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Technology Stocks : Rambus (RMBS) - Eagle or Penguin -- Ignore unavailable to you. Want to Upgrade?

To: Tony Viola who wrote (19555)	5/1/1999 1:14:00 PM
From: Alan Bell	Read Replies (2) \| Respond to of 93625

Tony, The Rambus clock runs at 400Mhz (and is a differential signal.) Data is clocked on both edges. The data lines toggle at a max of 400Mhz (and are non-differential.) As you point out, the data rate is 800mb/sec even through no signal transitions faster than 400Mhz. The layout guidelines are that all signals need to run on the top layer, there is a ground plane directly under these signals, and that vias be minimized. The impedance needs to be 28 ohms if you are using Rimms and between 25 & 50 ohms if the rambus chips are being mounted on the board. Vias need to be avoided. Details can be found in rambus.com Because Rambus was able to specify pinouts, they are able to route the signals so they require no vias and have no stubs - both major causes of impedance discontinuities. The motherboard will probably need to go to 6 layers from 4 layers. And it would be easy to make a non-operational layout. But doing it correctly does not look particularly hard if a competent engineer helps with the layout. -- Alan