Showing papers on "Output impedance published in 1992"

A new fault location technique for two- and three-terminal lines

Abstract: A method for the computation of fault location in two- and three-terminal high voltage lines is presented. It is based on digital computation of the three-phase current and voltage 60/50 Hz phasors at the line terminals. The method is independent of fault type and insensitive to source impedance variation or fault resistance. Furthermore, it considers the synchronization errors in sampling the current and voltage waveforms at the different line terminals. The method can be used online following the operation of digital relays or offline using data transferred to a central processor from digital transient recording apparatus. The authors start with a two-terminal line to explain the principles and then present the technique for a three-terminal line. The technique was first tested using data obtained from a steady-state fault analysis program to evaluate the convergence, observability, and uniqueness of the solution. The technique was then tested using EMPT-generated transient data. The test results show the high accuracy of the technique. >

High impedance, low polarization, low threshold miniature steriod eluting pacing lead electrodes

Abstract: A small diameter, unipolar or bipolar, atrial or ventricular transvenous or epimyocardial pacing lead with a porous, platinized, steroid eluting cathode electrode exhibiting an effective surface area in the range of 0.1 to 4.0 mm 2 , preferably 0.6 to 3.0 mm 2 , provides low stimulation thresholds in the range of 0.5 volts, 0.5 milliseconds, very high pacing impedance (800 to 2,000 Ω), relatively low polarization, good to excellent sensing, and adequately low source impedance. The high pacing impedance prolongs the longevity of pacing pulse generators and allows for the miniaturization of their components. The low thresholds allow large safety factors at low applied voltages, which also contribute to increased battery longevity.

Clinical application of an active electrode using an operational amplifier

Abstract: An active electrode (d10 mm, t6 mm) that functions as an impedance transformer (with an input impedance >10 G Omega and an output impedance >

An enhanced fully differential folded-cascode op amp

Abstract: An enhanced fully differential folded-cascode operational-amplifier topology that achieves improved DC gain and common-mode rejection without sacrificing slew rate is presented. The large-signal operation of the new topology is completely symmetric, providing equal positive and negative slew-rate behavior by making use of current mirrors rather than current sources as normally found in full differential folded-cascode op-amps. An additional advantage of the enhanced topology is that its common-mode output impedance is a factor of g/sub m/r/sub o/ (typically 1-2 orders of magnitude) lower than the differential-mode output impedance, significantly improving the common-mode rejection ratio. The predicted performance is verified by simulations and preliminary experimental results. >

HDI impedance matched microwave circuit assembly

Abstract: Active components of a microwave system are interconnected on a substrate by a dielectric-overlay, high-density-interconnect structure in a manner which provides close impedance matching, minimizes impedance discontinuities and substantially increases the yield of good circuits.

Temperature compensated cmos voltage to current converter

Abstract: A voltage to current converter circuit is provided which outputs a constant current independent of temperature. The temperature coefficient of a first onchip impedance network is canceled by a threshold voltage of a transistor which has a temperature coefficient that tracks the temperature coefficient of the first impedance network. The magnitude of the output current is adjustable using the first impedance network, and does not affect the temperature coefficient. A second impedance network effectively zeros out the temperature coefficient of the circuit by adjusting an input reference voltage assumed to be constant. Furthermore, the present invention uses no bipolar transistors or diodes.

Electrochemical measurement system having interference reduction circuit

Abstract: A system for electrically measuring certain chemical characteristics of electrically-conductive fluids, such as blood, located within a tube and subject to electrical current interference. The measurements are made by measuring the voltage potential between a reference electrode and a sensor electrode sensitive to a particular blood parameter such as pH or calcium, potassium or chloride concentration. A bypass path for the electrical current interference is provided by a pair of noise-reduction electrodes located on opposite sides of the reference and sensor electrodes and interconnected by an amplifier having a relatively low output impedance and a relatively high input impedance. The electrical current interference bypasses the signal electrodes by flowing directly into the amplifier's output terminal, such that the reference and sensor electrodes develop a potential between them that is independent of the electrical current interference.

Twin-MOSFET structure for suppression of kink and parasitic bipolar effects in SOI MOSFETs at room and liquid helium temperatures

Abstract: A twin-MOSFET structure is proposed for suppression of the kink and parasitic bipolar effects in SOI MOS transistors. It is also an attractive candidate to provide satisfactory linear device operation at liquid He temperature. The device consists of two transistors in series with a common gate but it operates as a single transistor. Kink effect can be confined to the one “slave” transistor while the other “master” transistor can be kept free from the kink effect. If the gate length of the master transistor is larger than that of the slave one, the kink-free master transistor dominates the overall output characteristics of the device. As a consequence, the kink effect is suppressed in the overall output characteristics of the device. Furthermore, the parasitic bipolar effect in SOI MOSFETs is also significantly reduced and the saturation drain output impedance as well as the output breakdown characteristics are drastically improved. Kink-free and very flat output characteristics are obtained at both room and liquid He (4.2 K) temperatures.

Dynamic bias amplifier

Abstract: The bias level of an amplifier is controlled by an active bias circuit. The active bias circuit establishes a predetermined amplifier bias level (such as class A mode) as a function of input signal level and load impedance. The load impedance value may be manually entered or determined automatically by a disclosed impedance measuring system. Power supply circuitry is responsive to the value of load impedance to vary the bias voltage applied to the amplifier's output devices.

A physical interpretation of Schwan's limit current of linearity.

Abstract: In this the second of a series of papers on the nonlinearity of the electrode-electrolyte interface impedance, the wealth of experimental observations which exists in the literature on AC impedance nonlinearity is physically interpreted. The interface impedance is well represented by the parallel combination of a constant phase angle impedance and a charge transfer resistance. The charge transfer resistance is the major source of the observed nonlinearities. As a result, the current limit of linearity, i L , increases with frequency such that i L is proportional to ωβ. The series resistance, R s , of the interface impedance initially increases with applied signal amplitude, reaches a maximum and then decreases. The series reactance, X s , decreases monotonically with signal amplitude.

Subscriber line interface circuit for controlling AC and DC output impedance

Abstract: A subscriber line interface circuit (SLIC) (10) sets AC and DC output impedances as seen by first (14) and second (12) transmission signals. The common mode variation and differential variation of the first and second transmission signals is AC-sensed to provide a common mode feedback signal (56,80) and a differential feedback signal which in turn controls the AC output impedance. The DC component of the first and second transmission signals is blocked allowing (24,30) downstream amplifiers to operate at reduced power supply potentials. The DC variation of the first and second transmission signals is also sensed (110,142) for providing a DC feedback signal to control the DC output impedance.

CMOS driver circuit having reduced switching noise

Abstract: In a driver circuit, high- and low-impedance drive means (26 and 28 respectively) operate in parallel to effect a desired output transition. Adaptive control means 32 respond to a threshold value of the output signal (VO) and turn off the low-impedance drive means in the course of the output transition. The low initial output impedance of the driver circuit effects rapid charging of a line capacitance CL, while toward the end of the output transition the higher output impedance of the driver circuit more closely matches the input impedance ZL of a load circuit. This higher impedance dampens ringing and thereby reduces induced supply line noise which is conventionally associated with high-speed driver circuits.

Method and apparatus for echo cancellation of a multicarrier signal

Abstract: When the transmitter and receiver of a duplex multicarrier modem are connected to a two-wire line, echoes of the transmitted signal are reflected back into the receiver by mismatches between the output impedance of the modem and the input impedance of the line. These echoes are cancelled by an echo emulator which operates on samples of the transmitted signal. The parameters of the emulator are adapted by correlating, in the frequency domain, the transmitted data with the received signal. A specialiyed phase-locked loop, which uses a unique phase detector, tracks both frequency offset and phase of the far echo seperately from the adaptation of the emulator parameters. Initial training of the canceller is performed with a simple cyclic training signal that allows the use of efficient fast transforms.

A broadband system for multifrequency static imaging in electrical impedance tomography

Abstract: A widely accepted method for static imaging in electrical impedance tomography (EIT) is to measure at two frequencies. The choice of measurement frequencies is application-dependent because some different tissues cannot be distinguished when using two fixed frequencies. We have developed a system that generates signals from 8-10(3) kHz and applies two of these signals simultaneously to the body through a broadband current mirror. Great care has been taken in the design of the current injection multiplexer in order to keep the current source output capacitance as low as possible. Furthermore design of the layout of the patient interface board, in order to reduce feedthrough capacitances, also needs great care. Other parameters for driving and detection sections have been designed according to our results from FEM and circuit simulations including skin and electrode effects. Simulations using FEM with available tissue impedance data and preliminary measurements in a discrete phantom show that static imaging is possible for both the real and imaginary parts of the impedance.

Fully automated on-wafer noise characterization of GaAs MESFETs and HEMTs

Abstract: A technique is described that permits the rapid determination of all four noise parameters of a MESFET or HEMT at wafer level. The fully automated procedure, which has been implemented in the 2-8 GHz range, uses 16 accurately measured, very repeatable source impedance standards. The standards have been selected for optimum coverage of the input impedance plane to result in stable and rapidly convergent least-squares solutions for the minimum noise figure, optimum source impedance, and noise resistance of practical devices. The resultant system is very stable and produces accurate noise parameters for a wide range of devices. >

Impedance meter capable of performing measurements at high precision over wide impedance and frequency ranges

Abstract: A system for measuring a broad range of impedance values with high precision and over a broad frequency band. Both the broadrange impedance measurement capability of the V-I method and the broadband frequency measuring capability of the reflection coefficient method are provided. A remote measurement capability is also available. Based upon the V-I method, a selection is made between a circuit to achieve an ideal open and a circuit to achieve an ideal short circuit in response to the impedance values. A boundary for selecting the impedance is, for instance, 50Ω. To measure a high impedance, the ideal open type circuit is selected; to measure a low impedance, the ideal short circuit is selected. The source and measuring instruments are extended by a coaxial cable. A floating measuring instrument is obtained by using a balun. Impedance measurements for 1 MHz to 2 GHz are possible.

Input filter design criteria for switching regulators using current-mode programming

Abstract: Design criteria are developed for a constant-frequency current-programmed switching DC-to-DC converter with an input filter to ensure stability and prevent performance degradation. The criteria are given in terms of the filter voltage transfer function H/sub S/, output admittance Y/sub s/, and the y-parameter model of the switching converter. The criteria are listed as four inequalities and illustrated graphically. The criteria may be summarized as follows: assuming a converter that satisfies its loop gain T, line-to-output transfer function A/sub gf/, and output impedance Z/sub of/ requirement is given, an input filter with H/sub s/ and Y/sub s/ can be used to attenuate the noise emissions from the converter without adversely affecting the converter if H/sub s/ >

Bias circuitry for content addressable memory cells of a floating gate nonvolatile memory

Abstract: A low power bias voltage generation circuitry for content addressable memory cells for a nonvolatile memory is described. The bias circuitry is comprised of a source follower pair and two cascaded high impedance voltage dividers. The source follower pair acts as a positive feedback loop coupling between the two high impedance voltage dividers for relatively quickly charging and settling the output node to a predetermined voltage level. The first high impedance voltage divider can relatively quickly provide an input signal to trigger the small-input-load second high impedance voltage divider. The second high impedance voltage divider comprised of two high impedance diode stacks allows most current drawing from the power supply to drive a relatively large output loading during switching. Both first and second high impedance voltage dividers help keep the DC current of the circuit to a relatively low level which helps to reduce the total power consumption of the circuit.

Boundary scan cell for bi-directional input/output terminals

Abstract: A boundary scan cell is disclosed. Bi-directional input/output terminals are connected to bi-directional input/output terminals of a logic circuit subject to test in order to store test data or a test result in a first latch circuit, the output impedance of which changes depending on whether or not the bi-directional input/output terminals are in an input mode or in an output mode. As a result, holding of data is carried out by a static operation, and potential does not change with the lapse of time. Accordingly, there is no restriction on time in the operation for storing data, and erroneous operation is avoided.

Error analysis for the four‐load method used to measure the source impedance in ducts

Abstract: The impedance of a sound source can be measured using direct approaches such as the standing wave and transfer function methods or indirect approaches such as two‐load, three‐load, and four‐load methods Unlike the direct and two‐load methods, the three‐load and four‐load methods do not require the measurement of a complex quantity such as the acoustic transfer function Therefore, a single‐channel signal analyzer can be used to measure the autospectra needed in the case of the three‐load and four‐load methods The formulation for the source impedance gives two and three second‐order, nonlinear algebraic equations for the three‐load and four‐load methods The unknowns in these equations are the real and imaginary parts of the source impedance The two nonlinear equations in the three‐load method can be solved graphically for each frequency of interest or by using well‐known mathematical methods However, in the four‐load method, there are three nonlinear equations in terms of two unknowns which means one of the equations is redundant The three nonlinear equations could also be reduced to two linear equations and the two equations could be solved for the real and imaginary parts of the source impedance The accuracy of the solutions depends on how accurately the original (nonlinear) equations are satisfied when the real and imaginary parts are substituted into these equations An error analysis of the formulation in the four‐load method of source impedance measurement was done It was found that the error due to apparent reduction of the nonlinear equations to linear equations was very large The source impedance values computed using the four‐load method were compared with those obtained from the direct (transfer function) method Although the formulation of the four‐load method satisfies the mathematical procedure, the error due to computation could be large, and further work is needed in the application of the three‐load and the four‐load methods

Inverter ballast circuit featuring current regulation over wide lamp load range

Abstract: A ballast circuit for driving fluorescent lamps characterized by a minimum of components has a power transformer constructed to present a source impedance integrated with the transformer and in series with the lamp load sufficient to regulate the load current to within 10% for a selected maximum wattage fluorescent lamp load, such as 18 or 36 watt, and any lesser fluorescent lamp loads. The transformer has a high voltage secondary winding with a reflected impedance at least 6.0 times greater than the reflected impedance of the selected worst case fluorescent lamp wattage load. The integrated magnetics design of this ballast also provides passive short circuit protection, filament current reduction after lamp strike, and cold temperature start-up with a minimum of circuit components.

Source impedance and current-control loop interaction in high-frequency power-factor correctors

Abstract: The authors introduce a model for the input port of the high-frequency power-factor corrector and determine the gain of the current control loop. Both the model and the expression for the loop gain are entirely general and can be used for analyzing the source impedance and current control loop interaction of virtually any corrector with any current control method, operating in continuous or discontinuous inductor current mode, and having any source impedance. Based on the model, the electromagnetic interference filter capacitor and the current-error amplifier can be designed to avoid instability of the current-control loop. The loop gain of a boost corrector with average current control was investigated in detail. The system was found to be unstable at low line voltage and at source inductance values frequently encountered in practical applications. A physical explanation for the instability is given together with recommendations on how to avoid the instability. Test data taken from an experimental boost corrector with average current control are in good agreement with theoretical predictions of the model. >

Series impedance of GaAs planar Schottky diodes operated to 500 GHz

Abstract: The author discusses the impact of ohmic contacts on the series impedance of a GaAs cylindrical planar Schottky diode. The expression for the high-frequency impedance of an annular ohmic contact is developed using a novel transmission line model. This formulation is used to ascertain the contribution of the ohmic contact impedance to the overall device series impedance at both DC and 500 GHz. Diode impedance characterization indicates that the ohmic contact impedance makes a small contribution to the series impedance in comparison to that of the other components, both at DC and submillimeter wavelengths. Hence, the dimensions of the contact pads can be scaled down significantly without any appreciable increase in series impedance but with a decrease in the parasitic pad-to-pad capacitance. Finally, this modeling establishes theoretical guidelines regarding the allowable limits for specific contact resistance in small geometry diodes, so that the device I-V characteristics are not significantly altered as a result of the ohmic contact impedance. >

Novel current-mode all-pass phase shifter using a current conveyor

Abstract: Using a single second-generation current conveyor (CC II), a current-mode second-order all-pass phase shifter network is proposed. The novelties of the network are the availability of high output impedance, the use of grounded capacitors, and the insensitivity of phase shift relative to the CC II device nonideality. >

Low-power consumption system configuration for non-contact ic card communication

Abstract: 5n7 A low-power consumption system configuration for non-contact IC card communication is provided in which a 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 (6) has a low output impedance. A current detecting circuit including a detecting coil (9) magnetically coupled with a transceiver coil (7) of the reader/writer through a magnetic coupling element (8) and a resistor (19) detects a current which flows through the transceiver coil (7). A voltage drop at the current detecting circuit 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 (2), a MOS switch (16) in the IC card is turned on and off in accordance with the data and a load of the driver (6) is correspondingly changed. However, the driver (6) drives the transceiver coil (7) in a constant voltage fashion so that a voltage applied to the transceiver coil (7) is kept approximately constant even if a current flowing through the transceiver coil (7) changes due to the change in load. Accordingly, input voltages of a rectifying/smoothing circuit (12) and a regulator (13) in the IC card become approximately constant. As a result, the amplitude of a high frequency output voltage of the driver (6) can be made small.

Power supply with improved circuit for harmonic paralleling

Abstract: A UPS device adapted for parallel connection to a load along with one or more other UPS devices, having circuitry for sharing of the load, including load harmonics. A feedback network has an error signal circuit which generates an error signal representative of the difference between the actual current provided by the device and the designated share of current it should provide. The error signal is transformed by a value representative of the effective output impedance of the UPS inverter, whereby the inverter is controlled to share the fundamental of the load current as well as the harmonics.

Derivation of common impedance coupling from the transmission-line equations

Abstract: Impedance of the return path common to two circuits can produce a component of crosstalk that is referred to as common impedance coupling. The current of one circuit flowing in this impedance induces a contribution to the crosstalk voltages in the other circuit. This is usually derived on intuitive grounds. The incorporation of the return conductor impedance into the transmission-line equations provides a solution obtained by the author that does not rely on intuition. >

Impedance matching and bias feed network

Abstract: An impedance matching and bias feed network for interfacing to a low noise amplifier of a receiver section of an electrically steered phased array antenna. The impedance matching and bias feed network includes an inductor and capacitor network for impedance transformation while providing in shunt with a 50 ohm input side of the network a gate bias path via the inductor to the low noise amplifier thereby substantially reducing the receiver noise figure.

Reference current loop

Abstract: Reference current loop comprising a group of identical ICs (1, 2, 3), comprising each a first impedance (7) connected in series to the first impedance of another IC of the group. The combination of first impedances is connected to a reference current source (4). The voltage across the first impedance (7) is convened to a current (I0) by a voltage-to-current converter (8) and made available as a current (I1, I2) proportional to the reference current (Iref) of the reference current source (4) by a current mirror circuit (20, 23). The relation between the currents I1 and I2 and the reference current Iref is determined by the ratio of the impedance value of the first impedance (7) to that of the second impedance (19). This ratio is the same for all the ICs, so that the currents I1 and I2 in all the ICs are mutually equal.