[SI-LIST] Re: 22.1 Ohm vs 50 Ohm Termination
- From: Ray Anderson <Raymond.Anderson@xxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Fri, 30 Aug 2002 10:06:35 -0700 (PDT)
>
>
>Hi,
>
>I am wondering what the reason for the use of 22.1 Ohm series
>termination on a 50 Ohm line, as opposed to matching it with 50 Ohm.
>
>I have simulated signals with both, and both look reasonable. Is
>there an electrical reason for using 22.2 Ohm or is it just lab
>experience.
>
>Thanks,
>kevin
>
The sum of the output impedance of your driver and the series
termination resistor usually add up to near 50 ohms.
Sometimes a resistor value a bit on the low side is selected
( Zdriver + Rresistor < 50). This causes a bit of overshoot at
the receiver and speeds up the ristime at the receiver compared
to the perfectly terminated case.
-Ray
Sun Microsystems Inc.
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