about the target matching Z for ST25R3916

[DSai.1]

Dear Sirs,

To achieve a longer reading distance, we are tuning the antenna matching parameters.

To use the ST25R antenna matching tool, we need to give a value for
target matching Z and target antenna Q. I wonder how to select the target matching Z for a longer distance.

In datasheet for ST25R3916, there is RFO driver resistance. Should we select target matching Z as same as RFO driver resistance? If possible, please give me some help information about the target matching Z.

best regards

Dai Sai

[Travis Palmer · Accepted solution]

Hello Dai Sai,

Most important for maximizing the read range is a proper (higher) Q-Factor. 

If you only target ISO14443-A a calculation is mentioned in the AN5276 Rev 6 page 16/44.

For other technologies the (e.g. ISO15693) the same calculation can be used.

Please ensure that the capacitive voltage divider is re-adjusted to not violate the voltage limit of the RFI pin.

The target matching impedance is together with the supply voltage and LDO drop-out (= supply stability) is defining the current consumption of the driver stage. You can lower the target matching impedance until you read the maximum current. You will also recognize that the read range will not significant increase.

At the end you have to find a trade-off between power consumption and read-range.

What is the reading distance you are targeting?

br Travis

[DSai.1]

Dear Travis

Thank you very much for your information.

We will do the matching adjust based on your advice, and

try higher Q-Factor. 

At current stage, we got a distance for 30cm, while the volage range

is about 13V. The simulation from ST25R Antenna Matching Tool 

show the voltage amplitude of V_out is over 60V, it is much

bigger than real measured.   

If possible, we hope to get a 40cm reading distance.

best regards