[SI-LIST] Re: ODT Impedance on DDR2
- From: "Cusanelli, Tony" <tony_cusanelli@xxxxxxxxxx>
- To: "Hermann Ruckerbauer" <hermann.ruckerbauer@xxxxxxxxxxxxx>, "sudarshan kr" <sudarshankr@xxxxxxxxx>
- Date: Thu, 10 Dec 2009 09:06:12 -0700
Disclaimer: I WORK FOR MENTOR GRAPHICS however, below is the header
from the DDR report. It is quite long, so it wraps in this email, but
you can see that we do compensate for derating.
The eye diagram does not use AC DC rules, it just shows the waveforms.
However, the timing measurements that are used in the spread sheet do
follow the DDR spec and use AC and DC thresholds when appropriate. The
wizard allows you to experiment with different ODT configurations.
Here is the header row for data bit simulation:
Net Name Pass/Fail Operation Driver Comp Ref Des &
Pin Name Receiver Comp Ref Des & Pin Name Associated
Clk/Strobe Net Name Associated Clk/Strobe Driver Comp Ref Des & Pin
Name Associated Clk/Strobe Receiver Comp Ref Des & Pin Name
Clk/Strobe Crossing Threshold Time, [ns] Setup Time (From Sim),
tDS, [ps] Min Setup Time, tDS(min), [ps] Base Setup Time,
tDS(base), [ps] Setup Derate Time Delta, d(tDS), [ps] Required Setup
Time, tDS(req), [ps] Setup Time Margin, tDS(margin), [ps] Hold
Time (From Sim), tDH, [ps] Min Hold Time, tDH - Initial Delay
Delta, [ps] Base Hold Time, tDH(base), [ps] Hold Derate Time Delta,
d(tDH), [ps] Required Hold Time, tDH(req), [ps] Hold Time
Margin, tDH(margin), [ps] Stimulus Offset, [ns] Comments
Regards,
Tony Cusanelli
Applications Engineer Consultant
http://www.mentor.com/products/pcb-system-design/analysis-verification/
http://www.mentor.com/products/pcb-system-design/products/icx-tau/
Cell - 772-349-4363
Voice mail only 407-999-2334
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Hermann Ruckerbauer
Sent: Thursday, December 10, 2009 7:35 AM
To: sudarshan kr
Cc: Mashook Ahamed Usman; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: ODT Impedance on DDR2
Hi,
usually just looking at a single trace or simulating just a view bits
gives only a qualitative answer, but no quantitative answer.
To decide on pass or fail you need to Calculate a timing budget.
This can be done by doing a (long enough) PRBS simulation with at least
3 (better 5) Signals (1 Victim and 4 Aggressors) and evaluate the
resulting dataeye according the spec. in DDR Case you would evaluate the
eye with AC/DC based setupHold times and adding the slew rate dependent
derating.
Additionally you add the Transmitter jitter and finally you will get a
pass or fail and how much margin the design has.
I have not seen the Hyperlinx wizard so far. Maybe somebody can comment
if this one does the eye evaluation ACDC based and add the Derating for
the DDR Memory ?
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
Fax: +49 (0)3212 / 121 9008
Mashook Ahamed Usman schrieb:
> Hi Sudarshan,
> Our usual practice is to simulate with these three
configuration(usually various models comes with the IBIS model of the
same chipset) and see which has the least shoot and proper rise time in
run interactive window of the tool. If possible use the DDR2
wizard(Hyperlynx8.0)and see the overall result in the excel sheet which
tells you how many cases passed and failed.
> All the best,
> M Usman
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of sudarshan kr
> Sent: Thursday, December 10, 2009 5:00 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] ODT Impedance on DDR2
>
> Hi All,
> I am validating the DDR memory controller from 3rd party IP. With
related to the ODT settings of the DDR device, how to qualify and
quantify which of the 3 options(75,150,50Ohm) gives the better results.
> I saw few waveforms on the website which shows an eye pattern of the
w/f.
> But i didnot understand how this is created using a differential
signal probed using an differential probe.
> Thanks in advance
> Regards,
> Sudarshan
>
>
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