Erwin, Higher damping will attenuate the signal highly. However, in digital world, we may allow to have unmatch damping as long as timing, such as setup time and hold time, can be met. John Lin Senior SI Engineer, Server Team, ARD4 Quanta Computer Inc.,Taiwan, R.O.C. Email: John@xxxxxxxxxxxx Tel: 886+3+3272345 ext. 5183 -----Original Message----- From: Bill Chen [mailto:billchen@xxxxxxxxxxx] Sent: Wednesday, March 20, 2002 4:25 AM To: erwin-sp_seow@xxxxxx; 'si-list' Subject: [SI-LIST] Re: Series termination value Erwin, If your tline Z=71 ohm, and the driver Zo=20 ohm, the 50 ohm serial termination value looks good. You may need to consider the PVT variations of the driver output impedance so you can determine an optimal termination value though. Thanks! Bill Chen Andiamo Systems -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of SEOW,ERWIN-SP (HP-Singapore,ex6) Sent: Tuesday, March 19, 2002 12:33 AM To: 'si-list' Subject: [SI-LIST] Series termination value Hi all, I have a question on series resistors termination. I have a 4 layer FR4 board with standard PCB stackup (Trace width = 6 mils). We have calculated the Characteristic Impedence to be about 71 Ohm. With an output impedence of about 20 Ohm, the resistor value for series termination is 71 Ohm - 20 Ohm = 50 Ohm. My question is this value too big? Will it attenuate the signal? We are running at about 90MHz. Your advice is appreciated. Thanks! Erwin ------------------------------------------------------------------ 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