DAC King

[Chris MacDonald]

Rene Schmitz wrote:
> 
> At 14:42 12.01.00 -0600, Paul Schreiber wrote:
> >
> >So, if we want a DAC to control a VCO over 6 octaves, we need how many
> >bits?? Anyone??
> >
> >8-bits? 6/256 = 23.4mv/step err no
> >12-bits? 6/2048 = 3.9mv/step  err no
> >14-bits? 6/16384 = 366uV/step OK!
> 
> Pardon, but I can't follow you here. Whats that maths?
> I assume 6V/256=23.4mV.
> 
> Divide 10.5833V by 127 steps = 0.00833V per step. Now its Ok. If LSB error
> can be neglected. As you say a matter of scaling, and accurracy.
> 

I believe 12 bits would suffice for 10 octaves of semitone-step control
if the DAC had 1/4 LSB relative accuracy.  Using the seven most
significant bits for semitone selection and holding the 5 least
signifacant at zero:

127 * 1/12V = 10.583 full scale DAC voltage

10.583 / 4096 = .002584V LSB step size

.00258 / 4 = .000645V 1/4 LSB error

So the error would be +/- 645uV.

Or have I got it wrong...