nRF52811 ADC resolution and enob

[JsSenso]

Hi,

I am developing a custom board with nRF52811 where I will measure analog signals from op amp on ADC (single ended mode). Signals will be very small, so I need a good resolution. nF52811 and the board will operate on 1.9V supply, so I will need 12-bit resolution on ADC. This was actually the main reason for choosing nRF52 chip in the first place.

According to datasheet (SAADC Electrical Specification, page 281-282) the effective resolution (ENOB) is only 9bits, which is to low for me. There was already a similar topic on DevZone nRF52 ADC ENOB, but I still need some more clarifications regarding this topic.

• According to datasheet 9-bits ENOB is for differential mode with 1/1 gain. What will be the ENOB for single ended mode and gain 1/3?
• It was mentioned that the best ENOB for 12-bit can be 10.5bits (with oversampling), which is not much better for me compared with 10bit. What is ENOB for 10-bits (this parameter is missing in datasheet)?
• What is VOS for 12-bits (this parameter is also missing in datasheet)?

Thanks for any help, Jure

[awneil]

JsSenso said:

I will measure analog signals from op amp on ADC (single ended mode). Signals will be very small

Surely, the whole point of an op-amp is to amplify the signals to take full advantage of the ADC's input range?

[JsSenso]

I am using strain gauge sensor before an op amp. Signal is already amplified to get the full ADC range (1.8V in my case). Actually, the changes in signal are very small, that is why I need good resolution (12-bit). I am just wondering if it is even possible to get that kind of resolution with nRF52811 given that the Enob is only 10.5-bits? Using of external ADC is just not possible for my case.