Backplane Termination using DDR Termination...

[Schatzy]

I am designing a new backplane that uses Eurocard connectors. It is an 18 slot backplane and uses signalling that is similar to the traditional VME style.

I have been looking at DDR termination as a means to control reflected signals in traces and I see that I might have better luck "tuning" my backplane if I were to use a Vtt regulator at about 2.6V and a single resistor to each trace of the backplane. This resistor would be set to a value of around 100 ohms and there would be a resistor placed at both ends of the backplane and connected to the Vtt bus.

Can anyone tell me if this is a good implementation? Are there any comments as to the values of the resistors or the Vtt voltage value?

 

[Schatzy]

I may have specified this termination technique incorrectly...
If I were to use a 100 ohm series termination resistor at each end of the strip-line on my backplane and it is connected to a 2.6V power supply there would be a reduction in the power loss of the backplane and it would be easier to 'tune the impedances of my larger backplanes.
I am having difficulty understanding what the effect would be to the backplane's traces if I terminated all of the lines this way. Also, I cannot find any literature that discusses this technique. Perhaps the technique is more of a GTL style than DDR.

Any comments?

 

[Schatzy]

Completed my first project with this kind of termination... Actually it is called "Active Termination" and uses a series resistor connected between each end of the backplane strip-line and a power supply (called Vtt).
I set the voltage level at 2.6V to balance the loading on the lines so that the drivers on each card have less of a current demand when transitioning. 2.6V is slightly into the logic "1" condition causing the backplane to still have the pullup characteristic which is typical.
The old termination technique required a constant current of about 1.5A to bias the pullups and pulldowns. My new backplane uses about 50mA or so! I made a 3 slot and am getting ready to try the 18 slot.