Showing papers on "Equivalent circuit published in 1987"

The Sheffield data collection system.

Abstract: Because of the intrinsically low sensitivity of any surface potential measurement to resistivity changes within a volume conductor, any data collection system for impedance imaging must be sensitive to changes in the peripheral potential profile of the order of 0.1%. For example, whilst the resistivity changes associated with lung ventilation and the movement of blood during the cardiac cycle range from 3 to 100% the changes recorded at the surface are very much less than this. The Sheffield data collection system uses 16 electrodes which are addressed through 4 multiplexers. Overall system accuracy is largely determined by the front-end equivalent circuit which is considered in some detail. This equivalent circuit must take into account wiring and multiplexer capacitances. A current drive of 5 mA p-p at 5 kHz is multiplexed to adjacent pairs of electrodes and peripheral potential profiles are recorded by serially stepping around adjacent electrode pairs. The existing Sheffield system collects the 208 data points for one image in 79 ms and offers 10 image data sets per second to the microprocessor. For a homogeneous circular conductor the ratio of the maximum to minimum signals within each peripheral potential profile is 45:1. The temptation to increase the number of electrodes in order to improve resolution is great and an achievable performance for 128 electrodes is given. However, any improvement in spatial resolution can only be made at the expense of speed and sensitivity which may well be the more important factors in determining the clinical utility of APT.

Quasi-Resonant Converters-Topologies and Characteristics

Abstract: In designing switching dc-dc converters, the effort to increase operating frequency to reduce weight, size, and cost of magnetic and filter elements is constantly hampered by higher switching stresses and switching losses. To overcome these obstacles, the concept of the "resonant switch" is proposed. By incorporating additional inductor and capacitor elements to shape the semiconductor switch's current waveform, a "zero-current switching" property can be realized. Based on the resonant switch technique, a new host of quasi-resonant converter circuits have been derived, which can be operated in the megahertz range.

Electrochemical Impedance Analysis of Polyaniline Films on Electrodes

Abstract: The ac response of polyaniline films on Pt electrodes in was measured at different applied dc potentials, varied in the positive and negative directions. Experimental complex capacitance plots were reproduced using a computer simulation program based upon the equivalent circuit approach. With 150 nm films the complex capacitance plots at +0.55V (vs. SCE) comprise a single capacitive element, which develops at more negative potentials into a parallel combination of two discrete elements (a capacitor) and (a finite transmission line) in series with a polymer resistance . and are interpreted as double‐layer and faradaic (diffusion‐controlled) components. The hysteresis observed in the voltammetric behavior of polyaniline is evident in the potential‐dependence of , , and , obtained under constant‐potential conditions.

Capacitance Requirements for Isolated Self Excited Induction Generators

Abstract: Capacitance requirements for isolated self excitd induction generators are discussed. It is shown that numerical methods based upon the steady state as well as operational equivalent circuit give similar predicted values. An analytical method is proposed to compute, Cmin, the minimun capacitance value required for self excitation under no load conditons. It is shown that Cmin is inversely proportional to the square of the speed. Furthermore, it is inversely proportional to the maximum saturated magnetizing reactance. The theoretical results are verified experimentally for a number of test machines and a good agreement is observed between the theoretical and the experimental values. The influence of load impedance and its power factor on the terminal capacitance required to maintain self excitation under steady state is also examined and it is shown that when machine is loaded, the terminal capacitance should be several times that required at no load. Furthermore, the influence of terminal capacitor upon the maximum available output power fron isolated induction generators is also examined.

Large signal nonlinear distortion prediction for a single-mode laser diode under microwave intensity modulation

Abstract: The large-signal nonlinear distortions from a directly-modulated single-mode GaAlAs laser diode are closely predicted by using a large-signal equivalent circuit model. Criteria for determining intrinsic parameter values are described. The simulations are done in the time domain and then transformed to the frequency domain by FFT. Second harmonics, two-tone third-order intermodulation, multicarrier intermodulation, and intermodulation due to two arbitrarily separated tones have all been simulated and match well with corresponding measured results.

On the Study of Microstrip Ring and Varactor-Tuned Ring Circuits

Abstract: Equivalent circuits have been derived for microstrip ring and varactor-tuned ring resonators. It was found that the resonant frequency is slightly lower as the coupling gap becomes smaller. Varactor-tuned ring resonators have been developed with up to 15 percent tuning bandwidth using packaged varactor diodes. A dielectrically loaded microstrip ring circuit with lower loss was demonstrated. The results should have many applications in electronically tunable oscillators and filters in both hybrid and monolithic integrated circuits.

A small-signal equivalent-circuit model for GaAs-AlxGa1−xAs resonant tunneling heterostructures at microwave frequencies

Abstract: This paper presents a study of the microwave impedance of GaAs‐AlxGa1−xAs resonant tunneling heterostructures. An equivalent‐circuit model is proposed that accounts for the frequency variation of the measured impedance and whose elements correspond to physical phenomena believed to be present in the device. Empirical formulas are obtained which can be used to calculate the values of the equivalent‐circuit elements from the structural parameters and the dc current‐voltage characteristics of the device.

The waveguide surfatron: a high power surface-wave launcher to sustain large-diameter dense plasma columns

Abstract: A novel microwave structure which allows a plasma column to be sustained through the propagation of an electromagnetic surface wave is investigated. This plasma source is analysed in terms of a simple equivalent circuit which correctly predicts the transfer of power from the microwave generator to the plasma as a function of the tuning system of the launcher; it further shows that such a microwave structure is the waveguide equivalent of the surfatron. This device seems a particularly well adapted substitute for the surfatron at 2.45 GHz (or higher frequencies) when there is a need to operate at high (>500 W) microwave power levels or with large (>or=15 mm) tube diameters.

Two-Tone Intermodulation in Diode Mixers

Abstract: This paper explores, experimentally and theoretically, the problem of minimizing second- and third-order intermodulation distortion in diode mixers. A numerical technique is presented which can be used to calulate internrodulation levels with unprecedented accuracy, and it is used to identify circuit and diode parameters which maximize dynamic range. It is shown that intermorhdation distortion is minimized by using low diode junction capacitance and series resistance, short-circuit embedding impedances, and high local-oscillator level. It is also shown that certain conditions which may optimize conversion loss, such as image enhancement, may severely exacerbate intermodulation.

Characteristic Impedance of Microstrip Lines

Abstract: It is shown that it is feasible to force the complex power P of microstrip line to be given by the usual circuit definition: P = I* V/2 where I and V are the current and voltage of the equivalent transmission line and * denotes complex conjugation. If this requirement is made, then the three common definitions of characteristic impedance (namely, the voltage-current, power-voltage, and power-current definitions) all become equivalent. The remaining arbitrariness in microstrip characteristic impedance 20 stems not from the choice of definition, as sometimes argued, but from the ability to choose one of the magnitudes |I|, |V|, and |Z/sub 0/| for convenience, and also to choose the phase of either I or V (but not their relative phase). This clarification should make it easier to simplify equivalent circuits for drivers, loads, and discontinuities.

Distributed Equivalent-Circuit Model for Traveling-Wave FET Design

Abstract: Based on reliable theoretical results, a distributed MESFET model is developed. It consists of equivalent-circuit elements which can be evaluated directly from FET material constants and geometry. The deviations with respect to full-wave-analysis results are investigated and some applications are shown.

Efficient Operation of Surface-Mounted PM Synchronous Motors

Abstract: The steady-state performance of the surface magnet PM synchronous motor can be modeled to a good approximation by a simple equivalent circuit that includes the effect of the stator core loss. For operation at constant power with no restrictions placed on voltage or frequency, this model shows that there exists a unique operating point that yields the maximum efficiency and that the efficiency at this point is a function solely of the motor loss parameters, independent of the particular power level. Loss contour plots are introduced to show the existence of the optimum point and to show the nature of the losses as one departs from the optimum. The impact of these results on different operating modes for the machine is discussed. Test results are presented to verify that the optimal efficiency point exists and that the simple model predicts the machine performance reasonably well.

Distortion In p-i-n Diode Control Circuits

Abstract: Traditionally, distortion in p-i-n diodes has been thought to be only a function of the carrier lifetime and frequency of operation. This understanding is based on empirical evidence and is not entirely accurate. This paper will discuss the origins of p-i-n diode distortion and study the effects of various devices parameters on distortion performance. Included in the investigation on single-diode circuits will be switching circuits and reflective attenuators. In switch circuits, the analysis shows that distortion can be minimized by maximizing the stored-to-charge resistance ratio in the diode. In attenuators, the analysis shows that maximizing the i-region thickness will minimize distortion, independent of the device carrier life-time. In attenuators where multiple p-i-n diodes are used (the bridged-tee and PI are discussed), maximizing the i-region thickness also minimizes the distortion, independent of carrier lifetime. The model accurately predicts distortion signal cancellation in both single and multiple p-i-n diode circuits.

Current Readout Of Infrared Detectors

Abstract: A buffered direct-injection (BDI) current readout for infrared detectors is described and analyzed. It is compared with the common direct-injection (DI) circuit with respect to injection efficiency, noise, and tolerance of low RoA product photovoltaic detectors. Power requirements and threshold control are also discussed. Throughout the analysis it is clear that much advantage is gained at relatively little cost by the use of a BDI structure for an integrated circuit focal plane.

A substitution algorithm for solving nonlinear circuits with multi‐frequency components

Abstract: In this paper, we present an efficient algorithm for calculating the steady-state response of nonlinear circuits such as forced circuits driven by multi-frequency-component signals, forced oscillators, and coupled oscillators. We call the technique a substitution method because the variation at each step is calculated by solving an associated time-invariant sensitivity circuit at each frequency component of the residual error, whose circuit is derived from a relaxation method. the algorithm is very simple and efficient, and it can be applied to a wide variety of nonlinear circuits.

Semiconductor integrated circuit with self-testing

Abstract: A semiconductor integrated circuit comprises a plurality of integrated circuit blocks constructed on a wafer. The integrated circuit blocks are electrically connected to each other so as to form a system. Each of the integrated circuit blocks comprises a logic circuit for carrying out a logic operation, a pseudo-random pattern generating circuit for generating a pseudo-random pattern signal, a switching circuit for selecting either an input signal to be processed by the logic circuit or the pseudo-random pattern signal and a data compressing circuit for compressing an output data signal of the logic circuit. The switching circuit is responsive to a test enabling signal which is independently applied to each integrated circuit block so that each integrated circuit block is independently set to either a test mode or a normal mode, and outputs the selected signal to the logic circuit.

Noise cancelling circuit

Abstract: A noise cancelling circuit includes a delay circuit (19) for delaying an input signal which is supplied to an input terminal (18), and a signal processing circuit (Q1 to Q6, 23) responsive to the input signal and an output signal from the delay circuit (19), to generate an output signal corresponding to the input signal. The signal processing circuit has a first switching circuit, which includes first and second switching elements (Q1 and Q3) connected in series between a first power supply terminal (Vcc) and an output (20), and a second switch­ing circuit, which includes third and fourth switching elements (Q2 and Q4) connected in series between a sec­ond power supply terminal and the output (20), wherein the first and third switching elements (Q1 and Q2) are responsive to the aforementioned input signal, by which they are set in mutually opposite conduction states, and the second and fourth switching elements (Q3 and Q4) are responsive to the output signal of the delay circuit (19), by which they too are set in mutually opposite conduction states.

An improved GaAs MESFET equivalent circuit model for analog integrated circuit applications

Abstract: An improved equivalent circuit model of a gallium-arsenide (GaAs) MESFET that is optimized for the design and analysis of precision analog integrated circuits is described. These circuits entail different modeling requirements from digital or microwave circuits, for which existing equivalent circuit models are optimized. Improved techniques are presented to model the drain-to-source conductance, device capacitance, and the functional dependence of drain-to-source current.

Design and construction of a high-speed high-performance direct-drive handpiece

Abstract: The electrical and mechanical design of a precision handpiece (or handtool) delivering 10 W at 150 000 rev/min is described. The 2-pole synchronous drive motor has a samarium-cobalt rotor magnet of axial length 7 mm and diameter 3 mm. The motor has mumetal laminations and a bar winding which is supplied at 2.5 kHz by three toroidal transformers built into the unit. An equivalent circuit and experimental data are given from a prototype constructed according to the design procedure.

Partial discharges in voids in solid dielectrics. An alternative approach

Abstract: Partial discharges in voids are traditionally discussed in terms of an equivalent capacitive network, the abc-model [1,2]. A void is represented by a capacitance, and discharges within the void are simulated as a partial or a complete discharge of this capacitance. This simple approach has been so successful with respect to measurement techniques that there is a tendency to identify the equivalent circuit with the actual dielectric system. This may lead to erroneous conclusions, e.g. about transfer of charges within a void, or to concepts which, although they are meaningful with respect to the equivalent circuit, may have no direct relation to the actual dielectric system.

Easily testable semiconductor LSI device

Abstract: In a large scale integrated (LSI) circuit, a through-passage circuit together with a selector circuit is provided between an input circuit and an output circuit, thereby enabling to selectively short-circuit the input circuit to the output circuit. In testing a complex circuit including two or more such LSIs, the internal circuit of the LSIs can be selectively extremely simplified to enable easy and fast testing.

Small signal ac equivalent circuit modelling of the series resonant converter

Abstract: The small signal dynamics of the series resonant converter are investigated using an equivalent circuit modelling approach. The converter input and output ports behave essentially as nonideal current sources, so the most suitable form is the two-port y parameter model. Two such models are proposed: a continuous time version valid for low perturbation frequencies, aand a discrete time version which models the inherent sampling in the converter and is valid for any perturbation frequency less than the switching frequency. Experimental verification of the control to output transfer function and the output impedance is presented, and good agreement between theory and experiment is obtained.

Temperature compensation circuit for a delay circuit utilized in an FM detector

Abstract: A circuit for compensating change in delay time of a delay circuit due to variation in temperature employs, as a phase shifter of a pulse FM detection circuit, a delay circuit whose delay time is subject to change due to variation in temperature and can be controlled in response to a control signal. A dc component in an output of this pulse FM detection circuit is compared with a preset reference value and a resulting comparison output is used for controlling the delay time of the delay circuit and thereby compensating the temperature characteristic of the delay time. In a device using plural delay circuits, these delay circuits can be disposed on the same substrate and the delay times of these delay circuits can be controlled by the same comparison output. Since a signal which is handled by a delay circuit is utilized for the temperature compensation, an accurate temperature compensation can be realized with a simple circuit construction.

MOS no-leak circuit

Abstract: A CMOS inverter circuit is coupled to a power source by a cut-off circuit which prevents current flow through the CMOS inverter circuit when the input signal to the CMOS inverter is of a first bi-level state. The cut-off circuit responds to the output signal from a second inverter circuit that is connected to receive the output of the CMOS inverter circuit. A second embodiment of the invention provides a latching function by connecting a feedback path from the output of the second inverter circuit to a toggle gate circuit connected to the input to said CMOS inverter circuit.

Impedance characteristics of an rf parallel plate discharge and the validity of a simple circuit model

Abstract: Measurements of the electrical characteristics of a parallel plate rf discharge at pressures from 0.1 to 10 Torr in argon and at frequencies from 7.1 to 20 MHz are reported. The discharge impedance reaches a minimum for all frequencies at a pressure of about 1 Torr and the impedance decreases with increasing frequencies. The phase variation over the pressure range is as high as 40°. With added attaching gas, the impedance increases and the minimum occurs at lower pressures. A simple equivalent circuit with a capacitance representing the electrode sheaths can model the measured impedance behavior at pressures up to 1 Torr when the capacitance is made proportional to pressure, analogous to the sheath characteristics. At higher pressures, a good fit can be achieved by making the resistance, which represents the power losses in the discharge volume, a function of pressure. Derived sheath dimensions correlate with observed variations versus pressure and frequency. The fact that at the lower pressures the resistive part of the impedance is independent of pressure and that the resistance no longer properly represents the voltage drop across the discharge volume indicates that collisional losses in the volume no longer dominate the power deposition. The ‘‘wave‐riding’’ mechanism is suggested as the dominant process in this pressure range. Its frequency characteristic correlates well with the frequency characteristic of the measured impedance.

Magnetic equivalent circuit presentation of electric machines

Abstract: The fundamentals of the magnetic equivalent circuit concept are described. This principle is illustrated by several examples. The position of the method in modem theory and design of electric machines is defined and discussed.

Calculation of Series Capacitance Eor Transient Analysis of Windings

Abstract: Knowledge of the series capacitance of a winding (transformer, reactor or magnet) is essential in order to analyze its transient behavior. A method of computing the series capacitance of a winding is proposed which is mathematically rigorous but simple to execute. As a check, the equivalent series capacitance of a four-turn double-disk winding was computed by the proposed method as well as by simple circuit reduction. This method of calculating the series capacitance was applied to determine the natural frequencies of large magnets.