Showing papers on "NQS published in 2010"

Accurate small signal modeling and extraction of silicon MOSFET for RF IC application

Abstract: A simple scalable non-quasi-static (NQS) small signal equivalent circuit (SSEC) model of Si MOSFET and corresponding direct extraction methodology are developed in this paper. Compared with the conventional SSEC, a parallel gate drain branch is supplemented to describe parasitic gate-drain coupling under high frequency up to 40 GHz together with the impact of substrate loss, terminal resistances and inductances. The new extraction methodology is developed that all extrinsic parasitic components are extracted from zero bias Z-parameters and intrinsic components are extracted from ON state Y-parameters. The proposed model and extraction methodology are verified to achieve good agreement between simulated and measured S-parameters from 0.1 to 40 GHz for devices fabricated with 0.13 μm CMOS technology. The extracted bias dependent model could be further used to construct a nonlinear model in large signal applications.

Spectrophotometric determination of memantine in bulk and in pharmaceutical formulations

Abstract: Two simple, sensitive and reproducible colorimetric methods have been developed for the estimation of Memantine (MEM) in bulk and in pharmaceutical formulations. Method A is based on the reduction of Folin‐Ciocalteau (F.C) reagent by the drug and the reduced species posses a characteristic intense blue color (λmax 760 nm). Method B is based on the condensation of Memantine with 1,2‐Napthaquinone‐4‐sulphonate(NQS) in an alkaline medium to form an orange colored product (λmax 460 nm). Beers law is obeyed in the concentration range of 4‐12 µg/ml (Method A) and 7.5‐17.5 µg/ml (Method B) with good correlation coefficients of 0.997 and 0.999 respectively for Methods A and B respectively. These methods have been statistically evaluated and found to be precise and accurate.

Spectrophotometric Method for Determination of Chloramphenicol in Pharmaceutical Preparations Using 1,2-Naphthoquinone-4-Sulphonate as a Chromogenic Reagent

Abstract: A simple, sensitive and rapid spectrophotometric method for the determination of chloramphenicol in pure as well as in dosage form is described. The method is based on the condensation reaction of reduced chloramphenicol with sodium 1,2-naphthaquinone-4-sulfonate (NQS) in an alkaline medium to form an orange-red colored Schiff's base of maximum absorption peak (λmax) at 480 nm. Under the optimized reaction conditions, Beer’s law correlating the absorbance with chloramphenicol concentration was obeyed in the range of 0.814 μg ml. The molar absorptivity was 1.02×10 L molcm. The limits of detection and quantitation were 0.124 and 0.473 μg ml, respectively. The accuracy and precision of the method were satisfactory; the average recovery was 99.54 % and values of relative standard deviations better than 3.5 %. The stoichiometry of the reaction was studied, and the reaction mechanism was postulated. The proposed method was successfully applied to the determination of chloramphenicol in its pharmaceutical capsule, syrup and ointment with good accuracy and precisions. The results obtained by the proposed method are compared with those obtained by the official method.

Modeling the input non-quasi-static effect in small signal equivalent circuit based on charge partitioning for bipolar transistors and its impact on RF noise modeling

Abstract: This paper models the input non-quasi-static (NQS) effect of bipolar transistors using charge partitioning. The input NQS effect associated with the base minority carrier transport is modeled with a RC network, while the input NQS effect associated with the base-collector space charge region (CB SCR) carrier transport is modeled with a RLC network. With the proposed input NQS equivalent circuit model, Y-parameters and RF noise parameters using the van Vliet model are successfully modeled for frequencies up to fT. The transport noise model is extended to represent the van Vliet model by using two noise related time constants, which eliminates the need of Y-parameter in the description of the noise source. The input NQS effect for such model is verified to be important only for frequencies above fT/3. Analytical Y-parameter and noise solutions of a 1-D bipolar transistor at low injection level are used for validation.

Non-Quasi-Static Modeling of Silicon Nanowire Metal–Oxide–Semiconductor Field-Effect Transistor and Its Model Verification up to 1 THz

Abstract: In this work, the radio-frequency (RF) performances of a silicon nanowire (SNW) metal–oxide–semiconductor field-effect transistor (MOSFET) were modeled by being grafted into the non-quasi-static (NQS) small-signal equivalent circuit for the first time. The parameters were analytically extracted from three-dimensional (3D) device simulations. The cutoff frequencies of an SNW MOSFET with a 30 nm channel length and a 5 nm radius were 504 and 545 GHz in the linear and saturation regions, respectively. The reliability of modeling results was verified by the simulations including realistic models. It was confirmed that the SNW MOSFET would be the promising candidate as a core component for RF systems aiming 1 THz operation.

Evaluation of lookup-table non-quasi-static nonlinear models at microwave and mm-wave frequencies

Abstract: A comparison between two different, yet analytical approaches for lookup-table large-signal model construction is presented in this study. Both approaches use the same linear (small-signal) model as the starting point to construct the large-signal model. The first nonlinear model employs the charge- and current-sources to represent the nonlinearity of the active part of the device where the extended charge- and current-sources are added to compensate for the non-quasi-static (NQS) effects at mm-wave frequencies. The second nonlinear model employs the small-signal model schematic and adapts it to be used directly for large-signal simulations. The study was performed on SOI multi-Fin MOSFET transistors. Both modeling approaches can reproduce the device behavior at microwave and mm-wave frequencies and under highly nonlinear conditions with good accuracy.

Estimation of the rate constants of second order reactions using mean centering of ratio spectra

Abstract: A new application of the mean centering of ratio spectra method is proposed for estimation of the rate constants of second order reactions, using kinetic-spectrophotometric data. The method is based on the mean centering of the ratio spectra to obtain a kinetic profile of the product. Using computational fitting, the rate constant can be obtained without any ambiguity. An interesting feature of second-order reactions is that the number of steps in the reaction is less than the number of absorbing species, resulting in a rank-deficient response matrix. Through using row mean centering of ratio spectra, the pure response of the product of the reaction could be obtained, and thus an accurate estimation of rate constant would be possible. The applicability of the method was evaluated by using several model data. The reaction of 1,2-naphthoquinone-4-sulfonate sodium (NQS) and 3-nitroaniline (TNA) in ethanol as a real system was also studied applying the proposed method.

Modeling of NQS effects in carbon nanotube transistors

Abstract: Time-dependent quantum simulations are used to rigorously identify non-quasi-static (NQS) effects in Carbon nanotube transistors. A complete physics-based small signal equivalent circuit is derived which captures important NQS effects for circuit design and simulation. This model agrees well with high-frequency measurements. Additionally, the impact of Schottky barriers on the kinetic inductance and the charging resistances is discussed and the role of the contact resistances is investigated.

New Spectrophotometric Methods for Quantitative Determination of 7-ADCA in Pharmaceutical Formulations

Abstract: Three simple, sensitive and accurate methods are described for the determination of 7-Amino deacetoxy cephalosporanic acid (7-ADCA) in bulk drug and in formulations. Methods Ma to Mc are based on ion association complex between 7-ADCA and NQS (Ma), vanillin (Mb) and Ninhydrin (Mc) solutions. The chromogen being extractable with chloroform could be measured quantitatively at 480 (Ma) and 560 nm (Mb&c). All variables were studied to optimize the reaction conditions. Regression analysis of Beer's Law plot showed good correlation in the concentration range 4-24 for Ma, 0.4-2.4 for Mb and 0.5-3.0 g/mL for Mc. The calculated molar absorptivity values are 5.945 x 10 3 , 1.722 x 10 5 , and 6.701 x 10 4 L/mol/cm for Ma to Mc, respectively. The methods were successfully applied to the determination of 7-ADCA in formulations and the results tallied well with the label claim. The results were statistically compared with those of a literature method by applying the Student's t-test and F-test. No interference was observed from the concomitant substances normally added to preparations. The accuracy and validity of the methods were further ascertained by performing recovery experiments via standard-addition method.

Visible spectrophotometric methods for determination of Sitagliptine in tablets

Abstract: Two simple and sensitive visible spectrophotometric methods have been developed for the estimation of Sitagliptine in pure and pharmaceutical dosage forms. These methods are based on the nucleophillic substitution reaction between NQS and Sitagliptine resulting in the formation of colored chromogen ( λ max 450 nm) and the reaction between Picric acid (PA) and Sitagliptine resulting in the formation of molecular salt (λmax 420 nm). The absorbance is measured against the corresponding reagent blanks. These methods have been statistically evaluated and found to be precise and accurate.