[SI-LIST] Re: Calculating rise time from IBIS
- From: Ferhat Yaldiz <ferhatyaldiz@xxxxxxxxx>
- To: Arpad_Muranyi@xxxxxxxxxx
- Date: Sat, 29 Nov 2014 14:29:50 +0200
Hi Arpad,
Thanks for your detailed explanations why IBIS use resistive load.I mean if
you want to correlate simulation
and measurement for rising time you use result of real topology not IBIS
file and compare your ossiloscope result.
Best Regards,
Ferhat Yaldiz
On Thu, Nov 27, 2014 at 7:33 PM, Muranyi, Arpad <Arpad_Muranyi@xxxxxxxxxx>
wrote:
> From: Muranyi, Arpad
> Sent: Thursday, November 27, 2014 11:26 AM
> To: SI-List
> Subject: RE: [SI-LIST] Re: Calculating rise time from IBIS
> Ferhat,
>
> Regarding âreal systems have capacitive load(s)â, true, butâ¦
>
> Most faster systems use (resistive) on-die terminations these days.
> But even if there are no resistive terminations, the PCB traces act
> as a transmission line. Unless the capacitive loads are connected
> directly to the driver, the driver will first âseeâ the T-line, not
> the capacitance at the end of the T-line. If the buffer switches
> faster than the signal travels a round trip on the T-line (which is
> the case in most modern designs), during the time the signal travels
> from the driver to the load capacitance and back, the driver sees the
> impedance of the T-line. During this time the T-line looks like a
> resistive load to the driver, and the driver has no clue that there
> is a capacitor at the end of the T-line until the reflection arrives
> bat at the driver. So the waveform you will see at the driverâs output
> during this time will be the same as if you connected a resistor to
> it with a value equal to the T-line impedance.
>
> This is actually reason IBIS deals with resistive loads when it
> comes to extracting the data for the waveform tables and the [Ramp]
> keyword.
>
> I hope this helps,
>
> Arpad
> =====================================================================>
>
> From: Ferhat Yaldiz [mailto:ferhatyaldiz@xxxxxxxxx]
> Sent: Thursday, November 27, 2014 2:57 AM
> To: Muranyi, Arpad
> Cc: SI-List
> Subject: Re: [SI-LIST] Re: Calculating rise time from IBIS
>
> Hithesh,
> Actual rise time depends on loading. IBIS contains for resistive load, but
> real systems
> have capacitve load(s). You can use your simulated waveform for comparing
> measured
> waveforms. As initial you can use it for estimating bandwidth of signal,
> but lastly you must use real
> topology for real spectrum of signal.
> Ferhat Yaldiz
>
> On Thu, Nov 27, 2014 at 7:05 AM, Muranyi, Arpad <Arpad_Muranyi@xxxxxxxxxx>
> wrote:
> Aubrey,
> You are correct, but note that he wants to scale to 10-90% of
> 3.3 V, not the swing of the buffer as the waveform data in the
> IBIS file might have it. We have yet to find out why he wants
> to do that...
>
> Also note that in his calculation he "scaled" both the time and
> voltage values. A buffer doesn't do that. The switching time
> of a buffer stays pretty much the same, no matter how many
> ohms the load resistance is, so for that reason he shouldn't
> "scale" the time value of the [Ramp] (other than recalculating
> from 20-80 to 10-90 which for me would give 253 ps, not 720 ps
> that he got. (190/0.6*0.8%3)
>
> Thanks,
>
> Arpad
> ===============================================================
>
> -----Original Message-----
> From: Aubrey Sparkman [mailto:asparky@xxxxxxxxxxxxxxxxxxxxxxxx]
> Sent: Wednesday, November 26, 2014 10:25 PM
> To: tom@xxxxxxxxxxxxxxxxx
> Cc: Muranyi, Arpad; SI-List
> Subject: Re: [SI-LIST] Re: Calculating rise time from IBIS
>
> Hitoshi,
>
> If your model has waveform data, you can get the 10/90 time from that.
> Better than scaling.
>
> Aubrey
> SparkRight Solutions
>
> Sent from my iPhone
>
> > On Nov 26, 2014, at 12:11 PM, Tom Dagostino <tom@xxxxxxxxxxxxxxxxx>
> wrote:
> >
> > Be very careful about scaling from a 20-80 % risetime to 10-90%.
> Scaling assumes the risetime is linear from the 10 to 90% points on the
> edge. It is very unlikely to be the case.
> >
> > Tom Dagostino
> >
> > Teraspeed Labs
> > 9999 SW Wilshire Street
> > Suite 102
> > Portland, OR 97225
> >
> > tom@xxxxxxxxxxxxxxxxx
> > www.teraspeedlabs.com
> >
> > 971-279-5325 office
> > 503-430-1065 cell
> >
> >
> > -----Original Message-----
> > From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of Muranyi, Arpad
> > Sent: Wednesday, November 26, 2014 7:51 AM
> > To: SI-List
> > Subject: [SI-LIST] Re: Calculating rise time from IBIS
> >
> > From: Muranyi, Arpad
> > Sent: Wednesday, November 26, 2014 9:47 AM
> > To: SI-List
> > Subject: RE: [SI-LIST] Re: Calculating rise time from IBIS Hitesh,
> >
> > What are you trying to do with the 10-90% of 3.3 V?
> > The reason I am asking is because the âscaledâ value might be wrong
> depending on what you are using it forâ¦
> >
> > Thanks,
> >
> > Arpad
> > ======================================================> >
> > From: Hithesh [mailto:hitheshn@xxxxxxxxx]
> > Sent: Wednesday, November 26, 2014 12:59 AM
> > To: Muranyi, Arpad
> > Cc: SI-List
> > Subject: Re: [SI-LIST] Re: Calculating rise time from IBIS
> >
> > Thanks.
> > So for 10-90% of 3.3V, I just scale the 700mV/190ps.
> > This will be 2.65V/720ps.
> >
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