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  • 1.
    Duppils, Mattias
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    CMOS mixed analog/digital building blocks for signal processing1999Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    A mixed analog/digital multiply-accumulate unit is presented. The unit is composed of the multiplying D/A converter and a polarity switching network. It is featured by an analog continuous-time input port, a discrete­time output port, and a digital input port for the quantized multiplying coefficient. This unit constitute a core for mixed analog-digital computations, and its versatility can be compared to the all-digital multiply-accumulate unit. Mixed-signal computations is useful in environments where the input signals are analog in nature, but where signal processing in the digital domain is desired. A traditional system adapted for such an environment consist of an A/D converter, followed by digital signal processing elements, or a digital signal processor. It is shown that the system power drain can be reduced considerable if using the mixed analog/digital MAC unit followed by an A/D converter instead of the former configuration. This is true when the signal processing task reduces the required A/D conversion rate or accuracy, and when a low number of MAC units are required, since the complexity (chip area) of such units are considerable.

    Some proposed suitable signal processing tasks are pattern matching (not shown in the thesis) and narrow­band PIR filtering followed by decimation, which possibly are suitable for radio receiver applications. A design methodology for the realization of PIR filters suitable for implementation with a low number of MAC units is given. Mixed analog/digital MAC units have been designed with 1-bit and 8-bit coefficient resolution respectively and implemented in a double-poly 0.6µm CMOS process. Chip measurements have verified high performance of the 1-bit mixed analog/digital MAC unit, but the 8-bit counterpart still suffers from imperfections of unknown origin. The consequence of the imperfections show up as a coefficient dead zone.

    The bottom-plate sample-and-hold circuit is analyzed with simulations. It is shown that the track-mode linearity depends on the analog input frequency. If the track-mode linearity, the hold-mode introduced thermal noise, and the desired bandwidth as a fraction of the Nyquist frequency is considered - maximum spurious­free dynamic range, is achieved with a low bias voltage, and with a low input voltage swing.

  • 2.
    Greczynski, Grzegorz
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Photoelectron spectroscopy of conjugated polymer surfaces and interfaces for light emitting devices2000Licentiate thesis, comprehensive summary (Other academic)
  • 3.
    Hjort, Mattias
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Theoretical studies on one-, two- and three-dimensional carbon structures2000Licentiate thesis, monograph (Other academic)
    Abstract [en]

    This thesis deals with electronic structure calculations in large carbon based materials, Especially graphite like structures have been studied. For this the tight binding method together with more sophisticated quantum chemical methods has been utilised. The first part of this thesis provides a background to the theoretical models used in the papers.

    In paper one, single bonded fulleride polymers of all dimensions have been studied as a function of charge state.

    In paper two, the effect of vacancies in graphite is modelled within the tight binding formulation.

    In paper three, electron localization in quasi-one dimensional systems in the presence of disorder are investigated.

  • 4.
    Kindlihagen, Anders
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Theoretical modeling of bipolar double-barrier resonant-tunneling light emitting diodes1996Licentiate thesis, comprehensive summary (Other academic)
  • 5.
    Lennholm, Erik
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Effects of aperiodic order for Josephson junction arrays and discrete breathers2000Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Effects of the combination of nonlinearities and aperiodic order is studied in this thesis. The nonlinear systems considered are Josephson junction arrays (JJA) and Fermi-Pasta-Ulam (FPU) lattices. Both systems are discrete and one-dimensional. The traveling waves in a JJA are solitons, i.e., coherent structures which retain their shape and speed as they propagate. The properties of both these system is influenced by the ordering of their respective constituents. In the thesis some aperiodicaly orderd structures are described, including some typical effects on systems which are aper iodically orderd. Next, a description of Josephson junctions are given and also some physical features for system sconsisting of these junctions. A number of practical applications are given, Finally discrete breathers are described, including existence conditions and some possible applications.

    Paper 1: Fluxon propagation in discrete Josepson junction arrays is examined. Sometimes a fluxon can be pinned in the array and we derive an effective potential which can explain why this happens, and predict at which positions a fluxon can get pinned.

    Paper2; Discrete breathers are shown to exist in aperiodically ordered, diatomic FPU lattices. Localized modes survives for longer times in Fibonacci and Thue-Morse lattices compared to a periodic lattice. The conjecture is that the gaps in the linear phonon spectrum of the aperiodically orderd structures hinder resonances with the linear spectrum.leading to the longer life times.

    Paper 3: Moving breathers in FPU lattices are examined. These have frequencies in the linear bands. Interaction with noise and imourity atoms are further considered.

    Paper 4: Current-voltage (I-V) curves are calculated for Josephson junction arrays, which consist of two different types of junctions. A monoarray is compared to a periodic array and a Fibonacci array. There are marked differences in the I-V curves for these systems. New states with kink a structure superimposed on the rotating McCumber background are found in periodic array and in the Fibonacci array.

  • 6.
    Persson, Per
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Electron microscopy of ion implanted silicon carbide2000Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis investigates structural defects into Silicon Carbide (SiC) in processed Al and B ion implantated samples. Ion implantation is currently the preferred way to introduce impurity atoms into the SiC crystal lattice. The structural defects found was concluded to be extrinsic dislocation loops composed of excess Si interstitials. A model for these loops was developed and the mechanisms for loop evolution during processing were identified. The results of this thesis contributes to an improved processing technology of SiC as a semiconducting material, which will be used in electrical components for high power, high temperature and high frequency applications.

  • 7.
    Tulldahl, Michael
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Airborne laser depth sounding: model development concerning the detection of small objects on the sea bottom2000Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Airborne laser depth sounding is a promising technique for rapid and high -density sounding of shallow waters. Depth accuracy analysis for laser depth sounding has almost exclusively dealt with horizontal flat bottoms. The objective of this work is to simulate and compare the influence of different shapes of small objects placed on the sea bottom. For this purpose an analytical mode] approach is used to characterize the signals received from objects of size 1 m3 on bottom depths between 5 m and 12 m. Two object types are compared: a cylinder and a cube. The difference in the signal received is small between these objects. Simulated data are compared with experimental data and show good agreement. The probability of small shoal detection critically depends on the horizontal position of the shoal in the laser beam and the shoal height above the bottom. From comparisons between a large number of simulations and measurements the performance is discussed in terms of covered area for one laser shot enabling detection of the shoal.

  • 8.
    Tungasmita, Sukkaneste
    Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
    Epitaxial aluminum nitride thin films on 6H-silicon carbide, grown by magnetron sputter deposition2000Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The research presented in this thesis is focused on epitaxial wurtzite-structure Aluminum Nitride (AlN) thin film synthesis, by ultra-high-vacuum (UHV) de magnetron sputter deposition, on Silicon Carbide (6H-SiC) substrates. The emphasis of the work has been put on controlling the growth and quality of the films to be able to use this material in electronic device applications.

    The quality of epitaxial AlN films is significantly improved by using low­ energy ion assistance (Ei = 17-27 eV), during growth. The ion-assisted growth results in an increased surface mobility, which promotes domain boundary annihilation and epitaxial growth. This results in lateral expansion of column width (100 nm-wide at film thickness above 100 nm). The film characterization results show a very good crystal quality as well as high purity material. The measured concentrations of O, C, and Si in the film are at 3.5x1018, l. 3x1018 and 3.5xl 018 cm-3, respectively, which are among the purest AlN material as has been reported. The appearance of near band­ edge CL emission (6.02 eV at 4K) is also an evidence ofa high quality material.

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