Voltage-mode high-Q band-pass filters and oscillators employing single CDBA and minimum number of components

In this paper, voltage-mode second order high-Q band pass filters and oscillators which employ only single current differencing buffered amplifier (CDBA) as the active component are proposed. One of the four filter circuits and two of the four oscillators described have minimum passive component count properties, without using the internal pole of the active element. These BP filters can be easily cascaded without any recourse to impedance matching circuitry. The circuits have been analysed theoretically, simulated and experimentally tested in a laboratory. It is shown that the results of simulations and experimental work are in agreement with theoretical predictions.     

A 1-V 10-MHz clock-rate 13-bit CMOS ΔΣ modulator usingunity-gain-reset op amps

The problem of low-voltage operation of switched-capacitor circuits is discussed, and several solutions based on using unity-gain-reset of the opamps are proposed. Due to the feedback structure, the opamps do not need to be switched off during the reset phase of the operation, and hence can be clocked at a high rate. A low-voltage ΔΣ modulator, incorporating pseudodifferential unity-gain-reset opamps, is described. A test chip, realized in a 0.35-μm CMOS process and clocked at 10.24 MHz, provided a dynamic range of 80 dB and a signal-to-noise+distortion (SNDR) ratio of 78 dB for a 20-kHz signal bandwidth, and a dynamic range of 74 dB and SNDR of 70 dB for a 50-kHz bandwidth, with a 1-V supply voltage     

Direct-Charge-Transfer Pseudo-N-Path SC Circuit Insensitive to the Element Mismatch and Opamp Nonidealities

A novel pseudo-N-path switched-capacitor circuit is described. Its center frequency is insensitive to element mismatch as well as to the finite gain and bandwidth of the opamps used. In this new architecture, the charges from the input source to the output are not transferred by an opamp; rather the opamp is used only as a buffer. The performance of the circuit is superior to that of a regular pseudo-N-path structure.     

Multi-function biquad using single CDBA

A voltage-mode, multi-input single-ouput type multi-function biquad is proposed having the following features: (a) It uses only one current differencing buffered amplifier as the active element, (b) it contains grounded and virtually grounded capacitors, (c) using this biquad, one may realize all five filter functions (i.e., lowpass, highpass, bandpass, notch and allpass) without changing the circuit topology, (d) it can be directly cascaded without any need of impedance matching circuits, (e) its Q-factor can be independently adjusted if the natural frequency is fixed, (f) biquad offers low sensitivities, and its natural frequency is insensitive to tracking errors. Experimental results are in agreement with theory.     

Real-Time FFT Computation Using GPGPU for OFDM-Based Systems

In optical and wireless communications systems, the goal is to reach 10 Gbps or above data rates. In order to support such extremely high data rates, the physical layer generally uses orthogonal frequency division multiplexing (OFDM) modulation. Unlike serial transmission of symbols, the OFDM modulation transmits data with many parallel sub-carriers, which help to provide high bandwidth. Field programmable gate arrays (FPGAs) and digital signal processors (DSPs) are usually employed to process OFDM blocks in real time. However, FPGAs and DSPs are not cost effective, and they are difficult to adapt to new standards. One of the most computationally intensive functions in OFDM systems is the fast Fourier transform (FFT) computation process. This paper aims to accelerate the FFT process to achieve high communication throughput in real time. Two parallel approaches are implemented for two different NVIDIA graphics processing unit (GPU) architectures. To obtain the best performance values, several optimizations are implemented. Our general purpose graphics processing unit (GPGPU)-based FFT computation achieves up to 24 Gbps throughput in real time.     

Structural investigations of mechanical properties of Al based rapidly solidified alloys

In this study, Al based Al–3 wt.%Fe, Al–3 wt.%Cu and Al–3 wt.%Ni alloys were prepared by conventional casting. They were further processed using the melt-spinning technique and characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM) together with energy dispersive spectroscopy (EDS), transmission electron microscope (TEM), differential scanning calorimetry (DSC) and the Vickers microhardness tester. The rapidly solidified (RS) binary alloys were composed of supersaturated α–Al solid solution and finely dispersed intermetallic phases. Experimental results showed that the mechanical properties of RS alloys were enhanced, which can be attributed to significant changes in the microstructure. RS samples were measured using a microhardness test device. The dependence of microhardness H_V on the solidification rate (V) was analysed. These results showed that with the increasing values of V, the values of H_V increased. The enthalpies of fusion for the same alloys were determined by DSC.     

Using of cotton oil soapstock biodiesel–diesel fuel blends as an alternative diesel fuel

In this study, usability of cotton oil soapstock biodiesel–diesel fuel blends as an alternative fuel for diesel engines were studied. Biodiesel was produced by reacting cotton oil soapstock with methyl alcohol at determined optimum condition. The cotton oil biodiesel–diesel fuel blends were tested in a single cylinder direct injection diesel engine. Engine performances and smoke value were measured at full load condition. Torque and power output of the engine with cotton oil soapstock biodiesel–diesel fuel blends decreased by 5.8% and 6.2%, respectively. Specific fuel consumption of engine with cotton oil soapstock–diesel fuel blends increased up to 10.5%. At maximum torque speeds, smoke level of engine with blend fuels decreased up to 46.6%, depending on the amount of biodiesel. These results were compared with diesel fuel values.     

Effects of hydrogen addition into liquefied petroleum gas reductant on the activity of Ag–Ti–Cu/Cordierite catalyst for selective catalytic reduction system

In this study, low temperature activity of Ag–Ti–Cu/Cordierite catalyst was investigated with liquefied petroleum gas (LPG) and hydrogen-liquefied petroleum gas (H₂-LPG) mixture as reductant. The selective catalytic reduction (SCR) catalyst was synthesized by impregnation method and characterized by Brunauer-Emmett-Teller (BET), Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) analyzes. BET analysis of the catalyst revealed surface area as 12.89 m²/g. Silver (Ag), titanium (Ti) and copper (Cu) nanoparticles were observed on the catalyst surface with SEM analysis. XRD analysis showed high dispersion of catalytic elements. The SCR performance tests were carried out at 170–270 °C temperature range, 30,000 h^?1 and 40,000 h^?1 space velocities, 1 kW, 2 kW, 3 kW and 4 kW engine loads with diesel engine real exhaust gas sample. NO_x conversion efficiency increased significantly in the presence of H₂, especially at low exhaust temperatures. The maximum NO_x conversion ratio was obtained as 89.53% with H₂-LPG reductant at 270 °C, 4 kW engine load and 30,000 h^?1 space velocity.     

Usage of enzymes in a novel baking process

In this study, the effects of different enzymes (alpha-amylase, xylanase, lipase, protease) on quality of breads baked in different ovens (microwave, halogen lamp-microwave combination and conventional oven) were investigated. It was also aimed to reduce the quality problems of breads baked in microwave ovens with the usage of enzymes. As a control, bread dough containing no enzyme was used. Specific volume, firmness and color of the breads were measured as quality parameters. All of the enzymes were found to be effective in reducing the initial firmness and increasing the specific volume of breads baked in microwave and halogen lamp-microwave combination ovens. However, in conventional baking, the effects of enzymes on crumb firmness were seen mostly during storage. The color of protease enzyme added breads were found to be significantly different from that of the no enzyme and the other enzyme added breads in the case of all type of ovens.