Showing papers on "Equivalent circuit published in 2004"

Modeling of an equivalent circuit for dye-sensitized solar cells

Abstract: Internal resistance in a dye-sensitized solar cell (DSC) was investigated using electrochemical impedance spectroscopy measurements. Four resistance elements were observed in the impedance spectra, and their dependencies on the applied bias voltage were characterized. It is found that the resistance element related to charge transport at the TiO2/dye/electrolyte interface displays behavior like that of a diode, and the series resistance elements largely correspond to the sum of the other resistance elements. An equivalent circuit for DSCs is proposed based on these results.

1.156-GHz self-aligned vibrating micromechanical disk resonator

Abstract: A new fabrication methodology that allows self-alignment of a micromechanical structure to its anchor(s) has been used to achieve vibrating radial-contour mode polysilicon micromechanical disk resonators with resonance frequencies up to 1.156 GHz and measured Q's at this frequency >2,650 in both vacuum and air. In addition, a 734.6-MHz version has been demonstrated with Q's of 7,890 and 5,160 in vacuum and air, respectively. For these resonators, self-alignment of the stem to exactly the center of the disk it supports allows balancing of the resonator far superior to that achieved by previous versions (in which separate masks were used to define the disk and stem), allowing the present devices to retain high Q while achieving frequencies in the gigahertz range for the first time. In addition to providing details on the fabrication process, testing techniques, and experimental results, this paper formulates an equivalent electrical circuit model that accurately predicts the performance of these disk resonators.

Leakage current reduction in CMOS VLSI circuits by input vector control

Abstract: The first part of this paper describes two runtime mechanisms for reducing the leakage current of a CMOS circuit. In both cases, it is assumed that the system or environment produces a "sleep" signal that can be used to indicate that the circuit is in a standby mode. In the first method, the "sleep" signal is used to shift in a new set of external inputs and pre-selected internal signals into the circuit with the goal of setting the logic values of all of the internal signals so as to minimize the total leakage current in the circuit. This minimization is possible because the leakage current of a CMOS gate is strongly dependent on the input combination applied to its inputs. In the second method, nMOS and pMOS transistors are added to some of the gates in the circuit to increase the controllability of the internal signals of the circuit and decrease the leakage current of the gates using the "stack effect". This is, however, done carefully so that the minimum leakage is achieved subject to a delay constraint for all input-output paths in the circuit. In both cases, Boolean satisfiability is used to formulate the problems, which are subsequently solved by employing a highly efficient SAT solver. Experimental results on the combinational circuits in the MCNC91 benchmark suite demonstrate that it is possible to reduce the leakage current in combinational circuits by an average of 25% with only a 5% delay penalty. The second part of this paper presents a design technique for applying the minimum leakage input to a sequential circuit. The proposed method uses the built-in scan-chains in a VLSI circuit to drive it with the minimum leakage vector when it enters the sleep mode. The use of these scan registers eliminates the area and delay overhead of the additional circuitry that would otherwise be needed to apply the minimum leakage vector to the circuit. Experimental results on the sequential circuits in the MCNC91 benchmark suit show that, by using the proposed method, it is possible to reduce the leakage by an average of 25% with practically no delay penalty.

High-efficiency adaptive DC/AC converter

Abstract: A CCFL power converter circuit is provided using a high-efficiency zero-voltage-switching technique that eliminates switching losses associated with the power MOSFETs. An optimal sweeping-frequency technique is used in the CCFL ignition by accounting for the parasitic capacitance in the resonant tank circuit. Additionally, the circuit is self-learning and is adapted to determine the optimum operating frequency for the circuit with a given load. An over-voltage protection circuit can also be provided to ensure that the circuit components are protected in the case of open-lamp condition.

General equivalent circuit for intermediate band devices: Potentials, currents and electroluminescence

Abstract: A general model to describe the operation of intermediate band solar cells (IBSCs), incorporating a significant number of physical effects such as radiative coupling between bands, and impact ionization and Auger recombination mechanisms, is presented in equivalent circuit form. The model is applied to IBSC prototypes fabricated from InAs quantum dots structures to determine the value of the circuit elements involved. The analysis shows evidence of splitting between the conduction and intermediate band quasi-Fermi levels, one of the fundamental working hypotheses on which operation of the IBSC depends. The model is also used to discuss the limitations and potential of this type of cell.

Calculation of circulating bearing currents in machines of inverter-based drive systems

Abstract: The high-frequency circulating bearing current that may occur in machines of inverter-based drive systems can be described by an eddy-current model. The parameters of an equivalent circuit are derived from the model. The ratio between bearing current and common-mode current amplitudes for different machines is calculated. The theoretical maximum ratio is about 0.35. Copper loops applied for bearing current measurement may decrease the circulating bearing currents up to almost 40%

A soft error rate analysis (SERA) methodology

Abstract: We present a soft error rate analysis (SERA) methodology for combinational and memory circuits. SERA is based on a modeling and analysis-based approach that employs a judicious mix of probability theory, circuit simulation, graph theory and fault simulation. SERA achieves five orders of magnitude speed-up over Monte Carlo based simulation approaches with less than 5% error. Dependence of soft error rate (SER) of combinational circuits on supply voltage, clock period, latching window, circuit topology, and input vector values are explicitly captured and studied for a typical 0.18 /spl mu/m CMOS process. Results show that the SER of logic is a much stronger function of timing parameters than the supply voltage. Also, an "SER peaking" phenomenon in multipliers is observed where the center bits have an SER that is in order of magnitude greater than that of LSBs and MSBs.

Development of an equivalent circuit model of a fuel cell to evaluate the effects of inverter ripple current

Abstract: In this paper an impedance model of the proton exchange membrane fuel cell stack (PEMFCS) is proposed The proposed study employs an equivalent circuit of the PEMFCS derived by frequency response analysis (FRA) technique An equivalent circuit for the fuel cell stack is developed to evaluate the effects of ripple currents generated by the power-conditioning unit The calculated results are then verified by means of experiments on three commercially available fuel cells: Avista Labs SR-12 (500 W), Ballard Nexa (12 kW) and BCS-Tech (300 W) PEMFC system The relationship between ripple current and fuel cell performance: such as power loss and fuel consumption is investigated Experimental results show that the ripple current can contribute up to 10% reduction in the available output power

Concept and application of LPM: A novel 3-D local position measurement system

Abstract: Precise measurement of the local position of moveable targets in three dimensions is still considered to be a challenge. With the presented local position measurement technology, a novel system, consisting of small and lightweight measurement transponders and a number of fixed base stations, is introduced. The system is operating in the 5.8-GHz industrial-scientific-medical band and can handle up to 1000 measurements per second with accuracies down to a few centimeters. Mathematical evaluation is based on a mechanical equivalent circuit. Measurement results obtained with prototype boards demonstrate the feasibility of the proposed technology in a practical application at a race track.

RF circuit implications of moderate inversion enhanced linear region in MOSFETs

Abstract: The implications for radio frequency circuit design of the nonlinear behavior of a MOSFET transistor over all regions of operation, including moderate inversion region, are investigated. Third-order intermodulation distortion in a MOSFET amplifier is analyzed by means of Volterra Series representation. Analysis and measurements reveal a significant peaking, or "sweet-spot" of the third-order intercept point in the moderate inversion region. As a result, a significant increase in linearity with low power consumption is possible. Analysis and measurements shows the dependance of distortion on the frequency, and transistor parameters, as well as the effects of the load impedance and feedback.

Concept and application of LPM - a novel 3-D local position measurement system

Abstract: Precise measurement of the local position of moveable targets in three dimensions is still considered to be a challenge. With the presented local position measurement technology, a novel system, consisting of small and lightweight measurement transponders and a number of fixed base stations, is introduced. The system is operating in the 5.8-GHz industrial-scientific-medical band and can handle up to 1000 measurements per second with accuracies down to a few centimeters. Mathematical evaluation is based on a mechanical equivalent circuit. Measurement results obtained with prototype boards demonstrate the feasibility of the proposed technology in a practical application at a race track.

A delay-dependent stability criterion of neutral systems and its application to a partial element equivalent circuit model

Abstract: The real circuit model, such as a partial element equivalent circuit (PEEC), can be represented as a delay differential equation (DDE) of neutral type. The study of asymptotic stability of this kind of systems is of much importance due to the fragility of DDE solvers. Based on a descriptor system approach, new delay-dependent stability results are derived by introducing some free weighting matrices. As an application of the results, the delay-dependent stability problem of a PEEC model is investigated. The comparison of the results with the existing ones is finally given by using the PEEC model and another numerical example.

Nonlinear device model of microwave power GaN HEMTs for high power-amplifier design

Abstract: This paper presents a nonlinear equivalent circuit model of microwave power GaN high electron-mobility transistors (HEMTs), amenable for integration into commercial harmonic balance or transient simulators. All the steps taken to extract its parameter set are explained, from the extrinsic linear elements up to the intrinsic nonlinear ones. The predictive model capabilities are illustrated with measured and simulated output power and intermodulation-distortion data of a GaN HEMT. The model is then fully validated in a real application environment by comparing experimental and simulated results of output power, power-added efficiency, and nonlinear distortion obtained from a power amplifier.

VHF single-crystal silicon elliptic bulk-mode capacitive disk resonators-part I: design and modeling

Abstract: This work, the first of two parts, presents the design and modeling of VHF single-crystal silicon (SCS) capacitive disk resonators operating in their elliptical bulk resonant mode. The disk resonators are modeled as circular thin-plates with free edge. A comprehensive derivation of the mode shapes and resonant frequencies of the in-plane vibrations of the disk structures is described using the two-dimensional (2-D) elastic theory. An equivalent mechanical model is extracted from the elliptic bulk-mode shape to predict the dynamic behavior of the disk resonators. Based on the mechanical model, the electromechanical coupling and equivalent electrical circuit parameters of the disk resonators are derived. Several considerations regarding the operation, performance, and temperature coefficient of frequency of these devices are further discussed. This model is verified in part II of this paper, which describes the implementation and characterization of the SCS capacitive disk resonators.

Common mode noise modeling and analysis of dual boost PFC circuit

Abstract: To achieve high efficiency PFC front stage in switching mode power supply (SMPS), dual boost PFC (DBPFC) topology shows superior characteristics compared with traditional boost PFC, but it by nature brings higher EMI noise, especially common mode (CM) noise This paper deals with the modeling and analysis of DBPFC CM noise based on and compared with boost PFC, noise propagation equivalent circuits of both topologies are deduced, and theoretical analysis illustrates the difference Experiments are performed to validate the EMI model and analysis

Neural-network approaches to electromagnetic-based modeling of passive components and their applications to high-frequency and high-speed nonlinear circuit optimization

Abstract: In this paper, artificial neural-network approaches to electromagnetic (EM)-based modeling in both frequency and time domains and their applications to nonlinear circuit optimization are presented. Through accurate and fast EM-based neural models of passive components, we enable consideration of EM effects in high-frequency and high-speed computer-aided design, including component's geometrical/physical parameters as optimization variables. Formulations for standard frequency-domain neural modeling approach, and recent time-domain neural modeling approach based on state-space concept, are described. A new EM-based time-domain neural modeling approach combining existing knowledge in the form of equivalent circuits (ECs), with state-space equations (SSEs) and neural networks (NNs), called the EC-SSE-NN, is proposed. The EC-SSE-NN models allow EM behaviors of passive components in the circuit to interact with nonlinear behaviors of active devices, and facilitate nonlinear circuit optimization in the time domain. An automatic mechanism for EM data generation, which can lead to efficient training of neural models for EM components, is presented. Demonstration examples including EM-based frequency-domain optimization of a three-stage amplifier, time-domain circuit optimization in a multilayer printed circuit board, including geometrical/physical-oriented neural models of power-plane effects, and EM-based optimization of a high-speed interconnect circuit with embedded passive terminations and nonlinear buffers in the time domain are presented.

A comprehensive compact-modeling methodology for spiral inductors in silicon-based RFICs

Abstract: A new comprehensive wide-band compact-modeling methodology for on-chip spiral inductors is presented. The new modeling methodology creates an equivalent-circuit model consisting of frequency-independent circuit elements. A fast automated extraction procedure is developed for determining the circuit element values from two-port S-parameter measurement data. The methodology is extremely flexible in allowing for accurate modeling of general classes of spiral inductors on high- or low-resistivity substrate and for large spirals exhibiting distributed trends. The new modeling methodology is applied to general classes of spirals with various sizes and substrate parameters. The extracted models show excellent agreement with the measured data sets over the frequency range of 0.1-10 GHz.

Measurement of noise source impedance of SMPS using a two probes approach

Abstract: A novel approach to determine common-mode (CM) and differential-mode (DM) noise source impedances of a low-power switched mode power supply (SMPS) has been developed using a two current probes approach. The proposed approach allows measurement of noise source impedance of a SMPS without interrupting its normal operation. With proper setup calibration, the proposed approach can derive an equivalent circuit model, consisting of resistive and reactive components, to represent the noise source impedance with reasonable accuracy. Once the equivalent circuit model of the noise source impedance is obtained through the measurement, the most effective filter configuration and suitable component values for the built-in power line electromagnetic interference (EMI) filter of the SMPS could be designed with ease.

Limits of offset cancellation by the principle of spinning current Hall probe

Abstract: An equivalent circuit model for Hall plates with 90/spl deg/ symmetry - as are used in todays smart sensors using the principle of spinning current Hall probe - is derived. It becomes apparent that the commonly used H-bridge 4-resistor type equivalent circuit has to be completed by 2 resistors between the contacts of each diagonal. By use of this equivalent circuit, it is shown that the principle of the spinning current Hall probe works perfectly only for electrically linear probes supplied by a current source. In this case, two orthogonal current directions are enough to cancel the offset. Yet, in the case of voltage biased Hall probes, the offset is not completely eliminated. In practice, integrated Hall probes exhibit electrical nonlinearity due to the depletion layer to the substrate. Monte Carlo simulations show that this nonlinearity limits the performance of offset reduction to roughly 100 nT.

Computer-aided optimization of nonlinear microwave circuits with the aid of electromagnetic simulation

Abstract: This paper discusses some modern trends in nonlinear (NL) microwave circuit optimization based on electromagnetic (EM) simulation. In order to keep the CPU time required for a typical design within acceptable limits, the number of expensive EM analyses must be kept under tight control. This may be obtained by resorting to a systematic implementation of some modern algorithmic concepts such as space mapping, domain partitioning, and neural-network modeling of the passive subnetwork and/or of its most critical parts. Although these techniques are well established for linear microwave circuit design coupled with EM analysis, their extension to the NL case is not trivial, and deserves a specialized treatment. Several examples are presented in order to give a feeling of the state-of-the-art of NL/EM optimization.

Rotor temperature estimation of squirrel-cage induction motors by means of a combined scheme of parameter estimation and a thermal equivalent model

Abstract: This paper deals with a rotor temperature estimation scheme for fan-cooled mains-fed squirrel-cage induction motors. The proposed technique combines a rotor resistance estimation method with a thermal equivalent circuit. Usually, rotor resistance estimation works quite well under rated load conditions. By contrast, if the motor is slightly loaded, rotor resistance estimation becomes inaccurate due to the small slip. Therefore, rotor temperature estimation under low-load conditions may be estimated by a thermal equivalent model. In order to determine the rotor resistance and, thus, rotor temperature accurately, several machine parameters have to be obtained in advance. Load tests provide the leakage reactance and the iron losses of the induct machine. The stator resistance has to be measured separately. The parameters of the thermal equivalent model are a thermal resistance and a thermal capacitance. These parameters are derived from a heating test, where the reference temperature is provided from the parameter model in the time domain. This lumped thermal parameter model is based on the assumption that the total rotor temperature increase is caused by the total sum of the losses in the induction machine. Measuring results of a 1.5-kW and an 18.5-kW four-pole low-voltage motor and a 210-kW four-pole high-voltage motor are presented and compared.

Properties of a metamaterial element: Analytical solutions and numerical simulations for a singly split double ring

Abstract: An equivalent circuit, consisting of bulk and distributed elements, is derived for describing the properties of a potential metamaterial element capable of providing negative effective permeability. It is the singly split double ring (SSDR), a special case of the split ring resonator (J. B. Pendry et al., IEEE Trans. Microwave Theory Tech. 47, 2075 (1999)), obtained when the gap capacitance in the inner ring is infinitely large. The variables are the inter-ring voltage and the currents flowing in the inner and outer rings. The excitation is assumed in the form of a spatially constant temporally varying magnetic field. The functions, showing the angular variation of the variables, are found by solving a set of differential equations with boundary conditions imposed at the position of the split. It is shown from the analytical solution that the SSDR can have resonant frequencies in the full spectrum from very low to very high frequencies. It is pointed out in particular that whenever the mean diameter of th...

Numerical modeling of magnetic devices

Abstract: We present a general approach to directly couple finite-element models with arbitrary electric circuits for application to electromagnetic devices. We describe both two-dimensional (2-D) and three-dimensional (3-D) transient finite-element models, with emphasis on 3-D using a T-/spl Omega/ formulation. For 3-D transient and circuit coupling, the derivation of the induced voltage is an integral part of the coupling approach, and the induced voltage links the magnetic field and the electrical circuit together. The system of electric circuits is created automatically. Then graph theory is used to deduce the circuit by tree/cotree and loop analysis. The resulting field equations and circuit equations are coupled together and solved simultaneously at each time step in the time domain. We give three examples of applications: a brushless dc motor drive, a permanent-magnet synchronous motor drive, and a three-phase power transformer with rectifier and load circuit.

Design characteristics of the induction motor used for hybrid electric vehicle

Abstract: Design characteristics of the induction motor used for hybrid electric vehicle (HEV) are discussed. Equivalent circuits corresponding to the starting, operating performance, and harmonics are given. The selecting rules of the starting voltage and frequency are got. The relations between the iron core and copper loss versus frequency are analyzed and compared. The influence of harmonics on the induction motor is analyzed. The design principles of the induction motor used for HEV are given considering the impacts of the starting, operating performance, and harmonics.

Modeling skin and proximity effects with reduced realizable RL circuits

Abstract: On-chip conductors such as clock- and power-distribution networks require accurately modeling skin and proximity effects. Furthermore, to incorporate skin and proximity effects in the existing generic simulation tools such as SPICE, simple-frequency independent-lumped element-circuit models are needed. A rule based RL circuit model is proposed in this paper that is realizable and predicts skin and proximity effects accurately in the frequency range of interest. With this circuit model, wires are characterized by a few parallel branches of resistors and inductors while proximity effect is captured by mutual inductance between inductors in different RL circuits.

Far-field RF power extraction circuits and systems

Abstract: A method and apparatus for performing far-field power extraction are presented. The method includes receiving an electromagnetic radiation signal, rectifying the signal to produce a direct current (D.C.) voltage and providing the D.C. voltage to a circuit. A far-field power extraction circuit includes an antenna for receiving an electromagnetic radiation signal, a rectifier for rectifying the electromagnetic radiation signal. The circuit may further include a charge pump for amplifying the rectified voltage, an impedance matching network for coupling the antenna to the rectifier and a feedback tuning circuit for optimizing performance of the extraction circuit.

Efficient full-chip thermal modeling and analysis

Abstract: The ever-increasing power consumption and packaging density of integrated systems creates on-chip temperatures and gradients that can have a substantial impact on performance and reliability. While it is conceptually understood that a thermal equivalent circuit can be constructed to characterize the temperature gradients across the chip, direct and iterative solutions of the corresponding 3D equations are often intractable for a full-chip analysis. Multigrid accelerated iterative methods can be applied to solve the equivalent circuit problem that is provably symmetric positive definite; however, explicitly building the matrix problem is intractable for most full-chip problems. In This work we present a multigrid iterative approach for the full-chip thermal analysis which does not require explicit construction of the equivalent circuit matrix. We propose specific multigrid treatments to cope with the strong anisotropy of the full-chip thermal problem that is created by the vast difference in material thermal properties and chip geometries. Importantly, we demonstrate that only with careful thermal modeling assumptions and appropriate choices for grid hierarchy, multigrid operators and smoothing steps across grid points, can we accurately and efficiently analyze a full-chip thermal problem. Experimental results demonstrate the efficacy of the proposed multigrid methodology. Our prototyped thermal simulator is able to solve a steady-state problem with more than 10 million unknowns in 125 CPU seconds with a peak memory usage of 231 mega bytes.

A controllable reactor of transformer type

Abstract: This paper clarifies the operating principles of a controllable reactor of transformer type (CRT). In nature, a CRT is equivalent to a multi-winding transformer for which the low-voltage windings (control windings) operate at short-circuited states in turn. This kind of reactor possesses such advantages as smooth power regulation, low current harmonic content, and fast response. Taking account of the coupling of the control windings, this paper examined the current harmonic content for the work winding by Fourier series decomposition, and thus derived the current harmonic coefficients. Based on the solution of the branch current equation of a multi-winding transformer, and introduction of the concept of equivalent winding impedance, a polygon-type equivalent circuit is proposed for a multi-winding transformer. Subsequently, formulae for the branch impedances of the equivalent circuit are presented. According to the harmonic content constraints, the number of control steps is determined. Then, by combining the MMF and branch current equations, an expanded equation about the winding currents and current-limiting reactances is obtained. According to the feature that the control windings are short-circuited in turn, the current-limiting reactances are calculated for each control winding step by step. At last, based on the proposed equivalent circuit for a multi-winding transformer, a simulation model for a CRT is fabricated with MATLAB/SIMULINK/PSB. The simulation results confirmed the presented work, which underpins the further analysis and design of a CRT.