The driver should be matched to impedance. The length of the line does not matter. If your driver can drive 50 Ohm 3 inch line - it will drive 50 inch line. -----Original Message----- From: C.Y. Cheng [mailto:cyc@xxxxxxxxxxxxx] Sent: Monday, August 20, 2001 12:05 AM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] How does the loading affects the rise time of a PAD? Hi folks, I have got a basic problem to choose a PAD for GMII interface. The system requires a PAD which could drive a 5 pF loading in 1ns rise time. If I can choose a PAD which could drive a 3-inches long, 50 ohms transmission line and meet spec. . What if I use the same pad to drive a 15-inches long, 50 ohms transmission line? The lump capacitance may increase to be 5 times of previous case. Will it " slow down " the rise time of the PAD ? Thanks, C.Y. Cheng ASIC designer ADMtek Taiwan ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field 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 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