[SI-LIST] Re: [SI-LIST]Re:HowV-TtablebeenextractedforIBISmodel
- From: ZHENGZHIWEI <zhiweizh@xxxxxxx>
- To: weirsi@xxxxxxxxxx,si-list@xxxxxxxxxxxxx
- Date: Fri, 13 May 2011 16:53:27 +0800 (CST)
Hi Steve W,
Let's focus on the first question first.
>= Say, the first case, falling waveform with terminator connect to Vcc.=3D
It=
>only mention about Pulldown transistor turning on.
[Steve W] As= far as the termination is concerned, the Pull-up transistor
cannot
[St= eve W] supply current to a terminator that connects to Vcc.
My conce= rn 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 r= eply!
Steve Zheng
----- Original = Message -----
From:"steve weir" <weirsi@xxxxxxxxxx> To: si-list@xxxxxxxxxxxxx
Cc:
Sent:Fri May 13 15:35:4= 1 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-=3D T tabl= es
recommended:
>[Falling Waveform] Pulldown turning on (Resistor t= =3D o Vcc)
>[Rising Waveform] Pulldown turning off (Resistor to Vcc)=
>[Risi=3D ng Waveform] Pullup turning on (Resistor to GND)
>= [Falling Waveform] Pull=3D up turning off (Resistor to GND)
>
>= I have some questions for this.&nbs=3D p;
>Say, the first case,= falling waveform with terminator connect to Vcc.=3D
It
>only mentio= n about Pulldown transistor turning on.
As far as the termination is con= cerned, the Pull-up transistor cannot
supply current to a terminator th= at connects to Vcc.
>What is the status o=3D f
>Pullup tr= ansistor, is it trunning off or keeping off? There are some
docs=3D
>= point out that "real devices have slightly different switching
characteris= =3D
>tics", " turnning off is a little earlier than turnning on". Bu= t there
stil=3D
>l has overlap.
What is your question? Are you co= ncerned with crow barring /
shoot-through? To the extent that may happe= n in one device or another,
it shunts current that would have been avai= lable to drive the Tx-line
and/or terminator.
>Similar quest= ion came from "Under ideal conditions, no cu=3D rrent will
flow
>thr= ough the pulldown transistor" in the 62 page in the cook=3D book. It
isa> rising waveform with terminator connect to GND. I think there=3D has=
current
>flow through pulldown transistor in the turnning overlap t= ime.=3D
The answer is the same as with the pull-up and a terminator to V= dd. A
transistor operating in parallel to a resistor cannot supply curr= ent to
the resistor. Both cases ignore reactance.
>Am I misunder= stand?
>
>thanks!
>steve.
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--
Steve Weir
IPBLOX, LL= C
150 N. Center St. #211
Reno, NV 89501
www.ipblox.com
(775= ) 299-4236 Business
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