TAGSYS Australia MEDIOL120 Users Manual
GemWave™
C220 Chip & Medio L120/L121
Technical Description
Version 1.0
GEMPLUS
March 22 2000
C220 Chips & L120/L121 Couplers - Technical Description
Version 1.0
CONTENTS
GEMWAVE L120/L121 SMART TRACKING ........................................................................ 2
1 THEORY OF OPERATION................................................................................................... 2
2 COMPARISON WITH LOW FREQUENCY SYSTEMS .................................................................... 4
3 GEMWAVE SMART LABELS............................................................................................... 4
4 GEMWAVE ANTENNAS..................................................................................................... 5
4.1 Antenna field regions ............................................................................................ 6
4.2 External loop antenna (Standard) ........................................................................... 7
4.3 Dual polarized loop antenna.................................................................................. 7
4.4 Truck mounted loop antenna................................................................................. 8
4.5 AC206 Metal mounted antenna.............................................................................. 8
5 GEMWAVE MEDIO L120/L121 COUPLERS ........................................................................ 9
51 Coupler functions.................................................................................................. 9
5.2 System construction ...........................................................................................10
53 RF Section ..........................................................................................................10
54 CPU Section .......................................................................................................13
5.5 Power Supply......................................................................................................16
GEMWAVE C220 & L120/L121 SMART TRACKING
The GemWave Smart Tracking system offers extremely low cost smart labels for
use in shorter read range high volume areas such as library book identification,
transport and logistical labels, waste management etc. Read range is limited to
around 500-mm but the system offers very high read rates (up to 70 times per
second) making it ideal for use on high speed production lines.
Standard Features for these systems include:
• Low Cost Smart Labels
• High Read Speed
• High immunity to industrial noise
• Full I/O capabilities
• Networking capabilities
1 Theory of operation
The operation of the system can be explained by considering the three major
components of the system. These are the coupler, the antenna and the smart
label.
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C220 Chips & L120/L121 Couplers - Technical Description
P
P
P
P
k
Q
Q
Version 1.0
When a smart label is to be read, the coupler transmits an electromagnetic
signal to the labels via the antenna(s). Some of the transmitted energy is incident
on the label, some of this RF (AC) energy is then rectified into a DC level and
used to power the microchip while the remainder is used to carry the smart
label’s unique code back to the coupler.
The process of superimposing the smart labels unique code onto the carrier
frequency is referred to as modulation.
In total, 128 bits1 are transmitted including error detection information, taking a
typical time of 2.4 or 1.2ms (for long and short modes respectively). This data is
picked up by the antenna and decoded. The decoding process occurs in real
time in order to maximize the multiple label reading capabilities of the
L120/L121 couplers.
The power transfer mechanism between the smart label and the coupler is quite
unique and is worthy of a brief discussion. It can easily be shown that the power
transfer ratio of a near field interrogation system is given by
r
2
k QQ
t
t r=
Where
r is the power received by the smart label.
t is the power transmitted by the antenna.
is the coefficient of coupling.
r is the quality factor of the smart label antenna.
t is the quality factor of the transmit antenna.
Thus in order to maximize the received power within the smart label the quality
factors of both the interrogator and the smart label antennas should be made as
high as possible. Practical limitations to this include allowing enough bandwidth
to pass the reply sidebands and the susceptibility of the antenna to detuning due
to environmental influences.
Furthermore, in this type of system, a signal power fall off of approximately
60.log(distance) applies. This implies that the field strength is high in the
immediate vicinity of the antenna but a very low level exists in the far field, hence
well confined interrogation regions can be easily created. Under these
conditions, it can be shown that sixty four times more input power to the antenna
is required to double the read range.
When specifying GemWave C220 systems, it is important to keep in mind the
vortex nature of magnetic fields. This implies always ensuring an adequate path
for the field to circulate. It is also equally important to have a clear understanding
of the field patterns produced by these antennas to ensure that the smart labels
are in the correct orientation to read. For the best performance, the smart labels
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must always have their coil perpendicular to the direction of the field. If the smart
label is placed parallel to the field it will receive no power and will not work.
2 Comparison with low frequency systems
At these relatively low frequencies (13.56 MHz) there are several operational
characteristics that make these systems attractive for many applications.
Perhaps, the most significant of these is cost. Since at these frequencies all the
necessary components have been completely integrated into the proprietary
microchip, the smart label production costs are kept to a minimum. The next
most important characteristic of this frequency is that it allows much faster data
rates than its lower frequency counterparts.
The sub carrier modulation on the GemWave C220 chip allows greater than 70
reads per second to be achieved compared to 10 for our lower frequency
competitors.
Further advantages include the relative immunity to attenuation by non-metallic
objects placed in the interrogation path and the inherent hard cut off that ensures
the interrogation field is clearly defined.
Whilst being low enough in frequency not to be impaired by environmental
hazards that degrade the performance of UHF systems (such as water), HF
frequencies are considered to be high enough to be less susceptible to man
made noise due to motors, welding equipment, computers etc. that plague low
frequency systems often to the point of rendering them useless.
3 GemWave C220 Smart Labels
One of the major advantages of working in the 13.5MHz ISM band is the level of
integration possible in the smart labels. The tag antenna is less complex than for
the lower frequency systems because the value of inductance required to
resonate the tag decreases with increasing frequency. The tuning capacitor can
be integrated, which is impossible (or least uneconomical) at lower frequencies.
Low power semiconductor processes have not yet reached a level where UHF
tags can be completely integrated2, mainly due to efficiency of the rectifiers at
these frequencies.
There is a wide range of standard GemWave tags available for these systems
that are suitable for use in a variety of applications. These are presented in the
various GEMPLUS GemWave Marketing information sources.
Of the several GemWave chips we are concentrating on the proprietary
GemWave C220 chip, which not only features completely integrated rectifiers,
modulators and tuning capacitors but also contains a 128-bit EEPROM cell that
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C220 Chips & L120/L121 Couplers - Technical Description
MODULATOR
FSK OSCILLATOR
DC GENERATION
EEPROM
Lantenna
Cantenna
Cchip
C220
MEMORY
ANTENNA
Version 1.0
allows contactless programming. A simplified block diagram of a complete
C220 smart label is shown in Figure 1.
Figure 1: Simplified block diagram of a GemWave C220 Smart label
The GemWave C220 chip uses a Differential Frequency Shift Keyed (DFSK)
sub carrier where a logic “0” forces a change in frequency of the sub carrier
oscillator. This gives the chip excellent performance in noisy environments typical
for industrial installations.
The need for error correction and detection means that only 733 out of 128 bits
are available for use by the customer during programming.
It is important to realize that the maximum read range that can be achieved with
these systems is a function of the smart label size and antenna size, their relative
positions to each other and the power available at the antenna.
It should be noted that C220 based smart labels are not suitable for extreme high
temperature applications due to the temperature limitations of the microchip’s on
board EEPROM memory.
4 GemWave antennas
GemWave antennas use the current flowing in the antenna inductor to produce
the AC magnetic field that is used to power the smart labels. It is important with
these systems to always ensure an adequate path for this field to circulate. This
implies that if either the smart label or the antenna is to be mounted on or near
metal to ensure that the coil is always perpendicular to the metal.
In some circumstances, it is necessary to tune the antennas at the time of
installation since the environment cannot always be predicted at the time of
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manufacture. However most of the time the antenna will perform adequately as
long as care is taken with respect antenna installation.
A wide variety of antennas suitable for GemWave systems have been developed
because of the wide range of applications for this technology requiring different
antenna configurations. The Professional Services Team at GEMPLUS is
always prepared to discuss antenna(s) for your applications.
It should be noted that GEMPLUS is currently in the process of reviewing an
antenna tuning aid that will soon be made available to our customers for these
systems. This will allow antennas to be tuned by customers with inexpensive test
equipment.
4.1 Antenna field regions
The field created by GemWave antennas can be considered to be relatively
omnidirectional. However, the field is more concentrated is certain regions and
smart label orientation with respect to the antenna is important to ensure
optimum performance.
If it is accepted that the field is circulating around the conductors of the antenna,
then Figure 2 and Figure 3 show the regions of space where the field will be able
to excite a smart label in different orientations. (i.e. the points at which the
magnetic field will be at ninety degrees to the smart label’s coil)
The field regions shown in Figure 2 will give a shorter read range than the
regions in figure 3, however, this orientation can be useful in certain applications.
Figure 2: Field regions for a planar loop antenna for non-optimum smart label
presentation
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An example of a planar coil smart label is a Folio20 and an example of a ferrite
rod smart label is a TC251.
Figure 3 : Field region s for a planar loop antenna for optimum smart label
presentation
4.2 AC201, AC202 and AC212 loop antennas
This range of standard antennas available with GemWave L120 and L121
systems provide a good range of size and performance options. Please refer to
the Data sheet for each of these devices.
4.3 Dual polarized loop antenna
This antenna was originally developed to
identify cattle in a raceway, however its
simple construction and ruggedness
makes it an ideal for any applications
that require fast accurate identification
where smart label orientation cannot be
guaranteed. The larger size originally
made would require a site license for
legal operation, smaller versions for
conveyor application etc. can be made.
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C220 Chips & L120/L121 Couplers - Technical Description
ANTENNA
READER
Version 1.0
Figure 4: Dual polarized loop antenna
This antenna provides omnidirectional reading in the vertical plane and will read
a smart label placed anywhere within the loops. It can be constructed in almost
any size ranging up to 820mm x 2000mm for doorway access.
It should be noted that this antenna has also been adapted to allow complete
omnidirectional reading in all planes and is available in a 1m cubic arrangement
(AC205 3D Portal Antenna).
4.4 Truck mounted loop antenna
This antenna measuring 600mm by 350mm is used in the waste management
industry and boasts a read range of up to 500mm. It is similar in construction to
the larger loops and can be adopted for other applications with similar
requirements.
ISD MEDIUM FREQUENCYTAG
ON BOARD COMPUTER /
DATA LOGGER
Figure 5: Waste management application using truck mounted loop antenna
4.5 AC206 Metal Mount antenna
These antennas available with GemWave L120/L121 systems provide an
antenna that can be used in metallic environments where loop type antennas
cannot be used. It is tuned for use directly mounted to metal. We have used it on
Forklifts, in conveyor systems and in various other applications.
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GemWave L120 & L121 Couplers
The GemWave L120/L121 couplers were the first HF near field RFID systems
available in the world. They have proven to be extremely robust in harsh
environments where lower frequency systems have failed due to high levels of
industrial noise. The coupler can both read labels and also program them.
5.1 L120/L121 Coupler functions
The primary functions of the Medio L120/L121 coupler are to provide the
following:
• The generation of a RF signal of the required frequency, power level
and pulse width (or continuous signal as required) for use as the
interrogation rf power a portion of which is backscattered by the smart
label.
• Reception of the reply signal from an identification smart label placed
in the RF field.
• Decoding of the unique identity code from a smart label reply and
output the result to one or more peripherals devices.
• Producing a programming signal to write new data into the C220
smart label.
Some of the secondary functions include:
• Control and monitoring of various digital inputs and output bits for
interfacing to external equipment or additional interrogators.
• Operation of a set of relay changeover contacts for the control of
external functions.
• Data transfer to and from external peripherals using two available
serial ports. These ports can be hardware configured for a range of baud
rates, parity settings and stop bits. One port provides RS232 capabilities
only whilst the second can be configured for RS232, RS422 or RS485.
• Storage of smart label replies in battery backed SRAM for
transmission to external peripherals at a later time.
• Time and date stamping of smart label replies using a battery backed
real time clock.
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• RF multiplexing of the transmitter and receiver signal in multi-antenna
configurations.
5.2 System construction
The Interrogator Unit is housed in a polycarbonate plastic moulded case (IP55
for L120 and IP65 for L121 (these may be changed to metallic style Eddystone
enclosures in the near future).
Standard electrical connections are made via two separate connectors. The first,
a three-pin male, carries the power for the unit. The second, an eight-pin female,
provides communications and I/O signals.
The standard electronics consist of a transceiver module and power supply. The
transceiver module is composed of RF and CPU boards and will be explained in
the following sections. The transceiver module and power supply is mounted on
a base plate, which is placed inside the enclosure. This base plate can be easily
removed for servicing.
The power supply provides +12 V that is required for the various functions within
the system (the RF board also provides +5 V for the CPU board). The standard
power supply can be configured for either 240 or 110 volts AC mains input and
is located on the base plate adjacent to the transceiver. Other power supply
options may be available on request.
5.3 RF Section
A simple block diagram of the GemWave L120 RF section is shown in Figure 6.
It should be noted that there is a quadrature receiver section rather than the
single channel receiver shown.
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TEP
PULSE MODULATOR
ANTENNA
DIRECTIONAL COUPLER
OSCILLATOR
LPF LPF
AMPLIFIER POWER AMPLIFIER
DOWN CONVERTER
Note that there are 2
Baseband Channels I
and Q
BPF
AMPLIFIER
PLD
Decoded Tag
Data
Figure 6: Block diagram of a GemWaveL120/L121Smart Tracking System
A brief description of the major blocks is given in the following sections
5.3.1 Oscillator
The GemWave L120/L121 coupler features a low noise 13.56 MHz crystal
oscillator as its frequency source. The output of the oscillator is filtered to remove
unwanted harmonics before entering the power amplifier. (O/P level of the
oscillator section is –6.5 dBm @ Tx on Schematic 000869.SCH p2/10)
5.3.2 Transmit chain
The transmitter chain provides amplification and pulse modulation of the RF
signal. The signal level is lifted to a level of approximately 1 watts (30dBm) peak
for injection into the antenna. Modulation of the signal is performed under the
control of the CPU Section via the MOD Signal. CW and pulsed operation as
well as smart label programming are all valid modes of operation.
5.3.3 Directional Coupler
The directional coupler on these systems is located on the RF board, after the
PA.
5.3.4 Receiver chain
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The receiver used in the L120 and L121 systems is based on the homodyne
architecture. The received signal is mixed in both an In-phase and a Quadrature
channel making the receive chain very robust and largely immune to phasing,
cable length and other problems that plague some RFID systems.
The down conversion process in these systems is achieved using 2 Active
Mixers. The signal proceeds through a band pass filter to limit the noise
bandwidth and to remove any remaining RF that may be present. The signal is
then amplified with a low noise high gain base band amplifier and fed into a PLD
where demodulation takes place.
The output of the PLD is in the form of completely decoded smart label numbers
which are “piped to the System CPU. There is a buffer of 16 smart label numbers
as well as the provision for an asynchronous label time-out. It should be noted
that once a label has been read and reported, it will not be again until 16 other
labels have been decoded and pushed the original one out of the buffer or until
the asynchronous label time-out has occurred.
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5.4 CPU Section
The L120/L121 CPU system contains the necessary digital logic for the control
of system functions and the decoding of smart label replies under the control of
an 80C188XL embedded controller. In a standard configuration, the CPU sets
up two way system communications via RS232 on serial port O. This port can be
configured for a range of baud rates, parity and stop bits. Unless otherwise
specified, this port is configured as:
• 9600 bits per second
• No parity
• Eight bits per character
• One stop bit.
A functional block diagram of the board is shown in Figure 7 and a brief
description of important blocks follows.
In GemWave L12/L121 systems, the coupler default settings are stored in the 50
bytes of RAM available on the battery back Real Time Clock (RTC). Hence a
real time clock is available as standard on this system.
Some standard features of this board include:
• A parallel port which is available for use as either unbuffered
digital I/O or as a Centronics printer port.
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Figure 7: Functional block diagram of a GemWave L120/L121 CPU system
5.4.1 System Watchdog
The 'watchdog' can be used to trap software 'hanging' and also protects the
128k system RAM in the event of a power failure. It does this by switching the
RAM to an on-board lithium battery until power is restored.
5.4.2 Data Collection Sub-System
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The demodulated smart label replies are fed as TTL level signals to the data
collection system. When the PLD has new label information a system interrupt
process is used to copy the data into the CPU.
5.4.3 Application specific options
The following options are available on the main board at the time of manufacture.
• A de-bounced input switch connected to a CPU interrupt.
• A SPDT Relay.
• Two digital input and three buffered digital output bits are
available for user specification.
The CPU may also be fitted with one of two additional boards to assist for
special function operation:
Extended I/O
• Point to point RS422 or RS485 Communications
• RS232 with full modem control
• Parallel port for additional I/O, which can also implement
Centronics Printer Port.
• 2 additional buffered Output bits
• 2 additional buffered Input bits
• Extra 8 way DIP Switch for User Inputs
Network Card
• Serial Port 0: RS232 3 wire for Coupler Communications
• Serial Port 1: RS422 or RS485 Multi-drop Communications
with RTS / CTS available, or RS232 with full modem control
• additional 8 way DIP Switches for User Selections
• Real Time Clock for time-stamping other timing duties
5.4.4 Communications Interface
GEMPLUS can implement the following protocols as standard options. User
specified protocols are available on request.
• RS232 (3 wire)
• RS232 Full Modem
• RS422 Point to Point
• RS422 Point to Point with RTS / CTS
• RS422 Multi-drop ( 4 wire )
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• RS422 Multi-drop with RTS / CTS
• RS485 Multi-drop ( 2 wire )
• Wiegand
• Centronics Printer Port
• Relay Logic Outputs
• Phone Line Modems
5.5 Power Supply
The standard power supply is a 16 watt linear supply capable of providing the
transceiver with the require regulated +12V supply.
1
128 bits when the tag is in long mode, 72 bits when in short mode.
2
While at least one fully integrated UHF tag is available, the performance is far poorer than tags with
even just a couple of external components.
3
Note that in short mode this is reduced to 40.
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