Idea for a CV quantizer

[gstopp at fibermux.com]

     Juergen,
     
     I've had very good results from 6-bit R-2R ladders for semitone 
     intervals at 1v/octave. I match 1% resistors with a DVM first just to 
     be safe.
     
     Summing resistors I've never tried, and it seems to me that you would 
     need a trimpot for every bit.
     
     I know that Joachim likes the chip DAC idea, but I once had back luck 
     with a 1408 and have not tried any chip since (maybe it's a good 
     approach and I just don't know it).
     
     Guidelines - make sure your bits go between exactly between zero volts 
     and VCC, and use resistors in the 1K-50K range, and all will be 
     stable.
     
     - Gene


______________________________ Reply Separator _________________________________
Subject: Re: Idea for a CV quantizer
Author:  Haible_Juergen#Tel2743 <HJ2743 at denbgm3xm.scnn1.msmgate.m30x.nbg.scn.de>
at ccrelayout
Date:    2/29/96 11:00 AM


>     My impression is that this would not be any easier than a DAC, and
>     probably less accurate. For the DAC approach all you would need is a
>     clock, a counter (4040?), an bunch of resistors, and a buffer (maybe). 
     
>     However the DAC will be very clean and sterile, so perhaps the charge 
>     pump can offer some interesting analog-ish deviations.
>
>     -Gene
     
Gene, I am not very experienced in discrete DACs. I know that you 
have made some already. What I need is a precise 7-bit DAC,
because I have to cover at least -1V to +5V (so a 6-bit isn't enough). 
What I fear is the temperature drift of the buffers impedance that 
might be different from the external resistors' drift.
Would You suggest a discret R/2R ladder or just 7 different summing 
resistors?
     
JH.