STMicroelectronics M24LR64 R EEPROM Application note

AN2972
Application note
Designing an antenna
for the M24LR64-R dual interface I²C/RFID device
Introduction
The M24LR64-R device is an EEPROM designed for access via two different interfaces: a
wired I2C interface and a standard contactless ISO 15693 RFID interface.
Figure 1.
Dual interface EEPROM
Both interfaces are widely used industry standards. So the M24LR64-R can be integrated
into almost any electronic application provided that the processor offers an I2C interface. It
may also be accessed by any RFID reader that supports the ISO 15693 interface.
Integrating the M24LR64-R in an application is simple: on the I2C side, there is no specific
design requirement as the device interfaces exactly as any serial I2C EEPROM device. On
the RF side, the M24LR64-R needs to be connected to an external antenna to operate.
Figure 2.
M24LR64-R operating modes
The design principle of the M24LR64-R’s antenna is very simple: the external antenna
inductance (Lantenna) that needs to be designed on board the PCB should match the
M24LR64-R’s internal tuning capacitance (Ctuning) in order to create a circuit resonating at
13.56 MHz.
The basic equation of the tuning frequency is:
1
f tuning = -----------------------------------------------------------------2Π × L antenna × C tuning
The purpose of this application note is also to:
●
explain the basic principle of passive RFID
●
describe the basics of a 13.56 MHz inductive antenna design
●
provide some guidelines for a successful integration, from design to production.
February 2010
Doc ID 15629 Rev 5
1/23
www.st.com
Contents
AN2972
Contents
1
2
3
Basic principles and equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1
Passive RFID technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2
Simplified equivalent inlay circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.3
Basic equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.4
Optimum antenna tuning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
How to design an antenna on a PCB . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.1
Inductance of a circular antenna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2
Inductance of a spiral antenna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.3
Inductance of a square antenna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.4
ST antenna calculation tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.5
PCB Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.5.1
M24LR64-R-antenna distance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.5.2
Ground layer considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
How to check the M24LR64-R antenna tuning . . . . . . . . . . . . . . . . . . . 16
3.1
Antenna tuning measurements with a network analyzer . . . . . . . . . . . . . 16
3.2
Antenna measurements with standard laboratory tools . . . . . . . . . . . . . . 17
4
From design to production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
5
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2/23
Doc ID 15629 Rev 5
AN2972
List of tables
List of tables
Table 1.
Table 2.
K1 and K2 values according to layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Doc ID 15629 Rev 5
3/23
List of figures
AN2972
List of figures
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Figure 10.
Figure 11.
Figure 12.
Figure 13.
Figure 14.
Figure 15.
Figure 16.
Figure 17.
Figure 18.
Figure 19.
Figure 20.
Figure 21.
Figure 22.
Figure 23.
Figure 24.
Figure 25.
4/23
Dual interface EEPROM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
M24LR64-R operating modes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Power supply in RF mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Power transfer versus reader/M24LR64-R orentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
From the RFID reader to the M24LR64-R . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
From the M24LR64-R to the RFID reader . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Equivalent circuit of the M24LR64-R and its antenna. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Tuning the M24LR64-R antenna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Spiral antenna. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Square antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
User interface screen of the planar rectangular coil inductance calculator. . . . . . . . . . . . . 12
Rectangular planar antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
M24LR64-R close to antenna but ground plane distant from antenna . . . . . . . . . . . . . . . . 14
Bad implementation No.1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Bad implementation No.2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Not recommended implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Acceptable implementation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Measurement equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Example of the resonant frequency response of a prototype antenna . . . . . . . . . . . . . . . . 17
ISO standard loop antenna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Setting up the standard laboratory equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Example of a frequency response measurement of a prototype antenna . . . . . . . . . . . . . 18
Application examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Detuning effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Impact of housing/packaging material on RF communication . . . . . . . . . . . . . . . . . . . . . . 21
Doc ID 15629 Rev 5
AN2972
1
Basic principles and equations
Basic principles and equations
Definition
RFID reader: an electronic device used for communication between RFID tags (like the
M24LR64-R) and a host computer system. A reader generally consists of an RF transmitter
and receiver and an antenna for communicating with tags. A digital interface enables the
reader to communicate with the host computer system. RFID readers are capable of both
reading and writing the tags.
1.1
Passive RFID technology
The ISO 15693 protocol is based on a passive RFID technology, operating in the highfrequency (HF) band, at 13.56 MHz.
Power transfer
When the M24LR64-R operates in the RF mode, it is powered by the RFID reader. No
battery is then required to access it whether in write or read mode. With its external
inductive antenna, the M24LR64-R draws all of its operating power from the reader’s
electromagnetic field.
The RFID reader plays the same role as the primary of a voltage transformer that powers
the secondary (in this case, the M24LR64-R and its inductive antenna). The energy transfer
ratio from the reader to the M24LR64-R is similar to the coupling factor of a voltage
transformer. It is a function of:
●
how well the M24LR64-R and its antenna are tuned to the reader’s carrier frequency
(around 13.56 MHz)
●
the distance between the reader and the M24LR64-R board
●
the dimensions of the reader antenna and the M24LR64-R board
●
the reader power
●
the M24LR64-R antenna orientation with regards to the reader antenna
Figure 3.
Power supply in RF mode
How the RFID reader provides the required energy to the M24LR64-R
M24LR64-R’s external
antenna
M24LR64-R
VTag = V1sin(wt)
B = B0sin(wt)
RFID reader
V = V0sin(wt)
Doc ID 15629 Rev 5
Reader antenna
ai17177b
5/23
Basic principles and equations
AN2972
When the M24LR64-R is placed in the RFID reader’s electromagnetic field, the amount of
energy powering the device is directly related to the orientation of the M24LR64-R’s antenna
with regards to the RFID reader antenna. Indeed, this energy depends on how the
electromagnetic field lines generated by the reader flow through the M24LR64-R antenna.
This directly impacts the M24LR64-R/reader read range:
●
The best configuration is obtained when both antennas are parallel and face each
other.
●
The read range can drop to zero when both antennas are perpendicular to each other.
●
Any other orientation is possible and will result in different read ranges.
Figure 5 shows different power transfer configurations.
Figure 4.
6/23
Power transfer versus reader/M24LR64-R orentation
Doc ID 15629 Rev 5
AN2972
Basic principles and equations
Data transfer
Placed in the RFID reader’s electromagnetic field, the M24LR64-R’s built-in circuitry
demodulates the information coming from the reader.
Figure 5.
From the RFID reader to the M24LR64-R
1
0
1
0
M24LR64-R’s
external
antenna
M24LR64-R
Reader antenna
RFID reader
ai17181b
In order to send its response back to the reader, the M24LR64-R backscatters the data to
the reader by internally changing its output impedance back and forth, which is detected by
the reader.
Figure 6.
From the M24LR64-R to the RFID reader
20 mV
M24LR64-R’s
external
antenna
R
Tag
24 V
0
1
1
0
RFID Reader
Reader antenna
ai17182b
All this is part of the standard protocol and taken care of by the M24LR64-R embedded
circuitry and the RFID reader’s electronics.
So the main thing designers need to concentrate on is designing the M24LR64-R antenna
that meets the application requirements in terms of read range and antenna size.
1.2
Simplified equivalent inlay circuit
The chip and its antenna can be symbolized using their equivalent electrical circuit.
Figure 7 shows the equivalent electrical circuit of the M24LR64-R (parallel association of a
resistance which emulates the current consumption of the chip and a capacitance added to
the chip to ease tuning).
Doc ID 15629 Rev 5
7/23
Basic principles and equations
AN2972
The antenna is a wire, so its equivalent electrical circuit is a wire with a resistance
symbolized by Rant. The antenna also has an inductance denoted by Lant. The capacitance
Cant is the representation of parasitic elements (produced by the bridge).
Figure 7.
Equivalent circuit of the M24LR64-R and its antenna
Rant
A
Rchip
Ctun
Cant
Lant
B
M24LR64-R
External antenna
ai17178
In first-order equations, Rchip, Cant and Rant are negligible. This is why the basic equations
that follow will only take Lant and Ctun into consideration.
1.3
Basic equations
Resonant frequency
The resonant frequency of the LC circuit is defined by the equation:
LCω² = 1
where:
1.4
●
L is the inductance in Henry
●
C is the capacitance in Farad
●
ω is the angular frequency in radians per second (ω = 2 × π × f, with f = frequency in Hz)
Optimum antenna tuning
The total impedance of an LC loop is given by the sum of the inductive and capacitive
impedances:
Z = ZL + ZC
By writing the inductive impedance as ZL = jωL and the capacitive impedance as ZC = 1/jωC,
and then substituting in the previous equation, we have:
Z = jωL + 1/jωC
Now, extracting a common denominator yields:
Z = (1 – LCω²) /jωC
Note that the total impedance Z is zero at the resonant frequency of the LC circuit (the
numerator is zero when LCω² = 1). Consequently, the resonant frequency corresponds to
the maximum current received by the [L,C] loop, in our case: the M24LR64-R (capacitor C)
and the antenna (inductor L).
Consequently, the dual interface device’s antenna must be tuned so that its resonating
frequency matches the RFID reader antenna’s tuning frequency as much as possible. At this
8/23
Doc ID 15629 Rev 5
AN2972
Basic principles and equations
point, the coupling factor between the RFID reader and the dual interface EEPROM antenna
is the best, meaning from the application standpoint the best possible read range.
Figure 8.
Tuning the M24LR64-R antenna
Energy
Reader antenna tuning
Tag #1
antenna
tuning
Tag #2 antenna tuning
Tag #3
antenna
tuning
Frequency
ai17183
In Figure 8, Tag #2 is best tuned for this application configuration.
Doc ID 15629 Rev 5
9/23
How to design an antenna on a PCB
2
AN2972
How to design an antenna on a PCB
Designing an inductive antenna is about impedance matching. The antenna impedance
must match the conjugated impedance of the M24LR64-R in order to obtain the needed
tuning frequency.
A 13.56 MHz antenna can be designed with different shapes, depending on the application
requirements. As explained previously, the major parameter is the inductance L of the
antenna. The following paragraphs offer a way of computing the antenna dimensions for a
determined value of inductance L.
2.1
Inductance of a circular antenna
L ant = μ 0 × N
2.2
1.9
r
× r × ln ⎛⎝ ----⎞⎠ , where:
r0
●
r is the radius in millimeters
●
r0 is the wire diameter in millimeters
●
N is the number of turns
●
µ0 = 4π · 10–7 H/m
●
L is measured in Henry
Inductance of a spiral antenna
d
2
L ant = 31.33 × μ 0 × N × ----------------------- , where:
8d + 11c
●
d is the mean antenna diameter in millimeters
●
c is the thickness of the winding in microns
●
N is the number of turns
●
µ0 = 4π · 10–7 H/m
●
L is measured in Henry
Figure 9.
Spiral antenna
ai15812
10/23
Doc ID 15629 Rev 5
AN2972
2.3
How to design an antenna on a PCB
Inductance of a square antenna
d
2
L ant = K1 × μ 0 × N × ------------------------- , where:
1 + K2 ⋅ p
●
d = (dout + din)/2 in millimeters, where:
●
p = (dout – din)/(dout + din) in millimeters
●
K1 and K2 depend on the layout (refer to Table 1 for values)
dout = outer diameter
din = inner diameter
Figure 10. Square antennas
Table 1.
K1 and K2 values according to layout
Layout
2.4
K1
K2
Square
2.34
2.75
Hexagonal
2.33
3.82
Octagonal
2.25
3.55
ST antenna calculation tool
ST provides a simplified software tool (antenne.exe) to compute inductances of rectangular
planar antennas. The purpose of this tool is to give good approximations: the obtained
results should be verified.
This tool uses the Grover method (see Equation 1: Grover method). Figure 11 shows the
user interface.
Equation 1: Grover method
L ant = L 0 + ∑ M , where:
●
M is the mutual inductance between each of the antenna segments
●
L0 is as defined in Equation 2
s
Equation 2: L 0 =
∑ Lj , where:
j=1
●
s is the number of segments
●
Lj is the self inductance of each segment
Doc ID 15629 Rev 5
11/23
How to design an antenna on a PCB
AN2972
Figure 11. User interface screen of the planar rectangular coil inductance calculator
Examples:
The following antenna parameters have to be fed to the software to compute the antenna
coil inductance:
●
the number of turns
●
the number of segments
●
w: the conductor width in millimeters
●
s: the conductor spacing in millimeters
●
the conductor thickness in micrometers)
●
Length in millimeters
●
Width in millimeters
The number of turns is incremented each time a segment is added to a complete turn.
12/23
Doc ID 15629 Rev 5
AN2972
How to design an antenna on a PCB
Figure 12. Rectangular planar antennas
1
1
10
8
3 turns, 10 segments
2 turns, 8 segments
w
s
Width
thickness
(cross-section)
Length
ai15815
Once the antenna coil inductance has been calculated, a prototype coil is realized. The
value of the so-obtained prototype must then be validated by measurement. This can be
done using either a contactless or a non-contactless method.
2.5
PCB Layout
2.5.1
M24LR64-R-antenna distance
The M24LR64-R must be laid out as close as possible to the antenna (a few millimeters).
Any additional wire/trace would change the antenna characteristics and tuning.
2.5.2
Ground layer considerations
Designing an inductive antenna on a PCB means that special attention must be paid to
ground plane design:
●
no ground plane above or below the antenna
●
no ground plane surrounding the antenna
Figure 13 shows a correct layout.
Doc ID 15629 Rev 5
13/23
How to design an antenna on a PCB
AN2972
Figure 13. M24LR64-R close to antenna but ground plane distant from antenna
Ground layer
M24LR64
Front PCB side
Back PCB side
ai17194
The signal and energy transfers between the reader and the M24LR64-R board are good as
long as the antenna and the ground layer do not overlap.
Examples of bad implementations
Figure 14 and Figure 15 show two examples of bad implementation. In both cases the
electromagnetic flux cannot flow through the antenna, there is no energy transfer between
the reader and the M24LR64-R antenna.
Figure 14. Bad implementation No.1
ai17195
Figure 15. Bad implementation No.2
ai17196
14/23
Doc ID 15629 Rev 5
AN2972
How to design an antenna on a PCB
Figure 16 shows an example of a not recommended implementation. The electromagnetic
flux is greatly attenuated by the short-circuited loop surrounding the M24LR64-R antenna.
Figure 16. Not recommended implementation
ai17197
Figure 17 shows an acceptable implementation, if the antenna and the ground plane do not
overlap.
Figure 17. Acceptable implementation
ai17198
Figure 13 remains the best solution.
STMicroelectronics recommends designers to allocate a dedicated area of the PCB layout
to the antenna only, with no surrounding ground layer.
Doc ID 15629 Rev 5
15/23
How to check the M24LR64-R antenna tuning
3
AN2972
How to check the M24LR64-R antenna tuning
The methods of antenna design described in the previous section may lead to an
inductance slightly different from the value that would offer optimum performance in the end
application. This is because the overall inductance of the antenna might slightly drift in the
application (with magnetic and ferromagnetic materials in the proximity of the antenna). It is
therefore necessary to run actual measurements of the resonant frequency of the antenna.
3.1
Antenna tuning measurements with a network analyzer
The tuning frequency of the M24LR64-R antenna can be measured by using a network
analyzer with a loop probe.
The RF electromagnetic field is generated by connecting a loop probe (like the 7405-901
Eaton/Alitech 6 cm loop) to the output of the network analyzer set in reflection mode (S11
measurement).
Figure 18. Measurement equipment
.ETWORKANALYSER
,OOPPROBE
!NTENNAPROTOTYPEWITHTHE-,22
REPRESENTEDASACAPACITOR
AI
This equipment setup will directly display the system’s resonant frequency.
Experiments
As the objective is to find an [Lantenna + M24LR64-R Ctuning] tuned at 13.56 MHz, the
frequency sweep range has to be set around this value, that is:
●
Start frequency: 5 MHz
●
End frequency: 20 MHz
●
Output power: –10 dBm
●
Measurement: reflection or S11
●
Format: log magnitude
Place the antenna within the field generated by the network analyzer + loop probe. The
resonant frequency corresponds to the minimum observed on the S11 measurement curve.
16/23
Doc ID 15629 Rev 5
AN2972
How to check the M24LR64-R antenna tuning
Figure 19. Example of the resonant frequency response of a prototype antenna
12
12.5
13
13.5
14
14.5
15
13.56 MHz
S11 Log
magnitude
(dB)
Frequency (MHz)
Resonant frequency (13.56 MHz)
ai17199
3.2
Antenna measurements with standard laboratory tools
The antenna resonant frequency can also be measured with standard laboratory equipment
like:
●
a signal generator
●
an oscilloscope
●
two standard loop antennas
Experiment setup
Connect the first ISO 10373-7 standard loop antenna (see Figure 20) to the signal generator
to provide the RF electromagnetic field.
Connect the second ISO 10373-7 standard loop antenna to the oscilloscope (see Figure 21)
by using either a standard oscilloscope probe (1M or 10M input impedance) or a 50 Ω BNC
cable (oscilloscope input set to 50 Ω in this case).
Place the [antenna+M24LR64-R] inside the RF electromagnetic field.
Figure 20. ISO standard loop antenna
ISO/IEC 7810 ID-1 outline
72 mm × 42 mm coil
1 turn
connections
i15819
Doc ID 15629 Rev 5
17/23
How to check the M24LR64-R antenna tuning
AN2972
Figure 21. Setting up the standard laboratory equipment
/SCILLOSCOPE
3YNCHRONIZATIONFREQUENCY
0ROTOTYPEANTENNATOBEMEASURED
,OOPANTENNAS
3IGNALGENERATOR
AI
Experiments
Set the signal generator to output a sine wave with a peak-to-peak amplitude in the range of
200 mV. Starting from 5 MHz, increase the signal generator frequency until you reach the
maximum amplitude of the signal measured with the oscilloscope. The signal generator
frequency then corresponds to the resonant frequency of the [antenna+M24LR64-R] pair.
Figure 22 provides the frequency response curve of the prototype antenna, based on
measurements of the received signal amplitude at different frequencies.
Figure 22. Example of a frequency response measurement of a prototype antenna
Resonant frequency = 13.56 MHz
Voltage on
the second
ISO 10373-7
antenna
12
12.5
13
13.5
Frequency (MHz)
18/23
Doc ID 15629 Rev 5
14
14.5
15
ai17300
AN2972
4
From design to production
From design to production
Designers should expect some difference between the theoretical and the real performance
of the antenna on the PCB in the end application.
Here are a few considerations:
System level validation
It is paramount to take great care when validating the antenna tuning for the various
application use cases, whether it be programming traceability information on the
manufacturing line, performing inventory of several end-products in the warehouse or
reading data (end user).
Different reader profiles would result in distinct performance levels on a given M24LR64-R
board.
Figure 23. Application examples
ai17184
Considerations on the actual system tuning frequency
Even though all readers transmit at 13.56 MHz, the optimal tuning frequency of the
M24LR64-R antenna is not necessarily exactly 13.56 MHz.
Some mutual mechanisms such as detuning/coupling between the reader antenna and the
tag antenna may lead to an M24LR64-R antenna with an optimum tuning frequency different
from 13.56 MHz.
A good example is ST’s reference antenna (gerber files available from www.st.com) whose
tuning frequency is 13.74 MHz ((a)) to provide the best performance with the Feig MR101
reader.
a. Using the method described in Section 3: How to check the M24LR64-R antenna tuning.
Doc ID 15629 Rev 5
19/23
From design to production
AN2972
The read range varies depending on whether the M24LR64-R board is read alone or
stacked with others (detuning effect). Figure 24 illustrates the detuning effect.
Figure 24. Detuning effect
The vicinity of another M24LR64-R board may change the inductance dynamics. The
boards may couple with each other, leading to a resultant antenna resonant frequency
different from the individual one.
These are just examples of what may induce a difference between theory and real use
cases. They are meant to emphasize the need for real life validation of antenna designs.
PCB manufacturing process validation
The PCB fabrication parameters (such as the copper or epoxy layer thickness) have an
impact on the antenna inductance. Variations happen if the parameters of the PCB
fabrication process change or in case of a change of PCB supplier.
Departments such as quality, operations and manufacturing should therefore be made
aware of this.
Product packaging/housing considerations
The read range of the dual interface M24LR64-R board can be greatly affected by the
housing of the final product.
The most obvious case is when a metallic housing is used. The product packaging then
behaves as a Faraday cage, preventing the reader energy and signal from attaining the dual
interface EEPROM device.
The housing might also influence the PCB antenna’s tuning frequency, which is why it is
always recommended to measure the RF performance of the application in the final product
configuration.
20/23
Doc ID 15629 Rev 5
AN2972
From design to production
Figure 25. Impact of housing/packaging material on RF communication
Dual interface EEPROM
Nonconductive housing:
RF communication OK
Conductive housing:
no RF communication
ai17301
Process flow
●
Design:
–
Start from the dual interface EEPROM’s internal tuning frequency (Ctuning).
–
Calculate the theoretical Lantenna value based on Ctuning and ftuning.
Hint: check the device datasheet.
Hint: use the simplified models in this application note or other more sophisticated
models developed in the RF literature.
●
–
Define the antenna dimensions.
–
Compute the theoretical antenna design and layout.
Prototyping
–
Define an antenna matrix with different values centered around the targeted
Lantenna value.
Hint: select 6 to 10 antennas with inductances that vary around Lantenna by steps
of 5%.
–
Fabrication of the antennas and M24LR64-R mounting.
For each prototype:
●
●
–
Measure the antenna’s tuning frequency.
–
Measure the read range with all types of selected RFID readers.
–
Measure the read range in configurations close to the actual product usage.
Industrialization
–
Characterize tuning frequency dispersion on a significant number of samples.
–
Measure the read range of the lowest and highest tuning frequency boards with
various readers and in the various configurations.
–
Validate that the selected target Lantenna value is appropriate versus the process
variation.
Production
–
Process monitoring
Doc ID 15629 Rev 5
21/23
Revision history
5
AN2972
Revision history
Table 2.
22/23
Document revision history
Date
Revision
Changes
26-May-2009
1
Initial release.
06-Aug-2009
2
Modified:
– Introduction
– Section 1.1: Passive RFID technology
– Section 1.2: Simplified equivalent inlay circuit
– Section 1.4: Optimum antenna tuning
– Section 2.3: Inductance of a square antenna
Added: Section 4: From design to production
18-Aug-2009
3
Corrected equation allowing to compute the tuning frequency on
cover page.
04-Sep-2009
4
Figure 3: Power supply in RF mode, Figure 5: From the RFID reader
to the M24LR64-R and Figure 6: From the M24LR64-R to the RFID
reader modified.
Section 2.5: PCB Layout added.
Section 3.1: Antenna tuning measurements with a network analyzer
and Section 3.2: Antenna measurements with standard laboratory
tools modified.
Considerations on the actual system tuning frequency added. PCB
manufacturing process validation modified.
Product packaging/housing considerations and Process flow added.
Small text changes.
11-Feb-2010
5
Document classification level changed to public.
Power transfer updated in Section 1.1: Passive RFID technology.
Section 1.4 title modified.
Doc ID 15629 Rev 5
AN2972
Please Read Carefully:
Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries (“ST”) reserve the
right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any
time, without notice.
All ST products are sold pursuant to ST’s terms and conditions of sale.
Purchasers are solely responsible for the choice, selection and use of the ST products and services described herein, and ST assumes no
liability whatsoever relating to the choice, selection or use of the ST products and services described herein.
No license, express or implied, by estoppel or otherwise, to any intellectual property rights is granted under this document. If any part of this
document refers to any third party products or services it shall not be deemed a license grant by ST for the use of such third party products
or services, or any intellectual property contained therein or considered as a warranty covering the use in any manner whatsoever of such
third party products or services or any intellectual property contained therein.
UNLESS OTHERWISE SET FORTH IN ST’S TERMS AND CONDITIONS OF SALE ST DISCLAIMS ANY EXPRESS OR IMPLIED
WARRANTY WITH RESPECT TO THE USE AND/OR SALE OF ST PRODUCTS INCLUDING WITHOUT LIMITATION IMPLIED
WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE (AND THEIR EQUIVALENTS UNDER THE LAWS
OF ANY JURISDICTION), OR INFRINGEMENT OF ANY PATENT, COPYRIGHT OR OTHER INTELLECTUAL PROPERTY RIGHT.
UNLESS EXPRESSLY APPROVED IN WRITING BY AN AUTHORIZED ST REPRESENTATIVE, ST PRODUCTS ARE NOT
RECOMMENDED, AUTHORIZED OR WARRANTED FOR USE IN MILITARY, AIR CRAFT, SPACE, LIFE SAVING, OR LIFE SUSTAINING
APPLICATIONS, NOR IN PRODUCTS OR SYSTEMS WHERE FAILURE OR MALFUNCTION MAY RESULT IN PERSONAL INJURY,
DEATH, OR SEVERE PROPERTY OR ENVIRONMENTAL DAMAGE. ST PRODUCTS WHICH ARE NOT SPECIFIED AS "AUTOMOTIVE
GRADE" MAY ONLY BE USED IN AUTOMOTIVE APPLICATIONS AT USER’S OWN RISK.
Resale of ST products with provisions different from the statements and/or technical features set forth in this document shall immediately void
any warranty granted by ST for the ST product or service described herein and shall not create or extend in any manner whatsoever, any
liability of ST.
ST and the ST logo are trademarks or registered trademarks of ST in various countries.
Information in this document supersedes and replaces all information previously supplied.
The ST logo is a registered trademark of STMicroelectronics. All other names are the property of their respective owners.
© 2010 STMicroelectronics - All rights reserved
STMicroelectronics group of companies
Australia - Belgium - Brazil - Canada - China - Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan Malaysia - Malta - Morocco - Philippines - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States of America
www.st.com
Doc ID 15629 Rev 5
23/23
">