from 1 V supply. The power consumption for different parts is discussed  

A new phase noise calculation method is proposed in which noise sources are modeled with single tone sources. It uses a nonlinear frequency-domain analysis to calculate total gain from noise sources to the output phase noise. This single tone (ST) simulation directly calculates noise frequency contributions and is much faster than Hajimiri's impulse sensitivity function (ISF) method. A quadrature VCO has been implemented in TSMC 0.18-μm CMOS and the predicted phase noise matches measurement. © 2009 IEEE  

This article presents a comprehensive small signal model for a virtual synchronous generator (VSG) integrated into a microgrid. In the developed state-space, active and reactive power control loops of the VSG as well as resistances, and reactances of the lines are considered. Based on this model, the robust D-stable region in terms of different values of inertia constant $(M)$, and damping coefficient $(D)$ values of the VSG is obtained. To enhance both transient performance as well as guarantee the robust D-stable operation of VSG, an optimization problem is also proposed. Moreover, a new control method is suggested to damp frequency oscillations of the microgrid. The proposed controller is... 

An experimental study was carried out on an axisymmetric supersonic inlet with external compression. The scope of this study was to investigate the general characteristics of the inlet buzz under various design and off-design conditions. The model was equipped with accurate and high frequency pressure sensors and the tests were conducted at Mach numbers varying from 1.8 to 2.5, at various angles of attack, and at different mass flow rates. Shadowgraph flow visualization, together with a high speed camera, was used to capture the external shock structure in front of the inlet. Frequencies of buzz were obtained from both the shadowgraph pictures and analysis of the pressure data. The amplitude... 

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...