Simple 4 Bit ADC?

[honcho at paia.com]

Hi group - Gene, whom I highly regard, said:
> Actually the Polyphony design uses 4 op-amps plus some kind of 
divider networks that change the thresholds of the comparators 
depending on the current code value - that's why all the different 
resistors.
>>>

The polyphony design was from my old Lab Notes column and I always 
thought that the low parts count (1/4 the comparators and no need to 
do 16 to 4 encoding) pretty much compensated for the fact that all the 
resistors were not the same value. It is a "flash" converter since it 
requires no clock for the conversion, though it's not strictly 
self-clocking logic in the current sense of the term.

But the most interesting thing about the circuit that wasn't mentioned 
in the article is that it is really a neural network that maps a 
continuously variable function into binary 4-space. The different 
value resistors represent synaptic weights and it was "trained" by me 
with a calculator :-) It was a neat project but a dud in terms of 
sales. Then again, so was the Shephard Function Generator which is 
also one of my favorites. 

Why are the non-commercial projects always the most fun to do :-?

-John

ps - any DIYers on Oahu?

---------------------------------------------------------
John Simonton                  PAiA Electronics, Inc
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