Readers - RFID: Fundamentals and Applications in Contactless Smart Cards and Identification - page 307

received by the reader's antenna pass through a low-noise amplifier and are then
demodulated in a quadrature demodulator. This yields two orthogonal components ( I
and Q ), which facilitate the determination of the phase angle between the individual
pulses and between the pulses and the oscillator (Bulst et al. , 1998). The information
obtained can be used to determine the distance or speed between SAW transponder
and reader and for the measurement of physical quantities (see Section 10.4.3).
To be more precise, the reader circuit in Figure 11.8 corresponds with a pulse radar ,
like those used in flight navigation (although in this application the transmission power
is much greater). In addition to the pulse radar shown here, other radar types (for
example FM-CW radar) are also in development as readers for SAW transponders.

11.2.2 Control unit

The reader's control unit (Figure 11.9) performs the following functions:

• communication with the application software and the execution of commands from

the application software;

• control of the communication with a transponder (master-slave principle);

• signal coding and decoding (Figure 11.10).

In more complex systems the following additional functions are available:

• execution of an anticollision algorithm;

•

encryption and decryption of the data to be transferred between transponder and
reader;

• performance of authentication between transponder and reader.

The control unit is usually based upon a microprocessor to perform these complex
functions. Cryptological procedures, such as stream ciphering between transponder and
reader, and also signal coding, are often performed in an additional ASIC module to
relieve the processor of calculation intensive processes. For performance reasons the
ASIC is accessed via the microprocessor bus (register orientated).

Vcc
Data input

Power ON

Data

RAM
ROM

RS 23 2/485

Address

Data output

µ P

ASIC
(crypto,
Sig. cod.)

HF interface

Application
software

Figure 11.9 Block diagram of the control unit of a reader. There is a serial interface for
communication with the higher application software