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!!!
> Date: Mon, 22 Dec 1997 09:39:01 GMT
> From: email@example.com (alaa alani)
> To: firstname.lastname@example.org
> Subject: Re: [SI-LIST] : SSO : How to identify SSO groups?
> Cc: si-list@silab.Eng.Sun.COM
> 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).
> Dr. Alaa F. Alani
> Senior Signal Integrity Eng.
> LSI Logic
> > From si-list-approval@silab.Eng.Sun.COM 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 [126.96.36.199]) 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@example.com (Praveen G Shekokar)
> > To: si-list@silab.Eng.Sun.COM
> > Subject: [SI-LIST] : SSO : How to identify SSO groups?
> > Sender: owner-si-list@silab.Eng.Sun.COM
> > 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
Shuttle Technology Ltd.,
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