Coding and Modulation - RFID: Fundamentals and Applications in Contactless Smart Cards and Identification - page 188

Subcarrier 212 kHz

Data stream − baseband coded ASK-Modulation 1

Modulated subcarrier

ASK-Modulation 2
= Load modulation

Carrier signal 13.56 MHz

Load modulated signal with subcarrier

Figure 6.12 Step-by-step generation of a multiple modulation, by load modulation with ASK
modulated subcarrier

two spectral lines at a distance ± the subcarrier frequency f H around the operating
frequency (Figure 6.12). The actual information is now transmitted in the sidebands
of the two subcarrier lines, depending upon the modulation of the subcarrier with the
baseband coded data stream. If load modulation in the baseband were used, on the other
hand, the sidebands of the data stream would lie directly next to the carrier signal at
the operating frequency.

f T = 13.560 MHz

0 dB

Carrier signal of the reader,
measured at the antenna coil

Modulation products by load
modulation with a subcarrier

13.348 MHz 13.772 MHz

− 80 dB

f

f H = 212

Figure 6.13 Modulation products using load modulation with a subcarrier