Weston, I agree with your method in terms of function but want to add two things. Measuring the flight time at the logic levels includes the effect of dispersion, especially at really high speed signals or very fast edges. When the signal to noise ratio is poor the driver strength adds some errors too to the measured flight times. Compromise: Measuring the flight time at 50% of the signal amplitude for the properties of the printed crcuit board and measuring at the logic levels for design security. Just my 2 cents ;-) Michael -----Original Message----- From: Beal, Weston [mailto:weston_beal@xxxxxxxxxxx] Sent: Donnerstag, 31. Januar 2002 18:17 To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Still looking for input .... Todd, Maybe the silence is an admission of lack of knowledge. In my dealings with various hardware designers, some of them want the measurements done one way or the other, but the reason is usually something like, "That's the way RJ always does it." From all my understanding, I believe that the correct method is to measure at the logic thresholds. This statement also assumes that we've done our very best to correctly model all the parts of our circuit that we can. If the circuit works correctly at the corner cases then it's almost guaranteed to work over the range of manufacturing tolerances. Measuring to one reference voltage at the receiver doesn't tell you anything about the performance of the circuit after manufacturing. Later, Weston -----Original Message----- From: Todd Westerhoff [mailto:twester@xxxxxxxxxxx] Sent: Thursday, January 31, 2002 8:18 AM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Still looking for input .... Okay, folks ... So far we've seen two posts to my question of how flight times are measured. Since we've seen substantial discussion recently on questions related to higher education and Physics 101, I was REALLY hoping to see some more discussion on this particular SI issue. One line responses with a vote are fine. One line responses saying "your question doesn't make sense!" are even OK. But silence is NOT golden in this case. Thanks! 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 ------------------------------------------------------------------ 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 ------------------------------------------------------------------ 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