Bayesian inference‐based small‐signal modeling technique for GaN HEMTs

A new modeling methodology for gallium nitride (GaN) high‐electron‐mobility transistors (HEMTs) based on Bayesian inference theory, a core method of machine learning, is presented in this article. Gaussian distribution kernel functions are utilized for the Bayesian‐based modeling technique. A new small‐signal model of a GaN HEMT device is proposed based on combining a machine learning technique with a conventional equivalent circuit model topology. This new modeling approach takes advantage of machine learning methods while retaining the physical interpretation inherent in the equivalent circuit topology. The new small‐signal model is tested and validated in this article, and excellent agreement is obtained between the extracted model and the experimental data in the form of dc I–V curves and S‐parameters. This verification is carried out on an 8 × 125 μm GaN HEMT with a 0.25 μm gate feature size, over a wide range of operating conditions. The dc I–V curves from an artificial neural network (ANN) model are also provided and compared with the proposed new model, with the latter displaying a more accurate prediction benefiting, in particular, from the absence of overfitting that may be observed in the ANN‐derived I–V curves.     

Neural network modeling of microwave FETs based on third‐order distortion characterization

A new method for characterization of HEMT distortion parameters, which extracts the coefficents of a Taylor series expansion of I_ds(V_gs, V_ds), including all cross‐terms, is developed from low‐frequency harmonic measurements. The extracted parameters will be used either in a Volterra series model around a fixed bias point for 3^rd‐order characterization of small‐signal I_ds nonlinearity, or in a large‐signal model of I_ds characteristic, where its partial derivatives are locally characterized up to the 3^rd order in the whole bias region, using a novel neural‐network representation. The two models are verified by one‐tone and two‐tone intermodulation distortion (IMD) tests on a PHEMT device. © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006.     

Modeling power and intermodulation behavior of microwave transistors with unified small‐signal/large‐signal neural network models

This article presents a detailed procedure to learn a nonlinear model and its derivatives to as many orders as desired with multilayer perceptron (MLP) neural networks. A modular neural network modeling a nonlinear function and its derivatives is introduced. The method has been used for the extraction of the large‐signal model of a power MESFET device, modeling the nonlinear relationship of drain‐source current I_ds as well as gate and drain charge Q_g and Q_d with respect to intrinsic voltages V_gs and V_ds over the whole operational bias region. The neural models have been implemented into a user‐defined nonlinear model of a commercial microwave simulator to predict output power performance as well as intermodulation distortion. The accuracy of the device model is verified by harmonic load‐pull measurements. This neural network approach has demonstrated to predict nonlinear behavior with enough accuracy even if based only on first‐order derivative information. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13: 276–284, 2003.     

Mathematical modeling insight of hetero gate dielectric-dual material gate-GAA-tunnel FET for VLSI/analog applications

This paper presents a mathematical modeling insight for the novel heterogate dielectric-dual material gate-GAA TFET (HD-DMG-GAA-TFET) and validating the results with TCAD simulation. By using the appropriate boundary conditions and continuity equations, the Poisson’s equation is solved to obtain the potential profile. The developed model is used to study the analog performance parameters such as subthreshold swing (SS), threshold voltage (V_th), transconductance (g_m), drain conductance (g_d), device efficiency (g_m/I_ds), intrinsic gain (g_m/g_d), channel resistance (R_ch) and output resistance (R_o). Further, to optimize the effect of metal work function on analog performance, three different combinations of DMG configurations has been studied. The results demonstrated that for a difference of 0.4 eV, the analog performance of the device is optimized. Low off current and high value of on current resulting into a higher I_ON/I_OFF ratio has been obtained, which is appropriate for sub-nanometre devices and low standby power applications. The analytical results obtained from the proposed model shows good agreement with the simulated results obtained with the ATLAS device simulator.

     

DEPARTMENT OF SCIENTIFIC AND INDUSTRIAL RESEARCH: HUMAN SCIENCES COMMITTEE

Maximal power output during short term constant velocity cycling and vertical jumping from a force platform has been studied in five healthy young male subjects. From the measurements on the force platform the peak (instantaneous) power output (P), net impulse (I_N ), force (F₁ ). velocity of take-off(V_T ) and height of jump(h) were calculated. The corresponding values for power (H), force (F) and velocity (V) on the bicycle were obtained from analysis of the force-velocity relationship.

The results (mean ± S.D.) showed that on the force platform F₁ P, I_N, V_T and h were 1073± 167N, 2205±310W, 154±17Ns, 2·48+0·15ms^?1 and 31 +4cm. h was positively associated with both I_N (r= +0·77) and P (r = 0·67). The mean maximal power output for cycling was 854W(39%) greater than jumping and was achieved at a 271N (25%) increase in F and a reduction in V. Nevertheless they were closely related.

Platform P(W) = 717·6 + 0·483 bicycle H(W) r= +0·74

A comparison of linear and curvilinear (hyperbolic) analysis of the F/V bicycle data showed that the latter did not reduce the variance of observations and was not, therefore, statistically justifiable (Wilkie 1950). The mean intra-subject variations of P and H were 6·6%± 1·8 and 40%+1·2. The relative values of F and V at H were both found to be approximately 50% of their respective maximal values.

It was concluded that short term power output can be measured simply and accurately in man during the performance of two activities. Rotational movement of the legs as in cycling produces higher values of peak power output then vertically lifting body weight. For the achievement of peak power output in cycling, relative force and speed of movement must both correspond to approximately half of their respective maximal values.     

Growth and characterization of 0.8-μm gate length AlGaN/GaN HEMTs on sapphire substrates

AlGaN/GaN high electron mobility transistor (HEMT) structures were grown on 2 inch sapphire substrates by MOCVD, and 0.8-μm gate length devices were fabricated and measured. It is shown by resistance mapping that the HEMT structures have an average sheet resistance of approximately 380 Θ/sq with a uniformity of more than 96%. The 1-mm gate width devices using the materials yielded a pulsed drain current of 784 mA/mm atV _gs=0.5 V andV _ds=7 V with an extrinsic transconductance of 200 mS/mm. A 20-GHz unity current gain cutoff frequency (f _T) and a 28-GHz maximum oscillation frequency (f _max) were obtained. The device with a 0.6-mm gate width yielded a total output power of 2.0 W/mm (power density of 3.33 W/mm) with 41% power added efficiency (PAE) at 4 GHz.     

Electrical and photoelectrical characterizations of isotype GaAs15P85/GaP heterojunctions prepared by liquid phase epitaxy

The present work deals with the electrical and optoelectronic characterizations of the isotype GaAs₁₅P₈₅/GaP devices prepared by liquid phase epitaxy. The electrical properties of the fabricated junction were studied by analyzing its current–voltage (I–V) characteristics, capacitance–voltage (C–V) characteristics in the dark at different temperatures in the range of 300–450 K. The analysis of dark current–voltage (I–V) characteristics at different temperatures were presented in order to elucidate the conduction mechanism and to evaluate the important device parameters. The predominant charge transport mechanism in these devices was found to be thermionic emission in the depletion layer and over the barrier of GaAs₁₅P₈₅/GaP heterojunction at forward bias voltage. From the capacitance–voltage, measurements at high frequency (1 MHz) information can be obtained about the carrier concentration, the diffusion potential, the barrier height of GaAs₁₅P₈₅/GaP heterojunction. The current–voltage characteristics of the GaAs₁₅P₈₅/GaP heterojunction under different illumination intensities were studied. The power low dependence of the reverse current voltage is characterized by space charge limited conduction, SCLC dominated by exponential trap distribution at the higher reverse voltage region.     

Modeling and simulation of a grid connected PV system based on the evaluation of main PV module parameters

In this work we present a new method for the modeling and simulation study of a photovoltaic grid connected system and its experimental validation. This method has been applied in the simulation of a grid connected PV system with a rated power of 3.2 Kw_p, composed by a photovoltaic generator and a single phase grid connected inverter. First, a PV module, forming part of the whole PV array is modeled by a single diode lumped circuit and main parameters of the PV module are evaluated. Results obtained for the PV module characteristics have been validated experimentally by carrying out outdoor I-V characteristic measurements. To take into account the power conversion efficiency, the measured AC output power against DC input power is fitted to a second order efficiency model to derive its specific parameters.The simulation results have been performed through Matlab/Simulink environment. Results has shown good agreement with experimental data, whether for the I-V characteristics or for the whole operating system. The significant error indicators are reported in order to show the effectiveness of the simulation model to predict energy generation for such PV system.     

Look-up table based I-V model for GaN HEMT devices for Microwave Applications

In this work, a newly found innovative interposable lookup table based nonlinear empirical DC I-V model for GaN HEMT device has been formulated. Angelov and Yang's models have been taken as reference models to study the effects of bias (V_gs, V_ds) dependent traps (gate lag and drain lag), self-healing, virtual gate formation, etc. on I-V characteristics functions and their inclusion into I-V equation functions of the proposed model. A new polynomial ratio function of V_ds with its coefficients varying with V_gs has been formulated as a first function of the I-V model equation, to describe the transfer characteristics of the GaN HEMT. The obtained coefficients of the polynomial ratio function have been calculated by the curve fitting tool, are used to form a look-up table so that the I-V model is fast and accurate. Model verification has been done using 8 × 75 µm gate periphery and 0.25 µm gate length GaN HEMT of UMS foundry. The measured and modeled results of I-V characteristics as well as transfer characteristics are compared and found to be matched accurately with each other. Because of this, this model is more accurate and proficient in the representation of GaN HEMT I-V characteristics when compared to the Angelov DC I-V model. The proposed methodology can be used to model all GaN HEMT devices.Using the proposed nonlinear I-V equation, an empirical model has been generated in AWR MWO using an interpolable lookup table of coefficients varying with V_gs for the GaN HEMT of UMS, CREE and WIN foundry, which can be used for Computer-Aided Design (CAD) of RF circuits, etc.     

A simplification method for capacitance models in AlGaN/GaN high electron mobility transistors under large drain voltage using channel analysis

This article analyzes the bias dependence of gate‐drain capacitance (C_gd) and gate‐source capacitance (C_gs) in the AlGaN/GaN high electron mobility transistors under a high drain‐to‐source voltage (V_ds) from the perspective of channel shape variation, and further simplifies C_gd and C_gs to be gate‐to‐source voltage (V_gs) dependent only at high V_ds. This method can significantly reduce the number of parameters to be fitted in C_gd and C_gs and therefore lower the difficulty of model development. The Angelov capacitance models are chosen for verifying the effectiveness of simplification. Good agreement between simulated and measured small‐signal S‐parameters, large‐signal power sweep, and power contours comprehensively proves the accuracy of this simplification method.     

Are elderly construction workers sufficiently fit for heavy manual labour?

This study analysed the work ability of elderly construction workers. Forty male construction workers, 20 young (age < 33 yrs) and 20 senior (age>44 yrs) workers, were tested regarding aerobic power (VO_2max) and muscle strength. The aerobic demand of a number of tasks in construction work was measured and compared with the workers' aerobic power. VO_2max was higher for the young, and they performed better on most muscle strength tests. The measurements showed that about half of the senior workers had to use more than 30% of their maximum oxygen uptake on some tasks. In conclusion, because elderly construction workers decline in physical fitness, they are more exposed to overload when performing heavy manual work than are their younger peers. Increasing their individual fitness or adjusting their workload may be important for staying in the workforce for such workers.     

Measures on MV-algebras

 We study sequentially continuous measures on semisimple M V-algebras. Let A be a semisimple M V-algebra and let I be the interval [0,1] carrying the usual Łukasiewicz M V-algebra structure and the natural sequential convergence. Each separating set H of M V-algebra homomorphisms of A into I induces on A an initial sequential convergence. Semisimple M V-algebras carrying an initial sequential convergence induced by a separating set of M V-algebra homomorphisms into I are called I-sequential and, together with sequentially continuous M V-algebra homomorphisms, they form a category SM(I). We describe its epireflective subcategory ASM(I) consisting of absolutely sequentially closed objects and we prove that the epireflection sends A into its distinguished σ-completion σ _H (A). The epireflection is the maximal object in SM(I) which contains A as a dense subobject and over which all sequentially continuous measures can be continuously extended. We discuss some properties of σ _H (A) depending on the choice of H. We show that the coproducts in the category of D-posets [9] of suitable families of I-sequential M V-algebras yield a natural model of probability spaces having a quantum nature. The motivation comes from probability: H plays the role of elementary events, the embedding of A into σ _H (A) generalizes the embedding of a field of events A into the generated σ-field σ(A), and it can be viewed as a fuzzyfication of the corresponding results for Boolean algebras in [8, 11, 14]. Sequentially continuous homomorphisms are dual to generalized measurable maps between the underlying sets of suitable bold algebras [13] and, unlike in the Loomis–Sikorski Theorem, objects in ASM(I) correspond to the generated tribes (no quotient is needed, no information about the elementary events is lost). Finally, D-poset coproducts lift fuzzy events, random functions and probability measures to events, random functions and probability measures of a quantum nature. Supported by VEGA Grant 2/7193/01     

On efficient implementation of an approximation algorithm for the Steiner tree problem

Summary This paper studies the design and implementation of an approximation algorithm for the Steiner tree problem. Given any undirected distance graph G and a set of Steiner points S, the algorithm produces a Steiner tree with total weight on its edges no more than 2(1–1/L) times the total weight on the optimal Steiner tree, where L is the number of leaves in the optimal Steiner tree. Our implementation of the algorithm, in the worst case, makes it run in 0(¦E _g¦+¦V _g–S¦log¦V _g–S¦+¦S¦log ¦S¦) time for general graph G and in 0(¦S¦ log¦S¦+M log (M,¦V _g–S¦)) time for sparse graph G, where E _g is the set of edges in G, V_g is the set of vertices in G, M = min {¦E _g, (¦V _g–S¦–1)²/2} and (x,y) = min {i¦log⁽ⁱ⁾ y x/y}.The implementation is not likely to be improved significantly without the improvement of the shortest paths algorithm and the minimum spanning tree algorithm as the algorithm essentially composes of the computation of the multiple sources shortest paths of a graph with ¦V _g¦ vertices and ¦E _g¦ edges and the minimum spanning tree of a graph with ¦V _g–S¦ vertices and M edges.     

Characterisation of silicon carbide JFETs with respect to microsystems for high temperature applications

 In this work first commercially available SiC-transistor prototypes were tested with regard to their applicability in high temperature electronic circuits for sensor signal conditioning. The influence of the temperature on the device behaviour (drain-saturation current, gate leakage current, I–V-characteristics, long-term effects) was investigated. The devices showed reliable operation up to 450 °C. The maximum forward transconductance g _m and the short circuit drain source current I _DSS decreased to approximately 30% of the room temperature values. Also, a slight increase of the pinch-off voltage V _p was observed. The gate leakage current I _GSS rose with temperature, staying below 1 μA at 450 °C. A pre-ageing study was carried out to verify changes in the device characteristics with time. The devices were exposed to a 270 °C environment and it was observed that the DC parameters tend to stabilise after about 100 h. From the I–V-characteristics the SPICE parameters were extracted for a series of temperatures, allowing the design and optimisation of amplifier gain stages. The SPICE device simulation results are in good agreement with the measured characteristics. Received: 28 November 1996/Accepted: 2 December 1996     

A parameter extraction method of the PIN diode for physics‐based circuit simulation over a wide frequency range

The accurate physical parameters of the semiconductor devices are critical to the physics‐based circuit simulation, which solves the carrier transport equations to model the semiconductor devices. However, the conventional method extracts physical parameters from low‐frequency measurements such as the DC I‐V curve, which cannot work at high frequencies. To overcome this problem, we propose a physical parameter extraction method of the PIN diode working well from DC to microwave frequencies. Specifically, because the transit‐time effects are dependent on the working frequencies and input power levels, the operation modes of the PIN diode can be divided into three cases from DC to microwave frequencies; therefore, the proposed method extracts the parameters from three measured curves, including the DC I‐V curve, a small‐signal, and a large‐signal voltage waveform both at a microwave frequency. Experiments of a PIN diode SMP1330 circuit show that the error of the conventional method is about 45% at frequencies above 300 MHz, but the maximum error of the proposed method is only 9.5% from DC to 2 GHz. Moreover, the conventional method is unable to characterize the conductance modulation phenomenon, which leads to unexpected signal reflections in PIN limiter circuits and the missing of information in radio transceivers.     

Relation between power and endurance for treadmill running of short duration

Abstract

An exercise test was devised to investigate the relationship between power and endurance for treadmill running. The subjects were 19 males aged 21-25 yr (11 distance runners and 4 sprinters of provincial grade, and 4 non-competitive runners). Each subject ran to exhaustion on a treadmill at 15kmhr^?1at five different inclinations (31%-9%), giving maximum performance times in the range 10s to 3 min. An iterative least-squares procedure was used to fit the following exponential model to each subject's data: I₁= I_∞+ (I₀?I_∞)exp(?t/τ) where I₁, I₀and 1_∞are inclinations at time t = t, t = 0 and t → ∞, and τ is a time constant. The fit was excellent (r ²= 0.96? 1.00). I₀and 1_∞are interpreted as measures of maximum anaerobic (instantaneous) and maximum aerobic (continuous) power respectively. Inclinations corresponding to performance times of 10-180s (I₁₀?I₁₈₀) were calculated from these parameters. Test-retest reliability was highest for I₀-I₃₀(intraclass r= 0.97?0.94), lower for I₆₀-I_∞(r= 0.89?0.84), and lowest for τ (r= 0.78). Good correlations were observed between I₀-I₃₀and peak power in a 30s all-out test on a cycle ergometer (r= 0.73?0.81), and between I₁₈₀, I_∞and maximum oxygen consumption (r= 0.87, 0.81). The test may be useful for ranking or monitoring running performance for events of up to 1 min duration.     

Local uncontrollability for affine control systems with jumps†

This paper investigates affine control systems with jumps for which the ideal I_f(g₁, …, g_m) generated by the drift vector field f in the Lie algebra L(f, g₁, …, g_m) can be imbedded as a kernel of a linear first-order partial differential equation. It will lead us to uncontrollable affine control systems with jumps for which the corresponding reachable sets are included in explicitly described differentiable manifolds.     

High-K Spacer Dual-Metal Gate Stack Underlap Junctionless Gate All Around (HK-DMGS-JGAA) MOSFET for high frequency applications

High-K Spacer based Dual-Metal Gate Stack Junctionless Gate All Around (HK-DMGS-JGAA) MOSFET has been proposed and analyzed in this paper for high frequency analog ad RF applications. It has been done by comparing it with the existing Junctionless devices in particular, Junctionless-Gate All Around, Junctionless Gate All Around Underlap and Dual-Metal Junctionless Gate All Around Underlap MOSFET. It is so found that HK-DMGS-JGAA MOSFET shows higher I_ds, g_m, g_d and f_T over existing Junctionless device architectures making it a suitable device for high frequency analog applications. It has also been established that HK-DMGS-JGAA MOSFET has better I_ON/I_OFF ratio, Subthreshold Slope (SS) most close to the ideal values, lower Channel Resistance, R_ch, higher Early Voltage (V_EA), higher Frequency Transconductance Product, superior Transconductance Generation Factor, Maximum gains in terms of current gain, Maximum Transducer Power Gain and Unilateral Power Gain, superior noise performance in terms of the Noise Conductivity and Noise Figure. All these improved figure of merits warrant HK-DMGS-JGAA MOSFET as the best suited device design for various analog and digital applications along with high frequency applications.

     

Bioelectricity: a new approach to provide the electrical power from vegetative and fruits at off-grid region

In this research, we studied the performance of different vegetative and fruits electrochemical cells namely PKL, Aloe Vera, Tomato and Lemon juice electrochemical cells with load condition for 2:1 Zn/Cu based electrodes. It was also studied the variation of Load Voltage (V_L), Load Current (I_L), and Load Power (P_L), with the variation of time for PKL, Aloe Vera, Tomato and Lemon juice electrochemical Cells. Among those cells the PKL electrochemical Cell was more efficient than the other three types of Cells regarding the load Current (I_L), Load Voltage (V_L), and Load Power (P_L). However, we investigated the performance of different types of Cells without load condition for 1:1 Zn/Cu based electrodes. Moreover, the variation of open circuit voltage (V_oc), short circuit current (I_sc) and maximum power (P_max) with the variation of time for those cells were explored. The discharge characteristic of the PKL electrochemical cell was more effective than the other three electrochemical Cells as the Open circuit voltage (V_oc), Short circuit current (I_sc) and Maximum Power (P_max) are more stable and steady in comparison with others. Heat treatment temperature was a new approach by which we can enhance the performance of these electrochemical cells. Most of the results have been tabulated and graphically discussed.

     

On a reduction of the interval coloring problem to a series of bandwidth coloring problems

Given a graph G=(V,E) with strictly positive integer weights ω _i on the vertices i∈V, an interval coloring of G is a function I that assigns an interval I(i) of ω _i consecutive integers (called colors) to each vertex i∈V so that I(i)∩I(j)=∅ for all edges {i,j}∈E. The interval coloring problem is to determine an interval coloring that uses as few colors as possible. Assuming that a strictly positive integer weight δ _ij is associated with each edge {i,j}∈E, a bandwidth coloring of G is a function c that assigns an integer (called a color) to each vertex i∈V so that |c(i)−c(j)|≥δ _ij for all edges {i,j}∈E. The bandwidth coloring problem is to determine a bandwidth coloring with minimum difference between the largest and the smallest colors used. We prove that an optimal solution of the interval coloring problem can be obtained by solving a series of bandwidth coloring problems. Computational experiments demonstrate that such a reduction can help to solve larger instances or to obtain better upper bounds on the optimal solution value of the interval coloring problem.