[sdiy] Pet Peeves

rsdio at audiobanshee.com rsdio at audiobanshee.com
Sun May 6 19:48:22 CEST 2018

Excellent writeup! Thanks for the information, Florian. Very interesting.

This reminds me, a recent client was adding Bluetooth support to their powered speakers, and the lead engineer pointed out something that stuck in my head: Bluetooth is a commodity feature with intense competition for huge purchasing deals by big manufacturers of consumer electronics. The number one deciding factor is cost, although buyers also look at support for various optional Bluetooth features. One common occurrence is that every Bluetooth chip manufacturer will include certain “features” in their bullet list, even if that feature is rarely used by the majority of customers, just to make sure that they look like a good choice on paper. Adding the feature to the list makes the sale, and therefore it gets added. However, when a client company actually tries to use that rare feature, they may find that it was never tested or perhaps never even implemented. By that point, however, it’s too late for the customer to change chip suppliers because all of the deals have been signed and the product has been announced with a ship date. Besides, it might take forever to confirm whether that same feature is actually just vapor on every other chip option on the market, so there’s little hope that picking a different chip will actually achieve better results.

Let’s pray that analog synth chips never get so popular in mass electronics that the data sheets include completely false claims.

On May 6, 2018, at 2:22 AM, Florian Teply <usenet at teply.info> wrote:
> Am Fri, 4 May 2018 21:38:27 -0700 schrieb rsdio at audiobanshee.com:
>> We clearly live in an age where companies are designing chips without
>> the level of testing or guarantees that we used to rely upon.
> There are a multitude of things now playing a role in that game that
> more or less were unthinkable twenty, thirty years ago:
> * Silicon manufacturing is a highly specialized business. Has been like
>  that for decades. But what has changed is access to manufacturing.
>  Back then, everything from chip idea up to sales and customer
>  service was done within the same company. And quite often it was the
>  same engineer or at least the same team who took the chip all the way
>  from inception to production including documentation. Nowadays,
>  there are often several companies involved, from the design house
>  which has no intimate knowledge of the actual manufacturing
>  process, through fab staff which doesn't have the faintest idea of
>  what Chip X is supposed to do, in some cases several test houses
>  running each just parts of the test such that nobody can actually
>  infer aynthing on the operation of the chip just from test results
>  from one test house alone, to the sales company which has contact to
>  the customers and somehow comes up with what might be considered a
>  datasheet by non-tech managers. That way only the most often asked
>  parameters actually make it into the datasheet. And companies have to
>  rely on the help of field application engineers covering all the
>  omissions.
> * Testing is expensive. I just had the opportunity to learn this myself
>  as I am characterizing low frequency noise on just a simple MOS
>  transistor. One single meaningful noise measurement easily takes a
>  minute or two. Add settling time of the necesary filters on the same
>  order and you'll get to about five minutes per device and bias point.
>  Eventually I'd like to put reasonable numbers into the simulation
>  model for the device and I'll have to wait for the yearly maintenance
>  period to actually do the measurement as five minutes times two dozen
>  bias points times thirty different device geometries times a good
>  dozen sites per wafer times at least three wafers from three lots
>  evaluates to a LOOOOOONG time. So if one can justify not measuring
>  something by not putting it in the datasheet in the first place, that
>  can save quite a lot of time-to-market and money. What's not spec'ed
>  doesn't need to be tested.
> * Simulation models do not come for free: One has to understand the
>  different models including their limitations pretty well in order to
>  choose the right simplifications to get to a model that's actually
>  useful. To do that properly one would first have to understand the
>  device itself, and second also have some experience in circuit design
>  and simulation to get an idea of the various applications the device
>  might see. It's something like a permanent rehearsal as a new
>  apllication idea might depend on device behaviour that hasn't been
>  considered important (and therefore not modeled at all or not
>  properly) before. It also needs a good deal of understanding of
>  modeling on the customers side to notice that this or that special
>  case is not included in the model in the first place. I do know of
>  companies which generally create custom simulation models of
>  commercial devices for their internal use. These models then often
>  come with a different (not necessarily smaller) set of shortcomings
>  which is tailored to their needs compared to the official
>  manufacturers model.
> I still don't like the fact that datasheets are getting more and more
> sparse to the extreme that they can be applied to a whole family of
> devices without change. I'd even prefer to not have a second source for
> parts in exchange for good documentation and testing.
> In the end this all is driven by the expectation that the monetary
> implications of moore's law are expected to apply to analog chips as
> well, even though these don't scale well. 
>> I mean, chips are such a commodity that people are stealing duds and
>> reprinting them with expensive part numbers on them just to scam the
>> market. Is it a stretch to say that putting out a chip without a
>> complete data sheet is somewhere on the same spectrum, a little
>> closer to the fakes?
> It's definitely not a stretch to say that. Into the same direction goes
> putting out incomplete datasheets with the proposition to get the real
> thing under NDA for IP protection reasons. If something is sufficiently
> secret to justify that it should not be in a public datasheet, it
> probably isn't a good idea to put it publicly on sale in the first
> place. 
> So much for my part of the rant....
> Florian Teply

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