13.56 MHz power amp, antenna and buffer design

[Kevin Weiss]

I am trying to extend the range of a Vivo paypass 3000 to 1m for university project. The chip that it's using is MFRC531 (www.nxp.com/documents/data_sheet/MFRC531.pdf). I have made the antenna from the TI cookbook (www.ti.com/rfid/docs/manuals/appNotes/HFAntennaCookbook.pdf). It is the 1m x 1m antenna for which I will attach the dimensions. I am using a power amp design found in a previous experiment located on pg 7 of (eprint.iacr.org/2006/054.pdf). My design is a bit different and the schematic is included in the attachment.

I have not been able to the the signal large enough across the antenna. I measured from TP1 on the attached schematic and the most I have gotten was 60Vpp. I believe that I should get alot more. The impedence from the antenna is about 70 ohms and it is designed for 50 so I am wondering if that is a problem?

I have built a recieve circuit using a J310 chip (**broken link removed**) but was not able to get a signal back.

I am wondering if it is possible to power an antenna that size, will an antenna that size pick up the signal from a passive credit card tag and where should I attempt to retrieve the signal from?

Please as questions if things are not clear.

Your help is much appreciated.

Kevin Weiss

 

[tony_lth]

Of course the impedance of antenna and circuits should be matched.
And the signal is 13.56MHz, so the lamda is 22.1m, it seems your antenna is mall and the distance (1M) is in the near field. Do you simulate the EM field strength?

 

[FvM]

There are two points involved with your project.
- achieving the minimum required field strength at the tag location. I would calculate ISO 14443 specified 1.5 A/m as a first guess. Probably a value between 0.5 and 1 A/m can be sufficient.
- receiving the tag signal

Did you calculate the loop voltage required for 1 A/m in 1 m distance. It's several kV.