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    A novel, low voltage, precision CMOS current reference with no external components

    , Article 2003 10th IEEE International Conference on Electronics, Circuits and Systems, ICECS2003, Sharjah, 14 December 2003 through 17 December 2003 ; Volume 1 , 2003 , Pages 156-159 ; 0780381637 (ISBN); 9780780381636 (ISBN) Dehghani, R ; Atarodi, S. M ; Sharif University of Technology
    A novel, precision current reference with low temperature and supply sensitivity and without any external component has been designed in a 0.18μm CMOS mixed-mode process. The circuit is based on a bandgap reference (BGR) voltage and a CMOS circuit like a beta multiplier. The simulation results show max-to-min fluctuation of about 1% over a temperature range of -20°C to +100°C and supply voltage range of 1.1V to 2V with ±30% tolerance for all of the used on-chip resistors. The maximum nominal current variation in process corners is less than 3.5%. © 2003 IEEE  

    A 1-volt, high PSRR, CMOS bandgap voltage reference

    , Article Proceedings of the 2003 IEEE International Symposium on Circuits and Systems, Bangkok, 25 May 2003 through 28 May 2003 ; Volume 1 , 2003 , Pages I381-I384 ; 02714310 (ISSN) Mehrmanesh, S ; Vahidfar, M. B ; Aslanzadeh, H. A ; Atarodi, M ; Sharif University of Technology
    A low voltage bandgap reference (BGR) in CMOS technology, with high power supply rejection ratio (PSRR) is presented. The proposed circuit uses a regulated current mode structure and some feedback loops to reach a low voltage, low power and high PSRR voltage reference. The circuit was designed and simulated in 0.25um CMOS technology, with a power supply of 1 volt. The results show PSRR is below -70dB at 1MHz and the output voltage variation versus temperature (0-70) is less than 0.3%. This circuit shows robustness against process variation  

    Design and analysis of photonic quasi-crystal hollow core fibers

    , Article Proceedings of SPIE - The International Society for Optical Engineering ; Volume 8794 , May , 2013 ; 0277786X (ISSN) ; 9780819496348 (ISBN) Bahrampour, A ; Iadicicco, A ; Bahrampour, A. R ; Campopiano, S ; Cutolo, A ; Cusano, A ; Innovative Economy National Cohesion Strategy; InPhoTech Ltd.; AMS Technologies; PHOENIX ; Sharif University of Technology
    We present a new class of hollow core photonic crystal fibers taking the advantages of quasi-crystals structures. We analyze two structures based on modified 8-fold and 12-fold symmetries and we presente the ability of air guiding propagation having two photonic bandgap in the λ/Λ<1 In this paper bandgap of both structures as well as the behavior of the guided modes via finite element method are investigated  

    A sub 1 v high PSRR CMOS bandgap voltage reference

    , Article Microelectronics Journal ; Volume 42, Issue 9 , 2011 , Pages 1057-1065 ; 00262692 (ISSN) Chahardori, M ; Atarodi, M ; Sharifkhani, M ; Sharif University of Technology
    A Bandgap circuit capable of generating a reference voltage of less than 1 V with high PSRR and low temperature sensitivity is proposed. High PSRR achieved by means of an improved current mode regulator which isolates the bandgap voltage from the variations and the noise of the power supply. A vigorous analytical approach is presented to provide a universal design guideline. The analysis unveils the sensitivity of the circuit characteristic to device parameters. The proposed circuit is fabricated in a 0.18μm CMOS technology and operates down to a supply voltage of 1.2 V. The circuit yields 20 ppm/°C of temperature coefficient in typical case and 50 ppm/°C of temperature coefficient in worst... 

    Tight-binding analysis of coupled dielectric waveguide structures

    , Article Fiber and Integrated Optics ; Volume 25, Issue 1 , 2006 , Pages 11-27 ; 01468030 (ISSN) Khalili Amiri, P ; Ranjbaran, M ; Mehrany, K ; Rashidian, B ; Fathololoumi, S ; Sharif University of Technology
    Based on the mathematical similarity of the Schrödinger and Helmholtz equations, the tight-binding method has been employed for solving optical waveguide problems, in a manner similar to the methods commonly used in solid-state physics. The solutions (TE mode electric field waveforms and propagation constants) of a single dielectric slab waveguide are considered to be known, and tight-binding is used to compute the propagation constants of several multi-waveguide structures. Analytical solutions are derived for linear and circular arrays of adjacent waveguides. The problem of two similar adjacent waveguides is treated in detail for two cases of similar and different propagation constants of... 

    An area and power optimization technique for CMOS bandgap voltage references

    , Article Analog Integrated Circuits and Signal Processing ; Volume 62, Issue 2 , 2010 , Pages 131-140 ; 09251030 (ISSN) Tajalli, A ; Chahardori, M ; Khodaverdi, A ; Sharif University of Technology
    This article explores the main tradeoffs in design of power and area efficient bandgap voltage reference (BGR) circuits. A structural design methodology for optimizing the silicon area and power dissipation of CMOS BGRs will be introduced. For this purpose, basic equations of the bandgap circuit have been adapted such that can simply be applied in the optimization process. To improve the reliability of the designed circuit, the effect of amplifier offset has been also included in the optimization process. It is also shown that the minimum achievable power consumption and area are highly depending on the fabrication process parameters especially sheet resistivity of the available resistors in... 

    A new low voltage, high PSRR, CMOS bandgap voltage reference

    , Article 2008 IEEE International SOC Conference, SOCC, Newport Beach, CA, 17 September 2008 through 20 September 2008 ; 2008 , Pages 345-348 ; 9781424425969 (ISBN) Ashrafi, S. F ; Atarodi, M ; Chahardori, M ; Sharif University of Technology
    A new low voltage bandgap reference (BGR) in CMOS technology, with high power supply rejection ratio (PSRR) is presented. The proposed circuit uses a regulated current mode structure and some feedback loops to reach a low voltage, low power and high PSRR voltage reference. The circuit was designed and simulated in 0.18um CMOS technology, with a power supply of 1.4 volt. The results show PSRR is 65dB at 1MHz and the output voltage variation versus temperature (-40 to 140) is less than 0.1%. This circuit shows robustness against process variation. ©2008 IEEE  

    Effect of simultaneous chemical substitution of A and B sites on the electronic structure of BiFeO3 films grown on BaTiO 3/SiO2/Si substrate

    , Article Journal of Materials Science: Materials in Electronics ; Volume 24, Issue 6 , 2013 , Pages 2128-2134 ; 09574522 (ISSN) Ahadi, K ; Nemati, A ; Mahdavi, S. M ; Vaezi, A ; Sharif University of Technology
    Electrical properties and electronic structure of Bi1-xCa xFe1-yMnyO3-δ grown by pulsed-laser deposition on BaTiO3/SiO2/Si substrate were investigated. Results showed that Ca has drastic effect on symmetry of crystal and electrical poperties of BiFeO3. On the other hand, Mn revealed to have more radical effect on optical properties and energy gap of the compound. XPS results represented that although Ca tend to decrease Fe valence state, Mn tends to stabilize it at 3+ (at least in this concentrations). UV-visible study yielded bandgap of 2.51-2.81 eV (at 300 K) for different concentrations of Ca and Mn. UV-visible spectra also revealed sub-bandgap defect transitions at 2.2 and 2.4 eV.... 

    Effect of iron oxide and silica doping on microstructure, bandgap and photocatalytic properties of titania by water-in-oil microemulsion technique

    , Article Transactions of the Indian Ceramic Society ; Volume 70, Issue 4 , Jan , 2011 , Pages 227-232 ; 0371750X (ISSN) Karbassi, M ; Nemati, A ; Zari, M. H ; Ahadi, K ; Sharif University of Technology
    The microemulsion method was successfully used to prepare a series of TiO2, Fe oxide and SiO2 doped TiO2 nanoparticles at Fe/Ti atomic ratio of 10% and Si/Ti atomic ratio of 15%. The molar ratio of water to surfactant (W0) was 2. The samples were calcinated at 350°C. The structural features of TiO2, Fe oxide and SiO 2-TiO2 were investigated by XRD, UV-Visible spectroscopy, SEM and TEM. XRD data verified the formation of typical characteristic anatase form in all the prepared Fe and SiO2-doped TiO2 samples. In comparison with the pure TiO2, Fe oxide and SiO 2-TiO2 samples were relatively large in particle size, indicating that doping with Fe oxide and SiO2 can help in increasing the particle... 

    Optical properties and surface morphology of evaporated (WO 3)1-x-(Fe2O3)x thin films

    , Article Thin Solid Films ; Volume 484, Issue 1-2 , 2005 , Pages 124-131 ; 00406090 (ISSN) Moshfegh, A. Z ; Azimirad, R ; Akhavan, O ; Sharif University of Technology
    Thin films of (WO3)1 - x-(Fe2O 3)x composition were deposited by thermal evaporation on glass substrates and then all samples were annealed at 400 °C in air. Optical properties such as transmittance, reflectance, and optical bandgap energy of the "as deposited" and the annealed films were studied using ultraviolet-visible spectrophotometry. It was shown that the annealing process did not substantially change the optical transmittance and reflectance of all the films except the films having x = 0.75. By increasing Fe2O 3 content in the films from x = 0 to x = 0.75, optical bandgap energy decreased from 3.4 to about 1.3 eV and from 3.1 to 2.1 eV for the "as deposited" and the annealed samples,... 

    Sonochemical synthesis and measurement of optical properties of zinc sulfide quantum dots

    , Article Chemical Engineering Journal ; Volume 209 , 2012 , Pages 113-117 ; 13858947 (ISSN) Goharshadi, E. K ; Sajjadi, S. H ; Mehrkhah, R ; Nancarrow, P ; Sharif University of Technology
    A facile sonochemical method has been developed to prepare very small zinc sulfide nanoparticles (ZnS NPs) of extremely small size about 1. nm in diameter using a set of ionic liquids based on the bis (trifluoromethylsulfonyl) imide anion and different cations of 1-alkyl-3-methyl-imidazolium. The structural features and optical properties of the NPs were determined in depth with X-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), Fourier transform infrared (FTIR) spectroscopy, dynamic light scattering (DLS) analysis, and UV-vis absorption spectroscopy. The energy band gap measurements of ZnS NPs were calculated by UV-vis absorption... 

    Analytical approach in finding the semi-optimum hollow-core Bragg fiber with minimum loss

    , Article IEEE Journal of Quantum Electronics ; Volume 47, Issue 5 , 2011 , Pages 552-560 ; 00189197 (ISSN) Jazayeri, A. M ; Mehrany, K ; Sharif University of Technology
    Since it is quite difficult to analytically optimize hollow-core Bragg fibers to have minimum confinement loss without using the Floquet theorem, which does not hold for cylindrical structures, the cylindrical Bragg mirror is approximated by its planar counterpart. For this reason, first, the optimum planar waveguide formed by sandwiching a hollow layer between 1-D Bragg mirrors is found in this paper. The optimization for the dominant transverse-electric mode is analytically performed by using the pointwise wavenumber closely related to the wave admittance. A closed-form expression is then found to relate the propagation constant of this waveguide to the thickness of the hollow layer. This... 

    Influence of asymmetry on the band structure of photonic crystals

    , Article Proceedings of SPIE - The International Society for Optical Engineering, 26 January 2010 through 28 January 2010 ; Volume 7609 , January , 2010 ; 0277786X (ISSN) ; 9780819480057 (ISBN) Moosavi Mehr, S. H ; Khorasani, S ; Sharif University of Technology
    Computer calculation of photonic band structure for unit cells of various symmetry in the two-dimensional square lattice suggests that the bandgap calculated by traversing the ΓXM triangle in k-space is only reliable when the unit cell is C4v symmetric. For structures of lower symmetry, examining a two-dimensional subset of the first Brillouin zone will give smaller bandgaps  

    Micro-optoelectromechanical systems accelerometer based on intensity modulation using a one-dimensional photonic crystal

    , Article Applied Optics ; Volume 55, Issue 32 , 2016 , Pages 8993-8999 ; 1559128X (ISSN) Sheikhaleh, A ; Abedi, K ; Jafari, K ; Gholamzadeh, R ; Sharif University of Technology
    OSA - The Optical Society 
    In this paper, we propose what we believe is a novel sensitive micro-optoelectromechanical systems (MOEMS) accelerometer based on intensity modulation by using a one-dimensional photonic crystal. The optical sensing system of the proposed structure includes an air-dielectric multilayer photonic bandgap material, a laser diode (LD) light source, a typical photodiode (1550 nm) and a set of integrated optical waveguides. The proposed sensor provides several advantages, such as a relatively wide measurement range, good linearity in the whole measurement range, integration capability, negligible cross-axis sensitivity, high reliability, and low air-damping coefficient, which results in a wider... 

    Tunable bandgap and spin-orbit coupling by composition control of MoS2 and MoOx (x = 2 and 3) thin film compounds

    , Article Materials and Design ; Volume 122 , 2017 , Pages 220-225 ; 02641275 (ISSN) Erfanifam, S ; Mohseni, S. M ; Jamilpanah, L ; Mohammadbeigi, M ; Sangpour, P ; Hosseini, S. A ; Iraji Zad, A ; Sharif University of Technology
    Elsevier Ltd  2017
    We report on the MoS2 and MoOx (x = 2 and 3) composite thin layers, electrodeposited, onto a Florine doped Tin Oxide (FTO) substrate. Our results show a change in relative content of these compounds in different thicknesses ranging from ∼20 to 540 nm. This change in the relative content at different thicknesses leads to a change in optical and electrical properties including bandgap and the type of semiconductivity. A sharp transition from p to n-type of semiconductivity is observed by scanning tunneling spectroscopy measurements. We find that the spin-orbit interaction of Mo 3d electrons in the MoS2 and MoO3 enhances by significant reduction of the MoO3 content in thicker layers. © 2017... 

    Dirac leaky wave antennas

    , Article 5th International Conference on Millimeter-Wave and Terahertz Technologies, MMWaTT 2018, 18 December 2018 through 20 December 2018 ; Volume 2018-December , 2019 , Pages 1-5 ; 21570965 (ISSN); 9781538677179 (ISBN) Rezaee, S ; Memarian, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    Dirac leaky-wave antennas (DLWAs) are derived from photonic crystals exhibiting Dirac cone dispersion around their Γ-point. DLWAs provide high directive beams and continuous frequency beam scanning, non-fluctuating leakage constant and real non-zero Bloch impedance at and around broadside, due to the closed and linear Dirac dispersion relation around broadside. These features, along with their inherent compatibility for higher frequency designs (larger unit cells compared to metamaterials), make DLWAs an ideal candidate for the upper microwave, mm-wave and terahertz frequencies, and for applications such as radar, 5G, spectroscopy, etc. In this review, we cover the recent developments on... 

    Surface/edge functionalized boron nitride quantum dots: Spectroscopic fingerprint of bandgap modification by chemical functionalization

    , Article Ceramics International ; Volume 46, Issue 1 , 2020 , Pages 978-985 Angizi, S ; Shayeganfar, F ; Hasanzadeh Azar, M ; Simchi, A ; Sharif University of Technology
    Elsevier Ltd  2020
    Promising properties of boron nitride nanomaterials such as their chemical, thermal, and mechanical stability have made them suitable materials in a various range of applications. However, their low electrical conductivity and wide bandgap, particularly in the case of boron nitride quantum dots (BNQDs), have given rise to severe limitations. Efforts on bandgap engineering through doping and surface functionalization have gained little success due to their high thermodynamic stability and inertness. Herein, we present a novel approach to functionalize BNQDs by hydroxyl, methyl, and amine functional groups aiming to adjust the electronic structure. The successful exfoliation is demonstrated by... 

    Investigating the different conditions on solution processed MoOx thin film in long lifetime fluorescent polymer light emitting diodes

    , Article Materials Chemistry and Physics ; Volume 204 , 2018 , Pages 262-268 ; 02540584 (ISSN) Alehdaghi, H ; Marandi, M ; Irajizad, A ; Taghavinia, N ; Jang, J ; Zare, H ; Sharif University of Technology
    Elsevier Ltd  2018
    Transition metal oxides are being more frequently used as hole injection layer (HIL) in organic light emitting diodes (OLEDs), in place of polymer HILs such as PEDOT:PSS. The very thin films of the metal oxide HILs are usually deposited using vapor deposition, in order to create uniform films. Here, we report OLEDs fabricated using solution processed MoOx films as the HIL and super yellow as the emissive layer. The performance of the devices is comparable to PEDOT:PSS based devices, while the stability tests show the lifetime of MoOx-based devices is 4 × 106 h, about 40 times longer than PEDOT:PSS devices, at typical working condition. X-ray photoelectron spectroscopy (XPS) indicates both...