Daryl G. Beetner

Prediction of Radiated Emissions Using Near-Field Measurements

A procedure is developed to predict electromagnetic interference from electronic products using near-field scan data. Measured near-field data are used to define equivalent electric and magnetic current sources characterizing the electromagnetic emissions from an electronic circuit. Reconciliation of the equivalent sources is performed to allow the sources to be accurately applied within full-wave numerical modeling tools like finite-difference time domain (FDTD). Results show that the radiated fields must typically be represented by both electric and magnetic current sources if scattering and multiple-reflections from nearby objects are to be taken into account. The accuracy of the approach is demonstrated by predicting the fields generated by a microstrip trace within and outside of a slotted enclosure, and by predicting the fields generated by the microstrip trace close to a long wire. Values predicted from near-field scan data match those from full-wave simulations or measurements within 6 dB.

A Practical Superheterodyne-Receiver Detector Using Stimulated Emissions

The accurate and timely discovery of radio receivers can assist in the detection of radio-controlled explosives. Superheterodyne receivers emit low-power radio signals during normal operation. These are known as unintended emissions. In this paper, the unintended emissions of superheterodyne receivers are analyzed. Such receivers are exposed to known stimulation signals, and their behavior is measured. Recorded emissions demonstrate that it is possible to inject arbitrary signals into a radios unintended emissions using a relatively weak stimulation signal. This effect is called stimulated emissions. A novel detection system that uses these stimulated emissions is proposed. The performance of this system is compared with passive-detection techniques using artificially generated emissions signals. The proposed system offers a 5- to 10-dB sensitivity improvement over existing techniques.

Statistical Prediction of “Reasonable Worst-Case” Crosstalk in Cable Bundles

Worst-case estimates of crosstalk in cable bundles are useful for flagging potential problems, but may also flag problems that only occur very rarely, due to the random variation of wire positions and other characteristics of the harness. Prediction of crosstalk that may realistically occur requires statistical methods. Monte Carlo simulation techniques are often used to account for statistical variation, but are time consuming and do not provide intuition toward the cause of, or solution to, problems. Here, we investigate prediction of the statistically ldquoreasonable worst-caserdquo crosstalk by forming probability distributions using inductance and capacitance parameters from a single harness cross section and using lumped-element approximations for crosstalk that account for strong coupling within the harness when the circuit is electrically small. The accuracy of this technique was evaluated through comparison to simulation results using the random displacement spline interpolation method for multiple random instantiations of several harness configurations. Tests were performed while varying the size of the bundle, its height above the return plane, the value of load impedances, and the presence of a return wire. The reasonable worst-case crosstalk was estimated within about 5 dB or less in each case.

Quantifying electric and magnetic field coupling from integrated circuits with TEM cell measurements

One of the most widely used methods for evaluating the electromagnetic compatibility of integrated circuits (ICs) involves mounting the IC on a printed circuit board embedded in the wall of a TEM cell. TEM cell measurements are influenced by both electric and magnetic field coupling from the IC and its package. This paper describes how a TEM cell and a hybrid can be used to isolate electric field coupling from magnetic field coupling. Knowledge of the dominant field coupling mechanism can be used to troubleshoot radiated emissions problems due to ICs.

A Nonlinear Microcontroller Power Distribution Network Model for the Characterization of Immunity to Electrical Fast Transients

A nonlinear power distribution network model for characterizing the immunity of integrated circuits (ICs) to electrical fast transients (EFTs) is proposed and validated. The model includes electrostatic discharge (ESD) protection diodes and passive impedances between power domains. Model parameters are based on external measurements using a vector network analyzer and curve tracer. Impedance is measured between pins while the IC is biased and operating, and is used to determine individual elements of the network model. Inclusion of active power-clamp circuitry is also explored. The model is able to successfully predict pin currents and voltages during EFTs on the power pin when the IC is operating or turned off and when the ESD power clamp is either activated or not activated. This model might be used to evaluate the immunity of the IC in a variety of systems and to better understand why failures occur within the IC and how to fix them.

Using TEM Cell Measurements to Estimate the Maximum Radiation From PCBs With Cables Due to Magnetic Field Coupling

Common-mode currents can be induced on cables attached to printed circuit boards (PCBs) due to electric and magnetic field coupling. This paper describes a technique for using transverse electromagnetic (TEM) cell measurements to obtain an effective common-mode voltage (or magnetic moment) that quantifies the ability of traces and integrated circuits on PCBs to drive common-mode currents onto cables due to magnetic field coupling. This equivalent common-mode voltage can be used to reduce the complexity of full-wave models that calculate the radiated emissions from a system containing the board. It can also be used without full-wave modeling to provide a relative indication of the likelihood that a particular board design will have unintentional radiated emissions problems due to magnetic field coupling.

Modeling of the immunity of ICs to EFTs

Investigation of the immunity of ICs to EFTs is increasingly important. In this paper, an accurate model of a microcontroller is developed and verified. This model consists of two parts: a passive Power Distribution Network (PDN) model and an active I/O protection network model. Measurement methods are designed to extract the parameters of the passive PDN model. The accuracy of the overall model of the IC is verified using both S parameter tests and EFT injection tests. The model is able to accurately predict the voltage and current at power-supply and I/O pins and correctly accounts for the active components of the I/O protection network.

Validation of Worst-Case and Statistical Models for an Automotive EMC Expert System

Previous papers have presented algorithms for an EMC expert system used to predict potential electromagnetic compatibility problems in a vehicle early in the design process. Here, the accuracy of inductive and capacitive coupling algorithms are verified through representative measurements of crosstalk within an automobile. Worst-case estimates used by the algorithms are compared to measured values and are compared to values estimated using statistical methods. The worst-case algorithms performed well up to 10-20 MHz, but overestimated measured results by several dB in some cases and up to 10-15 dB in others. An approximate statistical variation of the current expert system algorithms also worked well and can help avoid overestimation of problems; however, worst-case estimates better ensure that problems will not be missed, especially in the absence of complete system information.

Modelling electromagnetic field coupling from an ESD gun to an IC

IC designers require fast and accurate methods of simulating immunity of ICs to ESD events to adequately predict and analyze ESD issues. The common method of predicting electromagnetic field coupling from an ESD gun to an IC, however, requires substantial simulation time and does not typically account for the full IC layout. Here we propose an efficient methodology for calculating the electromagnetic field coupling from an ESD gun to an IC while fully considering the non-linear circuit elements in the IC core. Voltages and currents within the IC are found by merging full-wave simulations of an ESD gun with a SPICE model of the IC and the coupled electromagnetic energy. The capability of the proposed method was verified through experiments on a pseudo- integrated circuit structure. Results show the promise of the method. This hybrid modelling method can significantly accelerate simulation time compared with traditional full-wave modelling techniques and can allow the designer to better explore the variation in coupling that occurs with small changes in the test setup, such as the position and orientation of the gun and IC.

Predicting TEM cell measurements from near field scan data

A procedure is proposed for predicting TEM cell measurements from near field scans by modeling near-field scan data using equivalent sources. The first step in this procedure is to measure the tangential electric and magnetic fields over the circuit. Electric and magnetic fields are estimated from probe measurements by compensating for the characteristics of the probe. An equivalent magnetic and electric current model representing emissions is then generated from the compensated fields. These equivalent sources are used as an impressed source in an analytical formula or full wave simulation to predict measurements within the TEM cell. Experimental verification of the procedure using a microstrip trace and clock buffer show that values measured in the TEM cell and calculated from near field scan data agree within a few decibels from 1 MHz to 1 GHz.