Documentation suggests that the 16MHz crystal trim process should be performed while measuring a 2.4GHz RF output. Yet it is possible to route the 16MHz oscillator to a PIO pin using PioSetAnaMonClk(pio_ana_clk_16M). Since the RF output on a given channel should be a fixed multiple of the 16MHz oscillator it seems to me that the crystal could be trimmed by monitoring the 16MHz signalon a PIO pin, rather than the RF signal.
Is this the case? If so, should the crystal be trimmed to exactly 16.0000MHz, or some slightly different frequency?
Regards - Charles
How you route the 16Mhz to PIO ?
And why not use RF for that ?
I have tuned a number of boards to give the correct 2.4GHz frequency as measured by a spectrum analyser. In each case the 16MHz crsytal frequency (routed to a PIO pin and measured with a low-frequency digital counter) was 15.99985MHz.
This what I would expect: a phase-locked loop frequency synthesiser multiplies the low frequency by a rational number (n/m) and so the 2.4GHz frequency to crystal frequency ratio should always be the same.
I postulate that RF tuning can be done with only an inexpensive frequency counter, setting the crystal to 15.99985MHz.
Any comments?