The Architecture of Electronic Data Carriers - RFID: Fundamentals and Applications in Contactless Smart Cards and Identification - page 266

Data carriers for
RFID applications

Electronic
circuits (IC)

Physical
effects

State machine
memory

(Programmable)
microprocessor

SAW
components

1-bit transponder

Figure 10.1 Overview of the different operating principles used in RFID data carriers

Address and
security logic

HF
interface

Vcc EEPROM

or FRAM

ROM

Chip

Figure 10.2 Block diagram of an RFID data carrier with a memory function

The HF interface incorporates a load modulator or backscatter modulator (or an
alternative procedure, e.g. frequency divider), controlled by the digital data being trans-
mitted, to return data to the reader (Figure 10.3).
Passive transponders , i.e. transponders that do not have their own power supply, are
supplied with energy via the HF field of the reader. To achieve this, the HF interface
draws current from the transponder antenna, which is rectified and supplied to the chip
as a regulated supply voltage.

10.1.1.1 Example circuit - loadmodulationwith subcarrier

The principal basic circuit of a load modulator is shown in Figure 10.4. This generates
an ohmic load modulation using an ASK or FSK modulated subcarrier . The frequency
of the subcarrier and the baud rates are in accordance with the specifications of the
standard ISO 15693 (Vicinity coupling smart cards).
The high-frequency input voltage u 2 of the data carrier (transponder chip) serves
as the time basis of the HF interface and is passed to the input of a binary divider.