فهرست مطالب

  • Volume:7 Issue: 1, 2013
  • تاریخ انتشار: 1392/02/11
  • تعداد عناوین: 9
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  • Najmeh Khanian Page 1
    Low dropout regulators are one of the most important factures of many portable devices. Thus, consider to the complexity of the circuits and increasing request for portable devices, for increasing battery life and minimizing supply noise, regulators with high efficiency, low output noise and small size is required. In these paper two methods to improve the efficiency of LDO regulators is proposed. First method is increasing gain of error amplifier by using cascode technique, to improve steady-state specification. Second method is using a simple subtractor circuit between error amplifier and pass transistor of LDO regulator to improve power supply rejection, slew-rate and steady-state specification. In addition, both methods are used to achieve area efficiency replacing MIM capacitors with MOS transistor. These low dropout regulators has been simulated in TSMC 0.18μm CMOS process. Simulation results show enhancement settling time, good line and load regulation and power supply compare with others LDO regulators.
  • Hassan Farsi, Sajad Mohamadzadeh Page 9
    Image retrieval is one of the most applicable image processing techniques which have been used extensively. Feature extraction is one of the most important procedures used for interpretation and indexing images in content-based image retrieval (CBIR) systems. Reducing dimension of feature vector is one of challenges in CBIR systems. There are many proposed methods to overcome these challenges. However, the rate of image retrieval and speed of retrieval is still an interesting field of researches. In this paper we propose a new method based on combination of Hadamard matrix, discrete wavelet transform (HDWT2) and discrete cosine transform (DCT) and we used principal component analysis (PCA) to reduce dimension of feature vector and K-nearest neighbor (KNN) for similarity measurement. The precision at percent recall and ANR are considered as metrics to evaluate and compare different methods. Obtaining results show that the proposed method provides better performance in comparison with other methods.
  • Zahra Boor, Seyyed Mehdi Hosseini Page 16
    This paper presents determination of optimum size and location of distributed generators (DGs) for reliability improvement of distribution systems in the presence of time varying loads using Genetic Algorithm (GA). The main innovation of this paper is considering of annual load duration curve for determination of size and location of DGs for reliability improvement. For this purpose a load duration curve including four load levels with different weighting factor is considered. For reliability assessment, the customer-oriented reliability indices such as SAIFI, SAIDI, CAIDI, ASUI and also load- and energy-oriented indices such as ENS are evaluated. In this paper, the effects of system reconfiguration and load shedding are also considered for reliability improvement. The best size and location of DGs in distribution systems is determined based on different reliability indices, separately. The effectiveness of the proposed algorithm is examined on a standard distribution systems consisting of 33 nodes and comparative studies are conducted in the different cases to investigate the impacts of optimal DGs placement and its size determination on reliability improvement. The results obtained show the effectiveness of the proposed method for reliability improvement.
  • Ali Abedini, Yousef Firouz Page 25
    This paper proposed a new converter topology to drive induction motors. The proposed topology has the ability to boost the DC link input voltage in case of DC link voltage shortage without any additional converter. This converter employs two additional switches and one capacitor in each phase compared to conventional converters. More over this new topology, brings additional advantages such as less torque and current ripple and lower switching loss. After a discussion of the basic principles of operation, the dynamics of the converter is developed for control purposes. Simulation results are given to illustrate the associated advantages of the proposed converter.
  • Amir Takhmar, Mansoor Alghooneh, S. Ali A. Moosavian Page 31
    Control of biped walking robots based on designated smooth and stable trajectories is a challenging problem that is the focus of this article. Because of highly nonlinear dynamics of biped robots, minor uncertainties in systems parameters may drastically affect the system performance, leading to chattering phenomenon. To tackle this, a new Sliding Mode Control (SMC) approach is proposed privileging a chattering elimination method based on Fuzzy logic to regulate the switching gain. To this end, first a desired trajectory for the lower body will be designed to alleviate the impacts due to contact with the ground. This is obtained by fitting proper polynomials at appropriate break points. Then, the upper body motion is planned based on the Zero Moment Point (ZMP) criterion to provide a stable motion for the biped robot. Next, dynamics equations will be obtained for both single support phase (SSP) and double support phase (DSP). Finally, the SMC approach is applied for both the SSP and the DSP, while a new chattering elimination method using Fuzzy logic will be proposed based on regulating constant switching gain. Obtained simulation results show that the performance of the system is properly accurate in terms of the tracking errors even in the presence of considerable uncertainties and exerted disturbances. Also, the new proposed method substantially reduces chattering effects and avoids the instability of the biped robot due to this phenomenon, resulting in stable smooth motion control of this complicated system.
  • Arash Taherian, Mahdi Aliyari Sh Page 43
    A biometric system provides automatic identification of an individual based on unique features or characteristics possessed by that person. Iris recognition is regarded as one of the most reliable and accurate biometric systems available. This paper, proposes an efficient iris recognition system that employs a novel method to localize the iris region in the eye image based on approximating the iris radius using the pupil characteristics and cumulative SUM based gray change analysis to extract features from the normalized iris template and also Fuzzy ARTMAP neural network to classify the iris codes. The results of simulations on a set of 756 eye images illustrate that a fast, accurate and noise resistant personal identification system has been successfully designed. The proposed system achieved 0 false acceptance rate using 1800-bit binary iris codes and recognized all authorized users with 100% accuracy.
  • Ahmad Norozpour Niazi, Ali Badri, Abdolreza Sheikhol, Eslami Page 53
    The completely Electric Power System encompass three parts: Generation, Transmission, and Distribution that all require maintenance to better system reliability and energy efficiency. Most generation maintenance scheduling (GMS) packages consider preventive maintenance scheduling for generating units over one or two year''s time horizon to lessen the total operation costs while fulfilling system energy requirements. In advanced power systems, The inclusion of network limitations, reserve index, forced outage rates of the units and demand for electricity have highly increased with related expansions in system size, which have led to higher number of generators and lower reserve margins making the generator maintenance scheduling problem more complex.
  • Siamak Talebi, S.Saleh Hosseini Bidaki, Behrouz Bagheri Ranjbar Page 60
    In this paper, a new full rate, full diversity 2 2 STBC with linear complexity in the receiver is introduced for keyhole channels where the rank-deficiency of channel matrix degrades system performance. This code is optimized based on the known criteria for these types of channels. Simulation results demonstrate that the proposed code outperforms some of the well-recognized STBCs when BPSK and 4-QAM constellation are utilized.
  • Arash Daghighi Page 66
    A silicon on diamond structure to improve DIBL is presented. The electrical field penetration through the buried insulator of diamond degrades the DIBL. In the new structure, a second, double insulating material, e.g. SiO2 is added on top of the buried insulator and partially covers the diamond. The second insulating material has lower electrical permittivity. Therefore the fringing field capacitance is smaller. Simulation results of 22 nm silicon-on-diamond transistor shows 18% improvement in DIBL comparing with conventional SOD structure. Lattice temperature increase of 5% is observed in the new structure compared with the conventional SOD which is still well below the silicon on insulator junction temperature.