CR95HF Antenna Design Query

[Margisha Dave]

Posted on April 03, 2018 at 12:29

Hello,

I am working with CR95HF IC. I have some questions regarding it.

1. How much read range can be achieved with how much Henry of antenna inductance. Can any one Please suggest.?

2. Is it required that Antenna inductance and Tag antenna inductance should be same for good read range.?

3. Does it support multi tag detection at same time ? If yes then how many tags at a time?

Thanks & Regards,

Margisha Dave

[Henry Crane]

Posted on April 23, 2018 at 17:34

Hello,

1) RFID readers read range depends on reader antenna but also on Tag antenna dimensions, tuning , and tag IC protocol and power consumption. As a consequence it is difficult to answer to predict it without knowing the system 

However we provide some tools to help customers to design their system

• NFC antenna module from e-Design suite at  

  https://my.st.com/analogsimulator/flex_app/bin/eds_antenna_design.html?msg=%7B%22action%22%3A%22new_design%22%7D

    allows to evaluate the antenna inductance based on its dimensions
• the STSW-95HF03: CR95HF EMI filter calculation excel sheet at 

  http://www.st.com/content/st_com/en/products/embedded-software/st25-nfc-rfid-software/stsw-95hf003.html

    allows to optimize the CR95HF tuning circuit and calculated the field strenght generated by the reader antenna. even if this tool doeas not take into account the mutual coupling effect between a tag and the reader, it may be helpful to estimate the powering range.

The CR95HF demo board delivered with the M24L-DISCOVERY kit features a 34x47mm/2 turns/0.5ohm~424nH antenna and NUCLEO-NFC03A1 board features a 

 34x47mm/4 turns/0.8ohm~1120nH antenna. First antenna example provides a high field strength, important to maximize the performance of Energy harvesting fonctionality demonstrated with M24LR04E-R ISO15693 I²C/NFC chip. Second antenna with 4 turns provides a good compromise in turn number and impedance to maximise performance in read mode in every protocol.

these 2 reference design allows up to 9 cm read range with credit card size ISO 15693 tags and 6 cm with ISO14443 tags. 

2)  There is no need to have same inductance for reader and tag antenna. Reader antenna inductance is usually less than tags antennas impedance. 

3) Multi tag detection is part of RF protocols supported by the CR95HF. However it is not managed automatically by CR95HF and It has to be manged at micro controller firmware level using the command set of CR95HF.

This inventory procedure (step by step tag UID detection) depends on tag visibility (detection volume, collision during communication) and protocol.

best regards,

NFC/RFID Support 

[achou.10]

I have some CR95HF Antenna Design Query

1) what is actual difference between in performance of 424nH antenna and 1120nH antenna?

2) In CR95HF-A demo Board Antenna impedance design guidelines document, they have mentioned formula to calculate antenna inductance using frequency 13.56MHZ

they have given Ra=0.5 Ohm and La=36.6 * w

where w= 2 * pi * f

so w= 2 * pi * 13.56 = 85.2

so as per calculation La= 36.6 * 85.2 = 3118.3

but they have give La= 430nH

can you explain this ?

3) In CR95HF chip datasheet I have read that ZOUT differential impedance between TX1 and TX2(1) 27 Ω and Small signal differential input resistance (Rx1/Rx2)(1) 100 kΩ , what this actual means?

Is this parameters taken in consideration without onboard mounting or with components?

because PCB manufacturer considered it without mounting components.

from above parameters TX1 and TX2 and (Rx1/Rx2) I have checked all matching circuit component in M24L-DISCOVERY kit  and NUCLEO-NFC03A1 board both have same (Rx1/Rx2) component 330 Ohm but TX1 and TX2 matching components are different on both the circuit,

I want to know why it is different? is it because of different antenna inductance or anything else?