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nanonical
nanonical
10/16/2014 3:26:18 AM
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Newbie
Re: Spice simulations of large SOC IC's
Barring component failures, often it's noise ...... What I've learned as a better way in the design phase is:

Extract steady-state current noise for (more manageable) individual IC blocks on a rail.  Convolve together.  Do this for > 10 vectors of sufficient length.  Next, take convolution and get estimated PSD.  Then std methods can estimate +3 sigma peak.  Scale convolution result up to this.  This avoids lengthy (5+ day) sims for IC or total PDN.  Post-layout IC sim using the result to get failure rate.  Iterate IC if necessary. Also, gets the bump and ball Vnoise spec.  Next, do same "std methods" with pcb, incl. dcaps, no pwr filter, VRM at gnd, using peak Inoise above.  This is the PDN result.  Tune pcb layout & dcaps to meet budget.  Last, a separate pcb time-domain sim using IC true I-transients @balls, incl. VRM filter, VRM model and other VRM-side noise sources; this gets the true transient cases.  Look at resultant ball Vnoise vs. IC transient budget.  Separately, pkg and pcb layout density can force dc analysis, esp. in pcb case with multiple ICs in a tight space & on a rail w/ one VRM sense.  The above isn't done, in my experience.  Worse, whatever's done is close to tapeout.  They never learn.  Too busy trying to sell jelly beans instead of chips.  Belief in the magic transformation of chicken poop into chicken salad.  To make better yield & a reliable spec, a comprehensive statistical approach is needed in each domain.

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B_Albing
B_Albing
7/22/2013 9:48:35 AM
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Editor
Re: Spice simulations of large SOC IC's
@WM - shipped somewhere where they drive wooden trucks - I'm stealing that line and using it. Thanks.

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B_Albing
B_Albing
7/18/2013 5:25:01 PM
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Editor
Re: It can also tell you a design is too complex to be safe
I think that's a selection on Expedia: "Safe Plane - check Y or N"

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B_Albing
B_Albing
7/18/2013 4:10:01 PM
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Editor
Re: It can also tell you a design is too complex to be safe
Of course - I should have thought of that.

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BillWM
BillWM
7/18/2013 4:09:07 PM
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Blogger
Re: It can also tell you a design is too complex to be safe
Only fly on the "Good" ones

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B_Albing
B_Albing
7/18/2013 3:55:31 PM
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Editor
Re: It can also tell you a design is too complex to be safe
Jeeze - you're making me want to not fly.

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BillWM
BillWM
7/17/2013 3:12:12 PM
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Blogger
Spice simulations of large SOC IC's
Often full-up SPICE simulations of SOC (System on Chip) I.C.'s cannot be done due to the complexity -- a very real issue is that at today's clock rates and gate counts the power rails do not behave perfectly and a "digital" simulation is based on spice analisys of smaller sections of the design.  Rare current "Slug" events on power rails that are marginal in some way are difficult to find even in board level V&V as a reference design may not perfectly match a customer's application for a complex device.   The other item to consider is the IC test equipment has a special socket and very robust board layout for production test, whereas the use in the field may be shaved down to a 4 layer board, from the 10-20 in the test station.  This all can cause returns for SOC and other complex devices that are "Analog" failures more than "Digital" failures -- and DO-254/DO-178B systems do not run the ATE code, nor do they do the full Qual test on every unit shipped.   They try and set margin in manufacturing test, but often there is a good, a maybe, a bad, and an ugly bin in the production test flow -- the good ones are saved for the good customers, the maybe ones maybe shipped somewhere where they drive wooden trucks and don't mind so much, and the bad, fixed, and retested.  The ugly are beyond repair.

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BillWM
BillWM
7/16/2013 8:48:33 AM
User Rank
Blogger
It can also tell you a design is too complex to be safe
Standards like DO-254, DO-178B, FAA-8110.105 etc tell one that one must meet a 10^-9 probablility for loss of the aircraft for each item in a system fault tree -- the issue can be if the system is so complex there are hundreds of thousands of different "Ankle Biter" things that can cause this at a low probability the aircraft can be lost more frequently than 10^-9 /hr due to the extreme complexity of the design.

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