Frequency tunable low ripple and fast response on-chip DC–DC converter for DVFS

Dynamic voltage and frequency scaling (DVFS) is an efficient method to reduce the power consumption in system on-chip. To support DVFS, multiple supply voltages are generated based on different work load frequencies and currents using on-chip DC–DC voltage converter. In this paper a frequency tunable multiple output voltage switched capacitor based dc–dc converter is presented. An analog to digital converter and phase controller is used in the feedback to change the switching frequency and duty cycle of the converter. An input voltage of 1.8 V is converted to 0.6 and 0.8 V for low and high signal frequency respectively. The proposed 2-phase switched capacitor architecture with gain setting of 1:2 is designed with the 90 nm technology. An output ripple of 45 mV is observed and the maximum transient response time of the converter is 17.3 ns (= 58 MHz).     

Perturbation-Based Fourier Series Analysis of Transistor Amplifier

A perturbation-based Fourier series model is proposed to approximate the nonlinear distortion in weakly nonlinear circuits. This general model is applicable to any set of multi-variable state equations that completely describe a nonlinear circuit. This model is applied to a common emitter amplifier circuit wherein the transistor is represented by Ebers–Moll nonlinear current equations. Appropriate state variables are defined, then the linear and nonlinear parts of the Ebers–Moll current equations are separated, and a small perturbation parameter is incorporated into the nonlinear part. Now these current equations are incorporated into the set of KCL, KVL equations defined for the circuit and the state variables are perturbatively expanded. Hence, multi-variable state equations are obtained from these equations. The state variables are approximated up to first order through Fourier series expansion, as described in the proposed model. The main advantage of the proposed model is that it is simple and straightforward approach to analyze weakly nonlinear circuits, as it involves matrix computations and the calculations of exponential Fourier coefficients.     

Organic inverter: Theoretical analysis using load matching technique

This paper reports the analysis of key parameters affecting voltage transfer characteristics of pseudo PMOS organic inverters. Pentacene has been used as active material for PMOS Organic Thin Film transistor (OTFT). We have used two different inverter configurations for thorough analysis. Each configuration comprises of an enhancement mode driver (V_Threshold = −9.7 V) and a depletion mode load (V_Threshold = 11.7 V). First configuration has its source and gate terminals shorted. While, second configuration differs with its drain and gate terminals shorted. In order to surmise the theoretical performance of the inverters, we have used load matching technique. After investigating various parameters such as inverting gain, noise margin values (immunity to noise error signals) and threshold voltage value, influencing the voltage inverting efficiency of the two configurations mentioned above, it was found that an inverter with shorted source-gate load configuration is better of the two due to privileges such as saturation mode operation of load, low driver current with early saturation of enhancement mode driver, which facilitates full swing output voltage operation. Second configuration with shorted drain-gate load, lacks saturation mode operation of load and fails to deliver high voltage swing along with acceptable noise margin values and inverting gain.     

Fully integrated 1.2-μA and 13-μA quiescent current LDOs with improved transient response

We introduce two extremely low quiescent current (I _Q ) low-dropout (LDO) voltage regulators. The Low I _Q -LDO (LI _Q -LDO) uses 13 μA of total quiescent current and is designed for a maximum load current of 50 mA. The Micro I _Q -LDO (MI _Q -LDO) uses only 1.2 μA of total quiescent current and is designed for a maximum load current of 5 mA. Detailed pole/zero analysis is performed to aid in the design of the LDOs. Two LHP zeros cancel the two non-dominant poles which extend the bandwidth and improve transient response. Both designs are fully integrated, stabilized with an on-chip capacitive load of 100 pF. In load transient, the total variation in output voltage for LI _Q -LDO and MI _Q -LDO is 1 V and 950 mV, respectively, and the total line transient variation is 668 and 599 mV, respectively. Both designs occupy an area of 0.26 mm² in a 0.5-μm CMOS process. Two process-independent figures of merit are proposed to compare LI _Q -LDO and MI _Q -LDO with other published work.     

Fullerenes and Nanotubes from Coal

Abstract

Graphite has normally been used to synthesise fullerenes and nanotubes. However, coal is a cheaper and more suitable industrial material. Because coal is a molecular solid, unlike graphite, the mechanism by which fullerene and nanotubes are formed is different. Moreover, other products such as polyaromatic hydrocarbons (PAHs) and microfibres are also formed. In this review, the mechanism of formation of fullerene and nanotubes from coal is discussed. It is shown that the pathway involved is other than through the C₁ intermediate route. The influence of other elements in coal such as hydrogen, oxygen, sulfur and iron is also discussed. It appears that, hydrogen, oxygen, iron and sulfur affect the yield and type of fullerenes and nanotubes formed.     

Der Einflu? der Wasserstoffion-Konzentration und der Temperatur auf die Milchgerinnung und Caseinhydrolyse durch Papain

Zusammenfassung Im Papain findet sich ein milchgerinnendes Ferment; sein Wirksamkeitsbereich reicht von p_H 4,2–8,0; sein p_H-Optimum liegt bei p_H 5,2, das Temperatur-Optimum bei 60° C. Bei steigender Temperatur wird die Gerinnungszeit abgekürzt.Das proteolytische Ferment spaltet Casein bei einem p_H -Bereich von 2,2 bis 5,2. Mit steigender Temperatur wird dieses Optimum nach der sauren Seite verschoben. Die Hydrolyse erfolgt in den ersten 30 min rasch, später langsam; nach 90 min tritt eine Inaktivierung des Fermentes durch hydrolytische Abbauprodukte ein. Die Acidität der Hydrolysenflüssigkeit sinkt ab, namentlich wenn das p_H < 2,2-3,2 ist..Im Papain kommt außerdem noch eine Decarboxylase vor, die außer Citronensäure auch Weinsäure und Salicylsäure decarboxyliert.Das in zwei Arbeiten eingegangene Publikationsmaterial wurde von den Herren Dr. H.Winter (Berlin) und Dr. K.Raible (München) gesichtet, übersetzt und zusammengefaßt.     

Sol-gel auto-combustion synthesis of Ba–Sr hexaferrite ceramic powders

We report the mechanism involved in sol-gel auto-combustion synthesis of Ba–Sr-hexaferrite (Ba_1-xSr_xFe₁₂O₁₉; x = 0, 0.25, 0.5, 0.75 and 1, BSFO) ceramic powders through the analysis of the phases evolved during annealing of the as-synthesized powders, along with their structure and morphological studies. The XRD patterns of the as-synthesized samples indicate the formation of barium/strontium monoferrite ((Ba/Sr)Fe₂O₄) and maghemite (γ-Fe₂O₃) phases along with a minute amount of hematite (α-Fe₂O₃) phase. Annealing of these samples facilitates formation of BSFO phase through the solid state reaction between BaFe₂O₄ and γ-Fe₂O₃ phase. Interestingly, after annealing the samples with x = 0, 0.5 and 1, at 1000 °C for 2 h, we observed that phase pure Ba–Sr hexaferrite structure forms, but for samples with x = 0.25 and 0.75, high amount of hematite (α-Fe₂O₃) phase is observed, especially for x = 0.75. The reason associated with this could be the large difference between the ionic radii of Ba²⁺ and Sr²⁺ ions occupying the oxygen site. Furthermore, our study on annealing dependent phase evolution confirms that, this difference in ionic radii forbids the formation of a single phase Ba–Sr hexaferrite. The growth of clear hexagonal-shaped plate-like particles with varied particle sizes was observed for all the samples. The particle size variation may be due to the influence of the ionic radii difference on the sinterability of the samples. Our study provides a better understanding of synthesis mechanism of Ba–Sr hexaferrite samples.     

Investigation of thermal residual stresses during laser ablation of tantalum carbide coated graphite substrates using micro-Raman spectroscopy and COMSOL multiphysics

Laser ablation of high-temperature ceramic coatings results in thermal residual stresses due to which the coatings fail by cracking and debonding. Hence, the measurement of such residual stresses during laser ablation process holds utmost importance from the view of performance of coatings in extreme conditions. The present research aims at investigating the effect of laser parameters such as laser pulse energy, scanning speed and line spacing on thermal residual stresses induced in tantalum carbide-coated graphite substrates. Residual stresses were measured using micro-Raman spectroscopy and correlated with Raman peak shifts. Transient thermal analysis was performed using COMSOL Multiphysics to model the single ablated track and residual stresses were reported at low, moderate and high pulse energy regimes. The results showed that the initial laser conditions caused higher tensile residual stresses. Moderate pulse energy regime comprised higher compressive residual stresses due to off centre overlapping of the laser pulses. Higher pulse energy (250 μJ), higher scanning speed (1000 mm/s) and moderate line spacing (20 μm) caused accumulation of tensile residual stresses during the final stage of laser ablation. The deviation of experimental residual stresses from COMSOL numerical model was attributed to unaccounted additional stresses induced during thermal spraying process and deformation potentials in the numerical model.