R
EM4223
1. GENERAL DESCRIPTION
The EM4223 is a monolithic integrated circuit transponder
for use in UHF passive backscatter RFID applications.
Operating power for the transponder circuit is derived
from the illuminating RF field of an RFID Reader by
means of an on-chip virtual battery rectifier circuit.
A user specified license plate or tag identifier is factory
programmed into the transponder by means of laser
trimming. This data is communicated to the reader by
means of backscatter modulation of the illuminating RF
carrier wave.
All commands received from the Reader will have an
immediate effect on the Transponder. In addition, certain
commands will have a persistent effect. The possible
immediate effects are one or both of the following:
A change of State (see Fig. 19)
A Data Message sent to the Reader.
The possible persistent effects are:
Data Messages to the Reader will contain SUID (as
described later in this section) or Data Messages to
the Reader will contain USER DATA of 128 bits,
The Round Size (Number of Slots) over which all of
the Transponders in the population will spread their
Data Messages to the Reader will be configured.
The Transponder will switch between ISO and FST
modes of operation (as described below).
A sub-population of Transponders will be enabled to
send Data Messages to the Reader dependent on
either the AFI or on all or a portion of the USER
DATA of 128 bits.
The EM4223 supports both the ISO18000-6 type A and
the Fast Supertag™ (FST) Protocols. The EM4223 may
be configured to wake-up in either of these modes
according to user requirements. Once active, the
transponder will automatically respond to either protocol
(and eventually switch modes) on receipt of the
appropriate commands.
2. FUNCTIONAL DESCRIPTION
When a Transponder is placed in the RF energising field
of a Reader it powers up. When the power supply has
reached the correct operating voltage, the Configuration
Register is loaded with the contents of the three pre-
programmed personality flags. Depending on the state of
these wake-up flags, the Transponder will be placed in
either ISO 18000-6 Type A (ISO) or Fast Supertag (FST)
mode and in one of three states: READY, ACTIVE or
ROUND_STANDBY. After this process is complete the
Transponder is able to receive commands and to transmit
data to the Reader.
The start of a command from the Reader has a special
significance if a Transponder is operating in the FST
mode and is in the ROUND_ACTIVE state. When the
falling edge of the first symbol of a command (SOF) is
received by a Transponder in the ROUND_ACTIVE state
while in FST mode, it will immediately move to the
ROUND_STANDBY state. If a command is successfully
received, the Transponder will move back to the
ROUND_ACTIVE state. If the Transponder does not
receive
a
valid command it will remain in the
ROUND_STANDBY state until a valid command has been
received. This enables the Reader to silence all
Transponders that have not already started sending their
Data Messages to the Reader in compliance with the FST
protocol. It is important to note that the Reader does not
have to send a full command or indeed even a part of a
command, as long as it sends a low going pulse of
approximately ½ Tari (Type A Reference Interval Time)
duration.
The Transponder is half-duplex and is thus in either
receive mode (default) or transmit mode. When not
actively transmitting messages to the Reader on the
Return Link, the Transponder will wait for the start of a
new command, which will be detected as a quiet period of
specific duration, followed by a valid Start Of Frame
(SOF) symbol (see Fig. 11). The Transponder requires
the quiet period in order to ensure that it does not detect
partial transmissions by a reader as a valid command.
This can occur if a transponder enters the field of a reader
and powers up part through a reader transmission. The
received SOF symbol is used to calibrate the command
An important feature of this transponder is its ability to
switch seamlessly between ISO mode and FST mode
whatever its “wake up” personality setting, depending only
on the mode or characteristics of the controlling reader. A
Transponder that “wakes up” in the ISO mode on power-
up will switch to the FST mode if it receives a
Wake_Up_FST command. Similarly, a Transponder that
“wakes up” in the FST mode on power-up will switch to
the ISO mode if it receives an INIT-ROUND, INIT-
ROUND-ALL or BEGIN-ROUND command.
decoder every time
a command is received. This
calibration is used to establish a pivot to distinguish
between subsequent data ‘0’ and data ‘1’ symbols. Each
time that a new command is received by the Transponder,
the SOF re-calibrates the decode counter thereby
compensating for any variation in the Transponder clock
frequency due to changes in RF excitation levels or
temperature variations. The circuit has been designed to
accommodate a Transponder clock frequency variation of
+/-40% from nominal. When the Transponder is
transmitting the receive circuitry is disabled.
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