Load Impedance Variations Research Articles

Multipath Characterization of Indoor Power-Line Networks

The time- and frequency-varying behavior of an indoor power-line network is the result of variable impedance loads connected to its termination points. In fact, any signal transmitted through such a communications network is subject to time-varying multipath fading. In this paper, an analytical calculation method is presented, which can be used to determine the multipath components of any point-to-point channel in the indoor power-line environment. The method calculates all transmission characteristics of the network and, therefore, it can be exploited in the process of designing proper transmission algorithms for optimizing system performance. The proposed method is applied to an example network to demonstrate its usefulness in explaining the network's time-dependent behavior and in estimating channel parameters, such as subchannel bandwidth, multipath delay spread, fading conditions, etc.

A discrete multitone transceiver at the heart of the PHY layer of an in-home power line communication local area network

A networked home is a micro-version of the Internet, connecting home appliances, PCs, and other smart devices not only to one another but also to a globally connected world through the Internet. For consumers to embrace home networking, a solution that utilizes the existing infrastructure within the home, such as electrical wiring, is significant. However, the use of power lines as a home networking platform presents quite a troublesome and noisy environment that fluctuates with varying load impedance and time, and is also plagued by impulse noise. The latest developments in VLSI and DSP technologies have enabled power line communication (PLC) networks to compensate for the impairments of the environment. This article discusses the use of discrete multitone technology at the PHY layer of an in-home PLC network, particularly with reference to bit-loading techniques.

A differential 160-MHz self-terminating adaptive CMOS line driver

A wide-band differential line driver is presented for transformer-coupled cables integrated in standard 0.35-/spl mu/m CMOS. It achieves 160-MHz bandwidth and no loss in implementing the cable termination. While operating from a 3.3-V supply, the driver dissipates 155 mW and exhibits a -47.5-dB THD for a 2-V/sub pp/ signal across a 75-/spl Omega/ load. Automatically tuned termination and a voltage gain independent of process and load impedance variation are provided by the architecture.

Power reduction techniques for a 1-Mb ECL-CMOS SRAM with an access time of 550 ps and an operating frequency of 900 MHz

This paper describes power reduction circuit techniques in an ultra-high-speed emitter-coupled logic (ECL)-CMOS SRAM. Introduction of a 0.25-/spl mu/m MOS transistor allows a Y decoder and a bit-line driver to be composed of CMOS circuits, resulting in a power reduction of 34%. Moreover, a variable-impedance load has been proposed to reduce cycle time. A 1-Mb ECL-CMOS SRAM was developed by using these circuit techniques and 0.2-/spl mu/m BiCMOS technology. The fabricated SRAM has an ultrafast access time of 550 ps and a high operating frequency of 900 MHz with a power dissipation of 43 W.

A comparison of modified Howland circuits as current generators with current mirror type circuits

Multi-frequency electrical impedance tomography (EIT) systems require stable voltage controlled current generators that will work over a wide frequency range and with a large variation in load impedance. In this paper we compare the performance of two commonly used designs: the first is a modified Howland circuit whilst the second is based on a current mirror. The output current and the output impedance of both circuits were determined through PSPICE simulation and through measurement. Both circuits were stable over the frequency ranges 1 kHz to 1 MHz. The maximum variation of output current with frequency for the modified Howland circuit was 2.0% and for the circuit based on a current mirror 1.6%. The output impedance for both circuits was greater than 100 k for frequencies up to 100 kHz. However, neither circuit achieved this output impedance at 1 MHz. Comparing the results from the two circuits suggests that there is little to choose between them in terms of a practical implementation.

The effects of variability in ear canal geometry and middle ear impedance on noise exposure level

If a group of industrial workers is uniformly exposed to a particular noise level, each person develops a different amount of hearing loss. The reasons for individual differences in susceptibility to noise are not entirely clear, but might relate, in part, to variability in ear canal acoustics and middle ear impedance. This variability alters the sound field to eardrum SPL transformation, effectively changing the magnitude of the exposure, and potentially producing differences in hearing loss. To study these effects, a computer simulation was created from an electrical analog model of the middle ear and a network representation of the ear canal. The model predicts how variation in ear canal geometry (length and diameter) and middle ear load impedance influences the eardrum SPL, both for individuals wearing hearing protector devices (‘‘leaky’’ earplugs) and for the unprotected ear. The model also estimates the amount of attenuation offered by the earplug and the amount of conductive hearing loss created by changes in the middle ear. Therefore, it was possible to evaluate whether changes in exposure levels would likely result in hearing loss, given the amount of protection offered by either earplug attenuation or conductive hearing loss.

A novel AC current source for capacitance-based displacement measurements

A 100 kHz bandwidth AC current source suitable to be used with capacitive sensors in displacement measurement applications has been designed and constructed. The high output impedance of the source is obtained by sensing the load voltage with a buffer stage having very low input capacitance. The sensing-buffer power supply, its shield, and the input shielding connections are driven at the buffer input potential in such a way that the effect of all input parasitic admittances, including the buffer common-mode impedance, are almost suppressed. The load impedance variations, which are directly proportional to displacements, are monitored by the output voltage of the sensing buffer. Measurements made at different frequencies with calibrated capacitance loads ranging from (1 to 20) pF have shown that the load-impedance values are proportional to the output voltage of the sensing buffer with a linearity better than 4/spl times/10/sup -4/ and resolution of about 3/spl times/10/sup -5/ over a 1 kHz bandwidth of load variation signal. The features of the current source and its performance in a displacement measurement application are described.

Experimental comparison of load-pull measurement systems for nonlinear power transistor characterization

Load-pull measurements are essential to accurately characterize power devices. This paper presents a comparison of measurement systems based on a load-pull configuration. The experimental results performed on a power MESFET transistor (1 W) are compared in terms of output power level and power added efficiency under variable operating conditions, i.e., load impedances and input power levels.

A Digital Current Controller for a PWM Inverter using a Neural Network.

Performance of a digital current controller for a PWM inverter is degraded by changes of load impedances and delay necessary for calculation of the controller.This paper presents a digital current controller for a PWM inverter using a neural network. The current controller automatically tunes its gains to the optimal ones for varying load impedances and compensates the calculation delay. Stability condition for the learning rate of the neural network is analyzed. The feasibility of the new controller is verified by simulations and experiments. Stable region of the current controller with deviations of the load impedances is obtained by simulations.

Transmission characteristics of a power line used for data communications at high frequencies

The transmission characteristics of an installed power line used for data communication, and of a model of this actual line, were measured over the frequency range of 10 kHz-50 MHz. It was found that impedance characteristics were not greatly influenced by the working loads at high frequencies, but changed drastically at lower frequencies. For frequencies of less than 100 MHz, the transmission loss did not increase significantly with frequency. The effect of the length of the connections and variation in load impedance were both studied. It was found that for frequencies above 100 MHz, attenuation loss in the power line is divided into losses due to attenuation constant of the line and the loss occurring at wire connections located between the various wires in the wall sockets. The latter loss is proportional to the number of connections. When the transmission loss was measured by opening and closing the wire connections, the fluctuation in the loss was found to be smaller at frequencies above 1 MHz than at lower ones. The transmission loss at the higher frequency shows only fairly slight fluctuations to variations in working load on the power line. The intensity of the noise power spectrum shows a decrease of -40 B/decade. This degradation rate in the noise spectrum is greater than the rate of increase in transmission loss. The increasing transmission loss can be sufficiently compensated by amplification at the receiving end, but it is possible to keep the amplified noise below the level of disturbance.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Computer control of a Class-E amplifier

High frequency electrical power supplies used in many industrial applications have to be able to withstand appreciable variations in load impedance. This paper describes the use of a computer to control a Class-E amplifier power supply which is being developed for high frequency induction and dielectric heating applications.

Optimised class-E amplifier with load variation

High-frequency electrical power supplies used in many industrial applications have to be able to withstand appreciable variations in load impedance. The letter describes the use of a computer to control a class-E amplifier power supply which is being developed for high-frequency induction and dielectric heating applications.

A 256K CMOS SRAM with variable impedance data-line loads

A 256K (32K/spl times/8) CMOS SRAM utilizing variable impedance loads and a pulsed word-line (PWL) technique is described. In the WRITE cycle, the variable impedance loads of the data lines enter a high impedance state and reduce the operating power. During the READ cycle, the PWL technique is used to achieve high-speed operation and low power dissipation. The internal clocks generated by the address transition detectors activate word-line and sense amplifiers for READ operation and disable them after the data are sent to D/SUB out/ buffers. This PWL technique eliminates the precharge time of 20 ns, which corresponds to 30% of the access time. The RAM offers 45-ns address access time and 40-mW operating power in the WRITE cycle of 1 MHz.

Self-Consistent Klystron Simulations

A numerical analysis of large-signal klystron behavior based on general wave-particle interaction theory is presented. The computer code presented is tailored for the minimum amount of complexity needed in klystron simulation. The code includes self-consistent electron motion, space-charge fields, and intermediate and output fields. It also includes use of time periodicity to simplify the problem, accurate representation of the space-charge fields, accurate representation of the cavity standing-wave fields, and a sophisticated particle-pushing routine. In the paper, examples are given that show the effects of cavity detunings, of varying the magnetic field profile, of electron beam asymmetries from the gun, and of variations in external load impedance.

Recovery characteristic of exploding wire fuses in air and vacuum

The dielectric strength of exploded wire fuses during the vaporization and after recovery period and fuse resistivity are functions of time and depend on the medium surrounding the fuse channel. When fuses are used as opening switches in inductive storage systems, the above parameters determine the efficiency of power flow from the storage to the load. Specifically, design of experiments using loads with variable impedance, such as imploding plasma, requires detailed information on the fuse characteristics during the time when the load impedance is changing. To provide data that determine the interaction between fuses and variable impedance loads, inductive and recovery electric fields and fuse resistance in air and vacuum were studied. The results show that inductive field amplitude follows the dependence on time needed to vaporize the fuse in a manner similar to that established for fuses in other media. The characteristics of recovery rates of fuses in air and vacuum differ drastically due to the early onset of ionization in fuse channels in vacuum.

Microwave enzyme inactivation system: electronic control to reduce dose variability.

The use of microwave energy to inactivate enzymes by rapid heating permits measurement of heat stable metabolites with minimal postmortem artifact. Reproducible results, however, require that the energy applied (dose) and the exposure geometry be reproducible. The commercial systems that we have examined are limited in this regard. A method to achieve a reproducible dose by electronic control of the applied power and exposure time is described. The electronics are compatible with any 220 V, signal phase commercial microwave power source. Without electronic control, exposure time varies by 50 ms, due to random contacter closure time. Output power varies by 15%, due to tube aging and variations in line voltage, magnetron temperature, and load impedance during exposure. With the addition of electronic circuitry, the exposure time can be controlled within 3 ms, and the power within 2%. Timing is done by counting energy bursts from the triac controlled magnetron. Leveling is accomplished using a feedback loop to vary the magnetron magnet current to keep the output power constant. The use of these electronic controls makes microwave irradiation systems more reliable as a biochemical research tool.

Cycloconvertor amplifier allowing wide variation in load impedance

An improved cycloconvertor design is described, in which the output-voltage waveform is substantially independent of the load impedance. The variation of low-frequency voltage gain of the new ‘commutating cycloconvertor’ and of the conventional cycloconvertor are compared for a range of load phase angle.

Simple ultra-lowpass filter (diode brake)

A circuit is described that uses two point-contact diodes and a capacitor to remove frequency content down to 0.1 Hz or lower, while transferring d.c. signal levels at low impedance and without loss. To operate, the filter requires a moderately high load impedance and input-signal amplitude variations of at least 100mV.

Electromagnetic Interference Reduction Filters

This paper presents the theory and application of lumped-image parameter reactive filter networks, absorptive-type filter networks, and combined absorptive-reactive filter networks as conducted electromagnetic interference reduction circuits. A comparison of the passband characteristics by specific examples is given for filter configurations of the pi, T, absorptive, and absorptive-reactive type under implementation conditions of a fixed source impedance and a varying load impedance as encountered when filtering prime power sources feeding ac to dc converters. This paper illustrates the problem the design engineer faces when applying the usual data given in filter catalogs. The filter characteristics are presented for 50-ohm resistive source and load conditions because of MIL-STD-220A quality control testr equirements. A test configuration is recommended to determine the admittance transfer of a filter network, indicative of the networks performance characteristics under application conditions.

A Stabilized 100 A. Power Supply

A system is described for maintaining constant currents of up to 100 A. through highly inductive loads. The system stabilizes against changes in mains voltage and generator characteristics, reducing the short-period current variations to less than I part in 2000. Current changes due to load-impedance variations are reduced by a factor of approximately 20. The main interest in the system is the electromagnetic method of comparing the load current with a standard current.