[SI-LIST] Re: Power Supply Distribution/Filtering/Decoupling Guide]
- From: Chris Cheng <Chris.Cheng@xxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Tue, 13 Jan 2004 12:55:07 -0800
Ok, I want to start this thread again free of attachments.
There is no need to form another benchmark committee or develop some
industrial standard tool to address the high speed power distribution
issues.
What I've been preaching is just plain common sense and what I call "total
system approach" where you attack the problem at die, package, PCB and power
supply level. You simply cannot focus on just one section of the chain of
distribution and expect it to do all for you.
Maybe I start off as too sarcastic and lead you to believe finger pointing
is the only way to solve this problem. It is not. And if you buy into my
"total system approach", you should also look into its corollary :
A certain component that cause system problem usually mean there is some
problem internal to the chip also.
If you see huge EMI radiation coming out of a chip, it probably also suffers
a large core noise on die or some sort of SSO noise. For every poor system
engineer trying to quiet down the EMI noise coming out of a chip, there is
another chip designer scratching his head trying to suppress the core noise
on his silicon. We are not working in an island in the middle of nowhere.
Every thing we do on chip has direct impact on the system and vice versa.
The sad thing is there are only a few people or companies that have the
luxury of having done a complete analysis through the entire path. And
chances are they will lock up this knowledge and treat it as their own "core
competency". I am sorry to sound cut throat but that's the way the big boys
play. There is a reason why you go with a company that sell a 100 million
pieces a year instead of a few thousands. They are the big boys and they
(although not always) tend to know what they are doing. Or at least they
have enough volume to see every possible problem that exist under the sun
and have enough resources to spend men years to analyze and solve them.
Every power analysis group I ran in those company takes men years to
complete. And every bit of the techniques and methodology are in house and
proprietary. All I can say is tools are never a problem, I did most of them
with plain old SPICE and freely available FastHenry. It is the insight into
every detail of the components like on die power grids, package structures
etc that really make or break the design. Unfortunately, you cannot learn or
gain those insights simply by joining the "Si-list". This is just a simple
way of natural selection. If you find a chip that cause you noise problem in
a system, you either make the vendor fix it or you switch vendor. I don't
feel sorry for the semiconductor house that have a lousy design and loose
their business. On the other hand, a chip house that does its homework and
has a clean design deserves to win your business no matter they are a
semi-monopoly or charge you an arm and a leg. They pay their dues and save
your from system level trouble down the road.
I have seen quite a few big shots in chip houses that told me "men, I would
have given you a few millions to turn back the clock and fix our problem
before we learn it through the hard way." Believe me, this is not just a
system company or chip company issue. They both suffer the same.
There are Yugos and there are Corvettes, you can't buy a Yugo and take it to
the race track and then complain "hey don't blame me, I have a lousy car".
Its your choice to pick the right component.
If there is anything to learn here, it is to take SI and packaging issues
seriously in your component selection. Don't just let the system architect
or board manager dictate what chip to use simply because it cost a few buck
less or have this feature extra. Ask questions, look into data, review their
package to make sure it also make sense in SI first. Assert yourself in the
selection process. If you think there is not enough signal to ground pin
ratio, raise you hand and ask why. Don't just sit at the corner and tell
your system manager "I think it will work". That's what we got paid for. Not
just putting in band-aids as an after the fact thing. We also got paid to
prevent bad things from happening in the first place.
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