Basic principles and equations

AN2972

8/25

Doc ID 15629 Rev 6

Data transfer

Placed in the RFID reader’s electromagnetic field, the M24LRxx built-in circuitry

demodulates the information coming from the reader.

Figure 5.

From the RFID reader to the M24LRxx

In order to send its response back to the reader, the M24LRxx backscatters the data to the

reader by internally changing its output impedance back and forth, which is detected by the

reader.

Figure 6.

From the M24LRxx to the RFID reader

All this is part of the standard protocol and taken care of by the M24LRxx embedded

circuitry and the RFID reader’s electronics.

The main thing designers need to concentrate on is designing the M24LRxx antenna that

meets the application requirements in terms of read range and antenna size.

1.2

Simplified equivalent inlay circuit

The chip and its antenna can be symbolized using their equivalent electrical circuit.

Figure 7 shows the equivalent electrical circuit of the M24LRxx (parallel association of a

resistance which emulates the current consumption of the chip and a capacitance added to

the chip to ease tuning).

Reader antenna

M24LRxx

external

antenna

M24LRxx

00

1

1

00

1

1

RFID reader

ai17181c

ai17182c

Reader antenna

M24LRxx

external

antenna

Tag

20 mV

24 V

R

0

1

1

0

RFID Reader