[sdiy] FPAA for analog synthesis?

[Dave Manley]

cheater cheater wrote:
> I assume the arrays in the CEMs are still just the parts that were
> necessary for the chip?
> The difference between the complexity required for that and a
> general-purpose solution is obvious.
>
>   
Assuming I understand what you're asking, the array underlying a CEM 
design is general purpose device.  It contains a number of transistors, 
resistors and capacitors, that can be hooked together.  There was a 
family of base arrays that had different numbers of these raw 
components, allowing some cost optimization for different complexity 
designs.  The metal mask customizes a general purpose array into a 
specific device. A given design would not use all the raw components in 
the base array, but would only hook up those that were needed.  The 
arrays are general purpose solutions, with inherent limitations based on 
the process technology used and the size of each array.

Here's an example of what might be found in a base array:

"17 pads  -  27 small NPN/PNP transistors - 10 small Schottky NPN 
transistors - 1 large NPN
transistor - 1 large PNP transistor - 157kOhms base resistance - 9 base 
pinch resistors
  2 epi pinch resistors - 2 junction capacitors - 70 cross-unders "

This is from a manual that was on the Array Design website.  The largest 
device had 48 pads and ~350 transistors.

In the early days of this technology, the manufacturer would sell a 
design kit that contained a small number of the raw components packaged 
into small DIP packages.  The designer could wire these building blocks 
up on a bread board and test the design with the actual components that 
would be in the final array.  

Perhaps the only reason the CEM series of parts even exists is because 
the manufacturer of these analog arrays, Interdesign,  held a contest, 
asking anyone interested to submit a design.  The designs would be 
judged, and the winner would get 100 ICs in return.  Doug Curtis 
submitted a synthesizer related design (I'm not sure I've ever heard 
what that specific design was), and won the contest, and then went on to 
work for Interdesign.

Google up his website, the story is online.

Tying this back to the A6 discussion, what is known about the custom 
analog devices in the A6?  Are they truly full custom, or are they a 
metallized base array type device?

-Dave