[SI-LIST] Re: Transmission line impedance

Yafei 

One reason that impedances can't go higher is that that would force
interconnect and chip packages to space contacts farther apart. So on one
hand, you have a drive to miniaturize and on the other hand a drive to
increase impedance. The result helps explain where we are today and why it
is unlikely to change.

michael munroe
www.copperalliance.net 

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Yafei Bi
Sent: Wednesday, December 20, 2006 4:54 AM
To: cygnul@xxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Transmission line impedance

 
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=
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