AN3178 datasheet(3/11 Pages) STMICROELECTRONICS

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AN3178

Basic principle - inductance value

Doc ID 17256 Rev 2

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Basic principle - inductance value

Figure 1.

M24LR64 dual interface EEPROM

The basic principle of the M24LRxx's antenna is very simple: the external antenna

inductance (LINDUCTOR) that needs to be integrated on the PCB should match the

M24LRxx's internal tuning capacitor (CTUNING_IC) in order to create a circuit resonating at

13.56 MHz. This is because ISO15693 RFID readers operate in the 13.56 MHz High

Frequency band.

The equation is:

Which implies:

This is how the inductance value is calculated: fRESONANCE = 13.56 MHz and in the case of

an M24LRxx IC with an embedded 28 pF internal tuning capacitor, the theoretical value of

the inductance is 4.92 µH.

Refer to application note AN2972 Designing an antenna for the M24LR64-R dual interface

I²C/RFID device for further information on the basics of the RFID technology, and for

guidelines on antenna design, optimization and test.

TUNING

INDUCTOR

TUNING_IC

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INDUCTOR

RESONANCE

TUNING_IC

()

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