Direct Synthesis Technique Research Articles

Negative role of triphenylphosphine in the inhibition of benzotriazole at the Cu surface studied by surface-enhanced Raman spectroscopy

The adsorption behaviour and the formation of a surface complex film of benzotriazole (BTAH) on Cu electrodes have been studied by in situ surface enhanced Raman spectroscopy in acetonitrile solution. A potential-dependent Raman study revealed that the adsorption and film formation process of BTAH involves the formation of a chemisorbed adlayer and a compact polymer film in two different potential regions in the acetonitrile solution. The results showed that BTA − ion can interact with the Cu surface through the two N atoms of the triazole ring to form a surface polymer complex of [Cu(BTA)] n , which suppressed the dissolution and oxidation of Cu effectively. When triphenylphosphine (pph 3) was introduced into the solution, the formation of the surface polymer complex film was suppressed due to the formation of soluble Cu ( pph 3 ) n + . In solution, a complex of Cu with BTA − and pph 3 was formed leading to a significant decrease of the surface inhibition efficiency. These two kinds of surface complexes were prepared by the direct electrochemical synthesis technique in similar solutions, and characterized by normal Raman spectroscopy and elemental analysis. The results showed that the final complexes were insoluble [Cu(BTA)] n polymer and Cu n BTA m (pph 3) p complex with low solubility in the acetonitrile solution.

High silica zeolite Y nanocrystals by dealumination and direct synthesis

In this study, dealumination and direct high silica synthesis techniques were applied to zeolite Y nanocrystals in an attempt to produce dispersible zeolite Y nanocrystals in the 30–40 nm size range with high acid resistance. Dealumination of zeolite Y nanocrystals with SiO 2/Al 2O 3 = 4.38 with ammonium hexafluorosilicate was not successful in increasing the acid stability of the nanocrystals. By increasing the TMABr/TMAOH ( S) ratio in the synthesis mixture, synthesis of zeolite Y nanocrystals with a SiO 2/Al 2O 3 of ratio of 5.84 was demonstrated. Two distinct regions of supercage TMA weight loss were identified during the TG analyses of our as synthesized and Na + exchanged zeolite Y nanocrystals. The two distinct weight losses are attributed to the existence of TMA template free within the supercage and template bound to extraframework cation sites on the walls of the supercage. A detailed characterization of our zeolite Y nanocrystals is given, including powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), N 2 adsorption, dynamic light scattering (DLS), thermogravimetric (TGA) analyses, and inductively coupled plasma optical emission spectrophotometry (ICP OES) elemental analyses.

Arbitrary Waveform DDFS Utilizing Chebyshev Polynomials Interpolation

A new technique of arbitrary waveform direct digital frequency synthesis (DDFS) is introduced. In this method, one period of the desired periodic waveform is divided into m sections, and each section is approximated by a series of Chebyshev polynomials up to degree d. By expanding the resultant Chebyshev polynomials, a power series of degree d is produced. The coefficients of this power series are obtained by a closed-form direct formula. To reconstruct the desired signal, the coefficients of the approximated power series are placed in a small ROM, which delivers the coefficients to the inputs of a digital system. This digital system contains digital multipliers and adders to simulate the desired polynomial, as well as a phase accumulator for generating the digital time base. The output of this system is a reconstructed signal that is a good approximation of the desired waveform. The accuracy of the output signal depends on the degree of the reconstructing polynomial, the number of subsections, the wordlength of the truncated phase accumulator output, as well as the word length of the DDFS system output. The coefficients are not dependent on the sampling frequency; therefore, the proposed system is ideal for frequency sweeping. The proposed method is adopted to build a traditional DDFS to generate a sinusoidal signal. The tradeoff between the ROM capacity, number of sections, and spectral purity for an infinite output wordlength is also investigated.

A low-power DS-CDMA RAKE receiver utilizing resource allocation techniques

This paper presents architectural and implementation innovations made to realize a self-contained front-end processor for any DS-CDMA-based system. At the heart of the ASIC is a highly flexible RAKE processing engine that utilizes a unique resource allocation technique for maximum flexibility. The front-end of the chip consists of a matched filter and an all digital timing and frequency recovery loop based on interpolation and direct digital frequency synthesis (DDFS) techniques. A highly configurable multipath combiner is used to generate the final demodulated symbols by combining contributions from different multipath in a maximal ratio combining scheme. The combiner is also instrumental in performing channel estimation/correction and in closing the loop on the timing and frequency recovery circuits. The chip also features a multipath searcher which performs an energy scan of the wireless channel to decide on new valid multipath. To minimize power consumption and enhance the flexibility of the architecture a unique data tagging technique is utilized to decouple the sampling rate of the incoming data from the processing frequency of different blocks of the ASIC. All resources are programmable via a microcontroller interface that provides firmware control over system resources. Furthermore, the architecture supports the concept of design reuse by enabling simple modular expansion as a means of increasing resources. The resulting layout area is 8.29 mm/sup 2/ in a 0.18-/spl mu/m 1-poly 6-metal CMOS process and consists of 320000 equivalent gates. The core consumes a total of 4.032 mW in a typical load scenario including full demodulation of two RAKE fingers and simultaneous searching for new multipath.

Direct FAME synthesis for rapid total lipid analysis from fish oil and cod liver oil

A direct method for preparation of fatty acid methyl ester (FAME) via transesterification of fatty acids from fish oil and cod liver oil using methanolic sulfuric acid and chloroform as co-solvents was optimized. The synthesized FAME were subsequently analysed by gas chromatography (GC) to identify and quantify the individual fatty acid in the oils. Temperature and heating times had a significant effect on the total fatty acid (TFA) recovery. In general, temperatures of 90°C and 100°C and reaction times of 90 and 30 min, respectively, resulted in maximum recovery of TFA from the oils. TFA recoveries of more than 95% suggest that this method is suitable for quantitative analysis of individual fatty acids. In comparison, a conventional method which involved a separate extraction procedure using chloroform and methanol before FAME synthesis yielded approximately 30% lower TFA recovery from the oils. It can be concluded that the direct FAME synthesis technique is superior to the current conventional method, not only because of its simplicity, speed and economical use of solvents, but also its precision.

Hydrogen incorporation in titanium via laser irradiation

We have applied the technique of direct laser synthesis to the hydrogen–titanium system. Large amounts of hydrogen are incorporated into the sample surface by laser irradiating the samples in a hydrogen atmosphere at elevated gas pressures. The process of “laser hydriding” leads to the formation of TiH2 and the amount of incorporated hydrogen was found to be independent of the hydrogen gas pressure. Similarities to the laser nitriding process are briefly discussed and the results are interpreted with the help of thermodynamic simulations of the laser–material interaction.

Synthesis and Design of Novel In-Line Filters With One or Two Real Transmission Zeros

A direct synthesis and design technique of pseudoelliptic in-line filters with one or two real transmission zeros (TZs) is presented. It is shown that the phase of the reflection coefficient must be properly and uniquely determined for the synthesis to succeed. The TZs (attenuation poles) are brought about and independently controlled by dedicated resonators at the input and output. Each attenuation pole is located at the resonant frequency of its dedicated resonator. Frequency-independent reactances at the input and output are used to replace the phase shifts used in the extracted-pole technique. This novel approach is verified by several waveguide cavity filter designs. The analyzed characteristics of these filters, obtained with commercial full-wave computer-aided-design tools, agree very well with the synthesis results. A third-order filter with one TZ above the passband is designed, fabricated, and measured. Excellent agreement between the measurement and simulation is obtained.

Direct Synthesis of a New Class of Bandstop Filters

A direct synthesis technique of a new class of bandstop coupled resonator elliptic filters is presented. Two different coupling schemes, which both include source-load coupling are used. The first coupling and routing scheme is the standard folded structure used in implementing bandpass elliptic filters with N transmission zeros using N resonators. The second coupling scheme is identical to the multipath parallel structure, which was recently introduced for the synthesis of fully elliptic bandpass filters. In both cases, the source and load are directly coupled by an inverter in order to generate the required transmission zeros. It is shown that, for each coupling scheme, two distinct solutions that are not related by a similarity transformation exist. Furthermore, the two solutions both have realistic coupling coefficients in contrast to the bandpass case where only one solution, in general, is practical. It is also shown that the same coupling scheme can implement pseudoelliptic bandstop filters with N/sub z/ reflection zeros where 0/spl les/N/sub z//spl les/N.

Quadrature direct digital frequency synthesis using fine-grain angle rotation technique

An area- and power-efficient quadrature direct digital frequency synthesis technique called fine-grain angle rotation is presented. To reduce the large bitwidth requirement of the angle rotation, multiple start points are introduced and the angle rotation is applied to the remaining small angle. A prototype chip occupies 0.16 mm2 in 0.25 µm 1P5M CMOS technology and consumes 90 mW at 400 MHz clock frequency, which is a significantly improved performance compared to previous state-of-the-art chips.

Direct synthesis of folded symmetric resonator filters with source-load coupling

A direct synthesis technique of coupled symmetric resonator filters with source-load coupling is presented. An examination of the implications of power conservation on the possible solutions to the synthesis problem is examined. It is shown that at least two different coupling matrices whose entries differ not only in signs but in magnitude, as well, can be extracted. The two matrices have the same coupling and routing scheme. Typical examples of synthesized filters are presented to document the validity of the technique.

Analysis and design of a frequency-hopped spread-spectrum transceiver for wireless personal communications

Personal communications services (PCS) require low-power radio technologies. One such transceiver architecture employing frequency-hopped spread-spectrum techniques is presented. System features such as antenna diversity with equal-gain combining and sequential hop combining are incorporated into the transceiver design to achieve robust wireless digital data transmission over fading channels. A direct-conversion architecture from radio frequency (RF) to baseband reduces the overall power consumption by eliminating intermediate frequency (IF) components. High-rate frequency hopping with frequency-shift keying (FSK) modulation is implemented using a direct digital frequency synthesis technique. A multiplierless correlation FSK detector, suitable for direct-conversion receivers, has been designed for quadrature noncoherent detection. Robust acquisition algorithms based on energy detection and pattern matching and tracking architectures using digital phase-locked loops are also described for system synchronization. The proposed transceiver is well-suited for low-power PCS applications and other portable wireless communications.

An automatic calibrator for wattmeters with harmonic analysis capability

This paper deals with a three-phase phantom-power generator, which is designed for calibrating digital wattmeters with harmonic analysis capability. The calibration of such instruments is a critical task due to the lack of suitable calibrators. Fortunately, the calibration procedure can be limited to the first harmonic components when digital wattmeters are employed to characterise electrical machines, so that also simple calibrator design can be adopted. This paper describes a three-phase calibrator arrangement which is able to generate an arbitrary spectrum up to 5 kHz and a phantom power variable up to 3 kVA per phase. The uncertainty on the power associated to the first harmonic components is of about 0.1% in nonsinusoidal conditions. The calibrator employs a Direct Digital Synthesis technique, so that a frequency change of the output signal can be obtained without modifying the sampling frequency. Such a technique also permits to generate the frequency modulated signals that are often encountered at the output of static power converters that feed electrical machines.

The magnetic field and temperature dependent transport critical current density of Hg-Pb-Bi-Ca-Cu-O ceramic compounds

Mercury-based ceramic superconductors have been prepared by powder metallurgy, utilizing a technique of direct synthesis from the oxide powders. The tetragonal Hg-1223 phase was prepared and stabilized over a range of Pb and BiPb compositions. The most interesting material had an onset superconducting transition temperature of approximately 133 K. Critical current densities were obtained directly from transport measurements and indirectly from magnetization measurements, The transport critical current densities were orders of magnitude smaller than the intra-grain critical current densities. The data suggest that the transport critical current is limited by weak coupling between the grains, and that the intra-grain critical current densities deteriorate rapidly above 20 K.

An 0.8-μm CMOS mixed analog-digital integrated audiometric system

This paper presents a dual-channel fully integrated audiometric system, which generates the complete set of audio and control signals required for exhaustive audiometric tests. The system includes a novel signal generator, based on the direct digital synthesis technique, which fulfils the requirements of advanced audiometric tests. The proposed system faces two different problems, namely, the generation of a finely tunable pure sinewave and the generation of noise signals with a controlled spectrum. To achieve tuning capabilities down to 1 Hz at 20 kHz and 15 /spl mu/Hz at 100 Hz, a fractional division of a 40-MHz master clock based on noise-shaping techniques is performed. Moreover, for noise generation, a novel circuit based on pseudorandom sequences combined with analog switched-capacitor filters is used. The chip is fabricated in a 0.8 /spl mu/m CMOS process and occupies a 24.2 mm/sup 2/ silicon area. It consumes 45 mW from a single 5 V power supply and achieves less than -90 dB crosstalk between the channels.

Personal computer-based direct synthesis of optimum rectangular waveguide E-, H-, and EH-plane transformers

In this work a direct synthesis technique is presented for the optimum design of rectangular waveguide continuous and stepped impedance transformers. The synthesis technique is based on a generalized Fourier transform pair and it is implemented on a 486 DX2 machine. Unlike the conventional techniques, the proposed method is exact and does not rely on repeated analysis-based computer optimization that requires a large computer memory and speed. The proposed method requires less than a second to design a Chebyshev EH-plane transformer. The validity of the method has been shown by the design and analysis of several E-, H-, and EH-plane rectangular waveguide Ka-band transformers. The analysis subroutines were verified using published experimental results. © 1997 John Wiley & Sons, Inc. Int J Microwave Millimeter-Wave CAE 7: 289–308, 1997.

Sinewave modulation for data communication by direct digital synthesis and sigma delta techniques

AbstractDirect digital synthesis and sigma‐delta techniques have been proposed in recent years to realize sinewave generators and modulators for data communication. This paper explains the basic principles behind these techniques and presents schemes which implement popular modulation methods such as frequency shift keying, phase shift keying and amplitude modulation. The schemes are mostly implemented with digital circuits. They ensure a high degree of flexibility and are fully compatible with VLSI integration technologies. Experimental results obtained on integrated semicustom devices have demonstrated the validity of this approach.

A low-cost wide-frequency-range three-phase sine-wave signal generator using direct digital synthesis technique

This design note describes a three-phase sine-wave signal generator. The waveforms are digitally synthesized by using three weighting resistor networks and high-speed CMOS switches. The phase differences between the three sine waves are kept precisely at 120 degrees . This low-cost direct digital synthesis method provides excellent amplitude and frequency stability, small distortion and a wide frequency range, up to 3.3 MHz.

Direct synthesis and identification of benzo[a]pyrene diol epoxide-deoxyguanosine binding sites in modified oligodeoxynucleotides.

Adducts derived from the reaction of the benzo[a]pyrene metabolite model compound (+)-anti-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9, 10-tetrahydrobenzo[a]pyrene [(+)-BPDE] with the single-stranded oligodeoxynucleotide 5'-d(TATGCGTAT) were obtained according to direct synthesis techniques described earlier [Cosman, M., Ibanez, V., Geacintov, N. E., and Harvey, R. G. (1990) Carcinogenesis 11, 1667-1672]. Four major adducts, involving trans and cis addition (trans/cis adduct ratio approximately 4.5) of (+)-BPDE to the exocyclic amino groups of guanines G4 and G6 (the numbers denote the positions of the guanines counted from the 5'-side) were obtained. These adducts can be separated from one another by reverse-phase high-performance liquid chromatography methods. The site of BPDE binding on either G4 or G6 can be determined from the electrophoresis band patterns on 20% polyacrylamide gels of the BPDE-modified oligonucleotides subjected to the G+A and G Maxam-Gilbert strand cleavage reactions [Maxam, A. M., and Gilbert, W. (1980) Methods. Enzymol. 65, 499-560]. The electrophoresis gel band patterns are different for unmodified DNA and the two different BPDE-modified oligonucleotides because (1) the strand cleavage fragments bearing BPDE residues migrate slower than the corresponding fragments derived from the unmodified oligonucleotide and (2) strand cleavage tends to be inhibited on the 5'-sides of BPDE-modified guanines in the G+A, but not the G reaction.

A digital interface for phase control of PTS-300 synthesizers

Modern NMR spectrometers must be equipped to generate accurate, fast, reproducible radiofrequency phase shifts of essentially arbitrary angles under pulse programmer control. Many designs for phase shifting circuits have been used: analog circuits using delay lines ( I), RC networks (2)) hybrid networks (3)) digital designs based on clocked logic (4-7) or packaged phase shift units (S), high-speed analog designs using double-balanced mixers (9), and circuits using direct digital synthesis (DDS) techniques. The DDS designs using lookup tables have other advantages such as rapid phase-continuous frequency switching. Adding a phase shift option to such a circuit is relatively straightforward. Digital frequency synthesizers produced by Programmed Test Sources, Inc., are popular with designers of NMR spectrometers. In our homebuilt spectrometer we have used two PTS-300 synthesizers equipped with the “Type 2” frequency generation scheme that allows phase shifts in 0.225’ steps (2n/ 1600) using the DDS method. In this Note we describe a simple interface that allows the phase shift options of the PTS to be implemented in a convenient way. The design has the advantage that it allows the step size of the phase shifts to be preset, so that phase shifts can be expressed in multiples of a basic increment rather than in multiples of the basic resolution. The design can readily be adapted to other situations where such a feature is desirable. The PTS-300 uses 12 binary lines to encode the phase shift. Four lines specify the phase shift in multiples of 0.225” using binary coded decimal (BCD), and another four lines specify the phase shift in multiples of 2.25”, also using BCD. The final 4 lines specify the phase shift in multiples of 22.5”, but in contrast to the other lines, these 4 are coded in binary in the range 0 to 15 ,0 (in the older models the top 4 lines are also in BCD, giving 0.36” resolution). The relation between the desired phase shift and the requisite binary code is thus rather involved, although of course

Direct form active-R synthesis techniques and their critical assessment

A unified treatment is used to obtain the three active-R direct form synthesis approaches: the immittance (LC) simulation technique, the FDNR technique and the FDNC technique. All these methods are shown ultimately to require the active-R simulation of L, C, FDNR and FDNC elements. As simulated Ls and Cs are already available in the active-R form, this aper considers active-R realizations of FDNR and FDNC elements in grounded and ungrounded modes. These techniques are critically analysed in the light of available simulations. Experimental investigations are also included