Full CMOS continuous time filters for GSM applications

This paper describes full cmoscontinuous time filter design techniques which can meet the specifications commonly set for gsmapplications. First several cmosfilter design techniques are overviewed. The ota-ctechnique is discussed to some more detail. To overcome the main drawback of the lower total harmonic distortion in ota-ctechniques very linear operational transconductance amplifiers (ota)are required. Such an ota,together with the applied linearisation techniques is discussed. To fulfil high accuracy in cut- off frequencies of the filter an active tuning system is necessary. A new on- chip tuning system is presented. The paper concludes with a practical design example for the gsmsystem. Therein the different ota-ctechniques discussed are illustrated.     

Microcharacterization of composition modulations in epitaxial ZnSe1-xTex

Molecular beam epitaxial growth of the ZnSe_1-xTe_x (x=0.44-0.47) alloy on vicinal (001) GaAs substrates tilted four, six, and nine degree-[111]A or B results in partial phase separation of the alloy with a vertical modulation between different compositions. Transmission electron microscopy images of samples grown on four degree-tilted substrates showed superlattice-like structures, with periods in the range 13.4-28.9Â. Lattice images reveal diffuse interfaces between light and dark bands. Period variations were detected in isolated regions of some samples. We present evidence that the modulation develops at the growth surface, and remains stable in the bulk at temperatures up to 450°C. Satellite spot pairs with approximate indices (h k 1 + δ) were present near the zinc-blende spots in electron diffraction patterns and x-ray diffraction data, as expected from material with a sinusoidal composition profile. The orientation of the spots reveals that the modulation vector is parallel to the growth direction, rather than to [001]. The [111]A- and B-tilted samples showed significant modulation, while the five degree-[110] and on-axis material showed no detectable modulation. The modulation wavelength did not strongly depend on growth temperature in the range examined (285–335°C). Samples showing composition modulation did not exhibit significantly altered low-temperature luminescence spectra from material with no modulation.     

Hydrogen energy from coupled waste gasification and cement production—a thermochemical concept study

A plant concept for hydrogen production from waste gasification coupled with cement manufacturing is presented. Hot precalcined cement meal, from the operating cement process, is used as heat carrier to provide energy required by the parallel arranged gasifier. The amount of CaO present in the cement meal operates simultaneously as an effective in situ _CO2${\mathrm{CO}}_2$-sorbent. First, a practical case study was devised to be able to perform simulations for estimation of expected hydrogen yield. The influence of different operation parameters of the gasifier and the hydrogen separation unit (steam-to-fuel ratio, pyrolysis temperature, PSA efficiency) was studied based on chemical equilibrium calculations. The simulation results indicate, that the coupling provides advantages for both processes. The production of a hydrogen-rich gas via thermal gasification benefits from the continuously available fresh CaO, which improves fuel conversion reactions and captures _CO2${\mathrm{CO}}_2$ in situ. High-calorific streams from gasification process remaining after hydrogen separation may substitute fossil fuels needed for cement process. For a steam/fuel ratio of 0.3 and a PSA efficiency of 0.7, the calculated hydrogen energy yield is 46% of fuel energy input.     

Stability of wood fast pyrolysis oil

This study evaluates the effects of storage conditions on physical and chemical properties of biomass fast pyrolysis oils exposed to elevated temperatures over extended periods of time. It was performed on oak pyrolysis oil generated in the NREL vortex reactor. Oil samples were stored at three temperatures: 37, 60 and 90°C in glass vessels. Properties of the oils were measured after hours of storage at 90°C, and after days or weeks at lower temperatures. Chemical changes in the oils were measured using GPC (molecular weight distribution) and FTIR spectroscopy. The oil remained a single phase throughout the studied conditions. Its pH was not affected by storage. The water content, viscosity and molecular weight of the oil increased with the time and temperature of storage. First-order reaction kinetics were successfully used to predict changes in molecular weight of the stored oil. FTIR provided evidence that etherification or esterification are mechanisms for condensation of the oil during storage.     

Gallium gradients in Cu(In,Ga)Se2 thin‐film solar cells

The gallium gradient in Cu(In,Ga)Se₂ (CIGS) layers, which forms during the two industrially relevant deposition routes, the sequential and co‐evaporation processes, plays a key role in the device performance of CIGS thin‐film modules. In this contribution, we present a comprehensive study on the formation, nature, and consequences of gallium gradients in CIGS solar cells. The formation of gallium gradients is analyzed in real time during a rapid selenization process by in situ X‐ray measurements. In addition, the gallium grading of a CIGS layer grown with an in‐line co‐evaporation process is analyzed by means of depth profiling with mass spectrometry. This gallium gradient of a real solar cell served as input data for device simulations. Depth‐dependent occurrence of lateral inhomogeneities on the µm scale in CIGS deposited by the co‐evaporation process was investigated by highly spatially resolved luminescence measurements on etched CIGS samples, which revealed a dependence of the optical bandgap, the quasi‐Fermi level splitting, transition levels, and the vertical gallium gradient. Transmission electron microscopy analyses of CIGS cross‐sections point to a difference in gallium content in the near surface region of neighboring grains. Migration barriers for a copper‐vacancy‐mediated indium and gallium diffusion in CuInSe₂ and CuGaSe₂ were calculated using density functional theory. The migration barrier for the In_Cu antisite in CuGaSe₂ is significantly lower compared with the Ga_Cu antisite in CuInSe₂, which is in accordance with the experimentally observed Ga gradients in CIGS layers grown by co‐evaporation and selenization processes. Copyright © 2014 John Wiley & Sons, Ltd.     

ATM‐based wireless broadband access in the local loop

Broadband networks using wireless transmission techniques are a quick and flexible means of implementing subscriber access. Unoccupied frequency bands with sufficient bandwidth to allow the transmission of digital signals at very high bit rates are found only in the microwave bands. Because the path loss is fairly high at these frequencies, the diameter of radio cells is limited to a maximum of a few kilometres. This results in a microcellular system, which is best implemented in the form of a point‐to‐multipoint system, where one radio‐base station serves all subscribers registered in that radio cell. An interactive, broadband, ATM‐based radio local loop has undergone successful trials in Munich. Copyright © 2001 John Wiley & Sons, Ltd.     

Optical Interconnects on and in Printed Circuit Boards

Two types of short distance optical interconnects for on-board applications are presented: Small diameter plastic optical fibre (POF) links and multimode polymer waveguide layers integrated in multilayer printed circuit boards (PCB). POF links with fibre numbers up to 128 and link lengths up to 50 cm are realized with total transmission loss values below 2 dB at 660 nm. First tests of 10 cm long temperature stable multimode polymer waveguides laminated into standard multilayer PCBs demonstrate the capabilities of combined electrical-optical circuit boards.     

Living cationic polymerization of isobutyl vinyl ether, 2

Summary Living cationic polymerization of isobutul vinyl ether (IBVE), initiated by1-iodo-1-(2-methyl propyloxy)-ethane (1) and tetraalkylammonium perchlorate yields polymers of well defined molar masses and end groups. The controlled introduction of end groups was confirmed by a model reaction and was then applied to introduce and azo initiator function. The resulting polymeric initiator was used for the synthesis of a blockcopolymer.