Sam,=0A=0APage 141-144 of Thomas Lee's book "The Design of CMOS Radio Frequ= ency Integrated Circuits" - "Why 50 (or 75) ohm?" is an excellent reading i= n terms of how the 50 ohm comes about.=0A=0AFrom driver's perspective, it c= an be any value, as long as it matches the transmission line characteristic= impedance it is driving. To match the impedance is to minimize the reflect= ion at your driver output, thus minimize SI related problems.=0A=0AIf you h= ave access to a circuit simulator which supports transmission line, a simpl= e simulation with idea driver(voltage source + output impedance), plus tran= smission line and input termination can demonstrate why matching matters.= =0A=0ABest,=0A=0AYafei=0A=0A----- Original Message ----=0AFrom: Sam Pete <c= ygnul@xxxxxxxxx>=0ATo: si-list@xxxxxxxxxxxxx=0ASent: Tuesday, December 19, = 2006 10:27:44 PM=0ASubject: [SI-LIST] Transmission line impedance =0A=0AHi= Friends,=0A =0A Whenever we refer to SI books or application notes, the= impedance of the transmission line is mentioned as 50-ohms or 60-ohms. Wh= at is the speciffic reason behind this value? why can't it be something dif= ferent than this? OR Why this 50-ohms conceptualized from the driver's pers= pective? (evolution of transmission line theory for Digital Design)=0A Ple= ase flood me some info on this.=0A =0A Regards,=0A Sam=0A _____________= _____________________________________=0ADo You Yahoo!?=0ATired of spam? Ya= hoo! Mail has the best spam protection around =0Ahttp://mail.yahoo.com =0A= =0A------------------------------------------------------------------=0ATo = unsubscribe from si-list:=0Asi-list-request@xxxxxxxxxxxxx with 'unsubscribe= ' in the Subject field=0A=0Aor to administer your membership from a web pag= e, go to:=0A//www.freelists.org/webpage/si-list=0A=0AFor help:=0Asi-li= st-request@xxxxxxxxxxxxx with 'help' in the Subject field=0A=0AList FAQ wik= i page is located at:=0A http://si-list.org/wiki/wiki.pl?Si-= List_FAQ=0A=0AList technical documents are available at:=0A = http://www.si-list.org=0A=0AList archives are viewable at: =0A h= ttp://www.freelists.org/archives/si-list=0Aor at our remote archives:=0A = http://groups.yahoo.com/group/si-list/messages=0AOld (prior to June 6,= 2001) list archives are viewable at:=0A http://www.qsl.net/wb6tpu= =0A =0A=0A=0A=0A=0A=0A=0A =0A_____________________________________________= _______________________________________=0AYahoo! Music Unlimited=0AAccess o= ver 1 million songs.=0Ahttp://music.yahoo.com/unlimited ------------------------------------------------------------------ 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