Generally, at todays edge rates, all sso capacitive loading scenerios
must be analyzed as a transmission line environment. The current
profile produced can then be used to simulate sso effects in a Spice
simulator. Or a very good swag (approximation) can be achieved
by looking at the current waveform dI/dt and multiplying it by the
ground (or power, when appropriate) inductance of the package and
layout.
regards,
Scott McMorrow
SiQual
Peterson, James F (FL51) wrote:
> Manix makes a good point in regards to Praveen's question on SSO. But
> can you really lump all of that load capacitance together? It seems that
> with a bus that is large enough to contain 500pF, then to be accurate,
> the load has to be distributed, at least somewhat.
> best regards,
> Jim Peterson
> [email protected]
>
> > ----------
> > From: Manix Velu[SMTP:[email protected]]
> > Sent: Monday, December 22, 1997 11:51 PM
> > To: [email protected]
> > Cc: [email protected]
> > Subject: [SI-LIST] : How to identify SSO groups?
> >
> > Hi Alaa F.Alani,
> >
> > It is not even 1ns. Even switching within 10nsec width also may be
> > considered as SSO. What our vendors propose thus is to use a delay of
> > around half-a-clock (say for about 40 to 60 ns) to skew the outputs
> > of around 12mA typ sinking a load capa of 500pF!!!
> >
> > Regards,
> > Manix Velu.
> >
> > > Date: Mon, 22 Dec 1997 09:39:01 GMT
> > > From: [email protected] (alaa alani)
> > > To: [email protected]
> > > Subject: Re: [SI-LIST] : SSO : How to identify SSO groups?
> > > Cc: [email protected]
> >
> > >
> > > Hi Praveen,
> > >
> > > It depends on how long it takes for the current to drop to a certain
> > level (eg 0mA)
> > > but 1nsec seems to be acceptable (i.e. those i/o buffers switching
> > within 1nsec
> > > are considered as simultaneously switching).
> > >
> > > Rgds,
> > >
> > > Dr. Alaa F. Alani
> > > Senior Signal Integrity Eng.
> > > LSI Logic
> > > UK
> > >
> > >
> > >
> > > > From [email protected] Fri Dec 19 23:15:02 1997
> > > > X-From: uucp Fri Dec 19 15:13 PST 1997
> > > > >Received: from mars.Sun.COM (mars.Sun.COM [192.9.22.1]) by
> > mail1.lsil.com with ESMTP id LAA10882
> > > > (8.6.12/IDA-1.6); Fri, 19 Dec 1997 11:31:22 -0800
> > > > Date: Fri, 19 Dec 1997 10:50:28 -0800
> > > > From: [email protected] (Praveen G Shekokar)
> > > > To: [email protected]
> > > > Subject: [SI-LIST] : SSO : How to identify SSO groups?
> > > > Sender: [email protected]
> > > > Content-Length: 1126
> > > >
> > > >
> > > > We are using our foundaries SSO rules to calculate number of
> > VDD/VSS
> > > > pins required for our ASIC. Before we can use the SSO rules we
> > need to
> > > > identify signals that form a SSO group. The conventional technique
> > I know
> > > > of is to group signals of similar functionality into a SSO group
> > e.g.
> > > > Address/Data bus.
> > > >
> > > > In practice we have noticed that not all the signals of such a
> > group have
> > > > identical delays. Further they may not have identical output
> > loads. Variable
> > > > delays implies that not all the outputs switch at the same. E.g.
> > > >
> > > > Let output1 switch at time T and output2 at time T+t1. If t1 is
> > small then the
> > > > switching current for output1, say I1, will overlap with switching
> > current
> > > > for output2, say I2, leading to overall increase in the switching
> > current.
> > > > But if t1 is more than the time required for I1 to reduce to 0
> > then the
> > > > overall switching current is going to be limited to max of I1 and
> > I2.
> > > >
> > > > I want to know whether there are any guide lines for value of t1
> > that one
> > > > can use to decide whether a signal is part of a SSO group.
> > > >
> > > > Value of t1 is also required in designing address/data stepping.
> > > >
> > > > thanks,
> > > >
> > > > - Praveen Shekokar
> > > >
> > > >
> > >
> > >
> >
> > E-Mail: [email protected]
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> >
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> >