Hi All, I'm working on a small, portable, handheld device that is required to have gigabit ethernet available to a user for certain use-cases. In other words, this device will be used most of the time without the ethernet powered up. However, when ethernet is needed, I'll need gigabit. Since the device is very size-constrained, we'd like to include as little of the actual ethernet hardware lineup (RJ45, magnetics, phy) as possible on the actual device, opting for a plug-in dongle that interfaces with the unit to provide ethernet connectivity (RJ45 + whatever other hw is required) when needed. As a side-note, I was quite surprised to see that there didn't seem to be any slim form- factor connectors that supported gigE...after all, with SATA etc. becoming so prominent I figured there would be a comparable small, low- profile connector for ethernet. But I can't find one. So we're looking at using a low-profile, shielded connector with sufficient lines to pass the high-speed signals between our device and the dongle. We're still looking around, but it looks like Amphenol and Samtec both have options that may work here.
So this is where things get a bit tricky. Gigabit ethernet signalling can be fairly finnicky. We are exploring the options of where we could possibly split the hardware between the main device and the dongle. The interface between the MAC and the PHY (for RGMII) is ~12 single-ended digital lines running at 125 MHz (but the data lines are DDR, so these 8 lines are really running at 250 MHz). The interface between the PHY and the magnetics is 4 analog differential pairs, with each pair operating at 125 Msymbols/sec. The interface between the magnetics and the RJ45 is also 4 analog differential pairs (they are isolated, due to the transformer).
Does anyone have any wisdom/experience they would like to share regarding the least risky spot to drop a connector into the aforementioned lineup? One major feather in our cap is that we can control all parameters of the dongle (i.e., its length, the impedance matching, the cable type used, etc). This device is only intended to be plugged directly into a PC, so it isn't like we'll need to support the typical 100 meter requirements that IEEE specifies. Personally, I'm leaning towards making the split between the PHY and the magnetics, and passing the four analog differential pairs through our low-profile connector to the dongle. But I'd be interested in other opinions/experiences here.
Thanks for the bandwidth, John