[SI-LIST] Re: Why 50 ohms
- From: "Clewell, Craig" <cclewell@xxxxxxxxxxxxxx>
- To: "'siman_74@xxxxxxxxxxxxxx'" <siman_74@xxxxxxxxxxxxxx>,si-list@xxxxxxxxxxxxx
- Date: Mon, 21 Jan 2002 08:40:16 -0500
Mani,
There is actually a few reasons why we use 50ohms (depending on which camp
your from). 2 of which can be found in EDN magazine (Sept. 14, 2000 pg.30
and Jan 4, 2001 pg.28) One of the most widely known reasons is due to the
relationship between maximum power and minimum attenuation. You see in an
air filled coaxial line minimum attenuation occurs at an impedance of
77ohms, while maximum power occurs at an impedance of 30ohms. So, 50ohms is
a compromise between these 2 values.
Regards,
Craig
-----Original Message-----
From: mani kantan [mailto:siman_74@xxxxxxxxxxxxxx]
Sent: Saturday, January 19, 2002 1:52 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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