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 Power Integrity for I/O Interfaces: With Signal Integrity/ Power Integrity
In a passive high-speed channel, the speedy way to check for causality is to examine the S-parameter Smith Chart. If the data rotate clockwise, it has positive group delay; implying it to be causal. On the other hand, if the data rotates counterclockwise, this implies it is noncausal.
 一篇利用Smith Chart补偿Passivity与Causality的专利技术
Smith Chart can be used to monitor the passivity and causality of networks under study. For instance, Foster's reaction theorem dictates a general motion in the clockwise direction with frequency for the parameters of an arbitrary network.
 touchstone spec. 2.0
 TS1.0 and TS2.0 (推荐)
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