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.
During this project, I found some issues and inconsistencies with the 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.
|Specification||Test Method||Result PSM||Result PWM|
|Power Supply Noise and Spectrum||Oscilloscope||1.0mV RMS||1.3mV RMS|
|Input-Referred Noise||Histogram||0.97 LSB RMS||1.36 LSB RMS|
|Noise Free Resolution||Histogram||9.3 Bits||8.8 Bits|
|Effective Resolution (Not ENOB)||Histogram||12 Bits||11.6 Bits|
|Effective Number of Bits (ENOB)||Sine Curve Fit||8.92 Bits||8.84 Bits|
|Effective Number of Bits (ENOB)||Coherent Sampling/FFT||7.89 Bits||7.84 Bits|
|Signal to Noise and Distortion (SINAD)||Sine Curve Fit||53.77 dB||52.82 dB|
|Signal to Noise and Distortion (SINAD)||Coherent Sampling/FFT||49.27 dB||48.96 dB|
|Differential Nonlinearity||Sine Histogram||8.9 LSBs||Unchanged|
|Integral Nonlinearity||Sine Histogram||7.85 LSBs||Unchanged|
|Input Bandwidth||Sine Sweep||TBD|
|Power Supply Rejection Ratio?|
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