[sdiy] ADc & DAC voltage dividers.. fixed or trimmer adjustables ??

Mike Beauchamp list at mikebeauchamp.com
Sun Feb 14 18:31:10 CET 2021


On 2/14/21 6:59 AM, Roman Sowa wrote:
> . Not to 
> mention curious user turning it for fun.
You mean circuit bending? :)

Would it be advisable to run an auto calibration with the output fed 
back into the input and iterate on every single bit and then store the 
ideal DAC value into a 16bit look up table?

I'm glad Roman mentioned R5, that is definitely going to be a problem if 
you're expecting perfect 1V/oct tracking.

I recently did a similar design for a little digital sample and hold and 
have just used .1% resistors where the signal gets divided and 
multiplied. This has worked well enough for 1V/oct signals, although 
some software correction is sometimes needed.

The software correction is sometimes simply an offset, rarely a scale 
adjustment (my DAC and ADC both use the same reference voltage - so that 
helps presumably) - but the correction that needs to be made the most 
was correcting for a strange drop in the output that happens exactly at 
the halfway point - so with my 14bit dac, the output is fantastic from 
0-8191 and then is offset below the expected voltage from 8192 to 16313.

This is probably just an issue with the specific DAC i happened to have, 
but my point is that you're going to have to test your system and see 
what needs correcting.

Mike





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