Sharif Digital Repository

Improvement in switching techniques is one of the effective methods for increasing the voltage quality in Multilevel Inverters. In this paper, a novel switching technique using frequency modulation is proposed to achieve high quality output voltage of multilevel inverters. This method is employed to different configurations of multilevel inverters consist of Diode Clamped (or Neutral Point Clamped), Flying Capacitor and Cascaded H-bridge. Each multilevel inverter which utilizes this technique is modeled and simulated to investigate the performance of this method by the help of MATLAB/Simulink software. The Results show that this innovative method considerably reduces total harmonic... 

Harmonic information is necessary tools in the estimation of motors life and performance. The conventional expression of harmonic amount is carried out by total Harmonic distortion. This distortion factor is only related to amplitude of harmonics while the motor loss is affected by frequency domain of them. In this paper a new definition of this factor has been presented. This definition includes the frequency of harmonics as well as their amplitudes. Experimental results verify the validity of this new definition  

In this paper we make use of M-band discrete wavelet transform (MDWT) and Wiener filter for speckle noise suppression of ultrasound images. Assuming multiplicative model for speckle noise, by applying logarithmic transform to noisy observation we convert multiplicative noise to additive one. Then, speckle noise can be reduced by taking the M-band wavelet transform of log-transformed observation and employing an adaptive thresholding technique. In order to improve the performance of this denosing approach, we propose a preprocessing stage which exploits Wiener filtering. Through this stage logtransformed observation is separated into two images and then each of these two images is denoised... 

The design of a complex active-RC filter for low-IF Wireless applications is described. Fifth-order complex Butterworth filter is designed using Class-AB operational amplifier architecture. This new structure makes the filter suitable for low power applications with high dynamic range. Simulation results show that the filter provides more than 40 dB image rejection ratio (IIR) and dynamic range of 82dB. The complete filter including on-chip tuning circuit consumes only 4.3mW with 1.8V single supply voltage. © 2007 IEEE  

In this paper we present a novel approach for adjusting a multi band spectral subtraction filter coefficients based on speech recognition system results. Currently most speech enhancement techniques are designed according to various waveform level criteria such as maximizing SNR or minimizing signal error. However improvement in these criteria does not necessarily result in increasing speech recognition performance. Only if these methods generate sequence of features that maximize or increase the likelihood of the correct transcription relative to other incorrect competing hypotheses, speech recognition performance will increase. Here we use an utterance with a known transcription and... 

In this study, a simple and novel control technique for Power Factor Correction (PFC) is introduced, which is a SEPIC-based (Single-ended Primary-inductor Converter based) rectifier with high input power factor. Operation of the proposed method is based on sampling of input and output voltages in SEPIC rectifier. Using samples of input and output voltage, this control system makes the input current to follow a sinusoidal path. As a result, the line current?'s Total Harmonic Distortion (THD) is reduced and the input power factor is improved. This paper also compares the new method with the conventional control method for the power factor correction. In order to examine the proposed control... 

A novel control strategy based on predictive control is presented for continuous conduction mode boost converter which operates as a power factor correction. In the proposed algorithm two horizons for the behavior of the circuit are predicted which improves the total harmonic distortion, mainly the low frequency harmonics. The algorithm doesn't need elaborating calculations therefore, implementation of the controller using low price processor is feasible. Moreover, an extra horizon of the prediction leads to expansion of the calculation time. Reduction of the harmonic distortion of the input current and improvement of the power factor have been demonstrated on an isolated boost PFC converter... 

A novel N-path filter using a complex impedance is designed to replace the frontend SAW filters in receivers with on-chip bandpass filters. It is demonstrated that the center frequency of the filter can be tuned solely by changing the value of some capacitances without the need to change the clock frequency. In addition, thanks to the use of smaller capacitors, the silicon area is reduced compared to similar designs. The high-Q bandpass filter is realized utilizing two gyrators and an arrangement of four baseband capacitors with NMOS switches, driven by 4-phase 25% duty cycle clock signals. This paper also analyzes the performance of the proposed filter against imperfections such as thermal... 

Non-linear loads such as rectifiers are growing in industry. Three phase inverter with non-linear load can lead to highly distorted output voltage. This paper proposes a method for reducing voltage THD in three phase inverters with non-linear load. The proposed method considers the load current as a disturbance and provide a control strategy to reject it using the disturbance observer method. This method doesn't need any additional sensors or hardware and is implemented digitally in controller. Simulation results show that the presented method will reduce the total harmonic distortion of the output voltage. © 2017 IEEE  

The Taylor series-based representation of the maximally flat (MF) FIR fractional delay (FD) filter is manipulated to obtain a FD filter with a wider band-width. The band-width of the proposed filter can approach π / 2 rads / s, which is 1.5 times that of the prototype one. The design has closed-form coefficient formulas as well as a modular implementation. These two properties make it a practically favourable one. © 2008 Elsevier B.V. All rights reserved  

The design of a Gm-C filter for High-Frequency applications is described in this paper. A low-pass, sixth-order elliptic Gm-C filter based on the new biquadratic architecture in 0.18 um CMOS process is designed with the proper dynamic rang. A simple structure of the high Q biquadratic filter is used to enhance the linearity and tunability of the filter. The cut off frequency of this filter is 33 MHz. It has a THD of -45 dB for 0.2 Vpp, 8 MHz signal. The complete filter including on-chip tuning circuit consumes only 0.8mA with 1.8 V single supply voltage. ©2006 IEEE  

A novel method of transmitter (TX) leakage cancellation is presented to improve the dynamic range of the receiver for wideband code division multiple access applications. The large TX leakage is attenuated within the low noise amplifier (LNA) output using a feed-forward path without any LNA noise figure degradation. A prototype has been designed and laid out in 0.18 μm CMOS technology. It achieves a maximum TX rejection of 18.5 dB with only 5.2 mA current consumption from 1.8 V supply voltage. LNA P-1dBCP (1 dB gain compression point) against TX leakage improves by more than 10 dB. Post layout simulations verify these results. Proposed structure dispels the requirement of off-chip surface... 

The required linearity of wideband receivers for applications, such as software-defined radio in the absence of input surface-acoustic wave (SAW) filters, is studied. It is shown that the required linearity of wideband SAW-less receivers is surprisingly higher than what has been commonly assumed. For these receivers, although the out-of-band blockers can reduce the compression point of the receiver, they can also potentially generate interferers that appear in the desired frequency band, resulting in higher noise floor and signal corruption. The required out-of-band IIP2 and IIP3 of low-noise amplifier (LNA) and mixer for single and concurrent applications are analytically derived. The... 

It is widely accepted that the presence of a lossy network, such as a SAW filter or balun, at the input of LNA increases NF of the overall circuit by an amount equal to the insertion loss of the lossy network. In this work it is shown that this idea is not exactly true and it considerably underestimates the overall NF. To verify this claim, Z-model of the lossy network is added before the LNA and the overall noise figure is recalculated for some commonly used LNA topologies. It is shown that in common gate LNA and common source LNA with resistive feedback the accepted equation underestimates the overall NF by 1.3 dB for an insertion loss of 2 dB. In common source with resistive matching and... 

Nowadays position sensors are increasingly used in many applications. One of the most commonly used sensors are resolvers. There are different types of resolvers including Wound Rotor (WR) resolvers, Variable Air-gap Length Variable Reluctance (VAGL-VR) resolvers, and Sinusoidal Rotor Variable Reluctance (SR-VR) resolvers. Regardless of the resolvers’ configurations, including linear, cylindrical and disk type, finite element analysis (FEA) is inseparable part of design and performance evaluation of these magnetic sensors. The scope of this study is to discuss challenges in the FEA of resolvers. The influence of mesh quality, time steps, stop time, excitation methods including volt-age... 

Elimination of the surface acoustic wave (SAW) filter from the input of a receiver can render it extremely vulnerable to various blockers and interferers. The presence of large out-of-band (OOB) blockers will result in the required linearity of the SAW-less receiver to be considerably higher than that of the conventional receivers with the input SAW filter. The ever-present undesirable signals that arise in the absence of the input SAW filter can be divided into two classes of far and near OOB blockers and interferers. Removal of these harmful signals requires two distinct approaches according to their nature. Two different methods for blocker and interferer rejection are introduced in this... 

Nowadays, position sensors are increasingly used in many applications. One of the most commonly used sensors are resolvers. There are different types of resolvers including wound rotor resolvers, variable air-gap length variable reluctance resolvers, and sinusoidal rotor variable reluctance resolvers. Regardless of the resolvers' configurations, including linear, cylindrical and disk type, finite element analysis (FEA) is inseparable part of design and the performance evaluation of these magnetic sensors. The scope of this study is to discuss challenges in the FEA of resolvers. The influence of mesh quality, time steps, stop time, excitation methods including voltage source and current... 

Among position sensors, resolvers are superior from reliability point of view. However, obtaining lower output voltage harmonics and simple manufacturing process is a challenge in the design and optimization of resolvers. In this paper, a metaheuristic optimization algorithm is used to minimize total harmonic distortion of the output signals, and consequently the estimated position error in concentrated coil wound field resolvers. Meanwhile, to minimize total coil numbers, manufacturing costs, and complexity of the winding process, modified objective function and constraints are proposed. In this way, a modified winding function method is employed for performance analysis of the axial flux... 

A compact low power circuit for implementation of a direct conversion OQPSK modulator is proposed. The circuit consists of a digital to analog converter, a low pass filter and an up-converter mixer. By embedding these three blocks, the circuit performance is enhanced and the total power consumption is reduced. The mixer is designed base on a Gilbert cell with on chip inductor loads. Instead of transconductance transistors of Gilbert cell, a fully deferential current mode DAC is used and proficiently a low pass filter is embedded between them and therefore the linearity of total system is improved. All of circuits are designed based on 0.18 μm CMOS technology with a single 1.8 volt power... 

Transcranial Doppler ultrasound can be used to detect circulating cerebral eraboli. Embolie signals have characteristic transient chirps suitable for wavelet analysis. We have implemented and evaluated the first online selective selective wavelet transient enhancement filter to amplify embolic signals in a preprocessing system. Our approach is similar to wavelet de-noising for signal enhancement, but, in order to retain blood flow information, we do not use traditional threshold methods. The selective wavelet amplifier uses the matched filter properties of wavelets to enhance embolic signals significantly and improve classification performance using a novel noise tolerant approach. Even the...