David, You are certainly correct...as long as you stay in that "perfect world". As D.C. Sessions pointed out, there are always mismatches and parasitic elements in this (unfortunately imperfect) world. Depending on the speed (i.e., rise/fall times), just getting off the chip and package of the driver can provide some mismatches. Also, any receiver has some load capacitance, causing a glitch to be reflected back. If your driver is unterminated, that glitch is then bounced right back to the receiver. Regards, Mike David Kaiser wrote: > > Theory question. Assume perfect world with no parasitics. > > If a 50 Ohm trace on a board is terminated with a 50 Ohm resistor at the end > of the trace, is there any advantage in terms of SI > to driving the trace with a source that has 50 Ohm output impedance compared > to a source with 10 or 20 Ohms of output impedance? > > It seems to me that the only thing the series source impedance would do to a > 50 Ohm line that is terminated with a 50 Ohm resistive load would be to > divide the amplitude in half without improving the signal integrity. > Correct? > > David > ------------------------------------------------------------------ > 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 > -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Mike Jenkins Phone: 408.433.7901 _____ LSI Logic Corp, ms/G715 Fax: 408.433.7495 LSI|LOGIC| (R) 1525 McCarthy Blvd. mailto:Jenkins@xxxxxxxx | | Milpitas, CA 95035 http://www.lsilogic.com |_____| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ------------------------------------------------------------------ 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