Increase read range of ST25R3911B

[GPail]

Hi everyone,

I use ST25R3911B with differential antenna driving using the circuit recommended in datasheet, powered in 3.3V.

I initialize the chip with NFC-A mode. I can read NFC tag but in a very short range (maximum 15 mm).

I tried to increase this range by increasing the receiver first gain stage, by writing in receiver configuration register 3 (boost mode) but it did not improve the read range.

Is it normal that it did not increase the read range?

Is there another way to increase it?

Interresting facts:

 - The A/D converter output register value is not impacted by my change. 

 - As expeced, if I write the RFO normal level definition register to disabling first segments, the value of A/D converter output register decreases as the read range.

Thanks a lot for your help

[Ulysses HERNIOSUS · Accepted solution]

Hi,

I assume you are using the A/D to measure the amplitude on RFI. Which voltage do you measure? This voltage is not really related to the voltage inside the receiver to detect/demodulate load modulation.

On typical designs the boost does not increase read-range. I recommend to first use a field probe (scope tip ground loop) to see if the tag is power limited, i.e. it does not answer or if it answers but the ST25R3911B does not see/correctly interpret its load modulation.

Typically both cases are more likely to be addressed by improving the antenna/matching/voltage divider. Please have a look at AN4974 Antenna matching for ST25R3911B/ST25R391x devices.

Regards, Ulysses