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nRF52832 ANT grounded zero impedance burned?

CeDeROM

Hello, I am making my first custom board based on nRF52832. I have used a custom antena design (due to PCB layout I did not use reference design). That was the very first board prototype.. where I was testing some experimental firmware features.. I did not get the BLE connection.. I have verified the ANT resistance and it is zero! Did I burn my BLE radio? Is it possible or there are some protections and that may be caused by short circuit during assembly? Now I start to regret I did not use the reference design ;-) Anyway, how can I verify radio design in a safe way so I don't burn my BLE radio output?

  • +1

    Hi,

     

    The radio front-end has a transformer which is DC short to ground so this is as expected, your chip should not be damaged.

     

    Are you still not able to get a BLE connection even if you put the PCB and the device you use for testing right next to each other? Have you verified that the HFXO is starting?

     

    Best regards,

    Andreas

  • 0

    Hello, I happen to have the same problem in my design. I measured 2.7 Ohm on ANT pin but I think it might be due to the internal balun. Did you come up with the solution of your connectivity problem?

  • +1 in reply to Pero Krivic

    Hi,

     

    The short impedance of the ANT pin is as it should be. Even full reflection at 4 dBm output power it should not take damage. You can dial this down a bit, -8dBm should be possible to receive if you put the phone/measuring device right next to the PCB and have plenty margin to the levels where it might hurt. You can also look at the current consumption when set up as a TX carrier.

     

    If you do not see any radio activity it might be that the crystal is either not starting or incorrectly calibrated. Have you verified this? The load caps shall be approximately 2*CL-4pF, CL is specified for your crystal.

     

    Best regards,
    Andreas

  • 0 in reply to Andreas

    Thanks for the reply! I guess somehow I have destroyed the chip.. but others work fine..

    I have noticed that XTAL 32kHZ is mandatory for CPU to operate, and XTAL 32MHz is mandatory for RADIO to operate - these were also the main problematic points during further prototypes assembly..

    My PCB software short-circuited the RADIO GND to the board GND. That may caused the radio break. Next PCB had dedicated RADIO GND decoupled with 0.8pF to the ANT and below chip GND. Even with non-perfect antena design my radio works for a short distance.

    Here comes the question - do you sell/provide (priced around MCU) hybrid modules with nRF51 and nRF52 that has the antenna design included and certified by Bluetooth SIG so I could use it in my device and skip the radio certification?

  • +1 in reply to CeDeROM

    Hi,

     

    The 32kHz crystal is not mandatory, but if it is not populated you need to specify the internal RC oscillator to be used as LFCLK source when enabling the sofdevice.

    Connecting Radio GND with board GND as you describe should not be a problem for the radio to operate. The harmonic emissions might be too large for regulatory tests, but you should still see communication. I have not seen your design though so it is hard to give an exact theory than that, but if you could upload the schematic and layout here I could give it a try. We can also give you pointers on what to improve for future boards spins, and if you do not want to share it with the world you are welcome to register a 'private'  case (only visible to Nordic employees and your distributor).

    We do not sell modules, but a handful of other companies do. You can see a list of them here. I have no idea about pricing, but expect it to be quite a bit more than the chip alone, so you might not give up quite yet.

     

    Best regards,

    Andreas

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