In a lot of ways this relates to a previous question on how to measure time-of-flight and relate that properly to the CLK->Q data in a static timing program. Since the actual CLk->Q (Tpd or whatever) of the device is dependent on load, the datasheets will spec it into a specific load and then it becomes the job of the SI and Timing tools to figure out how to properly change that data for accurate total path timing. It used to be that most drivers were spec'd into 50pf loads because that happened to be the loads on the chip testers. Now days 50pf is so far away from the real load that that spec isn't good enough for many purposes. As other people have pointed out, if the load is closer to the driver than a round-trip, the C of the load is seen by the driver and can change the transition rate of the driver, which effectively changes Tpd. If the load is farther away than a round-trip it is effectively non-existent to the driver (at least starting from steady-state) and can have no effect on Tpd. -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Yoni Tzafrir Sent: Tuesday, June 10, 2003 5:45 AM To: Si-List (E-mail) Subject: [SI-LIST] delay vs. transmission line length hi, i run some simulations, for measuring Tpd from input of the of the = driver to the output of the driver.=20 |\ | \driver transmission line input------------| = \---------------------------------------------------LOAD | /out |/ I have noticed that the longer my transmission line, the Tpd becomes = shorter. does it make sense? as i understand it a longer transmission line means = more capacitance (and resistance) so the Tpd should be longer, doesn't = it? Yonatan (Yoni) Tzafrir *Tel: (972) - 3 - 7552300 (T/L: 351) *Fax: (972) - 3 - 6177130 *Mobile: (972) -54- 459469 *E-mail: <mailto:yonitz@xxxxxxxxxxxxx> ------------------------------------------------------------------ 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