CSA8000+ TDS8000+ CSA8000B+ TDS8000B+ CSA8200+ TDS8200+ DSA8200+ 80SICON+ 80SSPAR+ 80SICMX:What is an impedance profile and how can it be found in Iconnect?
The impedance profile of a device is its characteristic impedance as a function of distance along its length. Use of a post processing algorithm such as that implemented in IConnect is almost always necessary to get accurate impedance profile information from measured waveforms, since in raw TDR waveforms the effects of any multiple discontinuities are superposed on each other. Computation of the impedance profile gives the user access to information on the DUT which would otherwise be hidden.
The existence of an impedance profile assumes that the DUT can be modeled as a nearly lossless transmission line of non-uniform characteristic impedance. The impedance profile can be thought of as answering the question, "If this DUT can be modeled as a series of cascaded transmission line segments, what would be the impedance of each segment?" The nearly lossless assumption is a valid approximation in a large number of circuit board and packaging applications currently in use and development. For further technical discussion on impedance profile, the user is refered to the References listed at the end of this manual.
In IConnect, the impedance profile of a DUT is computed from its response to a TDR step input, based on how a non-uniform transmission line would respond to such a step. For this reason, computation of the impedance profile requires both a TDR input step andTDRresponse as parameters.
The impedance profile is computed via the computation window by choosing Z-Line from the Compute list box, or by simply pressing the red Z on the algorithms toolbar. It may be necessary to choose two operand waveforms from the drop-down list box in the group titled Waveforms. In the list box labeled DUT:, identify the waveform that is the reflection from the DUT. In the list box labeled Step:, identify the waveform which was the open-circuit or short-circuit response at the interface to the DUT. It may be necessary to change the value for the characteristic impedance of the measurement system in the parameter entry box labeled Z0: at the bottom of the computation window, and it may also be necessary to adjust the threshold value in the parameter entry box labeled Threshold: at the bottom of the computation window. Press the Compute button, and the resultant waveform will be placed in the selected waveform viewer.
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