[SI-LIST] Re: Test Loading Issues on Quad XTK

Wow,
We are having a discusion over a thing that was invented for technologies 15
years ago. Funny how things stick around. I remember when Larry Rubin
thought this up. He just did it so XTK would play with MOTIVE in the right
way to solve some design problem he was working on at the time.

End of History Lesson.

jon


-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of David Fogel
Sent: Monday, April 28, 2003 6:36 PM
To: Lawrence.Ting@xxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Test Loading Issues on Quad XTK



If timing measurement parameters are not present in the IBIS model than
IBIS2XTK will NOT generate TIME_TO_VM parameters in the translated XTK
model.
During simulations XTK will attemp to do the timing correction by generating
a correction value on the fly. You will see this value in the timing log or
timing report file. XTK calculates this value by linearising the driver's
rise time and by assuming a certain load which I no longer remember its
value. Timing measurement is done at the voltage measurement point specified
in the model.
At the time that this code was written the assumption was that it is better
to approximate the TVM value rather then using TVM = 0. This assumption will
give you approximate values for your flight time which is better than using
TVM = 0. Of course, the most accurate approach is to specify the CORRECT
values in the IBIS model.
Regards
David Fogel
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of lting168
Sent: Monday, April 28, 2003 6:14 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Test Loading Issues on Quad XTK



Thanks for your kindly help.

But, I don't understand if test loading parameters are not present in
the IBIS model and V(m) correction is enable in the XTK,
how XTK can still generate V(m) data.

Lawrence


--- In si-list@xxxxxxxxxxxxxxx, "Abe Riazi" <ariazi@xxxx> wrote:
>
> Dear Lawrence and others,
>
> In my opinion, when considering the effects of TIME_TO_VM in XTK
> simulations we need to focus on two operations:
>
> I.  IBIS2XTK
> II. XNS
>
> How TIME_TO_VM comes into existence and influences results are
> explained below.
>
> I. When translating an IBIS model into QUAD format,  IBIS2XTK
normally
> computes TIME_TO_VM (by calling the "mtest" program) if the timing
test =
> load=20
> parameters (e.g.  Vmeas, Vref, Rref, Cref ) are present in the IBIS
=
> file.=20
>
> However, to ensure reliable TIME_TO_VM values in XTK models, it is
a =
> good=20
> practice to manually determine/check TIME_TO_VM values. This
usually =
> involves=20
> obtaining the test load parameters ( Vmeas, Vref, Rref, Cref )
either =
> from the=20
> IBIS model (or preferably from the device data sheet), carrying out
XNS =
> simulation
> and then measuring the rise and fall delays (by definition
TIME_TO_VM is =
> the time
> it takes the driver output to cross the Vmeas voltage when the
driver is =
> connected to a=20
> desired test load).=20
>
>
> II. With the V(m) correction Enabled, XNS will subtract the driver =
> TIME_TO_VM and
> report the  corrected delays in .idd,  .rep and .gen files.  Such =
> TIME_TO_VM
> correction (to prevent double counting of buffer intrinsic delay)
can =
> prove critical when
> flight time values are to be applied for setup and hold margin =
> computations.
> Furthermore, the delays measured by the XNS (or TLC) cursors differ
from =
> the delays
> reported when TIME_TO_VM correction is enabled.  However, as noted
by =
> Jon Powell
> TIME_TO_VM does not have any effects on signal quality such a
> overshoot/undershoot, ringback, etc.
>
> In summary, it is important that during the model =
> translation/verification phase,=20
> accurate TIME_TO_VM parameters be incorporated into the model's =
> DRIVERSPEC.  This requires utilization of correct timing parameters
( =
> Vmeas, Vref, Rref, Cref )
> and measurement approach.   During the XNS simulations, with the V
(m) =
> correction
> enabled the reported rise and fall delays (in .rep , .idd, and .gen
=
> files) differ from those
> which can be manually measured by the XNS (or TLC) cursors.
>  =20
>
> Best Regards,
>
> Abe Riazi
> ServerWorks
>
> -----Original Message-----
> From: lting168 [SMTP:Lawrence.Ting@xxxx]
> Sent: Monday, April 28, 2003 3:30 AM
> To:   si-list@xxxx
> Subject:      [SI-LIST] Test Loading Issues on Quad XTK
>
>
> Dear all,
>
>  I am using Quad XTK to do simulation. When I get the rising delay
or=20
> falling delay data, those values should be substrated by the=20
> Time_TO_VM values from the IBIS model of driver. However, if the
IBIS=20
> model doesn't include Time_TO_VM data, XTK automatically
generates=20
> the Time_to_VM values. Does anyone know how these values come from?
>
> Thanks in advance
>
> Lawrence
>
>
>
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