[SI-LIST] Re: DDR simulation

Hi Zhangkun,
have you tried it with a series resistor (between 10 to 20 Ohms) at the
driver(s)? Check out the app notes on Micron's web site on DDR. They're
quite informative. And where does r_pull pull to? That one should be a 75
Ohm resistor to VTT, which should be 1.25V using a source/sink voltage
regulator.

Also, depending what 'load' represents in your system, 4 'loads' could be
quite a lot for DDR. If 'load' is just a single DDR SDRAM device, then
you'll be more than fine, of course, but if it's a double-sided DIMM, you
probably should consider using registered DIMMs for those.

Good luck!

Stefan Ludwig

--

Ludwig Systems Engineering         Consulting - Design - Implementation
WWW: www.ludwigsystems.com         System Architectures - FPGAs - PCBs
Ph/Fx: +41-43-355-58-73/74         Hardware - Firmware - Software


> Dear all
> I am simulating about DDR. The topology is following:
>
>                            (800mil)
> Driver==================================================r_pull
>            (4000mil)      |       |      |      |
>                           |       |      |      |
>                          load    load   load   load
>
> The simulaiton result shows that the waveform at the first load is very
> bad. How to improve it? The DDR is of 400MHz. The stub at near load is
> only 100mil.
>
> Best Regards
>
> Zhangkun
> 2005.2.26
>
>
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