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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

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  • 0

    Hi Kenneth,

    marking is following.

    CIAA chips are "N52832  CIAAE1 1803AA" all.

    QFAA chips are "N52832 QFAAB0 1740JK" and "N52832 QFAAB0 1701FH".

    And why don't you use our project?

    Our software engineer  took a long time (almost 3 days) to modify the project which can be submitted to other company. And Avnet also used this project  and confirmed to recreate this issue.

    You are going to waste all things ?

    I strongly recommend to compile our project, use our project and reproduce this issue at your Lab.

    This problem is almost on Hardware obviously, I think.

    Could you find the root cause of Hardware as soon as possible?

    (And please return this to public mode.)

     

    Best regards,

    Kiyoshi Iwai

     

  • 0 in reply to Kiyoshi Iwai

    Hi Kiyoshi,

    Thank you for providing the chip markings.

    The reason for not using your project is that the test lab must perform the tests in a controlled manner, to ensure we can identify if this is a hardware issue. If we test using your software, then we will not know if it's caused by software or hardware. This is currently the highest priority task to find out.

    The test lab are preparing test firmware, and hopefully the automated test can run during tonight, so we have results by tomorrow. That is the plan. I will let you know if there is any delay.

    Best regards,
    Kenneth

  • 0 in reply to Kiyoshi Iwai

    Hi Kiyoshi,

    There is some small problems delaying the start. They hope to start the test during lunch today. The test will take 3hours to run when they can start it.

    Best regards,

    Kenneth

  • 0 in reply to Kenneth

    Hi Kiyoshi,

    The test lab have tested 2 boards, however they are not able to recreate your symptoms yet. They will continue testing more boards to check.

    However, I believe I have made some progress by using the code and hardware description you sent.

    I have modified your software to write all data to the UART, so I could see the data while I was testing. I was able to trigger noise like shown below, I believe this is the same as you see.

    However I am only able to see noise if using CR2032 batteries, if I instead use 2x AAA batteries for supply and analog input, then I don't see such noise. I think part of the problem here may be that the CR2032 have problems feeding enough current during spikes, for instance when the radio and adc are operating at the same time. This may cause significant drop in supply voltage from the CR2032. I think part of the problem may be that the ESD protection diodes on the analog input somehow carry current if the power supply has quick drop in voltage, the 2x AAA batteries can handle this better.

    Using 2x AAA batteries with short wires seem to work here for the power supply, the analog input must have it's own 2x AAA batteries (or CR2032) for test. 

    It would be interesting if you could try with 2x AAA on your end and compare.

    Best regards,
    Kenneth

  • 0 in reply to Kenneth

    Hello Kenneth,

    Thank you for information.

    At what temperature did you do this experiment?

    At All temperatures you have this result in the case of CR2032?

    This data is not same our phenomenon, I think.

    Our case occurs only at a certain temperature range.(not all temperatures)

    And when i tried using the VDD/4 as reference voltage instead of internal 0.6V,

    I supplied power to the boards by normal power-supply (3.0V).

    But I still had this issue by using normal power-supply, not CR2032.

    According to your explanation, the internal resistance of CR2032 may affect to this issue.

    But the internal resistance of CR2032 is several ohms at max., so the voltage drop will be dozens mV when TX/RX.

    I don't think this drop may be a dominant.

    By the way, could you tell me what  does the test lab team check now concretely?

    Do they check by changing temperature?

    Best regards,

    Kiyoshi Iwai

  • 0 in reply to Kiyoshi Iwai

    Hi,

    Some results from the lab:

    Here is for instance the variation at 40degree C (manual measurement):

    The peak to peak deviation is about 35 LSB.

    If we plot the deviation as function of temperature (sweep -25 to +65C with 2C steps) the result (automatic test):

    As you can see the peak to peak deviation is pretty stable around 30-40 LSB peak to peak deviation. They are not able to see any significant noise peaks.

    Best regards,
    Kenneth

     

  • 0 in reply to Kiyoshi Iwai

    Kiyoshi Iwai said:

    And when i tried using the VDD/4 as reference voltage instead of internal 0.6V,

    I supplied power to the boards by normal power-supply (3.0V).

    But I still had this issue by using normal power-supply, not CR2032.

    If you have long wires for the power supply, I would expect you could see the same. So I want to ask nicely that you try:

    Use 2x AAA for supply (with short wires) and 2x AAA for analog input (or a single AAA is likely easier). Make sure power supply is connected directly to VDD without any diode in reverse direction.

    Another questions:

    - If you test the same board multiple times, does it always happen on the identical temperature?

    - Can you share boards you know is failing with us?

    Best regards,
    Kenneth

Reply
  • 0 in reply to Kiyoshi Iwai

    Kiyoshi Iwai said:

    And when i tried using the VDD/4 as reference voltage instead of internal 0.6V,

    I supplied power to the boards by normal power-supply (3.0V).

    But I still had this issue by using normal power-supply, not CR2032.

    If you have long wires for the power supply, I would expect you could see the same. So I want to ask nicely that you try:

    Use 2x AAA for supply (with short wires) and 2x AAA for analog input (or a single AAA is likely easier). Make sure power supply is connected directly to VDD without any diode in reverse direction.

    Another questions:

    - If you test the same board multiple times, does it always happen on the identical temperature?

    - Can you share boards you know is failing with us?

    Best regards,
    Kenneth

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