Radiated immunity test problem in home healthcare product

RE: Radiated immunity test problem in home healthcare product

ray — Mon, 08 Apr 2024 03:47:04 GMT

We solved the problem by using a bandpass filter after the antenna.
Thank you.

RE: Radiated immunity test problem in home healthcare product

wdabkus — Thu, 04 Apr 2024 11:27:51 GMT

I would like to know if the problem raised in this post is still valid.
I am currently designing a medical device that will also be exposed to 10V/m exposures during EMC testing, and I am wondering if the added SAW filter is necessary.

In the post 4 month ago: devzone.nordicsemi.com/.../immunity-issue-2-3ghz

it was reported that in revision 3 of nrf52840 the problem of immunity to 10V/m has been eliminated.

IN-141 rev 1.1 description for 3 rev nrf52840 and with IN-149 (for 2 rev nrf 52833)

"Improved wide band blocking:
The blocking performance improvement will be in the order of 10-15 dB for frequency offsets of 50-300 MHz from the carrier
frequency compared to previous nRF52840 revisions. "

Can I ask you to confirm this information and whether this means that it is safe to use in healthcare devices nrf52840 rev. 3 or nrf52833 rev. 2, without additional modifications to the radio path (we want to use precertified modules)

Thanks!

RE: Radiated immunity test problem in home healthcare product

ketiljo — Wed, 04 Jan 2023 08:23:56 GMT

It's bi-directional so it doesn't matter what way you connect it.

The nRF52840 matching network have 3 components depending on what version of the schematic you use. Place the filter between this and the antenna tuning components.

The schematic is mostly correct, you just need a shunt capacitor between L3 and the filter.

RE: Radiated immunity test problem in home healthcare product

ray — Wed, 04 Jan 2023 04:00:10 GMT

Thank you for reply.

We checked recommended parts and a little confused.
The chip have one pair input and output pin.
It is understood that it operates in one direction, and it is questionable whether Rx/Tx can be used.

Will be trying to design the circuit as below.

Is there any problem with ble communication even if I use it like this?

Thanks in advance.

RE: Radiated immunity test problem in home healthcare product

ketiljo — Thu, 29 Dec 2022 16:34:31 GMT

The energy from the disturber come in via the antenna. So you will always need a band pass filter and maybe the shielded box, not the other way around. There are several filters that will do this fine. You need >15 dB attenuation at the closest frequency, Something like this https://eu.mouser.com/new/qorvo/qorvo-885033-signal-conditioning/ Note that the insertion loss is higher when the attenuation is higher

All nRF devices are designed for 3 V/m as this is the standard for consumer electronics and it's relatively simple to increase this with a filter.

There's nothing FW related that can improve this.

RE: Radiated immunity test problem in home healthcare product

ray — Mon, 26 Dec 2022 07:26:58 GMT

Thank you for quick response.
We tried a shielded box around the nRF52840 and the RF section but still getting disconnected.
We will try a band pass filter after the antenna.
Could you advise us which a band pass filter to use?
and in the code something that I can try such as changing BLE config?

Additionally has any chip designed for 10V/m in nRF52 series?

Thanks in advance

RE: Radiated immunity test problem in home healthcare product

ketiljo — Thu, 22 Dec 2022 12:03:41 GMT

Yes, this is to be expected. The device is designed for 3 V/m. For higher field strength, you need a band pass filter after the antenna. Possibly also a shielded box around the nRF52840 and the RF section.