Hi everyone,
I have a board which uses DP83822IRHBR and is connected to our processor using RGMII. We decided to use 60 Ω ± 15% characteristic impedance on the RGMII for the first spin of the board. The MAC input and output impedance on the processor side is set to 60 Ω and the MAC impedance on the PHY side is set to 61.11 Ω using the configuration registers. We don't have discrete termination resistors on the traces. As far as we can see, we don't have any serious signal integrity problems on the RGMII bus, but the reflections on the Tx pins of the RGMII could look a bit better.
In the meantime, I've read the thread here, and my understanding of it was that the MAC impedance setting on the PHY sets series termination resistors on the output pins, but does nothing for the input impedance of the MAC.
We're re-spinning the board now, and we're thinking if we should move to a 50 Ω RGMII or not in the next re-spin. As far as we can see, we currently have 60 Ω everywhere except on the input of the PHY, where the impedance is unknown (or at least I can't find it in the datasheet). On the other hand, the datasheet recommends 50 Ω for RGMII impedance.
So should we move to the 50 Ω RGMII completely, or is it OK to stay with the 60 Ω? Are there any other aspects behind the 50 Ω the characteristic impedance that we missed?
