[SI-LIST] Re: control signals in DDR2
- From: Hermann Ruckerbauer <hermann.ruckerbauer@xxxxxxxxxxxxx>
- To: steve weir <weirsi@xxxxxxxxxx>
- Date: Thu, 24 Dec 2009 11:56:47 +0100
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
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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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