[SI-LIST] Re: [SI-LIST]Re:HowV-TtablebeenextractedforIBISmodel
- From: steve weir <weirsi@xxxxxxxxxx>
- To: ZHENGZHIWEI <zhiweizh@xxxxxxx>
- Date: Fri, 13 May 2011 10:10:42 -0700
Your concern is shoot-through / crow barring. In a practical system
where Vtt is between the rails this is a genuine concern:
1. Output driver stress
2. Peak power distribution load
3. Transmit signal integrity
However, the static V-I tables won't tell you anything about it. You
derive this behavior from the timing data.
Steve
On 5/13/2011 1:53 AM, ZHENGZHIWEI wrote:
>
> Hi Steve W,
>
> Let's focus on the first question first.
>
> > Say, the first case, falling waveform with terminator connect to
> Vcc.= It
> > only mention about Pulldown transistor turning on.
> [Steve W] As far as the termination is concerned, the Pull-up
> transistor cannot
> [Steve W] supply current to a terminator that connects to Vcc.
>
> My concern is,
> Pulldown transistor is turnning on while Pullup transistor
> turnning off, because there has overlap time, there has
> current flow from VCC through Pullup transistor, and through
> Pulldown transistor to GND. It will affect the output voltage.
>
> Thanks for your reply!
> Steve Zheng
>
> ----- Original Message -----
> From:"steve weir" <weirsi@xxxxxxxxxx>
> To: si-list@xxxxxxxxxxxxx
> Cc:
> Sent:Fri May 13 15:35:41 UTC+0800 2011
> Subject: [SI-LIST] Re: How V-T table been extracted for IBIS model
> On 5/13/2011 12:07 AM, ZHENGZHIWEI wrote:
> >
> > Hello Expert,
> > > From "ibis modeling cookbook for ibis-v4", four V-= T tables
> recommended:
> > [Falling Waveform] Pulldown turning on (Resistor t= o Vcc)
> > [Rising Waveform] Pulldown turning off (Resistor to Vcc)
> > [Risi= ng Waveform] Pullup turning on (Resistor to GND)
> > [Falling Waveform] Pull= up turning off (Resistor to GND)
> >
> > I have some questions for this.&nbs= p;
> > Say, the first case, falling waveform with terminator connect to
> Vcc.= It
> > only mention about Pulldown transistor turning on.
> As far as the termination is concerned, the Pull-up transistor cannot
> supply current to a terminator that connects to Vcc.
>
> > What is the status o= f
> > Pullup transistor, is it trunning off or keeping off? There are some
> docs=
> > point out that "real devices have slightly different switching
> characteris=
> > tics", " turnning off is a little earlier than turnning on". But
> there stil=
> > l has overlap.
> What is your question? Are you concerned with crow barring /
> shoot-through? To the extent that may happen in one device or another,
> it shunts current that would have been available to drive the Tx-line
> and/or terminator.
>
> > Similar question came from "Under ideal conditions, no cu= rrent
> will flow
> > through the pulldown transistor" in the 62 page in the cook= book.
> It is a
> > rising waveform with terminator connect to GND. I think there= has
> current
> > flow through pulldown transistor in the turnning overlap time.=
> The answer is the same as with the pull-up and a terminator to Vdd. A
> transistor operating in parallel to a resistor cannot supply current to
> the resistor. Both cases ignore reactance.
> > Am I misunderstand?
> >
> > thanks!
> > steve.
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>
> --
> Steve Weir
> IPBLOX, LLC
> 150 N. Center St. #211
> Reno, NV 89501
> www.ipblox.com
>
> (775) 299-4236 Business
> (866) 675-4630 Toll-free
> (707) 780-1951 Fax
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--
Steve Weir
IPBLOX, LLC
150 N. Center St. #211
Reno, NV 89501
www.ipblox.com
(775) 299-4236 Business
(866) 675-4630 Toll-free
(707) 780-1951 Fax
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