Basic principles and equations

AN2972

6/25

Doc ID 15629 Rev 6

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Basic principles and equations

Definition

RFID reader: an electronic device used for communication between RFID tags (like the

M24LRxx) and a host computer system. A reader generally consists of an RF transmitter

and receiver and an antenna for communicating with tags. A digital interface enables the

reader to communicate with the host computer system. RFID readers are capable of both

reading and writing the tags.

1.1

Passive RFID technology

The ISO 15693 protocol is based on a passive RFID technology, operating in the high-

frequency (HF) band, at 13.56 MHz.

Power transfer

When the M24LRxx operates in the RF mode, it is powered by the RFID reader. No battery

is then required to access it whether in write or read mode. With its external inductive

antenna, the M24LRxx draws all of its operating power from the reader’s electromagnetic

field.

The RFID reader plays the same role as the primary of a voltage transformer that powers

the secondary (in this case, the M24LRxx and its inductive antenna). The energy transfer

ratio from the reader to the M24LRxx is similar to the coupling factor of a voltage

transformer. It is a function of:

●

how well the M24LRxx and its antenna are tuned to the reader’s carrier frequency

(around 13.56 MHz)

●

the distance between the reader and the M24LRxx board

●

the dimensions of the reader antenna and the M24LRxx board

●

the reader power

●

the M24LRxx antenna orientation with regards to the reader antenna