Showing papers on "Capacitance published in 1990"

Performance characterization of a high-power dual active bridge DC-to-DC converter

Abstract: The performance of a high-power, high-power-density DC-to-DC converter based on the single-phase dual active bridge (DAB) topology is described. The dual active bridge converter has been shown to have very attractive features in terms of low device and component stresses, small filter components, low switching losses, high power density and high efficiency, bidirectional power flow, buck-boost operation, and low sensitivity to system parasitics. For high output voltages, on the order of kilovolts, a cascaded output structure is considered. The effects of snubber capacitance and magnetizing inductance on the soft switching region of control are discussed. Various control schemes are outlined. Coaxial transformer design techniques have been utilized to carefully control leakage inductance. The layout and experimental performance of a prototype 50 kW 50 kHz unit operating with an input voltage of 200 V DC and an output voltage of 1600 V DC are presented. >

Device modeling of ferroelectric capacitors

Abstract: A physically based methodology is developed for modeling the behavior of electrical circuits containing nonideal ferroelectric capacitors. The methodology is illustrated by modeling the discrete ferroelectric capacitor as a stacked dielectric structure, with switching ferroelectric and nonswitching dielectric layers. Electrical properties of a modified Sawyer–Tower circuit are predicted by the model. Distortions of hysteresis loops due to resistive losses as a function of input signal frequency are accurately predicted by the model. The effect of signal amplitude variations predicted by the model also agree with experimental data. The model is used as a diagnostic tool to demonstrate that cycling degradation, at least for the sample investigated, cannot be modeled by the formation of nonswitching dielectric layer(s) or the formation of conductive regions near the electrodes, but is consistent with a spatially uniform reduction in the number of switching dipoles.

Force microscopy with a bidirectional capacitance sensor

Abstract: A new method for sensing cantilever deflection in the atomic force microscope (AFM), based on capacitance measurement, is described. Parameters governing the design of such an instrument are considered in detail. Two different geometries are compared, wire on plate and an integrated flat plate sensor. The electronic circuitry, providing 6×10−19 F noise in a 0.01–1000 Hz bandwidth, is also described. Implementation of the design ideas into a working AFM in ultrahigh vacuum is demonstrated. This AFM allows simultaneous measurement of cantilever deflection in two orthogonal directions, necessary for our nanotribology studies. The theoretical sensitivity of 5×10−7 F/m is not achieved due to roughness. The bidirectional sensing and imaging capabilities are demonstrated for an Ir tip on cleaved graphite, and a diamond tip on diamond films. The capacitance detection technique is compared and contrasted with other AFM sensors.

Capacitance, Inductance, and CrossTalk Analysis

Abstract: General concepts formula sets crosstalk analysis discrete components ancillary circuit elements experiments and test data.

An investigation of the drive circuit requirements for the power insulated gate bipolar transistor (IGBT)

Abstract: The drive circuit requirements of the OGBT are explained with the aid of an analytical model. This model can be used to describe the turn-on and turn-off, gate and anode, current and voltage waveforms for general external drive, load, and feedback circuits. It is shown that nonquasi-static effects limit the influence of the drive circuit on the time rate-of-change of the anode voltage. Model results are compared with measured turn-on and turn-off waveforms for different drive, load, and feedback circuits and for different IGBT base lifetimes. The effective output capacitance of the IGBT at turn-off is several orders of magnitude larger than that of the structurally equivalent power MOSFET and depends upon the device base lifetime because the base charge at turn-off depends upon the device base lifetime. However, the gate drain feedback capacitance is unchanged from the value for the structurally equivalent power MOSFET. Thus, the minimum gate resistance that influences the anode voltage rate-of-rise at turn-off is several orders of magnitude larger than that for the power MOSFET and varies with device base lifetime. >

Capacitance requirement for isolated self-excited induction generator

Abstract: Advanced knowledge of the minimum capacitor value required for self-excitation of an induction generator is of practical interest. To find this capacitor value two nonlinear equations have to be solved. Different numerical methods for solving these equations are known from previous literature. However, these solutions involve some guessing in a trial-and-error procedure. A new simple and direct method is developed to find the capacitance requirement under RL load. Exact values are derived for the minimum capacitance required for self-excitation and the output frequencies under no-load, inductive and resistive loads. These calculated values can be used to predict theoretically the minimum value of the terminal capacitance required for self-excitation. For stable operation C must be chosen to be slightly greater than C/sub min/. Furthermore, it is found that there is a speed threshold, below which no excitation is possible no matter what the capacitor value. This threshold is called the cut-off speed. Expressions for this speed under no-load and inductive load are also given.

Influence of the terminal capacitor on the performance characteristics of a self excited induction generator

Abstract: The influence of the excitation capacitor on the steady state performance characteristics of an isolated self-excited induction generator feeding a balanced load is examined. It is shown that the terminal capacitor must have its value within a certain range to sustain self-excitation. If the value of the excitation capacitor is outside this range, self-excitation will not be possible. Moreover, if the load impedance is below a certain value, self-excitation will not be achieved irrespective of the value of the excitation capacitor. In the capacitance range where self-excitation is possible, it's value strongly influences the induction generator performance characteristics. The value of capacitance can be selected so that the terminal voltage is constant, regardless of the generator output power. It is further shown that under such condition, the value of capacitance is influenced by the load as well as by the load power factor. The generator performance is however independent of the load power factor and is only affected by the magnitude of the load impedance.

Negative capacitance at metal-semiconductor interfaces

Abstract: A negative capacitance effect has been observed in metal‐semiconductor contacts. This phenomenon is explained by considering the loss of interface charge at occupied states below Fermi level due to impact ionization. A modified Shockley–Read treatment is proposed to interpret the experimental observations. In particular, a two‐energy‐level simplified model is presented to simulate the capacitance spectrum. The results are in good agreement with the experimental data.

Transition from 'supercapacitor' to 'battery' behavior in electrochemical energy storage

Abstract: The storage of electrochemical energy in battery supercapacitor, and double-layer capacitor devices is considered. Supercapacitor systems based on 2-dimensional underpotential deposition reactions are highly reversible and their behavior arises from the pseudocapacitance associated with potential-dependence of 2-dimensional coverage of electroactive adatoms on an electrode substrate surface. Such capacitance can be 10 to 100 times the double-layer capacitance of the same electrode area. An essential fundamental difference from battery behavior arises because, in such systems, the chemical and associated electrode potentials are a continuous function of degree of charge, unlike the thermodynamic behavior of single-phase battery reactants. Quasi-2-dimensional systems, such as hyper-extended hydrous RuO/sub 2/, also exhibit large pseudocapacitance. Other examples are the conducting polymer electrodes and Li intercalate systems. The impedance behavior of an RuO/sub 2/ supercapacitor is illustrated but is far from that expected for an electrostatic capacitor. >

Design of capacitance electrodes for concentration measurement of two-phase flow

Abstract: Capacitance electrode systems for the measurement of the volumetric concentration of two-phase flows have inherently non-uniform sensitivity distributions over the pipe cross section and therefore have different responses to different flow regimes (eg core, annular and stratified flows) In processes with varying flow regimes, this can lead to significant measurement errors An electrode system which has a uniform sensitivity distribution and consequently a response independent of flow regime is therefore desirable The system performance parameters of surface electrode systems used with stray-immune measurement transducers have been characterised quantitatively using a two-dimensional finite-element model The electrode system design parameters have also been identified and their effects on system performance parameters have been investigated As a result, optimum electrode designs are proposed, with responses to different flow regimes having a minimum deviation from linearity

Amplex, a low-noise, low-power analog CMOS signal processor for multi-element silicon particle detectors

Abstract: AMPLEX is a monolithic analog signal processor fabricated in 3 μm n-well CMOS and originally designed for the inner silicon detector of the UA2 Experiment at the CERN SPS Collider. However, it is suitable for various other types of detectors, and results are also given for a multiwire proportional chamber (MWPC). The chip contains 16 channels, each consisting of a charge amplifier, a shaper amplifier and a track-and-hold stage. The channel outputs are connected to an analog multiplexer which is controlled by digital circuitry. For a power consumption of 1 mW per channel and an adjustable peaking time of 600 to 800 ns, the equivalent noise charge is 400 rms electrons plus 33 rms electrons per pF of input capacitance. The DC stabilisation of the charge amplifier is obtained using a non-linear feedback resistor. This novel MOS element is a key feature of the design and enables low noise as well as DC stability of the charge amplifier, even for increased detector leakage current up to several hundred nA. Such operating conditions can occur following radiation damage of silicon pad detectors.

Method for formation of a stacked capacitor

Abstract: A method is disclosed for forming a capacitor on a semiconductor wafer which utilizes top and back sides of a capacitor node for capacitance maximization. First and second dielectric layers, having different etch rates, are applied atop the wafer, and a contact opening is etched therethrough. Poly is applied and etched to begin formation of one node of the capacitor. A layer of oxide is then formed atop the poly capacitor node. The first dielectric layer is then etched, leaving a projecting or floating capacitor node which is surrounded by the second dielectric material and oxide formed thereatop. The surrounding material is then etched, the capacitor dielectric applied, and the poly of the second capacitor nod applied and selectively etched.

A capacitive pressure sensor with low impedance output and active suppression of parasitic effects

Abstract: This paper describes the design, operating principles and performance of a capacitive pressure sensor in silicon, combined with a dedicated CMOS interface circuit. The readout circuit is designed to suppress parasitics and to yield an output signal proportional to pressure. The sensor-specific part is fabricated using standard photolithography, silicon micromachining in KOH, and anodic silicon/glass bonding at wafer level. The devices measure 2.2 × 3.5 × 0.8 mm and show a typical zero-pressure capacitance of 10 pF, with pressure-induced changes up to 250%. The interface chip ‘CAPRICE’ (CApacitive Pressure sensor Readout IC) is processed in a 3 μ n-well CMOS process and was designed to anticipate the intrinsic drawbacks of the capacitive transducing principle, i.e. sensitivity to environment noise, nonlinear output response and effects of parasitic capacitances. These drawbacks have always prevented the breakthrough of integrated capacitive mechanical sensors. CAPRICE, however, converts small capacitance variations into a noise-insensitive output voltage and a first-order linearisation is achieved by inversion of the hyperbolic capacitance versus pressure relationship. A second-order linearisation is obtained by the adoption of a novel suppression scheme for parasitic capacitances to the substrate. Parasitic capacitance rejection ratios up to 80 dB can be achieved in this way, enabling the practical feasibility of capacitive pressure sensors with less than 0.5% of full-scale nonlinearity.

Proximity responsive capacitance sensitive method, system, and associated electrical circuitry for use in controlling mechanical and electro-mechanical equipment

Abstract: A method and system and associated circuitry for controlling and stopping the motion of dangerous moving parts such as power saw blades substantially instantaneously in response to body or human capacitance produced by an operator coming with a predetermined critical distance from the moving part. This method includes, and this system provides for, among other things, connecting an antenna to the moving part and then coupling a tunable circuit to the antenna so that the antenna provides a variable lumped capacitance parameter (dependent upon human body capacitance) within the tunable circuit. This lumped capacitance parameter is variable in response to body or human capacitance produced when an operator comes within a predetermined critical proximity to the moving part. This variation in lumped capacitance serves to tune the circuit at or near a point of resonance to thereby enable an RF signal to pass through the tunable circuit at a detectable level which is subsequently processed to activate safety equipment for controlling and stopping the motion of the moving part substantially instantaneously. This invention is also adaptable for use with non-dangerous mechanical apparatus such as automatic door openers, automatic robot equipment, and capacitance-sensitive lighting appliances, and the like. It is also adaptable for use on automobile safety equipment, such as the proximity sensing of persons approaching an automobile out of the normal line-of-sight vision angles of the driver.

Capacitive silicon accelerometer with highly symmetrical design

Abstract: The design and performance of a capacitive micromechanical accelerometer, as well as an electronic circuit for the conditioning of the output signal are described. The sensing element consists of a differential capacitance which is formed by a seismic silicon mass and two counter electrodes situated on anodically bonded glass plates. The mass is symmetrically suspended on at least eight cantilever beams located on both sides of the silicon wafer. For a ±5 g device a typical sensitivity of 1 pF/ g with a zero capacitance of 10 pF and a detection limit below 1 m g was achieved. For signal conditioning a switched capacitor CMOS-ASIC was developed, yielding an analogue voltage output signal.

A capacitor-over-bit-line (COB) cell with a hemispherical-grain storage node for 64 Mb DRAMs

Abstract: A novel capacitor-over-bit-line (COB) cell with a hemispherical-grain (HSG) poly-Si storage node has been developed. This memory cell provides large storage capacitance by increasing the effective surface area of a simple storage node and is manufacturable by optical delineation. The feasibility of the COB cell for 64-Mb DRAMs has been verified by a 64-kb test memory with 1.8- mu m/sup 2/ cells using a 0.4- mu m design rule, storage capacitance of 30 fF, 7-nm-SiO/sub 2/-equivalent dielectric film, and a storage node height of 0.5 mu m. >

Investigations of porous silicon for vapor sensing

Abstract: A 440% increase in capacitance in response to a humidity change from 0 to 100% has been measured in a Schottky-barrier r.h. sensor made using an alumin

Limits on the performance of the three-phase self-excited induction generators

Abstract: Dependency of the output voltage and frequency of the isolated self-excited induction generator on the speed, load, and terminal capacitance causes certain limitations on its performance. In this study, the performance of the induction generator under a wide range of operating conditions is examined. It is found that the machine operates only in certain element ranges and that all generated currents and voltages are bounded. It is also shown that a combination of these elements exists that is optimal for maximum power generation. >

Electric double layer capacitor

Abstract: PURPOSE: To obtain an electric double layer capacitor allowing large area and capacitance without liquid leakage and drip by providing an electrolyte thin film constituted by a solid-state electrolyte thin film which has fixed ion conductor in the holes of a porous thin film CONSTITUTION: An electric double layer capacitor possesses an electrolyte thin film between electrodes and its electrolyte thin film is constituted by a solid-state electrolyte thin film 1 which has fixed ion conductor in the holes of a porous thin film Therefore, the electrolyte thin film can be treated as a solid as a whole without liquid leakage and has excellent ion conductivity The porous thin film used has a function as the supporting body of the ion conductor and is made of polymeric material which has excellent mechanical strength Thus, the super thin electric double layer capacitor allowing large area and capacitance is obtained without liquid leakage and drip COPYRIGHT: (C)1991,JPO&Japio

Power and stability limitations of resonant tunneling diodes

Abstract: Stability criteria for resonant tunneling diodes are investigated. Details of how extrinsic elements, such as series inductance and parallel capacitance, affect the stability are presented. A GaAs/AlAs/InGaAs/AlAs/GaAs double-barrier diode is investigated, showing the effect of different modes of low-frequency oscillation and the extrinsic circuit required for stabilization. The effect of device stabilization on high-frequency power generation is described. The main conclusions of the paper are: (1) stable resonant tunneling diode operation is difficult to obtain, and (2) the circuit and device conditions required for stable operation greatly reduce the amount of power that can be produced by these devices. >

A method for determining the effective conductivity of dispersions of particles

Abstract: A general method is developed to predict the effective conductivity of an infinite, statistically homogeneous suspension of particles in an arbitrary (ordered or disordered) configuration. The method follows closely that of 'stokesian dynamics', and captures both far-field and near-field particle interactions accurately with no convergence difficulties. This is accomplished by forming a capacitance matrix, the electrostatic analogue of the low-Reynolds-number resistance matrix, which relates the monopole (charge), dipole and quadrupole of the particles to the potential field of the system. A far-field approximation to the capacitance matrix is formed via a moment expansion of the integral equation for the potential. The capacitance matrix of the infinite system is limited to a finite number of equations by using periodic boundary conditions, and the Ewald method is used to form rapidly converging lattice sums of particle interactions. To include near-field effects, exact two-body interactions are added to the far-field approximation of the capacitance matrix. The particle dipoles are then calculated directly to determine the effective conductivity of the system. The Madelung constant of cohesive energy of ionic crystals is calculated for simple and body-centred cubic lattices as a check on the method formulation. The results are found to be in excellent agreement with the accepted values. Also, the effective conductivities of spherical particles in cubic arrays are calculated for particle to matrix conductivity ratios of infinity, 10 and 0.01.

Variable capacitance integrated circuit usable in temperature compensated oscillators

Abstract: A variable capacitance circuit comprising a capacitor array, associated switching elements and transient impedance varying circuits. The capacitor array comprises a plurality of capacitor elements connected to a common node coupled to a crystal oscillator in a crystal oscillator portion and each capacitor element includes a connected switching element that controls activation of selected capacitor elements that are selectively placed in operation as load capacitance with the crystal oscillator to change and adjust its frequency. Further, circuits are provided in a temperature compensation portion to selectively control the activation of the switching elements based upon decoded compensating values provided in memory, such as based upon sensed oscillator temperature conditions. The transient impedance varying circuits comprise multi-level voltage generating circuits for changing the continuity impedance of activated switching elements, among switching elements being switched, to another impedance level or one of a plurality of additional impedance levels. As a result, an intermediate impedance value can be created between the ON and OFF states of the switching elements so that there is no rapid change in the total equivalent capacitance imposed by the capacitor array on the oscillator resulting in smooth capacitance switching which corresponds to smoother frequency adjustment of oscillator output.

Electrical capacitance clearanceometer

Abstract: A hot gas turbine engine capacitive probe clearanceometer is employed to measure the clearance gap or distance between blade tips on a rotor wheel and its confining casing under operating conditions A braze sealed tip of the probe carries a capacitor electrode which is electrically connected to an electrical inductor within the probe which is inserted into a turbine casing to position its electrode at the inner surface of the casing Electrical power is supplied through a voltage controlled variable frequency oscillator having a tuned circuit in which the probe is a component The oscillator signal is modulated by a change in electrical capacitance between the probe electrode and a passing blade tip surface while an automatic feedback correction circuit corrects oscillator signal drift A change in distance between a blade tip and the probe electrode is a change in capacitance therebetween which frequency modulates the oscillator signal The modulated oscillator signal which is then processed through a phase detector and related circuitry to provide an electrical signal is proportional to the clearance gap

Steady state analysis and performance characteristics of a three-phase induction generator self excited with a single capacitor

Abstract: Steady-state analysis and performance characteristics of a three-phase isolated star or delta connected induction generator self-excited with a single capacitor are discussed. Analytical expressions are derived to determine the no-load capacitance required to maintain self-excitation. The performance characteristics of a self-excited induction generator are affected by the terminal capacitance, C, machine speed, nu , and the load parameters. Generally, the value of C has a stronger influence on the performance characteristics and should be selected such that the terminal voltage, V/sub t/, is near its rated value while keeping C close to its lower limiting value. The accuracy of the method was experimentally verified, and good agreement is obtained between the two sets of results. The performance characteristics of star and delta connected induction generators are compared. In the mode of operation discussed, the voltages and currents are unbalanced with relatively high losses and rather low efficiency. Among the two configurations discussed, the delta connected generator offers a higher current and lower terminal voltage and a wider range of excitation capacitance. >

A micron-thickness, planar Schottky diode chip for terahertz applications with theoretical minimum parasitic capacitance

Abstract: The design and fabrication of a novel planar Schottky diode with greatly reduced shunt capacitance for millimeter- and submillimeter-wave applications is described. The dominant pad-to-pad shunt capacitance is minimized by replacing the substrate GaAs with a low-dielectric substitute. This replacement substrate can be easily removed by the user after the device is soldered into the mixer circuit. This will yield the minimum possible pad-to-pad shunt capacitance. >

Principles in design and microfabrication of variable-capacitance side-drive motors

Abstract: This paper presents a detailed discussion of the critical issues it the design and fabrication of polysilicon, rotary, variable‐capacitance, side‐drive, electric micromotors. Three different side‐drive motor architectures with stator pole number to rotor pole number ratios of 3:1; 3:2, and 2:1 are considered. For each architecture, output torque characteristics of typical microfabricated motors are simulated using two‐dimensional finite‐element solutions in the plane of the substrate. The 3:2 design is shown to provide superior torque coverage with higher minimum torque values as compared to the other two designs. An examination of the contribution of the axial fringing fields shows that, for typical micromotors, the rotor–stator capacitance is more directly a function of the rotor–stator thickness and not of the vertical rotor–stator pole‐face overlap. Furthermore, since the rotor–stator capacitance is not very sensitive to a vertical offset between the rotor and the stator, electric forces tending to vertically align the rotor to the stator are significantly smaller than would be predicted from a simple parallel‐plate capacitance calculation. A standard and a localized oxidation of silicon (LOCOS)‐based side‐drive micromotor fabrication process are described. The standard process is used as a case study to provide a detailed discussion of practical issues that need to be considered in the development of a polysilicon surface‐micromachined motor fabrication process. Specific motor design examples are described and a brief history of our experimental findings is presented. Typical 3:2 micromotors have been operated with bipolar excitations as low as 37 V across 1.5 μm gaps and at speeds as high as 15 000 rpm.

Capacitive liquid level sensor

Abstract: A capacitance liquid level sensor uses an inductance to isolate the probe of the sensor from the plastic tubing coupled to the probe thus reducing false signals generated by movement of the tubing.

Breakdown of transformer oil

Abstract: Some of the factors affecting the dielectric strength of transformer oil are investigated. These factors include the stabilization phenomenon, oil and electrode pretreatment, the effect of oil velocity, the effect of a capacitance parallel to the test cell, and the effects of electrode area and gap spacing. The experimental apparatus and procedure are described, and the results are presented for each of the above factors. Suggestions for future research are offered. >