[SI-LIST] Re: control signals in DDR2
- From: Jennifer Maharani <jennifer.maharani@xxxxxxxxx>
- To: Mostafa Abdulla <mostafa_abdulla@xxxxxxxxxxx>
- Date: Thu, 24 Dec 2009 23:48:05 +0100
Hi Mostafa,
What about LpDDR1? What is pvt ref then? Is it not used as reference?
Many thanks,
Jenni
On Dec 24, 2009, at 10:52 PM, "Mostafa Abdulla " <mostafa_abdulla@xxxxxxxxxxx
> wrote:
> In LPDDR2, commands and addresses have separate power and ground
> named VSSCA and VDDCA.
>
>
> Sent via BlackBerry by AT&T
>
> -----Original Message-----
> From: Hany Fahmy <hfahmy@xxxxxxxxxx>
> Date: Thu, 24 Dec 2009 21:37:24
> To: <jennifer.maharani@xxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
> Subject: [SI-LIST] Re: control signals in DDR2
>
> I think the same concept also apply to LPddr as well.
> ----- Original Message -----
> From: si-list-bounce@xxxxxxxxxxxxx <si-list-bounce@xxxxxxxxxxxxx>
> To: si-list@xxxxxxxxxxxxx <si-list@xxxxxxxxxxxxx>
> Sent: Thu Dec 24 12:46:43 2009
> Subject: [SI-LIST] Re: control signals in DDR2
>
> Hello,
>
> Is this also valid for low power ddr?
>
> many thanks,
> Jenni
>
>
> On Dec 24, 2009, at 8:29 PM, Hany Fahmy <hfahmy@xxxxxxxxxx> wrote:
>
>> Another reason for address/command bus ref to Vdd instead of GND is
>> to isolate the address/comman bus from the noise on GND due to DQ-
>> SSO, it degrades the perf of address/command especiaLly if u want to
>> run address/command at 1N mode which is much tighter voltage and
>> timing margin.
>> For ddr3, we have an isolated Vref-MA also ref to Vdd to carry the
>> same noise signature of address/command signals but for ddr2, it is
>> the same Vref for both address/command and DQ bus.
>>
>> Agree with Hermann that u do need to accurately model the return-
>> path discontinuity if the signals make transitions and changes ref
>> layers. Agree with Hermann that Momentum can accurately model it and
>> improve the performance by adding enough stitching vias or RF shorts
>> (coupling caps) close to the transistions.
>>
>> Hany Fahmy
>> Nvidia Corporation
>>
>> ----- Original Message -----
>> From: si-list-bounce@xxxxxxxxxxxxx <si-list-bounce@xxxxxxxxxxxxx>
>> To: hermann.ruckerbauer@xxxxxxxxxxxxx <hermann.ruckerbauer@xxxxxxxxxxxxx
>>>
>> Cc: prasad <hariprasad.palli@xxxxxxxxx>; si-list@xxxxxxxxxxxxx
>> <si-list@xxxxxxxxxxxxx
>>>
>> Sent: Thu Dec 24 03:09:35 2009
>> Subject: [SI-LIST] Re: control signals in DDR2
>>
>> 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 <http://www.EyeKnowHow.de>
>>> Hermann.Ruckerbauer@xxxxxxxxxxxxx
>>> Veilchenstrasse 1
>>> 94554 Moos
>>> Tel.: +49 (0)9938 / 902 083
>>> Mobile: +49 (0)176 / 787 787 77
>>> Fax: +49 (0)3212 / 121 9008
>>>
>>>
>>>
>>> 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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