If you’re interested in how delta-sigma modulators and ADCs work, you should check out this excellent introduction by Uwe Beis:

When looking for an introduction to delta sigma conversion I found that most explanations were from a very theoretical point of view. It took me a while to understand how Delta Sigma converters really work. So I decided to write this introduction for people who prefer circuit diagrams to reading abstract equations.

To understand what I’m talking about you should at least be familiar with:

- Standard analogue techniques (op-amps, comparators etc.)
- Standard digital techniques (latches, binary codes etc.)
- Standard ADCs and DACs (resolution, speed)
- What a low pass filter is (at least an analogue one)
- The sampling theorem (sample frequency > 2 x input bandwidth, alias effects)

Delta sigma converters are different from other converters. Note that I do not make a difference between analogue-to-digital (ADC) and digital-to-analogue converters (DAC). Both are very similar and what is realized in one of them using analogue signal processing circuitry is implemented in the other one using digital signal processing and vice versa. I will explain the delta sigma technique with the analogue-to-analogue delta sigma converter as the first object.

He explains the entire process clearly and thoroughly, with lots of great illustrations throughout. Illustrations in particular are important, because delta-sig is a process over time, and it’s hard to understand with only system diagrams. Nice work, Uwe!