Showing papers on "Output impedance published in 1994"

An investigation of harmonics attenuation and diversity among distributed single-phase power electronic loads

Abstract: Widely distributed single-phase power electronic loads are an increasingly important source of harmonics in power distribution systems. The objective of this paper is to investigate the cumulative harmonic current characteristics of a large number of such loads. A complete analytical model for the most common load type is derived. This model is then used to investigate the impact of: (1) interaction due to a shared source impedance; (2) variation in power level; and (3) variations in circuit parameters, on individual and cumulative current harmonics. The key findings of the paper are that diversity and attenuation are very important factors in predicting the behavior of distributed single-phase power electronic loads, especially for the higher-order harmonics, and that due to these two factors, the commonly-used fixed current injection method, using arithmetic sums of harmonic current magnitudes, can significantly overestimate the cumulative harmonic currents produced by these loads. >

Power control and delivery in plasma processing equipment

Abstract: The present invention relates to a system and method for control and delivery of radio frequency power in plasma process systems. The present invention monitors the power, voltage, current, phase, impedance, harmonic content and direct current bias of the radio frequency energy being delivered to the plasma chamber. In addition, the plasma mode of operation may be controlled by creating either a capacitively or inductively biased radio frequency source impedance. A radio frequency circulator prevents reflected power from the plasma chamber electrode to damage the power source and it further dissipates the reflected power in a termination resistor. The termination resistor connected to the circulator also effectively terminates harmonic energy caused by the plasma non-linearities. Multiple plasma chamber electrodes and radio frequency power sources may be similarly controlled.

Impedance tomography using internal current density distribution measured by nuclear magnetic resonance

Abstract: We have proposed a new method of image reconstruction in EIT (electrical impedance tomography). In EIT, we usually use boundary current and voltage measurements to provide the information about the spatial distribution of electrical impedance or resistivity. One of the major problems in EIT has been the inaccessibility of internal voltage or current data in finding the internal impedance values. The new method uses internal current density data measured by NMR imaging technique. By knowing the internal current density, we can improve the accuracy of the impedance images.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Impedance Tomography using Internal Current Density Distribution Measured by Nuclear Magnetic Resonance

Abstract: In electrical impedance tomography (EIT), we use boundary current and voltage measurements to provide the information about the cross-sectional distribution of electrical impedance or resistivity One of the major problems in EIT has been the inaccessibility of internal voltage or current data in finding the internal impedance values We propose a new image reconstruction method using internal current density data measured by NMR We obtained a two-dimensional current density distribution within a phantom by processing the real and imaginary MR images from a 47T NMR machine We implemented a resistivity image reconstruction algorithm using the finite element method and sensitivity matrix We presented computer simulation results of the image reconstruction algorithm and furture direction of the research

A wide-band AC-coupled current source for electrical impedance tomography

Abstract: A current source suitable for application in electrical impedance tomography (EIT) is described The first stage of the commercially available current-feedback amplifier AD844 constitutes a current-conveyor implementation and allows the construction of wide-bandwidth current sources, thus avoiding the mismatching and temperature-induced problems that arise in discrete realizations The lack in gain accuracy of this circuit is overcome by the inclusion of its input buffer in an operational amplifier (op amp) feedback loop Saturation problems that appear when placing a DC-blocking capacitor between the source and the electrode are solved by a DC feedback that maintains DC voltage at the output near to 0 V without reducing the output impedance of the source Two AC-coupled current sources, in both inverting and non-inverting configurations, are described and their possible applications to EIT are listed

Control of front-end three-phase boost rectifier

Abstract: Modeling and control of a three-phase PWM boost rectifier is presented. A current controller in rotating coordinates assures unity input power factor and fast output voltage regulation. Sensitivity of stability margins to different loads is analyzed. Two typical loads, a DC-DC power converter and an inverter supplying an AC motor, are considered. Linear and nonlinear current controllers in the direct axis are compared. With the nonlinear controller, which employs load current feedforward, the rectifier sensitivity to load variations is greatly reduced and a single optimal output voltage compensator can be designed for all load conditions. Small-signal output impedance is significantly improved, and faster transient response is obtained. The results are illustrated with simulations of a practical 10 kW rectifier. >

Non-contact, electromagnetically coupled transmission and receiving system for IC cards

Abstract: A non-contact IC card communication in which power consumption of a driver of a reader/writer is reduced and the size of a power supply circuit for operating the driver is made small. The driver has a low output impedance. A current detecting circuit including a detecting coil magnetically coupled with a transceiver coil of the reader/writer through a magnetic coiling element and a resistor detects a current which flows through the transceiver coil. A voltage drop to be detected is small and is approximately constant for a variation of the transceiver coil current. When data is read from an IC card, a load of the driver is changed. The driver drives the transceiver coil in a constant voltage fashion even if a current flowing through the transceiver coil changes due to the change in load. Input voltages of a rectifying/smoothing circuit and a regulator in the IC card become approximately constant. As a result, the amplitude of a high frequency output voltage of the driver can be made small. Also, a high frequency signal current sent from a reader/writer is subjected to double modulation including amplitude modulation by card data and modulation by second information, such as information indicative of the abnormality of an IC card, in synchronism with a timing at which data transmission between the reader/writer and the card is made, and the second information is extracted by the reader/writer.

Instrumentation for measurement of line impedance

Abstract: This paper presents instrumentation for nondisruptively measuring the impedance of a normally operating line. A small sinusoidal current of known frequency is injected into the line, and line impedance at that frequency is calculated from the magnitude and phase of the injected current and resulting voltage as measured by a network analyzer. Line impedance as a function of frequency is found by repeating the measurement over a range of frequencies. Lumped equivalent circuit models are extracted from the measured line impedance and applied to an example analysis of line voltage distortion. >

Small-signal model of the Cockcroft-Walton voltage multiplier

Abstract: The description of the small-signal dynamics of the Cockcroft-Walton voltage multiplier is obtained through state-space modeling in discrete time. Its small-signal equivalent circuit is a two-port linear network whose four transfer functions are given in the Z-transform. The main characteristics and general formulae of the multiplier with an arbitrary number of cells are derived. The expressions of cut-off frequency, gain and output impedance are given, and module and phase frequency responses are plotted. >

Common mode early voltage compensation subcircuit for current driver

Abstract: In a driver circuit for a twisted pair cable, a compensator for preventing appreciable common mode current flow into or out of the twisted pair cable in response to the device receiving a wide range of common mode voltage bias levels. A wide range of external bias voltages may be received as a result of variations in the ground node voltages of two coupled devices. The compensator circuit utilizes a feed back loop and monitors the bias voltage received on the twisted pair cable. As the magnitude of the common mode current increases due to external bias voltage variation from a reference bias voltage, the current flow of p-channel transistors, coupled in an arrangement of the present invention, is increased (or decreased, as necessary) so that reduced common mode current flows onto the twisted pair cable. The present invention reduces appreciable common mode current flow through the twisted pair cable from the driver that are due to variations in the external bias voltage between communication devices. The present invention provides high common mode output impedance for the driver circuit by altering the effective common mode common mode early voltage characteristics of the driver circuit while utilizing shorter channel length transistors for high speed communication capacity. The present invention also offers reduced current supply capacity of the common mode bias voltage source. The present invention operates ideally within driver circuits compatible with the IEEE P1394 communication standard.

Output buffer with variable output impedance

Abstract: An output buffer with a variable output impedance is described. The buffer is designed so that the output impedance is set relatively low during the initial portion of the output transition in which the step would occur. The output impedance is increased near the end of the transmission to approximate the characteristic impedance of a transmission line driven by the buffer. Specifically, a first feedback circuit in the variable impedance output buffer outputs a first control signal in a first state during a first portion of the output transition. The first feedback circuit outputs the first control signal in a second state during a second portion of the output transition after the first portion. A first switched resistive element receives the first control signal from the first feedback circuit. The first switched resistive element increases the output impedance of the buffer in response to the first control single being in the second state. The second portion of the output transition occurs when the buffer output voltage crosses the threshold as the output voltage approaches the end of the output transition.

Temperature field estimation using electrical impedance profiling methods. I: Reconstruction algorithm and simulated results

Abstract: Algorithmic methods for estimating complete temperature fields during hyperthermia treatments based on surface and internal electrical measurements are presented. The techniques utilized draw upon impedance imaging concepts, but rather than limit the measurements to positions on the body surface, internal impedance recording sites are allowed. Theoretical simulations show that this strategy improves the reconstructed image in the target region when either internal measurement locations are added to a given number of external recording sites or some external measurement locations are replaced by internal recording positions. The algorithms developed are tested on a set of problems with increasing levels of complexity. The culmination of these investigations is a complete simulation of a hyperthermia treatment and reconstruction of a thermal image for a body cross-section of an actual cancer patient. The results of this work suggest that the surface plus internal measurement approach holds some promise as a...

Automatic impedance matching with potential monitoring means

Abstract: A method and apparatus for impedance matching a transmitter to a transmission medium of a communication system during normal operation of the system. The method comprises feeding signals from the transmitter to the transmission medium through a variable impedance; monitoring the potential upstream and downstream of the variable impedance; generating a control signal related to the monitored potentials; and adjusting the impedance of the variable impedance in accordance with the control signal until the monitored potentials satisfy matching conditions in which the transmitter is impedance matched to the transmission medium.

Line driver with adaptive output impedance

Abstract: A line driver comprising: an input terminal (2) for receiving an input signal, an output terminal (10) for connecting a load (8), a first (12) and a second (22) transconductance-controlled transconductor having substantially equal transconductances, each transconductor having a non-inverting input (14; 24), an inverting input (16; 26), an output (18; 28) and a common control input (20) for controlling the transconductance, the non-inverting inputs (14; 24) of the first (12) and second (22) transconductors being coupled to the input terminal (2), the outputs (18; 28) of the first (12) and second (22) transconductors being coupled to the output terminal (10), the inverting input (16) of the first transconductor (12) being coupled to a point (6) of reference potential, the inverting input (26) of the second transconductor (22) being coupled to the output terminal (10), and an amplifier (32) having a non-inverting input (34), an inverting input (36) and an output (38) coupled to, respectively, the input terminal (2), the output terminal (10) and the common control input (20) of the first (12) and the second (22) transconductors.

Realization of current-mode biquadratic filter using CC IIs with current followers

Abstract: This paper proposes the circuit configuration of a current-mode biquadratic filter which uses a pair of four-terminal active-current conveyors (CFCC II) consisting of a current follower attached to a second-generation current conveyor (CC II). the circuit is composed of one current adder and two current integrators. This configuration is capable of synthesizing arbitrary current-mode second-order transfer functions by changing the conditions (grounding or connecting) at the output terminals of the CFCC IIs. Each of the proposed filters has high output impedance so they can be cascaded directly. Moreover, ω0 and Q0 is determined from the ratio of passive elements, and the element sensitivity is even lower than 0.5. Since all the passive elements are grounded, this configuration is very advantageous to IC fabrication. Again, the effect of imperfection of CFCC II on the transfer function is studied and it is found that ω0 is influenced by the current conversion factor of CFCC II and Q0 is affected by the imperfection of the integrator. Moreover, it is shown that the operating frequency limits of the filter are determined by the permissible change of Q0. Each type of filter actually is synthesized, and the useful operation is confirmed by experiments.

Low-voltage CMOS and BiCMOS triode transconductors and integrators with gain-enhanced linearity and output impedance

Abstract: CMOS and BiCMOS mode transconductors and integrators achieving a simulated THD of 0.03% for differential input signals of 0.5 V peak to peak with a supply voltage of 2.5 V are presented. Small phase errors and high g/sub m/ tunable by a factor of 10 allow the circuits to be used in continuous-time filters working at 100 MHz. >

Switching amplifier with impedance transformation output stage

Abstract: A broadband switching amplifier utilizes an output stage capable of variable impedance transformation in addition to conventional controlled pulsewidth coupling to accurately produce outpout power without regard for normal power supply or load impedance constraints. In a preferred embodiment, the present invention charges and discharges a reactance (406) with gated switches (404, 405, 407, 408) in accordance with pulsewidth-modulated signals representative of an input signal. For voltage amplification the reactance is inductive, whereas for current amplification, the reactance is capacitive.

Active current electrodes for in vivo electrical impedance tomography

Abstract: The characterization of tissue by means of electrical impedance tomography requires accurate impedance measurements at relatively high frequencies. The present study describes the design and fabrication of broad-band, active, current electrodes for in vivo measurements. This approach eliminates the lead capacitances of the sourcing electrodes. The value of the resistors used were computed according to a protocol taking into account the constraints of a given application and the values and tolerances of the available components. Additional selection of the components further reduced the variability in circuit performance. The current sources designed according to the method described are usable at frequencies higher than 1 MHz, for differential load impedances up to 2000 omega. The parallel output conductance for each active electrode is 0.85 microS +/- 2%. The design method is valid for either adjacent or diametric drive, and can be applied to various applications by modifying the shape of the electrode.

Physical interpretation of Schwan's limit voltage of linearity.

Abstract: The electrode/electrolyte interface impedance can be represented by the parallel combination of a non-faradaic pseudocapacitance and a faradaic, charge transfer resistance. The non-linearity of the overall electrode/electrolyte interface impedance is largely due to that of the faradaic resistance which is derived from the Butler-Volmer equation. As the charge transfer resistance dominates the interface impedance at low frequencies, it is in this region that non-linearities are first observed. The voltage limit of linearity has been investigated and found to increase gradually for higher frequencies. Although relatively linear compared with the charge transfer resistance, the non-faradaic impedance becomes non-linear at large applied voltage amplitudes and dominates the high-frequency non-linear behaviour of the overall interface impedance. Mid-frequencies are affected by a combination of the faradaic and non-faradaic non-linearities.

Single-phase three-wire transformerless inverter

Abstract: A single-phase inverter providing three wire two-voltage (generally 110/220 V) power is designed and implemented. Instead of using a full-bridge inverter and an output transformer with centre-tapped winding, a three-leg inverter is used to yield a single-phase three-wire circuit. In performing the switching control, the proposed inverter system is decoupled into differential-mode and common-mode subsystems. The controllers of the differential mode are designed mainly to shape and regulate the main output voltage (220 V). As to the common-mode subsystem, its controllers are arranged to compensate the imbalance between two suboutputs (110 V). Each subsystem has an inner current loop as well as an outer voltage loop. In addition, the feedforward control is augmented to the feedback control to yield sinusoidal output voltage with good regulating control performance. Furthermore, the output impedance of the proposed inverter can be significantly reduced and the voltage ratio of the two suboutputs can be programmable. The effectiveness of the proposed method is confirmed by simulation and experimental results.

Large signal analysis of the LCC-type parallel resonant converter using discrete time domain modeling

Abstract: Discrete state space modeling of the LCC-type parallel resonant power converter is presented. Using these large signal equations, small signal modeling of the power converter is obtained. State variable feedback control has been integrated with the linear small signal state space model and the associated control aspects are studied. The small signal equivalent circuit model has also been obtained. The small signal state space model has been used to study the small signal behavior of the power converter for open loop and closed loop operation for parameters like control to output transfer function, audio-susceptibility and output impedance. Theoretical results have been experimentally verified. >

Control of UPS inverters

Abstract: Many applications of UPS systems require sinusoidal outputs at frequencies ranging from 50 Hz to 400 Hz. Important performance specifications for such systems include voltage regulation, total harmonic distortion, output impedance, transient response and operation with nonlinear loads. The most significant factors affecting the overall performance of the system are the power converter topology and the control or modulation strategy used. The most popular approach for realising such converters is through the use of voltage source DC link inverters operated with an LC output filter. The inverter is typically operated with a pulse width modulated strategy under feedback control to realise the desired output waveform. The output power rating and the output distortion specifications are generally used as the basis for the choice of switching frequency and LC filter size. The regulation quality of the output voltage is arguably the most important specification of the UPS system. Regulation quality will depend on the control strategy used. This paper reviews the analogue and digital control strategies used for realising sinusoidal ouput UPS systems.

Driver circuit with self-adjusting impedance matching

Abstract: A CMOS driver circuit (20) has a high impedance driver (30) and a low impedance driver (36) connected to the near end of a transmission line (43). The output impedance of the high impedance driver (30) matches the characteristic impedance of the transmission line (43). As a digital signal from the CMOS driver circuit (20) transitions from one logic state to another, the low impedance driver (30) drives the transmission line (43) until a predetermined voltage before the signal reaches its steady state voltage. A sensing circuit (24) senses when the predetermined voltage is reached, and in response, provides a control signal to deactivate the low impedance driver (36). The high impedance driver (30) completes the signal transition. The high impedance driver (30) absorbs the reflected waves from the far end of the transmission line (43), reducing the effects of ringing, and increasing noise immunity.

The detection of the onset of electrode-electrolyte interface impedance nonlinearity: A theoretical study

Abstract: The equivalent series resistance and reactance of the electrode-electrolyte interface impedance have both been used to detect the onset of signal amplitude induced nonlinearity. Using a theoretical model, it is shown that the choice of the most sensitive indicator depends on the phase angle of the "polarization" impedance and on the applied frequency. >

Distortion generating circuit

Abstract: A distortion generating circuit of the present invention comprises a linear attenuator which has an input impedance substantially coincident with an impedance of a transmission path of input signal and an output impedance substantially coincident with an impedance of a transmission path of output signal; and at least one diode which is connected in an alternating current manner in parallel with the linear attenuator with respect to the input signal into the linear attenuator and which generates nonlinear distortion for a component in the input signal input thereinto; which outputs an AC sum of an output from the linear attenuator and an output from the diode. By this arrangement, desired distortion can be well given in a simple circuit arrangement while suppressing generation of unnecessary intermodulation distortion. An optical transmitter, an optical receiver or an amplifier can be constructed using the distortion generating circuit of the present invention, obtaining a signal with reduced distortion.

Practical considerations of impedance matching network design

Abstract: The paper investigates matchable range problems and Q-based design theory of Pi impedance matching networks. A method for determining impedance matching domains for any possible ranges of element values is presented. Boundary equations of matchable regions are formulated analytically and impedance realms are plotted with computers. The Q-based design method is thoroughly discussed from the viewpoint of power transmission. Element value determination formulas, the transducer power gain and harmonic power rejection, and transducer sensitivities to parasitic loss are explicitly expressed in terms of the two impedances and the loaded Q. Particularly actual power transmission relations taking the finite unloaded Q into account are accurately derived in terms of the loaded and unloaded Q. Various considerations of selection of the loaded Q are further discussed. Issues and techniques of handling complex impedance matching are also discussed.

Bilayer ultrasonic transducer having reduced total electrical impedance

Abstract: An ultrasonic transducer having reduced total electrical impedance is constructed by stacking a plurality of piezoelectric transducer element arrays on top of each other. For a given thickness, the electrical impedance of a multilayer stack of piezoelectric transducer element arrays is a function of the number of layers. If the number of layers equals two, then the electrical impedance of the total stack-up of layers is reduced by a factor of one-quarter relative to the electrical impedance of a single layer of equal thickness. This facilitates matching the overall transducer impedance to that of the connecting cable.

Continuously linear pulse amplifier/line driver with large output swing

Abstract: A transmission line driver circuit for use in data communication transmitters that is capable of meeting the return loss specifications as well as the electrical interface specifications as defined by C.C.I.T.T. standards for E1/T1 transmission. The line driver circuit of the present invention maintains minimum output impedance during the entire dynamic range of the transmit signal while meeting the pulse shape template requirements. The circuit includes a predriver stage that controls the slew rate of the transmit signal within the constraints of the pulse template. This allows a subsequent output driver stage to enjoy fast slew rates, large gain and dynamic range, and very small output impedance to meet the return loss specification.

Manipulator impedance accuracy in position-based impedance control implementations

Abstract: Compares two position-based impedance controllers obtaining desired end-effector impedances during robot interaction with the environment. It is shown that while these two controllers have similar structures, the Adept Controller yields more accurate impedances in the DC region because of the stiffness control properties of the force loop. In addition, adding a force feedforward component to offset the contact force was found to significantly reduce the impedance errors in both controllers. The effect of bandwidth and force feedforward are examined for a planar arm example for a typical set of desired impedance specifications. >

Voltage regulator having improved stability

Abstract: The preferred embodiment voltage regulator exhibits improved stability by offsetting changes in the output impedance of the regulator due to changes in load current. This compensation occurs virtually instantaneously with a change in load current. This enables an output capacitor to be selected primarily based upon filtering requirements rather than on frequency compensation requirements. Also in the preferred embodiment, a depletion mode pass transistor is used as the output transistor. A PMOS transistor on/off switch is connected between the source of the pass transistor and the output terminal of the regulator to effectively turn the regulator on or off without shutting down the depletion mode pass transistor. This avoids the need to form a negative supply voltage generator. An improved band gap voltage reference generator is also described which introduces a beta correction factor into the output voltage which offsets changes in beta due to process variations and other conditions. Thus, the output voltage of the reference generator is not affected by variations in the beta of transistors forming the reference generator.