[SI-LIST] Re: package SSN model accuracy requirements
- From: Chris Cheng <Chris.Cheng@xxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Fri, 11 Mar 2005 11:33:26 -0800
Gary=> Hmm. One could ask why go to the trouble of making a standard
for something that runs slow and has trouble converging, when we already
have a standard for a solution that runs fast and converges well ...
Chris->Because that's the way the I/O circuit designers design and lay it
out. Every circuit I dealt with has design tweaks that breaks a generic
behavioral model. Say tomorrow you can describe the main switching current,
what about the gate voltage modulation. Ah ha, we are going to create new
spec to describe that. How about if the pre-driver is on a separate power
domain and suffer a different SSO modulation... uhh let's give it another
spec or model. You will be going into this infinite loop of trying to
describe a new phenomenon every time a new circuit is design. Why not just
let the user have the original circuit and if it is appropriate, they can
always generate the behavioral model themselves. But the reverse is not
true. Once you confine yourself to what YOU think is a good behavioral
model, critical information may be lost and you will have no way of
verifying it. Why would I trust a EDA tool vendor to tell me "this level of
abstraction is good enough" when he/she has no clue of what my circuit
really looks like ? There are times even the I/O designer may not be fully
aware of the so call secondary effects is truly secondary until a full
detailed model is simulated and analyzed.
GARY=> But, I think there is a larger concern here ... I admit to much
ignorance in the latest encryption technology, but to be a standard it
seems it would have to be available to any SPICE vendor. Like Gary's
Garage Shop -- proud vendor of GSpice. Not sure how enthused silicon
vendors would be knowing Gary's Garage Shop has access to their IP.
(Though, I happen to personally know this shop is well above reproach.)
Gary=> Lame humor aside, even if we somehow limited it to the top 10
SPICE vendors, would there be a way for a silicon vendor to trace a leak
back to the leaky tool vendor? Somehow, I just don't think silicon
vendors would go for that. And, I'm not sure who would drive this and
who would support it, and how long it would take. But, I'm more than
willing to be proven wrong, if that's the way the industry wants to go.
Chris->BTDT, if I can convince the largest and most conservative Si company
in the world to do it, there is a way. What security measure is put into it
is something we are not going to talk here.
Gary=> I don't know. It seems to me that if one has 64 drivers
switching at the same time, and these all get their power from the same
set of bumps, one should really simulate all the drivers, traces, and a
good portion of the package power planes to get an accurate result.
But, I certainly make no claim to be an expert in this area. That is
actually what I was hoping to learn from this discussion.
Chris->If you go back to even those old and dated GTL papers we published in
the early 90's, there are already measured and simulated SSO analysis
included. The last time I have to make these methodology public outside my
employer is six years ago. That's the only reference I can refer to since
those are the things I can talk about. Things have changed and my I/O's are
getting much faster and complicated. There may be S-parameter added here and
there but overall I feel the basic remains the same. However, my new
employer has no incentive to make the world know what we are doing so,
sorry. No one needs to simulate 64 separate drivers to understand the worst
case SSO. There is a difference between BTDT designers and EDA tool vendors.
That's all I want to say.
All these constant back and forth on "hey I can do this in SPICE but why
can't you do it in IBIS" and "No no, I can add this to my description and do
the same thing as SPICE" makes me wonder, if at certain point of time,
wouldn't it be easier to just protect the circuit and hand it out ? Remember
that Cheech and Chong movie ? "It feels like SPICE, tastes like SPICE, man I
am so glad we didn't step on it"
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