Power Line Conducted Interference Measurement Differences Using U. S. and CISPR Line Impedance Stabilization Networks

Measurements of power line conducted interference are commonly made on commercial equipment throughout the world using line impedance stabilization network (LISN's) in accordance with industrial and governmental procedures. Procedures in the United States applying to the 0.15-30 MHz frequency range specify an LISN that presents a frequency-dependent RF impedance to the equipment under test (EUT) whereas other national practices specify as LISN having an invariant 150-ohm impedance. This paper explores the expected measurement differences resulting from use of the two LISN's for power line interference measurements. Calculated difference factors, which depend on the EUT power line RF-input impedance, are developed. The factors have utility in assessing expected conducted interference levels in one LISN measurement configuration, given the interference levels and impedance parameters of the other. Measurement differences, in addition to those introduced by the LISN, which are attributed to variations in specified field strength meter parameters (i. e., detector, bandwidth, mechanical time constants, etc.) are beyond the scope of this paper.     

Effects of Measurement Devices on Conducted Interference Levels

Measurements of power line conducted interference voltages are commonly made throughout the 150 kHz to 30 MHz frequency range on military, industrial, and consumer equipment using line impedance stabilization networks (LISN) and, more recently, current probe techniques. This paper presents some brief background information concerning power line conducted interference measurements and the results of a study to assess the effects of LISN and current probe measurement devices on the level of measured conducted interference. A model is defined which facilitates prediction of the effects. The model concept allows the procedures described in this paper to be extended to equipment of other impedance definitions. A comparison of the calculated and empirical differences is made and suggests an analytical approach in sizing the effects upon the conducted interference levels.     

Measurement of conducted electromagnetic emissions in PWM motordrive systems without the need for an LISN

This paper presents a technique for measuring the conducted electromagnetic emissions produced by pulse-width modulated (PWM) inverter induction motor drive systems. The method does not require an artificial line-impedance stabilizing network (LISN) but does, however, allow the emission levels to be calculated as if an LISN were present. Testing can be performed when an LISN is either unavailable, prohibitively expensive, or impractical to include in the supply. This is often the case for large drive systems or for systems already installed in the field. A normal RF voltage probe and a spectrum analyzer are used to measure the spectra of the common-mode and differential-mode excitation sources due to the inverter switching. Line inductors for high-frequency (HF) isolation are required for some of the tests, but the cost and complexity of these compared to an LISN is low. Common-mode and differential-mode Thevenin equivalent circuits are then derived from measured impedances. The emissions for any defined supply impedance (including an LISN) can then be determined. A laboratory test on a 15 kW PWM drive system is carried out to verify the accuracy and effectiveness of the proposed method     

A Low Frequency Current Probe System for Making Conducted Noise Power Measurements

A technique for accurately measuring conducted radio frequency interference has been developed at the U.S. Naval Civil Engineering Laboratory. The technique involves the use of two current probes simultaneously to determine the impedance levels of the lines or equipment under measurement. The noise currents of the lines or electrical equipment are measured directly using one of the two probes. Knowing the noise currents and the impedances through which it flows provides the necessary information for computing noise voltages and noise power. Further, it allows prediction of the noise power delivered by the measured device into any known impedance connection. The bandwidth covered by this technique is 20KC-30mc. This range is covered by two instruments, the first covers 20KC-2mc and the second 2mc-30mc. The high frequency instrument has been described before and will not be discussed here. The low frequency instrument is new and has several unique features. The main feature being a direct read out of both the impedance magnitude and the phase angle of the system being measured. This is accomplished by transistorized circuits which drive two front panel meters, one for impedance magnitude and one for phase angle and its polarity. By providing the phase information it is possible to specify the noise observed in terms of noise power. This technique removes the many ambiguities which are normally associated with conducted noise measurements using line impedance stabilization networks.     

A Low-Frequency Current Probe System for Making Conducted Noise Power Measurements

The two current probe technique of measuring conducted radio-frequency interference is a radical departure from conventional measurement techniques. The technique evolved from a dissatisfaction with present techniques, due to the lack of sufficient information obtained from measurements concerning the source of the interference. Normally, the wires concerned when testing for conducted interference are 60-Hz power lines of the two conductor type. If a pair of conductors comprising a power cord is considered as a transmission line, the factors which determine its performance at radio frequencies are primarily the wire length and loading. In practice, power lines do not have readily described configurations, which makes a transmission-line analysis extremely difficult. As a result, no attempt to analyze the situation is made at all. Usually, a line impedance stabilization network (LISN) is inserted into the line and the noise voltage developed is measured across a 50-ohm internal resistor which is effectively placed across the line. Thus, the only information obtained is a noise voltage which existed across a resistor at the time of measurement, but is nonexistent after the test. The noise voltage existing across the line after the LISN has been removed remains unknown. As a matter of fact, it cannot even be calculated, since the line characteristics are unknown. Thus insufficient information is the reason for pursuing the current probe techniques. The two current probe technique of measuring conducted interference overcomes the limitations of the LISN technique by supplying more information about the line.     

Time-Domain Characterization of RF Sources for the Design of Noise Suppression Filters

The filter development process, to reduce conducted emissions, is still a nonoptimized problem within the electromagnetic interference improvement of systems. Because the filter attenuation depends on the impedance values of the device under test, numerous attempts might be necessary to find an appropriate filter element. The presented method tries to characterize arbitrary active applications within the time domain for simulation and measurement setups. The evaluated noise sources are described as $Y$ or $Z$ matrices with additional active sources with respect to Thevenin's law. Using a transition from the time into the frequency domain, any circuitry with periodic and stable noise sources can be considered. The application of the method is demonstrated for an automotive buck converter in the frequency range up to 108 MHz. The characterization of the generated noise source model is verified by comparing calculated and measured noise voltages with different filter elements.      

Essential-coupling-path models for non-contact EMI in switching power converters using lumped circuit elements

This paper proposes a simple lumped circuit modeling approach for describing noncontact EMI coupling mechanisms in switching power converters. The resulting model assumes a minimum number of noise sources and contains essential coupling paths that allow easy physical interpretations. Essentially, all capacitive couplings are represented by an equivalent noise voltage source and six coupling impedances, whereas all inductive couplings are represented by an equivalent noise current source and three coupling impedances. The resulting coupled noise appears as currents flowing into the terminals of the line-impedance-stabilization-network (LISN). The equivalent voltage source can be conveniently approximated as the switching-node-to-zero voltage, which is typically a rectangular pulse of a few hundred volts. The equivalent current source can be modeled as the current flowing around a loop containing the equivalent voltage source and parasitics such as winding capacitance of the power transformer, the snubber capacitance and connection inductances. Also, the coupling impedances can be estimated by making simplifying assumptions about the geometry of the components and tracks, or by direct measurements. Simulations and experiments verify how inductive and capacitive couplings through each path may produce substantial EMI measured by the LISN. Being based on a lumped circuit approach, the proposed model is easy to apply in practice for understanding, diagnosing and approximating EMI behaviors.     

自动源调配器测量晶体管噪声参数的补偿计算

在微波噪声参数测量系统中,通过使用自动源调配器来改变源反射系数的方法,可以方便地求出各个参数。根据对所引入的自动源调配器的分析,总结出源调配器自身的额外噪声误差是可以忽略的,并在对自动源调配器与噪声源级联后组成的单端口网络进行误差分析后,做出了超噪比的补偿运算,这种误差修正方法在很大程度上减小了测量误差量级。使用该补偿方法可以在噪声参数测量时进行更大范围的源阻抗调配,并提高噪声测量的准确度。     

Technique for measurement of powerline impedances in the frequencyrange from 500 kHz to 500 MHz

A method for measuring power line impedances using two current probes is examined. This method is characterized by good isolation of the measurement equipment from the power line voltage and by the capability of measuring power line impedances between any pair of power-plug terminals. The use of this two-current probe method with the model described is effective in measuring power line impedances from 0.5 MHz to 100 MHz. Using purely resistive loads for calibration, the error is less than 5% for frequencies below 100 MHz, and less than 20% for frequencies between 100 MHz and 500 MHz. The error in an impedance measurement increases with the magnitude of the load impedance     

人工电源网络阻抗高频特性及其校准精度研究

本文根据人工电源网络的原理图,建立了阻抗测量的高频寄生参数模型,并分析了适配器寄生参数以及各独立元件在电路中的作用。通过分析接地和金属板的两种基本串扰形式,建立人工电源网络相应的等效电路模型,运用MATLAB仿真软件仿真分析了两种模型下的寄生参数对阻抗的影响。仿真得到的随频率变化的曲线表明,寄生参数及其耦合关系对阻抗测量有重要影响。     

An accurate analysis of noise in rectangular bipolar transistors including current crowding

An accurate analysis of noise in rectangular bipolar transistors is developed from a distributed model using a collective approach and the transport noise theory. In this model, emitter current crowding effect are taken into account and noise behaviour at intermediate and low values of source impedance is precisely described. The structure of teh equivalent lumped circuit is established, and the analytical relationships characterizing its elements in an extended range of current and frequency are given. It is shown that; (a) the active base region must be represented by a nonlinear impedance with a generalized thermal noise source; (b) for low source impedances the equivalent input voltage shot noise generator is higher than predicted by low injection theories. Furthermore it is found that emitter crowding induces a uniform and important decrease in (a) base impedance (b) thermal noise and (c) the correlation between shot noise generators of the equivalent lumped circuit. Finally it appears that classical low injection theories are valid when crowding occurs in transistors biased with high source impedances.     

Rectangular spiral coil analysis for inductively coupled RFID systems based on Partial Element Equivalent Circuit method

In order to achieve maximum power efficiency with inductively coupled RFID tags, the impedances of the spiral coil and the integrated circuit must be matched to each other. In this paper, we present a numeric approximation of the impedance of a rectangular spiral coil by means of a coupled electromagnetic and circuit analysis called Partial Element Equivalent Circuit method and verify our simulation with measurement results. We include the effective permittivity in our 3D capacitance extraction method and fit the simulated impedance to a simple RLC equivalent circuit model which is also used by our measurement device and compare the resulting element values. Our Matlab-based simulator shows good agreement over the frequency band of interest and allows for optimization for various design goals.     

Impedance spectroscopy of human erythrocytes: system calibration,and nonlinear modeling

The authors present an impedance measurement method, the cell embedding technique, for human erythrocytes, and an accurate calibration procedure for a four-electrode impedance measurement system that gives reliable results over a wide frequency range-1 Hz to 10 MHz. To achieve high sensitivity, the cells are embedded in the pores of a Nuclepore filter. The calibration procedure assumes that the measurement system is linear and require measurement of three reference impedances. The reliability of the procedure is demonstrated with various RC circuits. Its application to the bio-impedance measurement system eliminates a quasi-dispersion in the high-frequency range and increases the bandwidth at both the low- and high-frequency ends of the range by about a decade. The experimental data are fitted to, an equivalent circuit model of the impedance of the embedded cells. The impedance spectra display constant-phase-angle (CPA) characteristics, which are used to describe the AC response of the interface between the cell surface, and the external electrolyte solution. Such a CPA element may be related to fractal character of the interface     

Improved Microwave Noise Measurements Using Ferrites

The ferrite isolator and the ferrite circulator have been applied separately to improve the accuracy of measuring small microwave noise powers or small power differences. Either the isolator or the circulator effectively isolated the input circuit of a microwave receiver from the impedance of the source. As a result, the measurement errors introduced by mismatched source impedances were reduced by as much as 98 per cent. The added input circuit losses of the ferrite components reduced the receiver sensitivity by only about 10 per cent. Since the accuracy of measuring small noise power differences was limited principally by impedance errors, the addition of ferrite isolation to the receiver input circuit increased the sensitivity of measurement to near the theoretical limit. The ferrite isolator was used as a passive transmission element in these experiments. The ferrite circulator, however, was used as an electrically-operated, microwave switch. This switch was used to replace the mechanical chopper in a Dicke-type radiometer. In addition to impedance isolation, the ferrite switch makes possible rapid comparison measurements of the microwave noise powers from any two sources, or of the noise powers from the same source in two different polarizations.     

抑制PCB对直流电源噪声干扰的滤波器设计

采用电路测量的方法设计一款通用滤波器,用来抑制数字电路板给直流供电电源带来的噪声干扰。介绍了双探针测量技术,使用双探针法测量出直流供电电源和印制电路板在实际加电工作中的阻抗,用测量出的阻抗信息,选择出合理的滤波器拓扑结构,并通过计算确定元器件值,而并不需要反复做实验和付出额外的代价。通过实际进行的测试,验证了这种滤波器的有效性和可行性。     

Reducing the mutual coupling effect in adaptive nulling using are-defined mutual impedance

The effect of mutual coupling in an adaptive antenna array for the nulling of interferences is investigated. The concept of mutual impedance is re-defined to take into account of the scattering effect due to the other antenna elements in the array. The re-defined mutual impedances are used to reduce the mutual coupling effect by calculating the open-circuit voltages from the measured voltages on the antenna terminals. Results show that by using the re-defined mutual impedances, substantial improvements in term of the depths and the accuracy of the nulls can be obtained over a previous method     

Performance of a two-junction array SIS-mixer operating around 345GHz

The authors have made a detailed study of the gain and noise of a SIS (superconductor-insulator-superconductor) heterodyne receiver at 345 GHz. An array of two Nb-Al₂O₃-Nb SIS junctions in series are used as the mixing element. The array is operated in a waveguide mount with a backshort and an E-plane tuner. The best receiver noise temperature achieved is 140 K DSB (double sideband). The embedding impedances were determined by fitting theory to the measured pumped curves. High-quality fits were obtained, providing the first detailed test of the Tucker-theory at frequencies above 300 GHz. The impedances found by this method are in very good agreement with impedances measured in a scale model at 3.3 GHz. From these embedding impedances, the gain and noise of the mixer were calculated over a full bias range using the Tucker theory in the three-port low-IF approximation. The measured dependence of mixer gain and noise on bias voltage, pump power and embedding impedance is in good agreement with theory. However the absolute values show discrepancies that appear to be independent of the bias parameters of the mixer     

A Circuit for Contact Monitoring in Electrocardiography

A circuit for contact impedance monitoring in ECG is presented. An ac current in the same frequency band as the ECG signal is used for the measurement. This makes the measurement independent of polarization potentials and gives the correct weight to the impedances in the skin-to-electrode junction. The measurement of the contact impedance is made continuously during ECG monitoring and causes no interference in the ECG signal.     

Some RF Characteristics of Bonding Systems

The measurement of bonding impedance has been typically limited to dc or to relatively low (<20 MHz) frequencies. However, the impedance characteristics of the bonding system should not be simply ignored at higher frequencies. To do so may be neglecting a serious source of electromagnetic interference. This paper presents techniques for the measurement and interpretation of bonding impedance characteristics through the VHF region. A measuring device based on the insertion loss technique is described. Calibration curves of typical models of this device show its usefulness for measurements up to 400 MHz. The application of this device to the measurement of bonding systems in field installations is also explored. From data obtained with the insertion loss device, an equivalent circuit of a typical bonding system is developed which incorporates the contributions of the equipment case as well as those contributions of the bonding straps to the overall impedance characteristics. It is shown that typical bonding systems exhibit regions of parallel resonance which are often at relatively low frequencies. Within these regions, the impedance of the bonding path is often very high. Because of this high impedance, the equipment case can act as a very effective antenna. Evidence is presented to show that the case voltages induced by a radiated field in the resonant frequency region may increase as much as 25 dB for a bonded system over a system that is not bonded.