[SI-LIST] Re: Transmission line impedance
- From: Yafei Bi <yafei_bi@xxxxxxxxx>
- To: cygnul@xxxxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Wed, 20 Dec 2006 01:54:28 -0800 (PST)
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 _____________=
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