[Libre-silicon-devel] Status request: ADC

Christoph Maier cm.hardware.software.elsewhere at gmail.com
Wed Jan 2 15:47:29 CET 2019

On Wed, Jan 2, 2019, 15:40 ludwig jaffe <ludwig.jaffe at gmail.com wrote:

> Hi all,
> we should prototype all kinds of components, capacitors, resistors,
> bipolar transistors and mos transistors,
> in order to get a protfolio of parts, there parts need to be identified,
> so we get a spice model for them.
> Remember, all parts are analog, even nand gates.
> You can use 4000 cmos logic to build bad amplifiers, just by having
> feedback resistors likewise with op amps.
> So the process guys should try to make as many as possible parts on a
> wafer to get a parts lib.
> Then we can build circuits like SAR or Delta Sigma ADC.
> A flash ADC with 8 bit would be funny but not that fast, but why not.
> And always remember, our chips are not the fastest but the biggest :-)

Unless one or two of us here have a neuromorphic / translinear circuit
bucket list and access to bespoke process parameters, right, Mr. Potbox?


> Cheers,
> Ludwig
> On Wed, Jan 2, 2019 at 2:57 PM Tim Edwards <tim at opencircuitdesign.com>
> wrote:
>> Hello Christoph,
>> > First things first: What are appropriate test structures (like,
>> > transistor, resistor, and capacitor arrays)
>> > that allow us to characterize devices AND device matching in a way to
>> > allow meaningful analog/mixed signal design?
>> > I would assume that you already have put quite a bit of thought into
>> > this, if and when a really open silicon process ever became available
>> > (like, now, with these crazy guys here).
>> > I'm not sure yet (and open to whatever suggestions I could get from
>> > People Skilled In The Art) what ADC topologies would be suitable to
>> > try out.
>> I have thought about this much less than you seem to think.  I have never
>> built up a fabrication process from scratch like the Libre Silicon guys.
>> So test structures that go in the margins of wafers are things that I have
>> a basic understanding of, but I am more familiar with analyzing the
>> measurement results than with thinking about how the structures should be
>> designed and how to make the measurements in the first place.
>> Best capacitor matching for ADCs generally comes from MiM capacitors,
>> 2nd best from poly-poly capacitors, and for smaller feature sizes where
>> the layer thickness is on par with the metal width and spacing rules,
>> fingered MoM caps are probably 3rd best.  Common centroid geometry with
>> dummy devices on the periphery is a must.  Beyond that, it really depends
>> on what's being offered in the process.
>> ADC topology depends more on the application than anything else.  My
>> preference is Sigma-delta with digital filtering, but sometimes an
>> SAR is called for.  I've never seen anyone do flash ADCs in practice.
>> > IIRC, efabless has venture capital, so what are the strings (i.e.,
>> > exclusive representation rights or some such) attached to importing
>> > designs and PDKs into your infrastructure?
>> Actually, no, efabless is not funded by venture capital.  We are currently
>> funded by a group of three people, one of whom is the CEO (Mike Wishart)
>> and the other two long-time Silicon Valley startup founder types (Lucio
>> Lanza and Jack Hughes).  We are looking for additional investment from
>> companies who can benefit from having IP in our catalog listings, or
>> benefit from the web-based collaboration tools.
>> > For now, I just established mumble communication with Hagen and
>> > Leviathan, and next I'm planning to dig into the gds, and how to use
>> > the magic et al. tool suite. I'll pester you with questions about your
>> > tools to the extent you'll let me.
>> I am always happy to answer questions.  Users are the lifeblood of open
>> source tools, and must be kept happy. . .
>>                                         Regards,
>>                                         Tim
>> +--------------------------------+-------------------------------------+
>> | R. Timothy Edwards (Tim)       | email: tim at opencircuitdesign.com    |
>> | Open Circuit Design            | web:   http://opencircuitdesign.com |
>> | 19601 Jerusalem Road           | phone: (240) 489-3255               |
>> | Poolesville, MD 20837          | cell:  (408) 828-8212               |
>> +--------------------------------+-------------------------------------+
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