| Published December
1999 Rubicad News
International Microcircuits,
Inc. (IMI) achieved higher performance through layout migration to a different
process technology
An Interview with Greg Richmond by Gabriele
Eckert
Greg Richmond is vice president of engineering
and chief technology officer (CTO) of International Microcircuits Inc.
(IMI), a leading supplier of frequency and timing generators, and low electromagnetic
interference clock circuits for the computer and communication industry.
Greg has extensive experience in leading advanced digital, analog and mixed-signal
integrated circuit development. He has two patents pending in the areas
of spread spectrum and low noise RF PLL (radio-frequency phase-locked loops).
???Recently
IMI used Rubicad’s design service for a layout migration project. Can you
tell our readers a little bit about this project?
Some of our products which were in a 0.35
micron technology were designed for a process that used epitaxial wafers.
The epitaxial process is not as common among alternative fabs, making it
difficult to migrate products if capacity issues occur. Also, the
wafer starting material is more costly, and for some applications the low
sheet resistance of the EPI layer can cause performance issues. Therefore
we wanted to migrate our designs to a non EPI technology.
On the epitaxial process the diffusion
spacing rules were very aggressive because they could be closer and still
avoid latch up compared to a higher resistance substrate. We needed to
convert the digital cells of our mixed signal library to accommodate the
larger spacing for the move to an alternate fab. In addition we anticipated
that we would have the potential to run this library in different fabs.
So we wanted to have a superset of design rules created that would allows
us to do that. In the process of evaluating our options we
become aware that we may need to make changes quickly and so we were interested
in a methodology that allowed us to have control of the layout by specifying
spacing parameters to be able to change the layout quickly.
We evaluated the options we had. One way
of course was to do it manually. But that option would take to long and
would impact our time to market, because we didn’t have the man power to
do it quickly. Therefore we chose RUBICAD’s layout migration service.
???What
are the most important reasons to use a layout compaction method versus
other methods to shift your design to another technology?
The primary reason for us to use an automatic
layout compaction method is time to market. Opportunity costs are
also important… you want designers to work on projects that open new markets,
not to transfer products. If you have a large number of cells and if you
have migration software, you can specify the compaction parameters and
design rules, and you can quickly run compaction and iterations as you
find issues.
???What
was the most important factor for you to make this project successful?
Of course accuracy. We needed to make
sure that the converted design passed the DRC so that the new product could
be fabricated. And as I mentioned before, the other very important thing
was time to market. We needed the design very quickly converted to the
other technology. Using the automatic layout migration we could focus our
own resources on the more critical aspects of the design, which were the
analog cells. Time to market is very critical to us. Our products are used
in data processing systems and personal computers, and the life cycle of
those products is very short. Their peak volumes are only about 6 months.
They may ramp up three months, peak for six months and ramp down for three
months. If you miss the market window you must wait for the next design
cycle.
???Which
design style or method is IMI using to personalize their designs for different
customers?
The nature of our products require a specific
design methodology. The method we use is to develop a base array or base
silicon and then we do personalizations for different customers whose systems
require slight modifications to our basic products. And as a result we
may have 20-40 personalizations of that base. The personalization is done
by customizing the metal layers. We program the ROM that’s on the chip
and reconfigure the logic of the product and also the I/O structure. The
digital library is a gate array library which has to meet the transistor
pitch and the contact pitch of the base gate array cell. It was this gate
array logic library as well as the ROM cells that RUBICAD migrated for
us.
Migration of a gate array library is a
little bit different compared to other designs where your concerns are
minimizing the area within the minimum design rules. Here we had constraints
that contacts could only fall in certain locations, poly had to fall on
a certain pitch, metal had to come in and out of the cells in certain locations
so they would be compatible with the router technology that we use in house.
RUBICAD did an excellent job in meeting all our special needs.
???What
was the largest benefit for you to get the layout migration done by Rubicad’s
design service?
The main benefit of the service was to
get the migration done quickly without tying up resources that were needed
for work on other critical tasks. Rubicad, as the expert in your design
migration tools, could implement the superset of our rules very quickly
and that allowed us a very short turn-around time.
???Did
the layout quality meet your design teams expectation?
Yes, the conversion project met our expectations.
In fact the migration project exceeded our expectations in that we benefited
from an area reduction of 10% for the logic library which we were not counting
on. We only wanted to convert the library. In our products about two thirds
of the core area is logic and so the 10% reduction of the digital part
contributed about a 5% reduction as part of the total chip area reduction
that we achieved.
???Was
there additional manual work necessary which was caused by the layout compactor
in order to make the layout pass DRC and LVS?
Other than the few iterations we went
through to get the technology file accurate for the trial SSI cells like
the nand cells and the flip flops, there weren’t any other edits needed.
We made some edits to the ROM because we changed the configuration of the
ROM after the conversion. The basic ROM cell was 128 x 8 and we changed
it to 64 x 16. But this was not an issue with the compactor.
???Can
you tell us what your design team thought about the migration project?
This is one of those cases where no news
is good news. Nobody came to me complaining, so I think that was a very
good sign. Rubicad’s people were very responsive. There was a time when
one person we were working with had to go on a business trip, but he assigned
somebody else and that worked out fine.
???What
are the recommendations you could suggest to other design teams who need
to migrate their design to different technologies or for reuse in silicon
systems?
The primary recommendation would be to
seriously consider the automatic layout compaction tool suite LADEE. If
they don’t foresee that they are migrating often enough to justify purchasing
the tool suite and building up the expertise in house I recommend to take
advantage of RUBICAD’s service to do that kind of layout migration.
???In
your opinion which meaning will Rubicad’s layout compaction technology
have in the future for chip design, specially if you think about deep-submicron
technology?
As you know, scaling to deep submicron
does not follow the same shrink factor for all design rules so the layout
changes must be done manually, or use specialized software for migration.
So when our applications move to a lower voltage level, or the primary
capacity has shifted below 0.35u, or if we feel that there is a performance
advantage, we will consider having the library migrated again by using
RUBICAD’s service. The technology files are all set-up to do that very
quickly.
???How
did you learn about RUBICAD’s Service and products?
When I was working at my previous employer
we had contacted RUBICAD for a similar reason. We wanted to convert our
0.8 micron library to a 0.5 micron technology. We contacted RUBICAD about
the migration. Based on that contact I was familiar with what RUBICAD’s
migration software and migration service could do and it seemed to be a
good fit for the need that we had here at IMI.
???Which
factors most influenced your decision to work with RUBICAD for your layout
migration project?
The fact that I knew that the technology
was viable from the stand point that RUBICAD had been in business for several
years. They had been making claims about being able to migrate not only
digital libraries but also analog libraries with certain constraints. I
felt good about the fact that the information I had seen in the press as
well as my previous contact indicated that Rubicad could do what they claimed
they could do. Therefore we initiated the project. Closely tied to that
is the fact that the RUBICAD people we met knew their business products
very well. We had specific questions about certain constraints and RUBICAD
showed that they could perform what we needed to be done by explaining
in detail how their software handled those issues.
???What
do you like about using Rubicad’s design service?
Rubicad did accurately what we wanted,
in this case the migration of the library and ROM to a design rule superset
allowing foundry portability, and the fact that we can call RUBICAD and
don’t need to carry this service as an overhead in house. RUBICAD’s migration
service is cost effective. The estimates that we had in terms of doing
the migration manually in house indicated that we probably would have gone
over budget, because its easy to underestimate transistor layout. But there
is no way that we would have been able to do it in the time frame RUBICAD
could do it, because we just did not have the resources in house. The automatic
migration service really accelerated our time to market, and the performance
of the end product is very good.
???
What
else do you want to tell the design community about your products and your
company?
IMI manufactures high performance frequency
timing generators, EMI reducing clocks, and high performance phase
locked loops. Our devices are designed for computing, datacom and
consumer electronics manufacturers. IMI is located at 525 Los Coches
St. Milpitas CA 95035. Tel (408)-263-6300, FAX 263-6571. Web
http://www.imicorp.com
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