32 MHz external clock source

RE: 32 MHz external clock source

JGusler — Mon, 19 Sep 2022 13:24:28 GMT

Okay, thank you so much ketiljo!

RE: 32 MHz external clock source

ketiljo — Mon, 19 Sep 2022 13:23:25 GMT

Yes, it's a transceiver (transmitter and receiver).

These are the minimum external components you need for the nRF52840:

https://infocenter.nordicsemi.com/topic/ps_nrf52840/ref_circuitry.html#unique_329143743

RE: 32 MHz external clock source

JGusler — Mon, 19 Sep 2022 13:13:22 GMT

And pardon this naivete, by radio you mean the bluetooth transmitter?

RE: 32 MHz external clock source

ketiljo — Mon, 19 Sep 2022 13:07:46 GMT

A 32 MHz _crystal_ is mandatory to be able to use the radio. The 32 MHz RC oscillator is way to inaccurate to be uses as a reference for the radio PLL. This is a requirement for the chip itself and has nothing to do with the FCC. The radio simple doesn't work without a crystal.

RE: 32 MHz external clock source

JGusler — Mon, 19 Sep 2022 13:00:45 GMT

I saw a reply to a post from Sigurd 2 years ago saying "You need external 32 MHz crystal in order to use the Radio and Bluetooth." and then on this post General PCB design guidelines for nRF52 series under Crystal and Clock it says a 32MHz crystal is mandatory. Could you clarify these please?

RE: 32 MHz external clock source

ketiljo — Mon, 19 Sep 2022 07:06:48 GMT

There's no such requirements from the FCC. Part 15 isn't specifically for Bluetooth, it's the other way around, a Bluetooth radio has to satisfy the requirement under part 15.