[SI-LIST] Re: DDR3 - Undershoot Area and Vss
- From: Hermann Ruckerbauer <Hermann.Ruckerbauer@xxxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Tue, 28 Jan 2014 07:14:57 +0100
Hello,
just one comment on the undershoot area:
I have seen several Scope compliance measurements that seem to calculate
this value wrong. At least when I do a manual calculation I can not
really find the area measured by the compliance application. The value
even seems way too high and not reasonable.
And second:
If the singal traces goes slightly below 0 and stays there for a long
time because there is no activity any more on the bus also the
compliance app complains.
In both cases I judge the compliance fail as non-critical. Maybe others
can share their opinion here too.
Both things are usually anyhow not issue with terminated busses.
Overall the DRAM compliance test (and the judgement of the results) is
much more critical than other compliance tests, especially due to the
bidirectional and burst type nature of the interface...
Hermann
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schrieb Orin Laney:
> 1- No. VSS is the reference for the measurement, therefore assumed as 0
> volts.
> 2- Volts times nanoseconds should not exceed the limit, e.g. 0.4V for 1
> nanosecond and 0.8V for 1/2 nanosecond are both at the limit. Typically
> though, max undershoot should be kept below one diode drop as a matter of
> good practice.
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
> Behalf Of Sriram A
> Sent: Monday, January 27, 2014 1:02 AM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] DDR3 - Undershoot Area and Vss
>
> Hello,
> Someone kindly help me in understanding few things to be more specific with
> DDR3 Spec.
>
> 1.Do Vss value will vary based on Typ, Min and Max conditions?
>
> Eg. Vdd/Vddq have voltage spec like 1.425V, 1.5 and1.575 respectively based
> on Min, Typ and Max Conditions.(Jedec Spec) My doubt is do Vss also vary
> based on this parameters?
>
> 2. Please help me in understanding Maximum undershoot area below Vss. Eg.
> 0.4 V-ns (as per DDR3 Jedec Spec).
> Please be more specific about Vns (What is V-ns means here?) and how to
> calculate the area for undershoot (in Vns) below Vss.
>
>
> Thanks and Regards,
> Sriram
>
>
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