nRF5340 bluetooth low energy signal never detected

[Diogo_Simao]

Hello,

I've been working with a custom board using the nRF5340, but I’ve been struggling with picking up any BLE signal from it. I flashed the network core separately with the hci_ipc sample, then flashed the beacon sample, and everything worked fine on the dev kit. I followed the same steps on my custom board, and while the debugger for the cpuapp indicates that advertising has started (just like on the dev kit), I cannot detect any BLE signal using the nRF Connect app on my smartphone.

I’m using a WiFi antenna connected via U.FL, so I expected to pick up at least some signal at close range.

Troubleshooting Steps So Far:

    Verified that my board flashes and runs correctly—both the dev kit and custom board behave identically according to the debugger.
    Modified the device tree and network core configurations, but none of the changes had any positive impact.
    Confirmed that my connections match the Reference Layout Config. 2: VDD supply, DCDC, USB, NFC.
    Other peripherals on the custom board are working correctly, which suggests that the nRF is at least functional.

At this stage, I suspect a possible hardware issue, such as the nRF not being soldered/attached correctly or an issue with the antenna.

I can share whatever is necessary to get to the bottom of the issue, and I'm very much out of ideas. Any thoughts on the matter are appreciated! At the very least I'd like to narrow it down to hardware or software flaw.

[AMarch01]

A quick response would be if you have followed the guidelines for layout...however they don't have specifics on UFL antennas so maybe that doesn't help. 

General PCB design guidelines for nRF53 series - nRF5x - Hardware design, test and measuring - Nordic DevZone

[Priyanka]

Hi,

It definitely looks like a hardware issue so far. Have you connected the antenna via an adapter or directly?

Also, have you followed the antenna and impedance matching exactly as on the reference design including the components and their values?

Faulty soldering can also cause issues, as you have mentioned, so I would recommend that you go through this.

It's also a good idea to go through the nRF53 PCB guidelines as mentioned in the previous comment by @Anthony A Marchini

-Priyanka

[Diogo_Simao]

Apologies for the late response, we assembled another custom board to troubleshoot this further.

The problem remains the same, firmware/application runs well, I get no signal.

I've done a couple more things, disabled the DCDC mode in VREGRADIO and VREGMAIN to see if DC/DC or LDO made a difference (didn't detect anything either way). Although I did note that VREGMAIN isn't retained, I assume it's because I'm forcing things in the application side of things and there might be some configuration setting this to a default value on boot.

Read the MAINREGSTATUS to confirm its running in normal voltage mode (it is).

I've used either a WiFi antenna directly into the uFL or a ceramic antenna. 

We haven't fully adapted the trace yet so the values of the passive components are subject to change, however I do believe I should be able to pick up any signal (small as it may be) with my phone on top of the antenna. Impedance matching should help a lot in a final application but when the antennas are 1 mm apart I should pick up something above -100dBm? Could it really be that off?

Here's the antenna bit of the schematic:

Could it possibly be some other register/configuration? The main differences from the dev kit is using USB-C data for debugging and using VDD 3V (I can't recall exactly how the nrf5340 dk regulated everything - VDDH setup with 3.0V external regulator?). Nothing else other than bluetooth and usb-c is being used at the moment.

P.S.: We'll be measuring the pins related to RF signal supply (DCC, DECR DECRF) to see if something is off, although I'm not sure what kind of values we should be expecting while the radio is trying to transmit.

Appreciate the help!