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Scattering or S-parameters obtained from direct measurements or through EM wave simulations may violate physical laws due to measurement or numerical errors. If used in simulations, such S-parameters lead to incorrect results and wrong conclusions. This paper focuses on three such properties of S-parameters – causality, passivity and reciprocity. Tests are provided to detect if any of the three conditions are violated. Separate algorithms are provided to make S-parameters causal, passive and reciprocal. The proposed algorithms are proven to be the best in the solution space, and are easy to implement.
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We explore in detail the relationship between discrete-frequency responses connected with sparameters and the implied continuous time response. This is done in both the frequency- and time-domain to develop the proper insight and explore issues with real time-domain responses, time-aliasing, causality, interpolation and re-sampling of discrete-frequency data. Using the insight gained, we identify the conditions for sufficiency of sampling and the side-effects of the invariable practical conditions when these side-effects cannot be completely dispelled. This paper is especially useful for understanding issues involved in direct application of sparameters in linear simulations, like those used in virtual probing applications in scopes.
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The SPARQ software includes the ability to limit the impulse response time as part of the S-parameter calculation process. Limiting the impulse response time has the main benefit of eliminating noise from the S-parameters returned by the SPARQ. When limiting the impulse response, the S-parameters measured by the SPARQ are smoother, and a better match to VNA results.
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We clarify the role of signal loss measurements, aka Total Loss, in specifying and qualifying circuit board materials for high-speed electronic design. We then demonstrate the NIST Multiline measurement technique in particular by characterizing test lines fabricated in conventional PCB materials. The paper describes and demonstrates this technique, and shows how to accurately report signal propagation loss as a function of frequency, even when using TDR-based systems. The paper also reveals how impedance mismatch and differential delay variance contribute to the reported loss for various test methods in practice today.
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A technique is presented for removing large amounts of noise present in time-domain-reflectometry (TDR) waveforms to increase the dynamic range of TDR waveforms and TDR based S-parameter measurements.
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The SPARQ Signal Integrity Network Analyzer uses TDR and TDT to characterize a network’s electrical behavior. The process to measure S-parameters includes 3 phases: 1) OSLT calibration, 2) DUT measurement, and 3) S-parameter calculation. When using “E” model SPARQs, all phases are done automatically, with a single button press, and without any user intervention whatsoever. This is accomplished by using an internal switch matrix assembly that routes signals to internally connected calibration standards and to the front panel ports. “M” models are calibrated with a user’s external OSLT calibration kit.
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This paper discusses the dynamic range of the SPARQ signal integrity network analyzer and considers the impact of several key specifications. It further compares dynamic range and key specifications of two competitive time-domain instruments and provides derivations and experimental results that support the calculations.
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