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You can try this, but it’s mucheasier to buy a 12 to 16 bit D/A converter. Basically the problem you’retrying to solve, D/A converter accuracy, has alreadybeen perfected by IC designers over the last 20 years.
John Loffink
jloffink@...
-----Original Message-----
From: J. Larry Hendry[mailto:jlarryh@...]
Sent: Tuesday, February 19, 2002 10:45 PM
To: MOTM List
Subject: Re: [motm] Quantizing
I have l long been thinking about a quantizer. Mythought process was that a very accurate circuit could be built in the 8 bitformat IF one used a ADC to get the digital quantities, but avoided the 8 bitDAC by going completely analog on the output. Then each of the 8 elementscould be trimmed accuracy so when you added the elements each together youwould have much greater than the accuracy expected from a 8 bit DAC. Ican see Paul shaking his head and sighing at me right now. But, I have beenthinking seriously about a replacement for the 822 when those PCBs aregone that uses pots instead of rotary switches. So, trimmer count wouldbe considerable less. Of course, then your basic circuit is aquantizer. I have done no development yet because of other projects, myneed to learn more, and the (cough, cough) significant stock of 822 PCBs Iwould like to make a dent in first. :) And, I fully admit to knowingalmost nothing about it and being significantly under-qualified for thejob. So, I'll probably play with it anyway.
On a related question, where would one normally expect theanalog out to track the input relative to step points. To simplify theexample, let's assume 1 volt steps. Would the output be desired to changefrom 1 to 2 volts at 1.5 or 1.9999 on the input? I don't see that isreally matters. But, I am still pretty ignorant on the subject.
Seems the 8 bit DAC might be fine for a mono synth andsingle oscillator, but would never do where oscillators might beattogether. I have a couple of the PAiA 8 bit MIDI 2 CV 8s that I usewith stuff other than my MOTM modular. For my mono synths (like myMicromoog) that 8 bit resolution seems to be OK.
Larry