Vref power source?

I’ve got some advice, use a regulated power supply, not a voltage divider. When you use a voltage divider, the resistors would have to be precisely matched and have a very tight tolerance. If they are not matched exactly, then your reference voltage may vary at the device input pin, and that will lead to signal level detection issues. It’s worth the extra money and board space if you want a robust interface.

We've successfully done both styles -- a dedicated vref supply, or a 1K pullup/pulldown on the VREF pins for that bank. This tends to be the individual designer's preference. Altera's Stratix II GX PCI Express dev kit board uses a regulator for generating VTT for a DDR2 interface and this regulator has a VREF output (TPS51100DGQ).

The VREF doesn't require much current so a voltage divider can work. Don't try using a voltage divider for VTT as these pins will require much more current during output buffer transitions.

Would anyone be concerned about VREF using a voltage divider? I would think the VREF could drift with a voltage divider causing marginal SI to be worse. Any comments?