Question for the group: Most commercial SI tools seem to measure flight times to the receiver's input thresholds. Thus, for a given transition, they report a "min" and "max" flight time based on the threshold settings. However, there is a school of thought in SI that says measuring flight times to Vil/Vih is too conservative. It's based on the observation that setup/hold specs for a part are measured the same way Tco is - with reference to a specific threshold. Therefore, the reasoning goes, you can measure flight times to the point where the receiver crosses the reference threshold, and, as long as the signal is within certain quality (i.e. non-monotonic) and slew-rate limits, the flight time measurement is valid. The required slew-rate is (or should be) part of the receiving device's input spec. If the input signal does NOT meet the quality/slew rate requirements, well, then you have to use Vil/Vih method, or in some cases, a derating formula. My question is: what techniques are people predominantly using: the Vil/Vih method, the reference voltage, or something in-between? For those who use the reference voltage method, I'm curious to know how post-route analysis is performed. You can adapt any post-route SI tool to measure at a single voltage by changing the models (if necessary), but - do any of the tools report slew rate at the receiver inputs during post route analysis? Your comments, both on and off the list, are greatly appreciated. Todd. Todd Westerhoff SI Engineer - Hammerhead Networks 5 Federal Street - Billerica, MA - 01821 email:twester@xxxxxxxxxxx - ph: 978-671-5084 ============================================ "Oh, but ain't that America, for you and me Ain't that America, we're something to see Ain't that America, Home of the Free Little pink houses, for you and me" - John Mellencamp ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu