Hello,
We are using eZ430-TMS37157 evaluation kit for RFID application. We have tested the kit as it is. It is working fine. For our application we need to change the reader and transponder antenna. With the reader antenna designed by us the communication is possible between the reader and the transponder. However if we are using the air core secondary coil designed by us instead of ferrite stick antenna on the transponder board, the communication is not possible.
We have designed the antenna with following specifications:
L= 1.52mH,
For F=134.2 KHz,
Cres = 918 pF (C11),
We have replaced the 470pF Cres capacitor with 880pF capacitor and performed the trimming functionality by referring the steps given in the user guide.
The trimming functionality is not working when we are connecting the secondary coil designed by us.
If the trimming functionality is not performed, we have observed that the data is being written into the EPROM of the transponder however it is sending an incorrect response resulting in failure of communication.
Can you please suggest is it possible to use the air core coil instead of the ferrite stick antenna at the transponder side. Or is there any other issue which we are not able to understand.
Thanks and Regards,
Rajani Karda
Rajani –
There are two documents out on the web for this.
http://www.ti.com/lit/an/scba029/scba029.pdf (this document covers LF antennas)
http://www.ti.com/lit/an/swra382/swra382.pdf (this document covers using Neosid antennas)
the key point here that must not be over looked is that the inductance cannot be “close” to the value of 2.66mH, it must be almost exactly 2.66mH.
the main reason is because of the FSK response (this is called uplink) from the transponder – the antenna must be in the correct range, otherwise, the part cannot make 123kHz and 134.2kHz correctly, thus giving bad result.
I have also attached a guide which should be super helpful in your efforts. This is for an older IC, but the values and concepts are identical.
0211.11-07-26-002 Rev1.pdf
BR-
Josh
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