NRF52 PDM Frequency Calculation

[Guilherme Costa]

Hi,

I am evaluating if it is possible to use the nRF52840 PDM peripheral with a low-power microphone and I need a different CLK frequency setting than what is documented. I am aware that frequencies outside of the ones defined in the Product Specification document have not been tested, but I am willing to evaluate the system performance outside those conditions.

For this end, I want to know the formula for calculating the CLK frequency, since the value provided in the Product Specification don't seem to bear a direct relationship with the generated signal frequency.

Regards,

Guilherme

[Jared]

Hi,

For this end, I want to know the formula for calculating the CLK frequency, since the value provided in the Product Specification don't seem to bear a direct relationship with the generated signal frequency.

What do you mean, the formula is shown in the register description. The PDM clock frequency is adjusted by the PDMCLKCTRL register. Do you mean there isn't a clear connection between the value that you write to the PDMCLKCTRL register and the value that is used to divide the 32 MHz clock and thus set the clock frequency?

regards

Jared

[Guilherme Costa]

Hi Jared.

For this end, I want to know the formula for calculating the CLK frequency, since the value provided in the Product Specification don't seem to bear a direct relationship with the generated signal frequency.

This is exactly what I mean. I might be missing something, but I couldn't figure out how the values in the table relate to the divisor values shown (like, how setting the register to 0x08000000 gives us a divisor of 32).

[Guilherme Costa]

By the way, I just found this in the Product Specification for the nrf5340:

Does this equation hold true in the nrf52 series as well?

[Jared]

Hi,

I think that should also be valid for the nRF52 series.

Let me double check with our developers and come back to you!

regards

Jared 

[Jared]

Confirmed from our developers, this is valid for the nRF52 series as well.