ST25RU3993 ADC Debug Usage

[Jeff C]

I see the ADC Pin runs to the STM32 MCU ADC Pin, and that in the firmware demos it prints the adc value to the screen.

However I don't see any place the ADC value is used for tuning or anything else other than just random information.

For example, for reflected power for tuning, it just uses the I/Q values and has nothing to do with the ADC.

How can I use the ADC reading to my advantage? I see that in the Eval that the T2 Input is "Coupled" with the input to the Log Detect Chip.

So it seems the Log Detect just helps verify my Tx power is on and perhaps give me some "number" to go along with it.

Is it for testing that Modulator control register 3  values for TX_lev is taking effect? Is the ST25RU3993 actually going to Tx a smaller amplitude into a fixed voltage PA? 🙂

Thanks for any knowledge you can share!

[Bart Herse · Accepted solution]

Dear Jeff C,

the 20 dB coupler T2 takes a sample of the TX power and feeds it to the power detector.

The power detector outputs a DC voltage that is then AD converted by the MCU and displayed in the GUI again as a voltage.

With this one could implement a closed loop TX power control. So in case the TX power drifts away from the desired target value the Modulator Control Register 3 (0x15) could be adjusted to counter the drift. In combination with register 0x15 the lower bits in register 0x0C can be used to set sub-1dB steps.

Note that a closed loop TX power control is not part of the current ST source code deliverable.

I hope this information answers your question.

Cheers,

B

[Jeff C]

Perfect answer! Thank you Bart!