MFRC630 antenna matching

[Marco_21]

Hello all,

We have designed Low Power RFID based device where we are using MFRC630 Plus reader chip,with Mifare 1K classic card with this NFC antenna (QI not used yet)

https://www.we-online.com/components/products/datasheet/760308103305.pdf

We follow application note about antenna design and matching using nanoVNA. All measure are done with hardware completly mounted and placed in it working position, so there are no problem with detuning.

This is schematic of MFRC630 antenna circuit.

This is VNA result after component tuning (different from schematich above): C1 = 46pf  C2 = 123.6pF  Rq=3.4ohm:right matched antenna

it seems matched with about 50ohm at 13.56Mhz. We test the system with real 1k mifare card and MFRC630 often return Authorization Error.

We change matching circuit with retry and try iteration and with very different C1 e C2 value: C1 = 87pF C2= 122.7pF Rq=3.4ohm. With this configuration system read always correctly 1k mifare cards. This is VNA result, obviusly unmatched and with high return loss.

We test this with 2 different calibrated VNA and result was the same.

I would to know why with detuned antenna system works well?

And a suggest where to continue investigate, software or hardware.

Thanks you 

Best Regards

Marco

[hedleydavidson]

Can anyone advise if the Mifare card frequency has changed . We have been using Mifare for over 25 years BUT all the new cards that we receive don't read on our system . We have to recover 1000's of readers from the field and modify the antenna matching - normally by reducing the value of C1 in the matching circuit from ~ 22pf to ~ 7-9 pf . When using the VNA and the Mifare spreadsheet to calculate C1 & C2 the spreadsheet provides the original values. Our cards are procured in batches of 30,000 so this is becoming an extreme stress item - any help / ideas will be appreciated. 

[hedleydavidson]

Cards are 1K and 4K Mifare Classic and we still use MFRC53101 interface IC

Our customer buys cards from Identa , so perhaps they have changed antenna / packaging 

Question : is there an updated antenna matching spreadsheet , ? as when we insert values from our network analyzer measurements C1 & C2 and rqa values , don't produce the expected results so we have to resort to trail and error. 

Regards

[Florian_Mikulik]

Hello,

As said, from our side for MIFARE Classic absolutely nothing was changed since years, neither any spec nor any chip.

Hence, the reason must lie in the used antenna. Do you have any possibility to measure the cards resonance frequency? There, a possible difference should be visible.

I'm sorry that I can not help you further here, I would recommend to approach the card manufacturer to provide possible differences to previous orders. Again, there is no change in MIFARE Classic done on our side since years.

 best regards,

Florian

[Florian_Mikulik]

Hi!

Can you please let us know what MIFARE Cards you are using exactly? (Classic/DESFire/Ultralight...)

Actually, I can assure you that nothing was changed in the chip, the operation conditions are standardized by the ISO/IEC 14443. Though, not only the chip influences communication, but also the used card antenna coil. This is out of our control, we are producing the chips (which never can change), and the card manufacturers build them into cards that you can use. Probably there was a change to the antenna made, or a wrong antenna used in those cards?

Best regards,

Florian

[Tomas_Parizek]

Hello Marco, 

Good to hear ! 

BR

Tomas 

[Tomas_Parizek · Accepted solution]

Hello Marco, 

I think it could be because of so high Rx Gain of the receiver. 

Could you try to adjust the Rx gain value? I recommend decreasing it and checking the performance with 50 Ohms tuning. 

BR

Tomas 

[Marco_21]

Hi Tomas,

  it was too high, i decrease Rx Gain and now it work like a charm. Thank you very much!

Best Regards

Marco