A couple of things that are important when doind those INL DNL plots :
- Make sure your meter is in FIXED range. never ever let it autorange. the problem is that , if it switches range, you get hit by the tolerance of the input scaler of the meter. this will be visible as a jump in the dnl/inl line.
for this 8 bit dac this may not be important but if you are going to do 16 bitters :
- turn of the autozero function of the meter. run one autozero at the beginning . at the end of the sweep :leave the dac at max setting , take a reading , autozero and take another reding. the delta between the two last readings gives you the zero drift of the meter. assuming constant ambient temperature this drift is linear. the number obtained can be used to adjust the slope. if you autozero every time you are throwing in 'noise' to the dnl inl.
- sync the entire setup to the powerline and measure at powercross.
- letting the meter do the oversampling is faster than doing this in software.