From my customer:
I’m using the 1Gb Ethernet on the i.MX6 SECO SOM board. Based on looking at lots of designs this is what I came up with. Directly to the SOM on one side, directly to the connector on the other.
Some documents said let the center taps float for 1GbE. Just in case not I have the 4 each 0 Ohms.
Speaking with a S/W engineer today he said he’s seen 1GbE with caps on the center taps to GND. And I learned today they’re having possible issues with this design on another board.
For 10/100 I often see an R to Vcc and cap to ground on the center tap. Plus a cap with 2 each 49.9 Ohm resistors on each Ethernet line on the IC side.
What do you recommend?
It depends on the Ethernet PHY. A voltage drive mode PHY requires capacitors to GND on transformer center taps. A current drive mode requires R&Cs that you described. I have never seen floating center taps.