nRF52832 SAADC issues (wrong values)

[juulee]

Hello, I'm developing SAADC on nRF52832.

While developing, I have problems now.

I applied sine wave on ADC input.

And the result is displayed on the figure that I attached.

It has kind of 'spikes'. (I checked using oscilloscope and saw that input signal doesn't have problem)

Does anyone had same issue like me?

It's bigger than noise, and also they appear regularly.

Thanks a lot.

[juulee]

Yes, I did nothing.

I'm using DK.

[Kenneth]

How does VDD look like? What is the distance between the spikes in time?

[juulee]

VDD is constant 3.1V, applied by external DC supply.

Distance between the spikes in time is different for every waves. If I apply high frequency sine waves, time interval is short and for low frequency sine waves, time interval is long.

[Kenneth]

My suggestion for debugging it to not enable BLE, but output the SAADC samples over UART or RTT to check if it's related to the radio in any way. The next suggestion is to look at the usage for the SAADC, and if you may be periodically calibrating the SAADC. Also do check if there may be any ripple on VDD on an oscilloscope.

Kenneth

[Turbo J]

Is that just me or are those spikes at exactly values for 256 and 512? That would suggest a software problem in buffer or value handling.