oscillation at the embed analog front end circuits of SAADC in nRF52832

[Kiyoshi Iwai]

Hello,

I found the strange phenomena on nRF52832.

By using the SAADC, I have some noise on ADC Data only at a certain temperature range.

Temperature range is depend on individual IC.

I might be the circuit oscillation at analog front end of SAADC, I think.

(internal reference voltage or op amp etc,)

I tried to switch DCDC on/off, but there's no difference on phenomena.

Anyone can resolve it?

I attach the files of real data and measurement condition.

Best regards,

Kiyoshi Iwai

3426.SAADC_noise_devzone.zip

[Kiyoshi Iwai]

Hi Kenneth,

That's the best information in a few weeks.

I do keep waiting for next information of root cause and counter measure.

Best regards,

Kiyoshi Iwai

[Kenneth]

Hi Kiyoshi,

The project manager is out travelling this week, but I have sent him an e-mail to inform him that we can see noise in the measurements, and asked him to suggest for further tests the lab can do to narrow down the source of the noise. 

I can only apologize for the time this is taking.

Best regards,
Kenneth

[Kiyoshi Iwai]

Hi Kenneth,

Do you have something updated?

I have to explain the current situation to other section in our company tomorrow.

Could you tell me the lab's result of the further tests , suggestion of the project manager and etc.,?

Best regards,

Kiyoshi Iwai

[Kenneth]

Hi Kiyoshi,

I believe our test lab are narrowing down the different causes. I can add a few of the measurements here:

Noise on ADC measurements due to noise on internal reference voltage (0.6V):

Noise on CRC2032 during sampling (128x bursts):

Cell voltage of CR2032 over temperature:

Both above measurements are without radio, which will cause even more noise.

As it looks now the recommendation will be to use external reference (VDD/4), but the external reference can't be a CR2032 directly.

My suggestion to confirm is to use 1xAAA (or 1x AA) for analog input, and 2xAAA (or 2x AA) for supply voltage (with short wires). The external crystal oscillator should also be started before measurements, since the internal RC oscillator is influenced by temperature.

Best regards,
Kenneth

 

 

 

 

 

[Kiyoshi Iwai]

Hi Kenneth,

Thank you for all your cooperation.

You mean that nobody can use the internal reference 0.6V with CR2032, right?

First of all, when I started to talk about this problem, I have pinned down the influence of temperature.

I have also good temperature range and bad temperature range at all same condition except for temperature.

If the cause were the temperature characteristic of CR2032, this issue shall occur at low temperature on all boards.

But the result was different. Some board has a failure on 25 degree C and other has it on 35 degree C.

And there are OK on -5 degree C and bad on 15 degree C on same board.

How do you explain that?

All causes are CR2032?  I don't think so at all.

I only want to operate the ADC with good performance at all temperature, because ADC has a low noise state  at a certain temperature range.

Could you please focus on only temperature difference and find the root cause of this issue soon?

I always greatly appreciate your kindness.

Best regards,

Kiyoshi Iwai