He, If reflections at the far end are problematic then something must be done to mitigate them. A far end termination impedance that matches the etch impedance is a possible solution. In this case the goal is to get a reflection coeffecient near 0 by solving: p =3D (Zt - Zo) / (Zt + Zo) where Zt =3D far end load, termination impedance, and Zo =3D TLine imp. One can also mitigate far end reflections by launching a half-amplitude wave by inserting a series resistor at the near end, and then employing a +1 reflection coeffecient at the far end to reach full amplitude. The near-end series resistor is sized such that: Rseries + Rds =3D Zo where Rseries is what we are solving for, i.e. the near end series R. where Rds is the on resistance of the output FET. where Zo is the etch, TLine impedance. I have left out a great bit of detail and assumptions, and if you want to continue this thread you can email me directly so as to reduce the BW on the list in general. Also, most of the si books and many on-line app notes cover this in great detail....=20 Jim - Jim Antonellis jim.antonellis@xxxxxxxxxxxxx Sandburst Corp www.sandburst.com Office: 978.689.1669=20 Cell: 978.618.4745 This message and any attachments are Confidential and may be Legally Privileged. It is intended solely for the addressee. If you are not=20 the intended recipient, please delete this message from your system=20 and notify us immediately. Any dis-closure, copying, distribution or=20 action taken or omitted to be taken by an unintended recipient in=20 reliance on this message is prohibited and may be unlawful. =20 =20 -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of He Hao Sent: Tuesday, October 26, 2004 9:46 AM To: si-list Subject: [SI-LIST] [SI-LIST]About Impedance If have implemented 50ohm trace impedance in board, then no need to add = 50ohm match resistor? Or I add match resistor in circuit, then no need to implement approciate = trace impedance? Perhaps silly question,welcome your response. He Hao hehao@xxxxxxxx 2004-10-26 ------------------------------------------------------------------ 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 FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: =20 //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 =20 ------------------------------------------------------------------ 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 FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org 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