[volt-nuts] 32-Bit PWM divider

[Randy Scott]

> I will do this for all steps PWMH = PWML =  0x0000,
> 0x1000, 0x2000, .... 0xF000, 0xFFFF (or even finer
> resolution).

Andreas,

Thanks for sharing the details of your project.  Building one of these DACs (or the 20-bit DAC described in LT's AN86 app note) has been on my to-do list for a while.

I'm wondering what your reason was for taking the measurements this way.  My first thought would have been to set one of the PWMs to a constant value and then manipulate the other.  For example, comparing H = 0x8000, L = 0x8000 with H = 0x8001, L = 0x8000 to measure the effect of single-step changes in the high PWM.  Or, fixing H at 0x8000 and stepping the L value through a range of values (with a step size equal to whatever you think is measurable above the noise).

And, FWIW, this link explains measurement of INL/DNL for a converter (specifically an ADC, but seems to apply to a DAC if you reverse everything):

http://www.maxim-ic.com/app-notes/index.mvp/id/283

Based on this, it would seem like you're computing what they call "End-point INL".  What Bruce describes is called "Best straight-line INL" and is the recommended approach.

Randy.