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# High antenna impedance evaluation of CR95HF

Associate II

Hello to everyone:

I am starting to evaluate and the possibility to design a transparent antenna on the glass, but I think I have an impedance problem. For example:

A. I design an ITO transparent antenna and estimated the total resistor is around 15Kohm. (ITO per square is 40ohm/sqr, and 2round 50x38mm antenna)

B. I know this Zout impedance is very high and I just want to consult experts, does it anyways to compensated/matching this high impedance requirement?

C. At the same time, how does the antenna resistor value limitation value? (don't exceed the 27ohm?)

Thanks for anyone reply to me.

Fox.

1 ACCEPTED SOLUTION

Accepted Solutions
ST Employee

​Hello Fox,

thank you for the clarification. Your original email stated a serial equivalent resistance of 15KOhm which was to big for any solution.

Removing the EMI filter (L01/L02 & CO1/C02) could help. in the EMI excel calculation tool, fill L01,2 with 0 and C01,2 with 1e-40. the result is C2=163pF and C11,12=560pF (see fig 1)

fig 1

bes regards,

Henry

4 REPLIES 4
ST Employee

Hi,

generally speaking, RFID/NFC antenna are spiral coil which impedance at 13.56MHz is complex, with real part and imaginary part. Imaginary part corresponds to the inductive behavior of the coil. Calculating the matching circuit for CR95HF consist in calculating the the component necessary to adapt the antenna coil impedance to the desired input impedance. The target impedance can be between 27 +0j and 50 + 0j.

Do you know the exact complex impedance of your IT0 antenna at 13.56MHz?

best regards,

Henry Crane

RFID/NFC support team.

Associate II

Hi! Henry:

Many thanks for your reply to my problem, let me organize my problem in detail.

1. Until now, my transparent antenna does NOT make yet before that, I want to evaluate the DC trace resistor that the CR95HF can afford or not.

2. So that, I calculate the antenna equivalent conductor value by designsuite int the first. Please see the Fig-1, that's my target geometry and condition. But the trace material is NOT copper, which I replace it with our transparent material. (The resistor value of square is 0.04ohm/sqr). According to our experience, this total length with our material the total DC trace resistor around 15ohm.

3. Finally, I fill the above condition to the "CR95HF EMI FILTER CALCULATION rev4_web.xlk" and please see the Fig-2.

You can find out the "Theoretical Tuning Capacitance Calculation" items are over the system/CR95HF criterion...

I'd studied the "UM1589User manual" & "AN4327Application note" & "AN3394 Application note" but it still can resolve my problem. Again, many thanks for you to reply my question, and if possible please guide me on how to do this evaluation due to I'm the first time using the CR95HF.

Have a nice day.

Fox.

Fig-1 : eDesignSuite

Fig-2 : CR95HF EMI FILTER CALCULATION rev4_web.xlk

ST Employee

​Hello Fox,

thank you for the clarification. Your original email stated a serial equivalent resistance of 15KOhm which was to big for any solution.

Removing the EMI filter (L01/L02 & CO1/C02) could help. in the EMI excel calculation tool, fill L01,2 with 0 and C01,2 with 1e-40. the result is C2=163pF and C11,12=560pF (see fig 1)

fig 1

bes regards,

Henry

Associate II

Hi! Henry:

Many thanks, you would like to reply to me. I'm going to make my antenna for evaluation, I'll share the result to you once I've got the experimental result. Thanks.