Analog to Digital Converter

dwight dkelvey at
Tue Aug 18 18:01:59 CDT 2015

Reading the note made me think of something else.
If it is an SAR, and you read to soon, the LSBs of the incomplete
conversion will always be the same. All ones or all zeros.
If it is a Sigma-Delta, and the input has noise
on it that is above the same rate, the LSB's will take on a
random, all ones or all zeros on different reading.
This is an indication that the input has not been properly
filtered or you have exceeded the slew rate, even if you are
within the frequency band width.
Most audio A/Ds assume a de-emphesis so that the higher
frequencies are reduced in slew rate.
Any noise above 1/2 the sample rate will be reflected into
the values. Anything above the sample rate will be as I
described, a mix of all 1's or all 0's on each sample.


More information about the cctech mailing list