Search for: ahmadi--a
0.006 seconds
Total 76 records

    Biologically inspired spiking neurons: Piecewise linear models and digital implementation

    , Article IEEE Transactions on Circuits and Systems I: Regular Papers ; Volume 59, Issue 12 , 2012 , Pages 2991-3004 ; 15498328 (ISSN) Soleimani, H ; Ahmadi, A ; Bavandpour, M ; Sharif University of Technology
    There has been a strong push recently to examine biological scale simulations of neuromorphic algorithms to achieve stronger inference capabilities. This paper presents a set of piecewise linear spiking neuron models, which can reproduce different behaviors, similar to the biological neuron, both for a single neuron as well as a network of neurons. The proposed models are investigated, in terms of digital implementation feasibility and costs, targeting large scale hardware implementation. Hardware synthesis and physical implementations on FPGA show that the proposed models can produce precise neural behaviors with higher performance and considerably lower implementation costs compared with... 

    A fully ZVS critical conduction mode boost PFC

    , Article IEEE Transactions on Power Electronics ; Volume 27, Issue 4 , October , 2012 , Pages 1958-1965 ; 08858993 (ISSN) Marvi, M ; Fotowat Ahmady, A ; Sharif University of Technology
    Boost converter operating in critical conduction mode is widely used in low-power power factor corrector because of its simplicity and low switching losses. The switching loss due to parasitic capacitor discharge at the on-time instant can also be reduced by a valley switching technique. In this paper, we introduce a new driver topology for the high-side switch in a synchronous boost converter operating in the critical conduction mode to obtain full zero-voltage switching. Using the proposed high-side driver topology, the conventional control circuit is sufficient to control the low-side switch, and no additional control circuit is required to adjust the timing of the switches. Finally, the... 

    A low-power current reuse CMOS RF front-end for GPS applications

    , Article 2011 IEEE International RF and Microwave Conference, RFM 2011 - Proceedings, 12 December 2011 through 14 December 2011, Seremban ; 2011 , Pages 416-419 ; 9781457716294 (ISBN) Jalili, H ; Fotowat Ahmady, A ; Sharif University of Technology
    A very low-power RF front-end based on a new current reuse QLMV cell (Quadrature VCO-LNA-Mixer) is proposed for GPS applications. The front-end, designed in 0.18μm CMOS technology, provides improved performance characteristics while consuming only 1 mA current. Simulation results are presented and compared with recently published works in the field  

    Blood inventory management in hospitals: considering supply and demand uncertainty and blood transshipment possibility

    , Article Operations Research for Health Care ; Volume 15 , 2017 , Pages 43-56 ; 22116923 (ISSN) Najafi, M ; Ahmadi, A ; Zolfagharinia, H ; Sharif University of Technology
    Despite significant advancements in medicine, human blood is still a scarce resource. Only humans produce it, and there is currently no other product or alternative chemical process that can be used to generate blood. For this reason, blood is a vital commodity in healthcare systems. Since blood is also a perishable product, its inventory management is difficult. The challenge is in holding enough stock to ensure a high level of supply while keeping losses from expiration at a minimum. This research will investigate blood inventory management in a hospital, and develop a mathematical model to manage blood ordering and issuing. This study will account for the fact that blood demand and supply... 

    Investigation of TLP behavior under tendon damage

    , Article Ocean Engineering ; Volume 156 , 15 May , 2018 , Pages 580-595 ; 00298018 (ISSN) Tabeshpour, M.R ; Ahmadi, A ; Malayjerdi, E ; Sharif University of Technology
    Elsevier Ltd  2018
    Exact calculation of stiffness matrix of TLP is important for investigation of its behavior in intact and tendon damage conditions and it is necessary to design a reliable TLP. A serious attention has been concentrated on this problem in API-RP-2T and various aspects of that such as dynamic and static behavior of TLP, tendon tensions after one tether failure. Also it has introduced safety factors in different loads and healthy conditions. This paper deals with effect of damage tendon condition of TLP on behavior and tensions of tendons in wave frequency range. Equilibrium of TLP is studied and stiffness matrix of TLP is derived in tendon damage condition. Wave loads and hydrodynamic... 

    A novel tunable UWB pulse design for narrowband interference suppression implemented in BiCMOS technology

    , Article Proceedings - IEEE International Symposium on Circuits and Systems, 24 May 2009 through 27 May 2009, Taipei ; 2009 , Pages 405-408 ; 02714310 (ISSN); 9781424438280 (ISBN) Hedayati, H ; Fotowat Ahmady, A ; Sharif University of Technology
    The unique properties of modified Hermite pulses is utilized to develop a novel pulse technique for Ultra Wideband (UWB) communications. The proposed method increases the bandwidth of the pulse up to 10 GHz and overcomes the coexistence problem of UWB and vulnerable narrowband systems through suppressing narrowband interference. Consequently it improves the range of UWB communications by increasing the power, without disturbing the narrowband systems. The pulse technique is implemented in high frequency pulse generation circuits and could be fully integrated in BiCMOS process. The nulls of the frequency response are tuned to be located in a definite narrowband system with the number of the... 

    A novel nonlinear function evaluation approach for efficient fpga mapping of neuron and synaptic plasticity models

    , Article IEEE Transactions on Biomedical Circuits and Systems ; Volume 13, Issue 2 , 2019 , Pages 454-469 ; 19324545 (ISSN) Jokar, E ; Abolfathi, H ; Ahmadi, A ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    Efficient hardware realization of spiking neural networks is of great significance in a wide variety of applications, such as high-speed modeling and simulation of large-scale neural systems. Exploiting the key features of FPGAS, this paper presents a novel nonlinear function evaluation approach, based on an effective uniform piecewise linear segmentation method, to efficiently approximate the nonlinear terms of neuron and synaptic plasticity models targeting low-cost digital implementation. The proposed approach takes advantage of a high-speed and extremely simple segment address encoder unit regardless of the number of segments, and therefore is capable of accurately approximating a given... 

    Sensitivity analysis of simple methods in determination of offshore jacket structures levels stiffness

    , Article Journal of Marine Science and Technology (Japan) ; 2021 ; 09484280 (ISSN) Tabeshpour, M. R ; Ahmadi, A ; Sharif University of Technology
    Springer Japan  2021
    Dynamic analyses are necessary problems in offshore jacket structures design and assessment. These analyses have various applications in recognition of dynamic behavior, fatigue analysis, damage detection, etc. Natural frequencies and mode shapes, as inherent vibrational features of a structure, are key parameters in referred analyses. These parameters are mainly affected by mass and stiffness matrices and slightly by damping. Therefore, it is more important to estimate the stiffness matrix of a structure accurately, especially in stiff structures such as offshore jacket platforms. In many cases, the stiffness of levels is required. For example, it can be useful in the construction of an... 

    Erratum: A new ir-uwb pulse for the compatibility of IEEE802.11.a wlan and ir-uwb systems

    , Article Journal of Circuits, Systems and Computers ; Vol. 23, issue. 5 , 2014 Mir-Moghtadaei, S. V ; Fotowat-Ahmady, A ; Nezhad, A. Z ; Sharif University of Technology
    [No abstract available]  

    A new IR-UWB pulse to mitigate coexistence issues of UWB and narrowband systems

    , Article 2013 21st Iranian Conference on Electrical Engineering ; May , 2013 , Page(s): 1 - 5 ; 9781467356343 (ISBN) Mir Moghtadaei, S. V ; Nezhad, A. Z ; Fotowat Ahmady, A ; Sharif University of Technology
    A new Ultra Wideband (UWB) pulse shape is proposed to mitigate coexistence issues of IEEE802.11.a WLAN and Impulse Radio UWB (IR-UWB) systems. The proposed method is applicable to the reduction of any given narrowband (NB) interference into UWB systems. This pulse shape is based on frequency up-converting of first derivative of Gaussian pulse which has an adjustable null in Power Spectral Density (PSD) depending on up-converting frequency. Both analytical and simulation results with an adaptive receiver show that an UWB system with interference from a WLAN has noticeable improved performance when using the proposed pulse in comparison with using conventional modulated Gaussian pulse  

    3D numerical modeling of wave forces on tandem fixed cylinders using the BEM

    , Article Journal of Marine Science and Application ; Volume 12, Issue 3 , September , 2013 , Pages 279-285 ; 16719433 (ISSN) Ketabdari, M. J ; Abaiee, M. M ; Ahmadi, A ; Sharif University of Technology
    In this paper a 3D numerical model was developed to study the complicated interaction between waves and a set of tandem fixed cylinders. The fluid was considered to be inviscid and irrotational. Therefore, the Helmholtz equation was used as a governing equation. The boundary element method (BEM) was adopted to discretize the relevant equations. Open boundaries were used in far fields of the study domain. Linear waves were generated and propagated towards tandem fixed cylinders to estimate the forces applied on them. Special attention was paid to consideration of the effect on varying non-dimensional cylinder radius and distance between cylinders, ka and kd on forces and trapped modes. The... 

    A 1-mW current reuse quadrature RF front-end for GPS L1 band in 0.18μm CMOS

    , Article 2012 19th IEEE International Conference on Electronics, Circuits, and Systems, ICECS 2012, Seville, Seville, 9 December 2012 through 12 December 2012 ; 2012 , Pages 157-160 ; 9781467312615 (ISBN) Jalili, H ; Fotowat Ahmady, A ; Jenabi, M ; Sharif University of Technology
    A new low-power current reuse topology is proposed for the GPS receiver's RF front-end that combines the higher conversion gain and suppressed noise figure characteristics of cascade structures with the low power consumption of stacked architectures. The presented circuit, called 1.5-stage LMV cell, consists of LNA, Mixer and VCO (LMV) in such a formation that boosts LNA gain and suppresses mixer's noise figure by cascading the two stages while reusing their currents in the two stacked quadrature VCOs and placing the mixer's upper tree switches at the vicinity of on-off regions. The circuit is designed and its layout is generated in TSMC 0.18μm CMOS technology. Post-layout simulations using... 

    Design of low-power temperature sensor architecture for passive UHF RFID tags

    , Article Informacije MIDEM ; Volume 45, Issue 4 , 2015 , Pages 249-259 ; 03529045 (ISSN) Karkani, M. R. G ; Kamarei, M ; Ahmady, A. F ; Sharif University of Technology
    Society for Microelectronics, Electric Components and Materials  2015
    A low-power wide-range CMOS temperature sensor architecture is proposed based on temperature-to-frequency conversion using supply voltage controlled sub-threshold ring oscillator. The principles of operation are investigated and proved via analytic and simulation results. Most errors are canceled out by this ratio-metric design. An inaccuracy of -0.84°C to +0.34°C occurs over a range of -40°C to 80°C after using a novel in-field digital two-point calibration. The entire sensor consumes less than 93nW to 305nW over the temperature range and can be digitally reconfigured for setting sample rate and resolution in a tradeoff  

    Phase calibration in mutual injection-pulled quadrature oscillators

    , Article Midwest Symposium on Circuits and Systems, 2 August 2015 through 5 August 2015 ; Volume 2015-September , 2015 ; 15483746 (ISSN) ; 9781467365574 (ISBN) Nikoofard, A ; Kananian, S ; Fotowat Ahmady, A ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2015
    An alternative approach to analysis, design and implementation of injection-locked quadrature oscillators is proposed in this paper. A novel technique is presented which allows the effects of the mismatches due to imbalances in the I/Q paths in transceivers (TRX) to be mitigated, and hence the orthogonality of the these vectors be maintained. This technique alleviates the effects of imbalances in a transceiver between I/Q paths, which would otherwise pose many threats to the performance of the system, namely image rejection ratio (IRR) degradation, gain reduction in mixers, desensitization of the RX, and ect. As a design example, a CMOS quadrature oscillator (QOSC) at the frequency of 3.5GHz... 

    A fully analog calibration technique for phase and gain mismatches in image-reject receivers

    , Article AEU - International Journal of Electronics and Communications ; Volume 69, Issue 5 , May , 2015 , Pages 823-835 ; 14348411 (ISSN) Nikoofard, A ; Kananian, S ; Fotowat Ahmady, A ; Sharif University of Technology
    Elsevier GmbH  2015
    A systematic approach to I/Q mismatch calibration in image-reject receivers is presented in this paper. A new error detection algorithm is proposed, which automatically calibrates for phase and gain mismatches limiting the performance of image-reject receivers. A dual-loop feedback is employed which looks for the minimum phase/gain error using a 2-dimensional analog-based search algorithm and then finds the minimum value for the error. An experimental CMOS prototype RF front-end for cognitive radio applications operating at 400-800 MHz is proposed and simulated in the 0.18 μm CMOS technology, achieving an image rejection ratio (IRR) better than 55-dB in post-layout simulation. The... 

    A unified solution for super-regenerative systems with application to correlator-based uwb tran

    , Article IEEE Transactions on Circuits and Systems I: Regular Papers ; Volume 62, Issue 4 , March , 2015 , Pages 1033-1041 ; 15498328 (ISSN) Fatemi, S. M ; Sharifkhani, M ; Fotowat Ahmady, A ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2015
    The conventional theory of super regenerative systems (SRS) has been divided into distinct modes of operation and limiting assumptions. These assumptions make the analysis of these systems inaccurate for wide bandwidth applications. In this paper, a novel theory based on the analysis of time varying systems using Magnus expansion is proposed which unifies all modes of operation and formulates the system response with high accuracy for a wide range of practical applications. Therefore, the theory can be used for the design of systems with wider bandwidth and higher data rates. Using the proposed theory, it is possible to analytically describe the effects of the parasitic elements and inter... 

    Digital implementation of a biological astrocyte model and its application

    , Article IEEE Transactions on Neural Networks and Learning Systems ; Volume 26, Issue 1 , 2014 , Pages 127-139 ; 2162237X (ISSN) Soleimani, H ; Bavandpour, M ; Ahmadi, A ; Abbott, D ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2014
    This paper presents a modified astrocyte model that allows a convenient digital implementation. This model is aimed at reproducing relevant biological astrocyte behaviors, which provide appropriate feedback control in regulating neuronal activities in the central nervous system. Accordingly, we investigate the feasibility of a digital implementation for a single astrocyte and a biological neuronal network model constructed by connecting two limit-cycle Hopf oscillators to an implementation of the proposed astrocyte model using oscillator-astrocyte interactions with weak coupling. Hardware synthesis, physical implementation on field-programmable gate array, and theoretical analysis confirm... 

    Optimisation of micro gas turbine by exergy, economic and environmental (3E) analysis

    , Article International Journal of Exergy ; Volume 7, Issue 1 , 2010 , Pages 1-19 ; 17428297 (ISSN) Mozafari, A ; Ahmadi, A ; Ehyaei, M. A ; Sharif University of Technology
    This research proposes a new method for optimisation of a power generation system based on exergy fuel cost and external social cost of air pollution. A thermodynamic model is provided to estimate the outlet mass flow rates of CO2, CO, NO and NO2 for a gas turbine based on maximising the first and second law efficiencies and minimising the objective function. Results show that inclusion of the external social cost of air pollution increases the optimum excess air ratio if temperature constraint due to metallurgical consideration is disregarded. Otherwise external social cost of air pollution is independent of optimised conditions  

    Reduction of multipath errors in spread-spectrum code tracking

    , Article 2010 IEEE International Conference on Communications, ICC 2010, Cape Town, 23 May 2010 through 27 May 2010 ; 2010 ; 05361486 (ISSN) ; 9781424464043 (ISBN) Ramezanpour, K ; Khalaj, B. H ; Fotowat Ahmady, A ; Sharif University of Technology
    Exact spread-spectrum code tracking in the presence of multipath is an important issue in distance and time measurement systems. Different tracking algorithms based on feedback, feedforward or a combination of them reduce multipath effects, however, the accuracy of the tracking in presence of short-delay multipath signals is still a problem. In this paper, we consider feedback delay lock loops (DLL) and gating function schemes that have shown better performance with lower complexity under multipath. We develop a shot-noise process model for the control signal of a DLL in the presence of multipath signals and determine the range of tracking errors they cause. Then, we propose a method based... 

    A new low phase noise LC-tank CMOS cascode cross-coupled oscillator

    , Article Proceedings - 2010 18th Iranian Conference on Electrical Engineering, ICEE 2010, 11 May 2010 through 13 May 2010 ; 2010 , Pages 397-402 ; 9781424467600 (ISBN) Teymoori, H ; Fotowat Ahmady, A ; Nabavi, A ; Sharif University of Technology
    In this paper we introduce a new low phase noise cascode Cross-coupled oscillator by use of the general topology of Cross-coupled oscillator and cascode amplifier. By simulation a comparison between the conventional Cross-coupled oscillator and the new cascode Cross-coupled oscillator is also presented, which shows that the latter improves the phase noise by 2dB under the same conditions. The figure of merit (FOM) of -186.4 dBc/Hz is achieved for the new oscillator by simulation