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Posted by Rich Seifert on July 1, 2008, 7:56 pm
> The paired MDI signals from the PHY to the magnetics in a GbE application
> are each terminated by a 50R resistor and then together to a 10nF capacitor
> to GND. However some applications connect the 2 resistors to Vcc (2.5V) as
> well. Can anyone explain why some configurations are like this and others
> aren't? Is it something specific to the magnetics?
>
It is not the magnetics; more likely, some implementations need a
"pullup" to the higher voltage to provide power to the output driver
through the terminating resistors. This is a function of the
configuration of the output transistors in the PHY chip.
--
Rich Seifert Networks and Communications Consulting
21885 Bear Creek Way
(408) 395-5700 Los Gatos, CA 95033
(408) 228-0803 FAX
Send replies to: usenet at richseifert dot com
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