Re: [oc] Output loading in digital circuit

["Kenneth Hung" <hungwaiming@hotmail.com>]

IBIS model are new to digital designer.
Before that, there're already 50pf, 500ohm
so I don't think this is the reason

----- Original Message ----- 
From: <johnsonw10@hotmail.com>
To: <hungwaiming@hotmail.com>; <cores@opencores.org>
Sent: Saturday, March 30, 2002 9:18 AM
Subject: Re: [oc] Output loading in digital circuit


> 50pf, 500ohm, etc happen to be the default load values specified by
> IBIS spec, so I guess that is why many IC manufacturers use those
> values for load modeling. Check http://www.eigroup.org/ibis/ibis.htm for
> more information.
> 
> HTH,
> Jim
> 
> ----- Original Message -----
> From: "Kenneth Hung" <hungwaiming@h... >
> To: <cores@o... >
> Date: Fri, 29 Mar 2002 10:18:31 +0800
> Subject: Re: [oc] Output loading in digital circuit
> 
> >
> >
> > No my question is why the datasheets in many logic design has such
> > output
> > loading.
> > I understand loading would cause effects but how these values come
> > about ?
> > Seems no one understand this before doing real design.
> >
> >
> > ----- Original Message -----
> > From: "John Sheahan" <jrsheahan@o... >
> > To: <cores@o... >
> > Sent: Friday, March 29, 2002 6:03 AM
> > Subject: Re: [oc] Output loading in digital circuit
> >
> >
> > > On Thu, Mar 28, 2002 at 06:05:12PM +0800, Kenneth Hung wrote:
> > > > Hi all guys
> > > >
> > > > I am a digital circuit designer. However, I am always
> > confusing why
> > > > in the datasheet spec, there're output loading with
> > different values.
> > > > Say 50pF and 500ohm in parallel with the output.
> > >
> > > remember, gates are analog things made of real transistors.
> > > they get to drive real bits of wire.
> > > That load causes even more deviation from the model of digital
> > > behaviour you rely on (as a digital designer) than usual.
> > > Use spice to help see more.
> > > But don't model a package IO too carefully, it might upset
> > you.
> > >
> > > john
> > >
> > > >
> > > > Can anyone suggest why it's the case ? And how to analyse
> > this ?
> > > >
> > > > Thanks
> > > > kenneth
> > > >
> > >
> > >
> >
> 
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