SI
SI
discoversearch

We've detected that you're using an ad content blocking browser plug-in or feature. Ads provide a critical source of revenue to the continued operation of Silicon Investor.  We ask that you disable ad blocking while on Silicon Investor in the best interests of our community.  If you are not using an ad blocker but are still receiving this message, make sure your browser's tracking protection is set to the 'standard' level.
Technology Stocks : Rambus (RMBS) - Eagle or Penguin
RMBS 87.20-3.3%Nov 20 3:59 PM EST
 Public ReplyPrvt ReplyMark as Last ReadFilePrevious 10Next 10PreviousNext  
To: Alan Bell who wrote (29460)9/14/1999 4:26:00 AM
From: John Walliker  Read Replies (1) of 93625
 
Alan,

For a signal with a rise time of 2ns, the maximum acceptable length would be 2.3 inches.

Thank you for expressing this so clearly. This is at the heart of the disagreement between Carl and myself.

I suspect though that the rise times for SSTL2 are much shorter than this, especially when driving a short bus. I routinely find that perfectly ordinary HCMOS devices with typical rise times specified as a few ns often achieve rise times of as little as 400ps when loaded with only a few inches of pcb track and one CMOS load. I use a four channel, 2 Gsa/s simultaneously sampling HP digital oscilloscope with 800MHz FET probes to do measurements like this. (And I do know how to use it properly, especially with respect to artifacts relating to proper grounding. I usually do differential measurements to avoid them.) With lesser instruments the wild ringing that often occurs is simply not visible.

John

PS Yes, I did forget to compensate for the 10ns cycle time rather than 8ns as Carl pointed out. However, he was wrong to assume that power consumption scales linearly with frequency, because the sense amplifiers will draw a relatively constant current. Also, Samsung quote maximum currents for Rambus parts, whereas IBM appear to quote typical values for supply current of DDR devices. Therefore I think this error will have little or no effect on the final outcome of the calculations.
Report TOU ViolationShare This Post
 Public ReplyPrvt ReplyMark as Last ReadFilePrevious 10Next 10PreviousNext  

HomeMailHotSubjectMarksPeopleMarksKeepersSettings
Terms Of UseContact UsCopyright/IP PolicyPrivacy PolicyAbout UsFAQAdvertise on SI
© 2025 Knight Sac Media.  Data provided by Twelve Data, Alpha Vantage, and CityFALCON News