ADC internal ref accuracy compared to VDD/4 as ref

[bart]

Hi, I read a couple of post that asked about the accuracy / tolerance of the internal REF, and the answers mention it's included in the gain error.

This made me wondering: if VDD would be perfectly stable, how would using VDD/4 as reference compare to using the internal 0.6V REF? What gain error would that result in?

[hmolesworth]

Depends more on whether the signal is ratiometric or not. If the signal is unrelated to VDD, for example an external device like a tiny photocell which generates a voltage completely independent of nRF52 VDD then the internal reference will always be better. However if the signal voltage is related to VDD such that it rises and falls as VDD rises and falls (say a potentiometer or load cell which uses VDD as the voltage source) then VDD/4 will be more stable as the reference VDD/4 tracks the excitation voltage.

[bart]

Yes, that makes sense. However, suppose the signal is unrelated to VDD, but we have a perfect VDD of 3.3V, then what kind of gain error would I get? Basically I'm trying to find out what the error of the internal ref is, separately from the gain error.

[Karl Ylvisaker]

Hello Bart,

We have some additional information about the SAADC that is only available under NDA.
You may reach out to your Regional Sales Manager (RSM) to arrange the signing of the NDA so that we may provide you with this extra information. If you do not know who your RSM is please send me a direct message with your location, so that I may provide you with their contact information.

Best regards,
Karl

[Anne van Rossum]

I'll organize it.

[Karl Ylvisaker]

Great!
I have informed the RSM that you will be in contact about this matter soon.

Best regards,
Karl

[Anne van Rossum]

Resolved. If we have further questions we will use DMs given the confidential nature of the topic matter.

[Karl Ylvisaker]

Anne van Rossum said:

Resolved.

Great, I am happy to hear that, Anne!

Anne van Rossum said:

If we have further questions we will use DMs given the confidential nature of the topic matter.

Yes, or alternatively you could raise it as a private ticket - this would be preferable to Direct Messages.

Best regards,
Karl