[SI-LIST] Re: control signals in DDR2
- From: steve weir <weirsi@xxxxxxxxxx>
- To: hermann.ruckerbauer@xxxxxxxxxxxxx
- Date: Thu, 24 Dec 2009 03:09:35 -0800
At the Manor SI Laboratories it was said that all RF shorts were equal.
Some RF shorts were more equal than others.
Steve.
Hermann Ruckerbauer wrote:
> Hi,
>
> The VDD (not VTT) return path for CCA (Control/Command/Address) bus was
> choosen due to the pincount limitation on the Connectors.
> In order to have enough VDD pins the VDD pins have been chosen to
> provide the shielding and return path for this bus.
>
> Effects in simulation: as long as you have a good Power plane it is as
> good as a GND plane. In any case a nice RF Short between Power and GND
> should be created everywhere where a change of the return current
> between Power and GND is happening.
> If you want to consider it you need to extract a complete model where
> Return path is considererd e. g. by a 2.5D Field solver as Momentum.
>
> Many simulators (LineSim and ADS schematic sim) assume an ideal return
> path anyhow ...
>
>
> regards
>
> Hermann
>
> EKH - EyeKnowHow
> Hermann Ruckerbauer
> www.EyeKnowHow.de
> Hermann.Ruckerbauer@xxxxxxxxxxxxx
> Veilchenstrasse 1
> 94554 Moos
> Tel.: +49 (0)9938 / 902 083
> Mobile: +49 (0)176 / 787 787 77
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>
>
>
> steve weir schrieb:
>
>> They are to allow for low cost continuous return path on all DDR signals.
>>
>> Steve.
>> prasad wrote:
>>
>>
>>> Hi All,
>>> please suggest why the control signals in the DDR2 are referred to VTT
>>> instead of GND?
>>>
>>> what are the affects , if this is not considered in simulation and instead
>>> referring to GND is used?
>>>
>>> thanking you all in advance....
>>>
>>>
>>> Best Regards,
>>> prasad...
>>>
>>>
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>>>
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