[sdiy] $100 Chip fab service

Tom Wiltshire tom at electricdruid.net
Wed May 2 19:32:57 CEST 2018


I don’t think people are too concerned about variation across the chip, Cheater. It’s just that you’d be trying to use a device designed for digital switching in an analog way, and at 1.8V to boot. Digital devices can *sometimes* do a reasonable job of passing audio, but they’re far from great at it.

Ever played with CMOS invertors as basic op-amps? They work, just, but they’re not very linear (in fact, this use mostly turns up in distortion circuits (ARGH! Don’t cross the threads!)) and the gain is terrible. I imagine working on one of these digital chips would be like having a free playground of 10,000 CMOS invertors. If you can even get a recognisable signal from one side to the other as analog audio, I’d be impressed.

> On 2 May 2018, at 17:52, cheater00 cheater00 <cheater00 at gmail.com> wrote:
> 
> Why would the characteristics differ? They're monolithic on a single chip, and chips from different wafers will likely have the exact same characteristics. Sure, stuff needs to be characterised, but once you have that you're free to go. Bear in mind you get several orders of magnitude more transistors than in a normal synth module.. so this opens a lot of possibilities.
> 
> 
> On Tue, 1 May 2018 20:25 , <mskala at ansuz.sooke.bc.ca <mailto:mskala at ansuz.sooke.bc.ca>> wrote:
> On Tue, 1 May 2018, Ben Bradley wrote:
> > I'm wondering what you can do in 1.8V "180nm CMOS technology" that's
> > not digital. Does anyone even have the analog characteristics of such
> > small N-channel and P-channel mosfets (and no BJTs, the heart of just
> > about any exponential converter)? I'm guessing they only have specs
> > for required voltage levels for 0 and 1, switching times and fanout
> > and such.
> 
> That's be my concern.  Sure, any transistor can be used in an analog way,
> but if the relevant properties are not characterized and controlled, there
> may not be much point trying.
> 
> -- 
> Matthew Skala
> mskala at ansuz.sooke.bc.ca <mailto:mskala at ansuz.sooke.bc.ca>                 People before principles.
> http://ansuz.sooke.bc.ca/ <http://ansuz.sooke.bc.ca/>
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