RF Frequency Tolerance Question

[michaelbester101]

I have a general question about the RF frequency tolerance of Nordic devices in general. Is the following calculation correct?

1. Crystal spec = 16MHz, +/-50ppm tolerance, +/-30ppm stability.
2. RF Carrier Frequency set for 2457MHz.

The PLL will multiply/divide the 16MHz by a factor of 153.5625 to achieve the 2457MHz output.

2457MHz * 80ppm (50ppm + 30ppm) = 196.56Khz.

So over temperature the 2457MHz carrier will be off by a maximum of +/-196.56KHz, plus any PLL errors?

Is my thinking correct?

[Asbjørn]

The carrier is generated directly from the 16 MHz as you say. So the tolerance of the crystal will also be the accuracy of the carrier, just as you say. The product specification states that the total tolerance can be +/-50ppm. Not +/-80 ppm.

Other than that it's correct.

[michaelbester101]

Thanks. We are currently using a crystal that has 80ppm tolerance, and thought it may be a good idea to use a better (tighter) tolerance crystal. :)

[Asbjørn]

Yes, I would recommend you to tighten it up a bit. Good luck:)