Frequency stability

I am looking at the feasibility of using a Nano33BLE for a clock monitoring and control application. For this the stability of the processor clock is important (though there is the possibility of calibrating the system in service so absolute frequency is not so much a problem). I know that the standard Nano (in some variants at least) uses a ceramic resonator for its clock so setting and stability is dubious. I can't find any obvious information on the Nano33BLE - I know the core BTLE module and processor is based on the u-blox NINA module but the data sheet for that seems also silent on the topic.

Please could anyone confirm whether or not the Nano33BLE uses a crystal clock?

For a secondary frequency standard, we would use a TCXO (temperature compensated crystal oscillator).

Thanks, yes. But ideally we would not want to add any hardware, and the frequency can be sufficiently calibrated using NTP, but stability is useful. So I'm interested in what we can do with the NanoBLE as it stands.

The schematic doesn't show any crystal or resonator so the clock is internal. Check the nRF52840 Processor datasheet for precision data.

Internal oscillator tolerance:
Nominal +/-1.5%
Maximum +/- 8%

The requirements are listed as 40ppm for BLE short (<200 bytes) packets and 30ppm for BLE with longer packets.

1.5% is 0.015000 or 15000ppm. I don't know how that works.

Thanks - but that's just the Nordic chip that the module uses. I'll try my u-blox contacts to see if I can find out if it uses a crystal or resonator.

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