Using an external oscillator (TCXO) with a nrf52 as input to the HFXO

RE: Using an external oscillator (TCXO) with a nrf52 as input to the HFXO

bjorn-spockeli — Tue, 23 Jul 2019 08:32:02 GMT

Hi khunckl,

depending on what kind of signal the TCXO is feeding into XC1, the XC2 pin should be connected as listed below:

If low-swing sine: XC2 pin shall be grounded.
If rail-to-rail: XC2 can be left open or grounded. Voltage requirement from GND to VDD_NRF.

If the TCXO outputs a rail-to-rail clock signal, then it should have a 'high' voltage above 0.7*VDD and 'low' voltage below 0.3*VDD. It's advisable to have full rail-to-rail swing, because it minimizes current consumption in the pad cell.

If the TCXO outpus a low-swing signal, then it needs to have a peak-to-peak amplitude between 200mV and 1000mV. It can be either square wave of sinewave. DC level is not important, as long as the clock signal does not shoot above VDD or below VSS.

Best regards

Bjørn

RE: Using an external oscillator (TCXO) with a nrf52 as input to the HFXO

khunckl — Mon, 22 Jul 2019 13:24:49 GMT

Thanks. Any data/advice on the required minimum signal level would be appreciated.

RE: Using an external oscillator (TCXO) with a nrf52 as input to the HFXO

Kaja — Wed, 17 Jul 2019 11:19:18 GMT

Hi,

Andreas is on vacation, but we will get back to on you early next week, when one of my colleague with some experience with this is back at work.

Best regards,
Kaja

RE: Using an external oscillator (TCXO) with a nrf52 as input to the HFXO

khunckl — Mon, 15 Jul 2019 21:47:22 GMT

Andreas,

Disregarding potential problems with phase noise, can you advise us as to the required minimum signal level we would need to provide to the nRF52? Thanks

RE: Using an external oscillator (TCXO) with a nrf52 as input to the HFXO

Andreas — Thu, 11 Jul 2019 11:51:57 GMT

Hi,

It should be possible based on the requirements given for the clock source, but we have not done any testing or verification internally with TCXO as source. You are free to try this on your own however.
The oscillator will still need a stable source, potentially you could have problems related to timing or poor clock signals. The radio is regarded as the most sensitive module though.
We can not recommend using something which we have not verified. Note though that most non-radio functionality runs with the internal oscillator as source.
There is no documentation on this as it has not been tested or verified.
No, with TCXO as source the regular HFXO settings should be used.

Best regards,

Andreas