[sdiy] FPAA for analog synthesis?

[Antti Huovilainen]

On Wed, 3 Mar 2010, 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.

Possibly in the later chips, but the early ones at least were likely "mask 
programmable" analog arrays. Doing a full custom ASIC is quite expensive 
for small runs (and let's face it, synth business was small compared to 
consumer stuff).

The arrays typically (taking as example the zetex 700 series aka 
arraydesign.com ones) contain a bunch of transistors (NPN and PNP), a 
whole bunch of smallish value resistors (which are connected together in 
series & parallel to get the value you need) and a small number of special 
components like capacitors, pinch resistors etc.

The customer decides what size part he needs from the series (number of 
components & number of pads) and submits the interconnection mask. If the 
size of the devices increases gradually, the loss of efficiency (used 
silicon area out of total) is pretty good.

Disclaimer: I have never used or designed such devices, but merely read 
the manuals to gain better understanding of how the CEM chips were built.

Antti

"No boom today. Boom tomorrow. There's always a boom tomorrow"
   -- Lt. Cmdr. Ivanova