“The RP2040 datasheet has a woefully underspecified Analog to Digital Converter, only 3 lines
Compare this to the Digital IO Characteristics (Table 631); it has 18 lines! And ADCs have much more complexity and nuance than a Digital IO (however, Digital IO blocks have surprising complexity).
In this project, I will explain different ADC specifications, how they can be characterized, and the results of those tests on the PR2040.
Issues Found
During this project, I found some issues and inconsistencies with the ADC.
The biggest thing is that the ADC has some significant DNL issues. It looks like those were caused by a systematic error in the capacitors for the DAC portion of the SAR ADC.
The other thing I discovered is the “Low-Noise” mode of the DC-DC converter on the Pico has more noise (see below for the performance impacts) than the high-efficiency mode.”