Patent Publication Number: US-7222033-B1

Title: Electromagnetic emissions and susceptibility calculating method and apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of PPA Appl. No. 60/495,798, filed 2003 Aug. 18 by the present inventors. 

   FEDERALLY SPONSORED RESEARCH 
   Not Applicable 
   SEQUENCE LISTING OR PROGRAM 
   The Program associated with the instant disclosure has been submitted as .txt files on CD-R (in duplicate). Each CD-R is marked in indelible ink to identify the Applicants, Title, Application No., and Creation Date. The Program submitted on CD-R is hereby incorporated by reference as follows: 
   
     
       
         
             
             
             
             
           
             
                 
             
             
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               Biplanar.txt 
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               clsComplexMatrix.txt 
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               clsComplexNumberDoubles.txt 
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               CMInductor.txt 
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               CMInductors.txt 
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               ComplexNumCalcs.txt 
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               Coplanar.txt 
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               DMInductor.txt 
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               frmCableModuleResults.txt 
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               frmComponentLibrary.txt 
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               frmConfigurationSelector.txt 
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               frmDataTable.txt 
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               frmEMISoftware.txt 
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               IdealInvertingTransformer.txt 
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               Inductor.txt 
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               Materials.txt 
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               modApplications.txt 
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               modBranchImpedance.txt 
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               modCableCalculations.txt 
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               modFrequency.txt 
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               modMiniNEC4EMI.txt 
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               NonInvertingTransformer.txt 
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               oc_api.txt 
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               Resistor.txt 
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               Resistors.txt 
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               Schematic.txt 
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   BACKGROUND OF THE INVENTION 
   1. Field of Invention 
   The present invention relates to electromagnetic interference (EMI) prediction calculations for electric devices. 
   2. Prior Art 
   Regulatory agencies worldwide restrict radio frequency signals unintentionally conducted on power leads and interconnecting cable bundles by electric devices. Further, those agencies restrict electromagnetic field intensity unintentionally radiated by electric devices. Most regulatory agencies also require electric devices to withstand electromagnetically induced disturbances conducted on power lines and/or interconnecting cable bundles and incident upon the electric device as an electric or magnetic field. EMI requirements are regulated by numerous agencies from individual industries, countries, and combinations thereof. Requirements vary considerably across agencies and industries, but are applicable to nearly all electric, electrical, and electronic devices. 
   Compliance with EMI requirements is determined by testing the electric device. Testing is costly, as is redesign and retest if the device is found to be noncompliant. Analytical methods for predicting EMI performance are desirable but require knowledge in disparate intellectual disciplines heretofore not cost-effectively available to designers and manufacturers of electric devices. 
   Accordingly, it would be desirable to provide an apparatus that is capable of calculating electromagnetic emissions and susceptibility attributes of an electric device in four facets of EMI analysis: conducted emissions, conducted susceptibility, radiated emissions and radiated susceptibility. Such a device would overcome the limitations of the prior art which does not comprehensively address the subject of electromagnetic interference prediction. 
   It would further be desirable to provide an apparatus that allows for sources of electromagnetic interference, circuitry effect such as filtering and loading, interconnecting conductor configuration, conductor shielding, shield terminations, and a means for determining whether the device under analysis is predicted to comply with specified EMI requirements. 
   SUMMARY 
   The present invention is a method and apparatus for calculating electromagnetic emissions and susceptibility attributes of an electric device, comprising a simulation means for calculating conducted emissions, conducted susceptibility, radiated emissions, and radiated susceptibility. The method and apparatus comprise a means for simulating device active circuit signal attributes, a means for simulating device passive circuit electrical characteristics, a means for calculating device conductor electrical attributes, a means for calculating transfer impedance of device conductor shields, a means for calculating device conductor shield termination electrical attributes, and a means for comparing calculated attributes to prescribed values. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic diagram of the basic configuration of an electromagnetic emissions and susceptibility calculation system of the invention 
       FIG. 2  shows the basic procedure for an electromagnetic emissions and susceptibility calculation algorithm of the invention. 
       FIGS. 3 and 4  show the configuration of major components for the emissions analysis model and susceptibility analysis model, respectively, of the invention. 
       FIG. 5  is a flow chart for defining time domain sources. 
       FIG. 6  is a flow chart for defining frequency domain sources. 
       FIG. 7  is a flow chart for performing circuit synthesis. 
       FIG. 8  is a flow chart for selecting conductor configuration and defining conductor characteristics. 
       FIG. 9  is a flow chart for performing analyses applicable to selected application. 
       FIG. 10  is a flow chart for defining limits. 
       FIG. 11  is a flow chart for creating circuits using schematic capture CAD methods. 
       FIG. 12  is a flow chart for calculating circuit transfer functions. 
       FIG. 13  is a flow chart for calculating shield transfer impedance. 
       FIG. 14  is a flow chart for calculating shield termination transfer functions. 
       FIG. 15  is a flow chart for calculating conductor transfer functions. 
       FIG. 16  is a flow chart for performing conducted emissions calculations. 
       FIG. 17  is a flow chart for performing radiated emissions calculations. 
       FIG. 18  is a flow chart for performing conducted susceptibility calculations. 
       FIG. 19  is a flow chart for performing radiated susceptibility calculations. 
       FIG. 20  is a flow chart for calculating parasitic element values. 
   

   DETAILED DESCRIPTION—PREFERRED EMBODIMENT 
   An electromagnetic emissions and susceptibility calculating device of the present embodiment calculates conducted emissions, conducted susceptibility, radiated emissions, and radiated susceptibility of an electric device to be analyzed. 
   The method and apparatus of the present invention as described herein is capable of being applied in an array of contexts as provided below and allows for the following advantages:
         a. Provides a method and apparatus for predicting compliance with regulatory agency EMI requirements, thereby reducing the need for costly redesign and retest.   b. Integrates methods for emissions and susceptibility calculations for conduction and radiation effects into a unified analysis platform.   c. Provides comprehensive modeling of electric device circuits, wiring, and interference sources, including frequency domain sources, time domain waveforms, EMI filters, interconnecting conductor characteristics, circuit synthesis, including radio frequency circuit models, shield transfer impedance from shield construction details, shield termination impedance, conductor configurations (twisted pair, shielded, over ground plane, etc.), time domain and frequency domain limits for conducted and radiated emissions and susceptibility   d. Provides an integrated platform, wherein an electric device is analyzed to predict performance for all four facets of electromagnetic interference, and its function and response directly compared to EMI performance standards imposed by regulatory agencies. The four areas of analysis comprise:
           1. Conducted Emissions—Calculation of differential mode and common mode current and voltage conducted on power lines and interconnecting cable bundle leads.   2. Conducted Susceptibility—Calculation of induced effects of disturbances coupled to power lines and interconnecting cable bundles.   3. Radiated Emissions—Calculation of electromagnetic fields emitted by changes in current on device power leads and interconnecting conductors.   4. Radiated Susceptibility—Calculation of induced effects of electromagnetic fields impinging on device conductors. Facilitates prediction for present and future regulatory agency EMI requirements.   
           e. Displays graphically and numerically, electrical characteristics of circuits, conductors, shields, sources, and limits, induced current and voltage, and emitted radiation fields and conducted current and voltage.   f. Calculates and displays current and voltage in each circuit branch and calculates and displays current on interconnecting conductors.   g. Calculates and displays shield transfer impedance from shield construction details and material properties.   h. Calculates and displays shield termination impedance.   i. Calculates stray capacitance and inductance of circuit interconnects, such as printed wiring boards, connectors, and discrete wiring.       

   As shown in  FIG. 2 , the electromagnetic emissions and susceptibility calculating device  1  comprises a data library unit  10  for retrieving and saving configuration and calculation data, an analysis selector unit  20  for user analysis selection, a time domain source calculating unit  30  for defining voltage and current sources as time varying waveforms, a frequency domain source calculating unit  40  for defining voltage and current sources and electromagnetic field levels as a function of frequency, a circuit synthesis unit  50  for defining circuits, a conductor configuration unit  60  for defining physical configuration of conductors and shields between interconnected circuits, an application calculator unit  70  for performing conducted emissions, conducted susceptibility, radiated emissions, and radiated susceptibility calculations on an electric device defined by selected sources, circuits, and conductors, a limit unit  75  for defining limits for data comparison, and a display unit  80  for displaying calculated data. 
   The data device library unit reads data from and stores data to selected storage media. 
   The analysis selector unit allows the user to select the type of analysis to be performed on the electric device and to configure analysis model parameters. 
   The time domain source unit allows the user to define time-domain voltage and current waveforms, display time-domain waveforms, convert time-domain waveforms to frequency domain spectrum using the Fast Fourier Transform method, display frequency-domain spectra, store and retrieve waveform parameters, and store and retrieve waveform values. The time domain source unit  30  shown in  FIG. 5  comprises a waveform selection unit  300  for waveform selection, an input unit  310  for user data entry, a waveform synthesis unit  320  for calculating time-domain waveform values, a Fast Fourier Transform unit  330  for calculating frequency content of time-domain waveforms using Fast Fourier Transform method, a display unit  340  for graphing and tabulating waveform and frequency spectrum values, and a library unit  350  for storing and retrieving waveform parameters and calculated values. 
   The frequency domain source unit renders user-defined voltage, current, and electromagnetic field levels as a function of frequency. The frequency domain source unit allows the user to define spectral envelope, harmonic content, and frequency range, calculate amplitude over frequency, display amplitude values, and store and retrieve waypoints and calculated values. The frequency domain source unit  40  shown in  FIG. 6  comprises an input unit  400  for user data entry of spectral envelope, harmonic content, frequency range, a calculating unit  410  for calculating amplitude values between defined waypoints, a display unit  420  for graphing or tabulating amplitude values, and a library unit  430  for storing and retrieving amplitude parameters and calculated values. 
   The circuit synthesis unit allows the user to graphically define electric circuits, edit electric circuits, calculate circuit transfer functions, display circuit transfer functions, and save and retrieve circuit configuration and component values. The circuit synthesis unit  50  shown in  FIG. 7  comprises a schematic display unit  500  for displaying circuit schematic diagram, a schematic capture unit  510  that provides a graphical user interface for schematic diagram entry and editing, a transfer function calculating unit  520  for calculating circuit transfer functions, a transfer function display unit  530  for displaying circuit transfer functions, a library unit  540  for storing and retrieving circuit parameters and calculated transfer function values. 
   The schematic capture unit provides a graphic user interface that allows the user to create and edit schematic diagrams graphically. Circuit components are selected from a component library, assigned values, placed on the schematic diagram, and interconnected to other components. Components and their interconnections are translated into a circuit net list, from which circuit transfer function is calculated for subsequent display, storage, and retrieval. The schematic capture unit  510  shown in  FIG. 11  comprises an action selector  5100  which allows user to insert, append, modify, or delete components from the circuit, a component selector  5110  for selecting a component on the schematic diagram, a component library  5120  from which the user selects circuit components, an input unit  5130  for user data entry of component element values, a graphing unit  5140  for displaying component electrical characteristics, a component placement unit  5150  for user graphical placement of components, an interconnect unit  5160  for interconnecting circuit components, a mapping unit  5170  for tracking component placement and interconnections, a library unit  5180  for storing and retrieving circuit parameters and calculated values, and a parasitic element calculating unit  5190  for calculating values of parasitic elements. 
   The circuit transfer function calculation unit calculates the complex impedance of the circuit components from a circuit net list. The circuit transfer function calculating unit  520  shown in  FIG. 12  comprises a net list generator unit  5200  for translating the graphical schematic diagram into its numerical equivalent, a component impedance calculating unit  5210  for calculating the impedance of each component, a differential mode input impedance calculator  5220  for calculating differential mode impedance as seen from the circuit input terminals, a common mode input impedance calculator  5230  for calculating common mode impedance as seen from the circuit input terminals, a differential mode output impedance calculator  5240  for calculating differential mode impedance as seen from the circuit output terminals, a common mode output impedance calculator  5250  for calculating common mode impedance as seen from the circuit output terminals, a voltage transfer function calculator  5260  for calculating the voltage transfer function of the circuit, and a current transfer function calculator  5270  for calculating the current transfer function of the circuit. 
   The parasitic element calculating unit calculates inductance, capacitance, attenuation factor, propagation constant, impedance, and admittance of conductors. Whereas the value of these elements are typically considered insignificant compared to circuit element values at circuit operating frequencies they are often ignored in low frequency calculations and are considered to be parasitic. For EMI analysis, parasitic elements can have a significant effect on radio frequency device characteristics. The parasitic element calculating unit allows the user to define conductor parameters, initiate calculations, display calculated values, and store and retrieve parasitic element parameters and calculated values. Calculated parasitic values are used by the invention when performing calculations involving conductors. The parasitic element calculating unit  5190  shown in  FIG. 20  comprises an input unit  51900  for user data entry of conductor dimensions, geometry, and materials, a parasitic element calculating unit  51910  for calculating parasitic element values from supplied parameters, a display unit  51920  for displaying calculated values, and a library unit  51930  for storing and retrieving parasitic element parameters and calculated values. 
   The conductor configuration unit allows the user to specify dimensional and material properties of conductors interconnecting device circuits. The conductor configuration unit  60  shown in  FIG. 8  comprises a configuration selector unit  600  for user selection of conductor configuration, an input unit  610  for user entry of physical conductor parameters, a shield transfer impedance calculating unit  620  for calculating shield transfer impedance, a shield termination calculating unit  630  for calculating shield termination impedance, a conductor transfer function calculating unit  640  for calculating conductor electrical characteristics, and a library unit  650  for storing and retrieving conductor parameters and calculated values. 
   The shield transfer impedance calculating unit calculates shield transfer impedance from dimensional and material properties entered by the user. The shield transfer impedance calculating unit allows the user to define shield parameters, initiate shield transfer impedance calculations, display calculated transfer impedance, and store and retrieve shield parameters and calculated transfer impedance. The shield transfer impedance calculating unit  620  shown in  FIG. 13  comprises an input unit  6200  for user data entry of shield dimensions, construction, and materials, a transfer impedance calculating unit  6210  for calculating shield transfer impedance from supplied parameters, a display unit  6220  for displaying calculated graphical or numerical shield transfer impedance data, and a library unit  6230  for storing and retrieving shield transfer impedance parameters and calculated values 
   The shield termination calculating unit calculates complex impedance of shield terminations from dimensional and physical data entered by the user. The shield termination calculating unit allows the user to define shield termination parameters, facilitate shield termination impedance calculations, display calculated impedance, and store and retrieve shield termination parameters and calculated shield termination impedance values. Calculated shield termination impedance values are used by the invention when performing calculations involving shielded conductors. The shield termination calculating unit  630  shown in  FIG. 14  comprises a termination selector unit  6300  for user selection of shield termination method, an input unit  6310  for user data entry of shield termination dimensions, construction, material properties, etc., a shield termination impedance calculating unit  6320  for calculating shield termination impedance from supplied parameters, a display unit  6330  for displaying graphical and numerical shield termination impedance data, and a library unit  6340  for storing and retrieving shield transfer impedance parameters and calculated values. 
   The conductor transfer function calculating unit calculates characteristics such as impedance, admittance, and distributed capacitance and inductance of interconnecting conductors from dimensional and material values entered by the user. The conductor transfer function calculating unit allows the user to calculate conductor characteristics, display calculated characteristics, and store and retrieve conductor parameters and calculated characteristics. Calculated characteristics are used by the invention when performing calculations involving interconnecting conductors. The conductor transfer function calculating unit  640  shown in  FIG. 15  comprises an input unit  6400  for user data entry, a characteristic calculating unit  6410  for calculating conductor characteristics from dimensional and physical parameters, a display unit  6420  for displaying graphical and numerical conductor characteristics data, and a library unit  6430  for storing and retrieving conductor parameters and calculated values. 
   The limit unit renders user-defined voltage, current, and electromagnetic field limits as a function of time or frequency. The time domain limit unit allows the user to define a limit in the time domain by entering amplitude/time waypoints, calculate the limit envelope at time intervals between waypoints, display the limit, and store and retrieve waypoints and calculated values. The frequency domain limit unit allows the user to define a limit in the frequency domain by entering amplitude/frequency waypoints, calculate the limit envelope over frequencies between waypoints, display the limit, and store and retrieve waypoints and calculated values. The limit unit  75  shown in  FIG. 10  comprises an input unit  7510  for user data entry of amplitude/time waypoints or amplitude/frequency waypoints, an input  7520  for user entry of units, labels, etc., a calculating unit  7530  for calculating amplitude values between defined waypoints, a display unit  7540  for graphing or tabulating limit amplitude values versus time or frequency, and a library unit  7550  for storing and retrieving limit waypoints and calculated values. 
   The application calculating unit calculates interference produced by sources within the device under analysis (for emissions) and induced voltage and current resulting from sources applied to the device under analysis (for susceptibility). The application calculating unit  70  shown in  FIG. 9  comprises a conducted emissions calculating unit  710  for calculating conducted emissions in the time domain or as a function of frequency, a radiated emissions calculating unit  720  for calculating radiated emissions in the time domain or as a function of frequency, a conducted susceptibility calculating unit  730  for calculating conducted susceptibility in the time domain or as a function of frequency, a radiated susceptibility calculating unit  740  for calculating radiated susceptibility in the time domain or as a function of frequency, a display unit  750  for displaying graphical or numerical calculated values, and a library unit  760  for storing and retrieving setup parameters and calculated data. 
   The conducted emissions calculating unit calculates common mode and differential mode current produced by electric circuit operation. Calculations incorporate user-defined and calculated values for sources, filtering, circuit impedance, conductor configuration, shield construction, and shield terminations. The conducted emissions calculating unit  710  shown in  FIG. 16  comprises a frequency/time incrementing unit  7100  for incrementing frequency or time, a source application unit  7110  for applying voltage or current from time domain source  30  or frequency domain source  40  to the source side of Circuit A, a circuit calculating unit  7120  for calculating voltage and current in each branch of Circuit A, a conductor calculating unit  7130  for calculating voltage and current on each conductor, a circuit calculating unit  7140  for calculating voltage and current in each branch of Circuit B, and a display unit  7150  for displaying graphical or numerical conducted emissions calculations data. 
   The conducted susceptibility calculating unit calculates induced effects of signals coupled to conductors interconnecting electric circuits. Current and voltage induced in circuit elements at each end of the conductors are calculated and displayed. Calculations incorporate user-defined and calculated values for conductor dimensions, conductor configuration, coupled signal characteristics, coupling mechanisms, circuit impedance, shield construction, and shield termination to calculate voltage and current induced in circuit elements. The conducted susceptibility calculating unit  730  shown in  FIG. 18  comprises a frequency/time incrementing unit  7300  for incrementing frequency or time, a source application unit  7310  for applying voltage or current from time domain source  30  or frequency domain source  40  to the interconnecting conductors, a conductor calculating unit  7320  for calculating voltage and current induced on each conductor, a circuit calculating unit  7330  for calculating voltage and current in each branch of Circuit A, a circuit calculating unit  7340  for calculating voltage and current in each branch of Circuit B, and a display unit  7350  for displaying graphical or numerical conducted susceptibility calculation data. 
   The radiated emissions calculating unit calculates field strength generated by current flowing on conductors interconnecting electric circuits. Calculations incorporate user-defined and calculated values for sources, filtering, circuit impedance, conductor configuration, shield construction, and shield terminations to calculate radiated emissions produced by interconnecting conductors. 
   The radiated emissions calculating unit  720  shown in  FIG. 17  comprises a frequency/time incrementing unit  7200  for incrementing frequency or time, a source application unit  7210  for applying voltage or current from time domain source  30  or frequency domain source  40  to the source side of Circuit A, a circuit calculating unit  7220  for calculating voltage and current in each branch of Circuit A, a conductor calculating unit  7230  for calculating voltage and current on each conductor, a circuit calculating unit  7240  for calculating voltage and current in each branch of Circuit B, a radiation calculating unit  7250  for calculating field level generated by conductor current, and a display unit  7260  for displaying graphical or numerical radiated emissions calculations data. 
   The radiated susceptibility calculating unit calculates current and voltage induced in device circuits by an electromagnetic field impinging on conductors interconnecting electric circuits. Current induced on interconnecting conductors is calculated over a user-specified frequency range. Current and voltage induced in circuit elements at each end of the conductors are calculated and displayed. Calculations incorporate user-defined and calculated values for conductor dimensions, conductor configuration, incident field orientation, field strength, circuit impedance, shield construction, and shield termination to calculate voltage and current induced in circuit elements. 
   The radiated susceptibility calculating unit  740  shown in  FIG. 19  comprises a frequency/time incrementing unit  7400  for incrementing frequency or time, a field application unit  7410  for applying electromagnetic fields to the interconnecting conductors, a conductor calculating unit  7420  for calculating voltage and current induced on each conductor, a circuit calculating unit  7430  for calculating voltage and current in each branch of Circuit A, a circuit calculating unit  7440  for calculating voltage and current in each branch of Circuit B, and a display unit  7450  for displaying graphical or numerical radiated susceptibility calculations data. 
   DETAILED DESCRIPTION—OPERATION OF INVENTION 
   Electromagnetic emissions and susceptibility analyses are accomplished by applying circuit theory and field theory to mathematical models of the electric device under investigation. The mathematical models are derived from schematic diagrams of the electric circuits and equivalent circuit representations of interconnecting conductors. 
   The preferred embodiment of the present invention comprises four analysis applications: conducted emissions, radiated emissions, conducted susceptibility, and radiated susceptibility. 
   Each model consists of two electric circuits, interconnected by conductors and stimulated by one or more sources. For conducted emissions and radiated emissions analyses the sources simulate characteristics of active circuitry within the electric device, and are located such that Circuit A lies between the source and the interconnecting conductors. For conducted susceptibility analyses a single source is positioned between Circuit A and the interconnecting conductors. For radiated susceptibility, the source is an electromagnetic field that impinges on the interconnecting conductors. 
   The user defines a time domain source by entering parameter values that define the shape, amplitude, duration, frequency, and units of its waveform. The time domain source unit  30  calculates the source amplitude at prescribed time increments and displays the waveform. The time domain waveform is translated to its frequency domain equivalent using the Fast Fourier Transform method. 
   For conducted emissions and radiated emissions analysis a time domain source is any component within the electric device under investigation whose voltage or current changes over time. Examples are digital semiconductors, relays, oscillators, switch mode power converters, amplifier circuits, and switches. 
   For conducted susceptibility and radiated susceptibility analysis a time domain source is any time varying current, voltage, or electromagnetic field that can be coupled to the interconnecting conductors between Circuit A and Circuit B. Time domain waveforms are displayed to the user graphically or as numerical values. Input parameters and calculated values are stored for subsequent use by other calculating units and become a part of the user&#39;s source library. 
   A frequency domain source is defined by the user in one of two ways. (1) The user enters parameter values that define the source spectral envelope, i.e., frequency range, amplitude/frequency waypoints, spectral spacing, and units (current, voltage, or field strength). The frequency domain source unit  40  calculates the source amplitude at prescribed frequencies between waypoints and displays the spectrum. (2) The user enters parameter values that define the source time domain waveform. The frequency domain source unit  40  uses the Fourier Transform method to calculate the frequency domain spectrum. 
   For conducted emissions and radiated emissions analysis a frequency domain source is any component within the electric device under investigation whose voltage or current can be represented by a frequency spectrum. Examples are digital semiconductors, oscillators, amplifiers, and switch mode power converters. 
   For conducted susceptibility and radiated susceptibility analysis a frequency domain source is any current, voltage, or electromagnetic field that can be coupled to the interconnecting conductors between Circuit A and Circuit B. 
   Frequency domain spectra are displayed to the user graphically or as numerical values. Input parameters and calculated values are stored for subsequent use by other calculating units and become a part of the user&#39;s source library. 
   Circuit models are created by the user by interconnecting components selected from the component library to create a schematic diagram. Using CAD methods components are graphically placed and interconnected such that the circuit under analysis is modeled. Element values are assigned by the user. 
   For conducted emissions and radiated emissions analysis Circuit A comprises circuitry that is connected between the source and the interconnecting conductors. Circuit B comprises circuitry that lies on the opposite end of the interconnecting conductors from Circuit A as shown in  FIG. 3 . For conducted susceptibility and radiated susceptibility Circuit A comprises circuitry that is connected to the source end of the interconnecting conductors, while Circuit B comprises circuitry that is connected to the opposite end of the interconnecting conductors as shown in  FIG. 4 . 
   Circuit A and Circuit B are modeled as passive components whose values are selected to replicate the radio frequency characteristics of Circuit A and Circuit B, respectively, over the time interval or frequency range of interest. In the device under investigation Circuit A and Circuit B may consist of semiconductors, EMI filter components, printed wiring board lands, interconnect wires, connectors, or any other electrical components. In addition to displaying the circuits as schematic diagrams, the present invention displays the impedance of each circuit, and displays current through and voltage across each branch of each circuit when interconnected and supplied with a source. The user may thereby examine the performance of the circuit to determine the effect of each component in the subject analysis. Calculated values are displayed graphically or as numerical values. Circuit component values and calculated characteristics are stored for subsequent use by other calculating units and become a part of the user&#39;s circuit library. 
   The user synthesizes a schematic diagram of the circuit under analysis by graphically placing and interconnecting components selected from the component library. The schematic capture unit  510  allows components to be added, edited, appended, and deleted as required to model the circuit. 
   The component library is a repository of components that schematically describe electric devices found in circuits. Library components consist of one or more elements. Elements are fundamental circuit building blocks such as capacitors, inductors, and resistors. Element values are set by the user. 
   Component placement, element values, and interconnects are tracked and mapped for subsequent use by the schematic display unit and transfer function unit. 
   The transfer function unit  520  translates the graphical schematic diagram into a mathematical model. Circuit transfer functions such as input impedance, resonance, damping, and phase shift are then calculated and displayed. 
   The parasitic elements calculating unit  5190  is a tool for calculating element values of interconnecting conductors. Inductance, resistance, and capacitance are natural byproducts of physical circuit interconnections, such as printed circuit boards, wires, connectors, etc. The parasitic elements calculating unit provides common interconnect configurations and allows the user to enter dimensional and material properties. The parasitic elements calculating unit returns calculated values for inductance, capacitance, resistance, and characteristic impedance. These values can then be transferred to schematic diagram elements, thus allowing subtle aspects of the circuit under investigation to be modeled. 
   Circuits are interconnected by conductors. At the frequencies of interest for EMI interconnecting conductors are a significant constituent of the electric device model, providing a medium for interference produced by one circuit to conduct to another or radiate to the environment. Simultaneously interconnecting conductors are a medium through which interference can be conducted into a circuit either directly from the circuit to which it is interconnected or indirectly via capacitive or inductive coupling from adjacent conductors or from electromagnetic fields impinging on the conductor. 
   The role of the interconnecting conductors depends on the type of analysis undertaken. For conducted emissions analyses the interconnecting conductors are the path by which conducted emissions flow between Circuit A and Circuit B. For radiated emissions the interconnecting conductors are the radiator through which radiation producing current flows. For conducted susceptibility analysis the interconnecting conductors are the medium into which interfering current and voltage waveforms are coupled. For radiated susceptibility the interconnecting conductors are the receptors into which current is induced by the incident electromagnetic field. 
   The interconnecting conductors consist of printed wiring board lands or circular wires and may be configured as a conductor pair, a conductor over a ground plane, or conductors in a shield. The present invention displays the impedance of the interconnecting conductors as seen from the conductor terminals, and displays current through and voltage across and between the conductors when Circuit A and Circuit B are attached to opposite ends of the conductors. The user can thereby examine the effect of the conductors in a given application to determine the effect of each conductor parameter in the analysis. Calculated values are displayed graphically or numerically. Conductor parameters and calculated characteristics are stored for subsequent use by other calculating units and become a part of the user&#39;s conductor library. 
   The user selects from a library of conductor configurations the configuration that best simulates the physical arrangement of the conductor in the electric device. Conductor configurations include shielded conductors, unshielded conductors, paired conductors, and conductors over a ground plane. 
   Shield transfer impedance defines the voltage induced on conductors within the shield when current flows on the shield. It is the figure of merit that determines how well a shield performs over the frequency range of interest. Most conductor shields are constructed by weaving small gauge circular wires into a tubular shape. At low frequencies, shield conductivity and thickness determine transfer impedance. At higher frequencies other parameters, such as permeability, optical coverage, and aperture size predominate. The user specifies the physical construction details of the shield and the material properties of the shield constituents. The shield transfer impedance is then calculated and displayed. Calculated values are stored for later use in calculations involving shielded conductors and become a part of the user&#39;s shield library. 
   Shield termination impedance has a significant effect on how well a conductor shield performs at high frequencies. Generally, higher termination impedance results in lower shielding effectiveness. 
   The user selects a termination method from the termination library and assigns physical dimensions and material properties to the termination. The termination impedance is calculated and displayed. Termination impedance is stored for use in subsequent calculations involving shielded conductors and becomes a part of the user&#39;s shield termination library. 
   At the frequencies of interest for EMI analysis the dimensions of interconnecting conductors are often significant with respect to the wavelength of the current flowing on them. Conductor electrical characteristics such as characteristic impedance, self inductance, mutual inductance, and stray capacitance are significant. 
   The user specifies dimensional and material properties of the interconnecting conductors. The conductor characteristics are calculated and displayed. Values are stored for use in calculations involving interconnecting conductors and become a part of the user&#39;s interconnecting conductor library. 
   EMI limits are imposed on electric devices by regulatory agencies such as the Federal Communications Commission, Federal Aviation Administration, Department of Defense, European Committee for Electrotechnical Standardization, or other governing bodies. Limits may also be self-imposed for system self-compatibility or any other reason. 
   Emissions limits define the level of radio frequency conducted current, voltage or radiation a device may produce. If emissions exceed the applicable emissions limit the device is said to be noncompliant. Limits are used in conducted emissions and radiated emissions analyses to assess whether calculated values exceed predefined amplitudes. Emissions limits are graphically or numerically superimposed over calculated values for comparison to provide the user with predictions about the performance of the device under investigation, and whether it is likely to comply with applicable limits imposed by the regulatory agency or governing body. 
   Susceptibility limits define the level of conducted or radiated interference in which a device must function. Susceptibility limits define continuous and transient levels of interference. The operation of the device and its allowable response to the source of interference depends on the device and its intended use. Susceptibility limits are used to predict the tolerable level of current or voltage induced in the device circuits. 
   Limits are defined graphically by a line, sometimes discontinuous, that extends over a time interval or frequency range. An equivalent limit is readily defined numerically at discrete times or frequencies. Amplitude is commonly in units of current, voltage, or field strength, but may be any suitable metric. 
   A time domain limit defines amplitude over a time interval. Time/amplitude waypoints entered by the user, when sequentially connected, create a limit envelope. Time domain limits are stored for use in subsequent analyses where a limit overlay is selected, and become a part of the user&#39;s limit library. 
   Frequency domain limits define amplitude over a frequency range. Frequency/amplitude waypoints entered by the user, when sequentially connected, create a limit envelope. Frequency domain limits are stored for use in subsequent analyses where a limit overlay is selected, and become a part of the user&#39;s limit library. 
   The preferred embodiment of the present invention provides a unified platform across which the EMI performance of an electric device is analyzed. Having specified the source characteristics, circuits, and interconnecting conductors, calculations are performed to predict conducted emissions, conducted susceptibility, radiated emissions, and radiated susceptibility performance of the electric device. 
   By adjusting the source characteristics using the Time Domain Source Unit  30  and the Frequency Domain Source Unit  40 , the performance of the electric device under investigation is readily analyzed for emissions and susceptibility requirements. 
   Conducted emissions are defined as radio frequency current and voltage conducted by an electric device on its power leads or interconnecting signal leads. Conducted emissions produced by electric devices are limited by various regulatory agencies and therefore must be controlled. Conducted emissions are most commonly measured by placing a current probe around one or more conductors connected to the device and measuring current as a function of frequency or time, or by measuring the voltage developed across a known impedance (such as a Line Impedance Stabilization Network) as a function of frequency or time. 
   Current and voltage on the interconnecting conductors are the desired metrics for conducted emissions calculations. The present invention calculates and displays conductor current and voltage in a manner that can be directly compared with conducted emissions limits, either by displaying calculated conducted emissions graphically or numerically. A conducted emissions limit may be superimposed on the calculated values for comparison, thereby providing the user a prediction of whether the device under investigation complies with applicable conducted emissions limits. 
   Conducted emissions are calculated as follows: User selects conducted emissions analysis using analysis selector  20 . User inputs source characteristics using time domain source  30  or frequency domain source  40 . User inputs Circuit A using schematic capture unit  510  and parasitic element calculating unit  5190 . Circuit A transfer functions are calculated using circuit transfer function unit  520 . User selects a conductor configuration from conductor configuration unit  60  and inputs conductor parameters using input unit  610 . If the conductors are shielded, shield parameters are entered and characteristics calculated using shield transfer unit  620  and shield termination unit  630 . Conductor characteristics are calculated using conductor transfer function calculating unit  640 . User inputs Circuit B characteristics using schematic capture unit  510  and parasitic element calculating unit  5190 . Circuit B transfer functions are calculated using circuit transfer function unit  520 . Conducted emissions are calculated using conducted emissions calculating unit  710 . Results are displayed, printed, or stored using library unit  760 . User inputs a conducted emissions limit using the limit unit  75  and graphically overlays or numerically compares the limit to calculated conducted emissions. As desired source, circuit, and conductor parameters are adjusted and conducted emissions recalculated until predicted values are within conducted emissions limits or until suitable performance is achieved. 
   Radiated emissions are electromagnetic fields produced by time varying current flowing on a conductor. Radiated emissions produced by electric devices are limited by various regulatory agencies and therefore must be controlled. Radiated emissions are most commonly measured by placing a measurement antenna a known distance from the device under test and measuring the signal received as a function of time or frequency. 
   Electric field strength radiated from the interconnecting conductors is the desired metric for radiated emissions calculations. The present invention calculates and displays electric field values in a manner that can be directly compared with radiated emissions limits, either by displaying calculated radiated emissions graphically or numerically. A radiated emissions limit may be superimposed on the calculated values for comparison, thereby providing the user a prediction of whether the device under investigation complies with applicable radiated emissions limits. 
   Radiated emissions are calculated as follows: User selects radiated emissions analysis using analysis selector  20 . User inputs source characteristics using time domain source  30  or frequency domain source  40 . User inputs Circuit A using schematic capture unit  510  and parasitic element calculating unit  5190 . Circuit A transfer functions are calculated using circuit transfer function unit  520 . User selects a conductor configuration from conductor configuration unit  60  and inputs conductor parameters using input unit  610 . If the conductors are shielded, shield parameters are entered and characteristics calculated using shield transfer unit  620  and shield termination unit  630 . Conductor characteristics are calculated using conductor transfer function calculating unit  640 . User inputs Circuit B characteristics using schematic capture unit  510  and parasitic element calculating unit  5190 . Circuit B transfer functions are calculated using circuit transfer function unit  520 . Radiated emissions are calculated using radiated emissions calculating unit  720 . Results are displayed, printed, or stored using library unit  760 . User inputs radiated emissions limit using the limit unit  75  and graphically overlays or numerically compares the limit to calculated radiated emissions. As desired source, circuit, and conductor parameters are adjusted and radiated emissions recalculated until predicted values are within radiated emissions limits or until suitable performance is achieved. 
   Conducted susceptibility is a determination of induced current or voltage in a circuit subjected to current or voltage coupled to power leads or interconnecting signal leads. Conducted susceptibility threats simulate the induced effects of transients, surges, oscillations, variations, perturbations, etc. likely to be present on conductors connected to electric circuits. Conducted susceptibility is most commonly determined by capacitively or inductively coupling a current or voltage waveform to conductors connected to the device under test and measuring the response of the device. 
   The susceptibility of the circuit or device is a function of numerous variables and must be established by the user. The present invention calculates and displays induced circuit current and voltage values in a manner that can be directly compared with user defined limits by displaying calculated induced current or voltage graphically or numerically. A conducted susceptibility limit may be superimposed on the calculated values for comparison, thereby providing the user a prediction of whether the device under investigation will comply with applicable conducted susceptibility limits. 
   Conducted susceptibility values are calculated as follows: User selects conducted susceptibility analysis using analysis selector  20 . User inputs conduction source characteristics using time domain source  30  or frequency domain source  40 . User inputs Circuit A using schematic capture unit  510  and parasitic element calculating unit  5190 . Circuit A transfer functions are calculated using circuit transfer function unit  520 . User selects a conductor configuration from conductor configuration unit  60  and inputs conductor parameters using input unit  610 . If the conductors are shielded, shield parameters are entered and characteristics calculated using shield transfer unit  620  and shield termination unit  630 . Conductor characteristics are calculated using conductor transfer function calculating unit  640 . User inputs Circuit B characteristics using schematic capture unit  510  and parasitic element calculating unit  5190 . Circuit B transfer functions are calculated using circuit transfer function unit  520 . Induced current or voltage is calculated using conducted susceptibility calculating unit  730 . Results are displayed, printed, or stored using library unit  760 . User inputs a conducted susceptibility limit using the limit unit  75  and graphically overlays or numerically compares the limit to calculated induced current or voltage. As desired source, circuit, and conductor parameters are adjusted and induced current or voltage recalculated until predicted values are within conducted susceptibility limits or until suitable performance is achieved. 
   Radiated susceptibility is a determination of induced current or voltage in a circuit when its power leads or interconnecting signal conductors are subjected to an electromagnetic field. Radiated susceptibility threats simulate the world wide electromagnetic environment. Radiated susceptibility is most commonly determined by subjecting the device under test and its interconnecting cabling to an electromagnetic field having known amplitude and modulation characteristics and measuring the response of the device. 
   The susceptibility of the circuit or device is a function of numerous variables and must be established by the user. The present invention calculates and displays induced circuit current and voltage values in a manner that can be directly compared with user defined limits, either by displaying calculated induced current or voltage graphically or numerically. A radiated susceptibility limit may be superimposed over calculated values for comparison, thereby giving the user a prediction of whether the device under investigation will comply with applicable radiated susceptibility limits. 
   Radiated susceptibility values are calculated as follows: User selects radiated susceptibility analysis using analysis selector  20 . User inputs radiation source characteristics using time domain source  30  or frequency domain source  40 . User inputs Circuit A using schematic capture unit  510  and parasitic element calculating unit  5190 . Circuit A transfer functions are calculated using circuit transfer function unit  520 . User selects a conductor configuration from conductor configuration unit  60  and inputs conductor parameters using input unit  610 . If the conductors are shielded, shield parameters are entered and characteristics calculated using shield transfer unit  620  and shield termination unit  630 . Conductor characteristics are calculated using conductor transfer function calculating unit  640 . User inputs Circuit B characteristics using schematic capture unit  510  and parasitic element calculating unit  5190 . Circuit B transfer functions are calculated using circuit transfer function unit  520 . Induced current or voltage is calculated using radiated susceptibility calculating unit  740 . Results are displayed, printed, or stored using library unit  760 . User inputs a radiated susceptibility limit using the limit unit  75  and graphically overlays or numerically compares the limit to calculated conducted emissions. As desired source, circuit, and conductor parameters are adjusted and induced current or voltage recalculated until predicted values are within conducted susceptibility limits or until suitable performance is achieved. 
   DETAILED DESCRIPTION—DESCRIPTION AND OPERATION OF ALTERNATIVE EMBODIMENTS 
   An alternative embodiment of the present invention performs calculations simulating tests specified by regulatory agencies or governing bodies. Test requirements published by regulatory agencies and other governing bodies define test setups, waveforms, methods, limits, evaluation criteria, and operating conditions to which a device must be subjected. The results of analyses described in the preferred embodiment of the present invention may be further processed to determine compliance with requirements. Examples of specified requirements include, but are not limited to audio frequency conducted emissions, radio frequency conducted emissions, transient conducted emissions, inrush current, turn-on and turn-off voltage transients, audio frequency conducted susceptibility, radio frequency conducted susceptibility, electrical fast transients, lightning indirect effects, power surges, electrostatic discharge, radiated emissions, transient electromagnetic field emissions, electromagnetic pulse, continuous radiated susceptibility, spread spectrum effects, modulation effects, transient radiated susceptibility. Analyses are performed by applying requirements specified by the regulatory agency or governing body to the device under investigation using the preferred embodiment of the present invention. 
   An alternative embodiment of the present invention calculates filter insertion loss for the device under analysis. The results of analyses described in the preferred embodiment of the present invention may be further processed to determine filter insertion loss. Filter insertion loss is a measure of voltage or current reduction provided by circuit components in an electric device. Filter insertion loss calculations are applicable to conducted emissions, radiated emissions, conducted susceptibility, and radiated susceptibility analyses. Filter insertion loss calculated using the present embodiment is advantageous because it yields the actual effectiveness of filter components in the device under investigation. Filter insertion loss is traditionally specified for standardized impedance, i.e., with 50 ohm source and load impedance, which may be quite different than the circuit impedance. As a result, filter insertion loss in the device may be substantially different than specified filter insertion loss. Filter insertion loss is computed by first calculating device performance without the filter components in place, then calculating device performance with filter components in place, keeping other analysis variables constant. The two sets of calculated values are then used to calculate filter insertion loss. Filter insertion loss is calculated by subtracting or dividing values calculated at each time interval or frequency. If values are expressed in logarithmic units, e.g., decibels, filter insertion loss is the difference between values returned for the filtered circuit and values returned for unfiltered circuit. If values are expressed in linear units, e.g., volts, amperes, volts/meter, filter insertion loss is the quotient of values returned for the filtered circuit divided by values returned for the unfiltered circuit. 
   An alternative embodiment of the present invention calculates a transfer function relating conducted emissions to radiated emissions. The results of analyses described in the preferred embodiment of the present invention may be further processed to determine the transfer function between conducted emissions and radiated emissions. The transfer function is device dependent and configuration dependent. Radiated emissions are produced by conducted emissions on interconnecting cables and power leads connected to an electric device. It is therefore possible to calculate a transfer function expressing radiated emissions in terms of conducted emissions or vise versa. A conducted emissions limit derived from the radiated emissions limit is advantageous because conducted emissions are more readily measured in an electronics laboratory environment than are radiated emissions. Radiated emissions measurements require a shielded, preferably anechoic, chamber or open area test site having a low ambient background. Conducted emissions measurements do not require a shielded enclosure or low ambient background. Radiated emissions are calculated by first calculating conducted emission on a conductor, then applying field theory to the conductor current to determine the field produced. Having calculated radiated emissions for an electric device, a transfer function relating radiated emissions to conducted emissions is derived by dividing calculated field amplitude by calculated conductor current amplitude at each time interval or frequency. When the resulting transfer function is multiplied by field levels defining a radiated emissions limit, an equivalent conducted emissions limit is attained. 
   An alternative embodiment of the present invention calculates shielding effectiveness of braided cable shields. The results of analyses described in the preferred embodiment of the present invention may be further processed to determine cable shield shielding effectiveness. Cable shield shielding effectiveness calculations are applicable to conducted emissions, radiated emissions, conducted susceptibility, and radiated susceptibility analyses. Cable shield shielding effectiveness is computed by first calculating device performance with cable shields, then calculating device performance without cable shields, keeping other analysis variables constant. The two sets of calculated values are then used to calculate the shielding effectiveness. Shielding effectiveness is calculated by subtracting or dividing values calculated at each time interval or frequency. If values are expressed in logarithmic units, e.g., decibels, shielding effectiveness is the difference between values returned for unshielded conductors and values returned for shielded conductors. If values are expressed in linear units, e.g., volts, amperes, volts/meter, shielding effectiveness is the quotient of values returned for unshielded conductors divided by values returned for shielded conductors. 
   CONCLUSION 
   The present invention provides an integrated platform, wherein an electric device can be analyzed to predict performance for all four facets of electromagnetic interference, and its function and response directly compared to performance standards establish by regulatory agencies and other governing bodies. An electric device can be analyzed for conducted emissions, conducted susceptibility, radiated emissions, and radiated susceptibility, considering relevant device characteristics including active circuits, passive components, conductor configuration, shield construction, shield terminations, interconnected circuit characteristics, and characteristics of coupled fields and signals. 
   The present invention provides for analytical evaluation of the EMI performance of an electric device, prior to testing, thereby providing a means for improving EMI control methods, reducing EMI test costs, and reducing device redesign and retest. 
   Alternative embodiments of the present invention comprise several items of value to electric device designers, including EMI filter insertion loss, conducted emissions/radiated emissions transfer function, cable shielding effectiveness. Furthermore, alternative embodiments of the present invention comprise calculations simulating tests specified by regulatory agencies or governing bodies.