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Abstract

A method and apparatus for use in designing and evaluating filters to resolve undesired signal transmission in a device including, without limitation, EMI filters for suppressing an identified EMI in a device under test in a particular application. The complex impedance of the source impedance presented to the filter and the load impedance presented to the filter are separately determined over a frequency range of interest. The impedances are used to determine a complex power flow of the device under test without the filter. The power flow is used to identify frequencies corresponding to the undesired signal transmission. A filter is then designed or selected, based upon the complex impedances of the filter load impedance and filter source impedance at the identified resonant frequencies, to attenuate the identified resonances or undesired signal transmission over each frequency range of interest. The attenuation of the proposed filter design is then verified using either the frequency response of the designed filter or the determined power flow of the device with the filter design analytically inserted at the test point. The magnitude of the attenuation or the difference in power flow is evaluated to determine if the filter attenuates the undesired signal transmissions adequately. A computer controlled tool is used to conduct the measurements and comparisons.

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First Claim