DOS & DON'TS: Getting the most from WIDEBAND SCOPES

摘要

Despite high-performance scopes' copious built-in intelligence, you still must employ lots of your own brainpower to obtain meaningful results in high-speed serial-bus debugging. Modern high-performance digital oscilloscopes offer a wealth of features for making users' lives easier—so many features, in fact, that their effect can sometimes be the opposite of what the manufacturer intended. Whereas, typically, the presence of extra capabilities doesn't complicate instrument use, figuring out whether a wanted feature is present and learning how to invoke and properly use it sometimes can induce considerable frustration. Tutorials built into top-of-the-line scopes' help facilities simplify the job of getting up to speed, but manufacturers caution users to adopt the proper mindset when learning how to use unfamiliar features. As Mike Lauter-bach, PhD, director of product management at LeCroy, puts it, "Being in too much of a hurry can waste lots of time." Moreover, when you need to verify a design's compliance with a high-speed serial-data-transmission standard, you are likely to encounter an annoying reality of high-data-rate protocols. According to Lon Hintze, DSO 80000 product manager at Agilent Technologies, "Different protocols specify different methods of measuring similar things." Just because you know how to measure, say, the effect of bandwidth on ISI (intersymbol interference) in a XAUI (10-Gbps attachment-unit-Interface) system doesn't mean that you will necessarily get the correct answer if you apply an identical approach to measuring the equivalent effect in a PCI Express system.