The path from slave to master uses an 847.5kHz sub-

carrier, which is modulated using binary phase-shift

key (BPSK) modulation. Depending on the data rate,

the transmission of a single bit takes eight, four, two, or

one subcarrier cycles. The slave generates the subcar-

rier only when needed, i.e., starting shortly before an

SOF and ending shortly after an EOF. The standard

defines the phase of the subcarrier before the SOF as

0° reference, which corresponds to logic 1. The phase

of the subcarrier changes by 180° whenever there is a

binary transition in the character to be transmitted

(Figure 8). The first phase transition represents a

change from logic 1 to logic 0, which coincides with the

beginning of the SOF. The BPSK modulated subcarrier

is used to modulate the load on the device’s antenna

(Figure 9).

ISO/IEC 14443 Type B-Compliant

64-Bit UID

_______________________________________________________________________________________

5

DATA TO BE TRANSMITTED

INDICATES 180

° PHASE CHANGE (POLARITY REVERSAL)

OR

11

0

847kHz SUBCARRIER

BPSK MODULATION

TRANSMISSION OF A SINGLE BIT

POWER-UP DEFAULT = 8 CYCLES OF 847kHz (9.44

μs)

CAN BE REDUCED TO FOUR, TWO, OR ONE SUBCARRIER CYCLES FOR COMMUNICATION IN THE ACTIVE STATE.

Figure 8. Uplink: BPSK Modulation of the 847.5kHz Subcarrier

TRANSMISSION OF A SINGLE BIT

SHOWN AS EIGHT CYCLES OF THE 847kHz SUBCARRIER

DATA*

*DEPENDING ON THE INITIAL PHASE, THE DATA POLARITY MAY BE INVERSE.

10

1

Figure 9. Uplink: Load Modulation of the RF Field by the BPSK Modulated Subcarrier