The -6dB range with 11 bits looks quite linear, if only this 0.1V offset would not exist.
But for your application with a 0..10V Input you need anyway an external resistor voltage divider, so you can just add a third resistor to lift the voltage by 0.1 V. Here is a possible circuit:

....I'm not sure what else I can try. Maybe you can learn a bit of C, for example how to call a function instead of just declaring it? ;) Here is a stripped down version of what I used to test the ADCs (I've not tested if it works in this minimal version): int n = 0; void setup() { Serial.begin(115...

... - More than 2 cores: Not saying we won't do that, but just curious: can I ask if you have specific use cases you're able to do with more cores that you can't do with two? .... - Fast lo-res ADC: Can I ask what use case you have in mind for this? I think of several small cores tied to GPIOs for ...

I would like to see: - RISC-V ISA instead of Tensilica (spares some license costs and allows upscaling to 64/128 bits later, I see Espressif is already a Risc-V member) - more than 2 cores - Better ADC specs (range down to zero) - Maybe a fast, low resolution ADC, i.e. 8bit 32 MHz - Integrated Sigma...

There is some non-linearity in the ADC range, see my post here: viewtopic.php?f=12&t=1045#p4636

As you can see there the linearity is much better with the -0dB and -6dB settings. But there is always a little blind spot near zero.

Sorry for the late respond, just seen your question today.

Attached is my LibreOffice Calc-sheet I hope you can use it.

With 10 Bit resolution and averaging over 8 Samples, it looks now much better. The heavy linearity error is just in the -11dB range of the ADC. All ranges have the problem that they don't go down to zero, so input voltage under 0.04/0.08/0.1 Volt can't be measured without some analog offset generati...

Sure, oversampling and filtering helps to reduce the noise and increase the resolution, but not helps for the non-linearity. The datasheets for other microcontrollers normally say: non-linearity: + - 1 LSB, that is 1/4096 of the full range. SAR ADCs (successive approximation) have this high linearit...

Yeah the ADC of the ESP32 is a bit disappointing, compared to the rest. The result is not only noisy, but also not very linear. You can't measure values down to zero Volts, the ADC shows zero with an input of ~0.1V. Same problem at upper end, but that is not so important. Here is what I have measure...