Re: [SI-LIST] : 50 or 60 ohm impedance

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From: Michael Nudelman (mnudelman@tellium.com)
Date: Tue Dec 12 2000 - 09:01:54 PST


Well,

some parts may be on-chip terminated and you may have no choice but to use
matching termination.

Also - You drivers' current sourcing/sinking capability, your backplane traces'
impedances (if any) that you have to match to.

YOur board density - how wide your wires can be; your allowed stackup (same
reason).

Etc...etc....

Also - what you are comfortable with. If it is digital not so hi-speed signal
schematic (up to hundred megs) - and you have someething like 50 Ohm target
impedance- your 60 Ohm one will not (or may not) create so much reflection that
you have to worry about it ( the difference may be within tolerance), so I
would not loose a night's sleep over this in such a case.

Mike.

"Sampson, Scot" wrote:

>
> Hello All
>
> What are some of the criteria that is used when selecting 50 or 60 ohms
> for board impedance?
>
> Thanx Scot
>
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