Hi everyone,

I've got a question regarding choosing a fabrication process.. Let us imagine
for a moment that there is a fab out there with all possible processes
imaginable and is really cheap (a perfect fab).. I'm interested to know what
factors should be considered when choosing the process..

- How do we decide if we want to use 0.35 or 0.25 or 0.18 or 0.13 or any other
size for that matter??
- Does it matter if a design is fully digital/fully analog/mixed??
- Does power (W) and supply (V) come into the picture??
- Does speed (MHz/GHz) come into the picture??
- How do we decide which foundry/fab to use??
- Any other things to consider??

I'd appreciate any advice I can get.. Also:
- Is there any place to get circuit designs/pre-laid out designs like at
opencores but for analog/mixed designs??

I'm about to go down the full-custom analogue/mixed path and I'd like to have
some idea of what to expect...

cheers..

--
with metta,
Shawn Tan

On Wed, 12 Jan 2005 22:03:48 +0000, Shawn Tan Ser Ngiap shawn.tan at aeste.net> wrote:

Process is generally chosen on basis of price, so your perfect fab is
not a good example. :) Newer generation processes give lower
per-unit cost and power consumption, at a cost of higher NRE.



Yes, but analog is a special case in almost every process... Analog
parts are typically fabbed in larger processes that are better
characterized and less expensive to fix if you screw up.



The max and min voltages go down as your feature size gets smaller, so yes.



Smaller processes are faster.



What are your requirements? What skills does your team have? If you
haven't fabbed a chip before, you almost certainly want to go with
someone who handles your back-end (IBM, Agilent, LSI Logic).



Depending on how much analog logic you have, consider doing your
design in an FPGA and doing an FPGA->ASIC conversion through Orbit or
someone similar.



Honestly, I'm not trying to put a downer on things, but if you're
seriously going to design a full-custom chip, you shouldn't be asking
these questions. Most of this list is Chip Design 101, and custom
analog silicon is the Deep Voodoo of chip design.

Good Luck,

Guy

Hi,

Thanks for the quick reply..

On Wednesday 12 January 2005 22:59, Guy Hutchison wrote:


So, process scaling has *no* effect on the circuit design at all?? I believe
that process scaling will affect analog circuits.. Models change..


characterized and less expensive to fix if you screw up.

On Thu, 13 Jan 2005 00:27:20 +0000, Shawn Tan Ser Ngiap shawn.tan at aeste.net> wrote:

Process scaling does have effects on the circuit design (speed, power
consumption, capacitance, parasitics all change), but the primary
reason that people choose one process over another is price and
volume. That's another reason that analog circuits tend to be in
larger processes; analog circuits are much less complex (in terms of
transistor count) than digital designs, and are more likely to be
pad-limited instead of core-limited.



It's a pretty select bunch of people; I'm not sure how you'd find
them. Your best references are probably going to be offline. I would
pull down the Alliance package and the Electric HDL tool, and check
for mailing lists and documentation references for them.

- Guy