[SI-LIST] Re: Why 50 ohms
- From: Patrick_Carrier@xxxxxxxx
- To: siman_74@xxxxxxxxxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Sat, 19 Jan 2002 09:24:45 -0600
Mani--
PCB impedances are usually determined to closely match the output impedance
of a signal driver. This eliminates reflections from occurring and
distorting the transmitted signal.
Also, typical PCB trace widths and dielectric heights will give you a 50-ohm
line fairly easily, since impedance is a function of trace geometry.
The 27 ohms for RAMBUS is kind of a random one, and mostly had to do with
the fact the driver was much different than normal signal drivers.
Good question!
--Pat
-----Original Message-----
From: mani kantan [mailto:siman_74@xxxxxxxxxxxxxx]
Sent: Saturday, January 19, 2002 12:52 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Why 50 ohms
Hello SIexperts,=0D=0A I am a student, doing Engineering in Electri=
cal.=0D=0AWhile discussing with my friend, he told me that the PCB trace im=
pedance should be maintained as 50 Ohms (for differential=3D 100 and for so=
me RDRAM buses 27ohms).=0D=0AI tried to find the answer for this in some of=
the standard books but i could find the answer for this. Books also saying=
that we should maintain 50 ohms. But i couldn't find the reason for that.=
=0D=0A=0D=0ACould any body please through a light on me on this topic.This =
may be a newbie question. But i thought this group is the correct place to =
get my answer.=0D=0A=0D=0A=0D=0Athanks in advance,=0D=0ASiMan=0D=0A =0A
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