Application Note
Transceiver RFID 13.56MHz MLX90121
Cookbook
Scope
This cookbook is a tested collection of real applications and reference example circuits. The
detailed descriptions of the procedures for selecting the appropriate components will help get
your design up and running fast.
Please also consult the data-sheets and evaluation board / development kit descriptions for
detailed technical information. These can be found on the Melexis WEB site at
www.melexis.com. Assistance and questions can be accessed using Melexis Knowledge Base
WEB Forum at www.melexis.com/KnowledgeBase.aspx.
Applications
Portable data terminals,
Access control readers,
Contact-less payment terminals,
Smart label printers.
Related Melexis Products
MLX90121.
Main Features
Conforms with ISO/IEC 14443A1, 14443B (RATP / Innovatron
Programmable encoder and decoder for custom protocols
Low external component count
Technology) & 15693
1
Purchase of MLX90121s doesn’t imply any grant of any ISO14443A license. Customers are advised to sign patent licensing
agreem ents with all third parties, especially those companies listed in the introduction of the corresponding standard.
.
390119012109
Page 1 of 37
Rev.001
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Application Note
Transceiver RFID 13.56MHz MLX90121
Cookbook
Document Content
A.
1.
1.1.
1.2.
2.
B.
1.
1.1.
1.2.
1.3.
1.4.
1.5.
2.
A low power reader based on the MLX90121: Scope ................................................. 4
Application schematic .................................................................................................. 4
Recommended Components: .................................................................................................. 4
Theory of operation and design guidelines:.............................................................................. 5
Measured values for a typical application................................................................... 5
A power booster for the MLX90121: Scope ................................................................. 6
Power boost with external MOSFET ............................................................................ 6
Application schematic.............................................................................................................. 6
Recommended Components ................................................................................................... 7
Theory of operation and design guidelines............................................................................... 7
Waveforms at selected test points ........................................................................................... 8
Performance summary .......................................................................................................... 11
Receiver part ............................................................................................................... 12
2.1.
2.2.
2.3.
2.4.
3.
C.
1.
1.1.
2.
Solution 1: Attenuation of the RX input. ................................................................................. 12
Recommended components.................................................................................................. 12
Solution 2: External detector.................................................................................................. 13
Recommended Components: ................................................................................................ 13
Remarks about PCB layout. ....................................................................................... 14
A 1 Watt 5 volts power booster for the MLX90121: Scope ....................................... 15
Application schematic ................................................................................................ 15
Recommended Components: ................................................................................................ 16
Theory of operation and design guidelines............................................................... 16
2.1.
2.2.
2.3.
D.
1.
1.1.
1.2.
1.3.
1.4.
2.
Theory of operation. .............................................................................................................. 16
Fine tuning of the circuit. ....................................................................................................... 17
Printed circuit board layout issues. ........................................................................................ 18
MLX90121: Support of different modulation modes: Scope .................................... 19
Base band communication:........................................................................................ 19
Low data rates: ..................................................................................................................... 19
Medium Data Rates............................................................................................................... 22
High Data Rates:................................................................................................................... 23
Very High Data Rates............................................................................................................ 24
Applications with a sub-carrier of 212 KHz: .............................................................. 25
2.1.
2.2.
3.
E.
1.
1.1.
1.2.
1.3.
1.4.
2.
Configuration:........................................................................................................................ 25
Screen captures: ................................................................................................................... 26
Conclusion................................................................................................................... 27
Progressive field increase for the MLX90121: Scope ............................................... 28
Standard design (200 mW @ 5 Volts) ........................................................................ 28
Application schematic............................................................................................................ 28
Recommended Components: ................................................................................................ 29
Theory of operation and design guidelines:............................................................................ 29
Oscilloscope screen captures................................................................................................ 30
Power booster configuration ( 1 Watt @ 12 Volts )................................................... 33
2.1.
2.2.
F.
1.
Application schematic............................................................................................................ 33
Recommended Components ................................................................................................. 33
A modulation index switch for the MLX90121: Scope .............................................. 34
Standard design (200 mW @ 5 Volts) ........................................................................ 34
1.1.
1.2.
1.3.
1.4.
Application schematic............................................................................................................ 34
Recommended Components: ................................................................................................ 34
Theory of operation and design guidelines............................................................................. 35
Waveforms at the antenna connector .................................................................................... 35
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Application Note
Transceiver RFID 13.56MHz MLX90121
Cookbook
2.
Power booster configuration (1 Watt @ 12 Volts)..................................................... 36
2.1.
2.2.
2.3.
Application schematic............................................................................................................ 36
Recommended Components: ................................................................................................ 36
Waveforms at the antenna connector .................................................................................... 37
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Application Note
Transceiver RFID 13.56MHz MLX90121
Cookbook
A. A low power reader based on the MLX90121: Scope
This application note is a design guide to provide a means of reducing the power drain for an RFID reader
based on the MLX90121. In some applications, such as hand held readers, the maximum reading range
may not be of paramount importance while the operating life of the battery is much more critical.
The power consumption of an application using the MLX90121 can be reduced by different ways. The
most efficient way is to make the firmware which controls the application smart enough to configure the
MLX90121 in power down mode as often as possible and to perform a communication only when
requested (push button, computer request …). Another solution, describes by this application note, is to
regulate the power supply voltage of the MLX90121 by adding a regulation system.
1. Application schematic
1.1. Recommended Components:
Reference Value
R1
R2
Q1
M1, M2
C5
1.5K
8.2K
BD136
BS170
4.7 F (See notes)
Notes: Other component’s values do not differ from the standard recommended reader schematic.
C5 should have a very low ESR. Recommended type is AVX TPSD475K050R0300.
Transistor Q1 should be able to dissipate at least 500mWatt (100mA * 5V).
Transistors M1 and M2 must be the same.
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Application Note
Transceiver RFID 13.56MHz MLX90121
Cookbook
1.2. Theory of operation and design guidelines:
The transistors M1 and M2 compose differential pair which compares the voltage on C5 with the voltage
on the gate of M2 (Power Supply Control Line). The difference is amplified and fed the base of Q1 making
a deep negative feedback loop. As a result, the voltage on C5 will be equal to the voltage on the gate of
M2 (Power Supply Control Line).
To obtain different power supplies controlled by a microcontroller, it is possible to add several resistors
connected to the gate of M2, as shown in the following schematic. Therefore, by controlling the two lines
MSB and LSB, the power supply voltage of the MLX90121 can be set to a fraction of the Vcc voltage (0,
1/3Vcc, 2/3Vcc and Vcc).
2. Measured values for a typical application
The measurements are made according to the values of the schematic above. The power supply is set to
+5V and standard Melexis antenna 12 cm x 12 cm is used. The reading distance is measured with an
ISO15693 FSK / dual sub-carrier tag and is given for reference only.
Note:
V C5 (V)
Current
consumption (mA)
Power stage
Consumption (mW)
Antenna
Power (mW)
Power
Efficiency (%)
Reading
distance (cm)
5
4
3
2
1,5
99
83
65
47
39
495
332
195
94
58
250
178
104
49
27
51
53
53
52
47
25
23
21,5
18
14
The antenna power was measured by substituting a 50 ohm load to the antenna. The capacitance
of a standard oscilloscope probe would otherwise change the tuning of the reader matching
network and hence destroy the measurement accuracy.
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Application Note
Transceiver RFID 13.56MHz MLX90121
Cookbook
B. A power booster for the MLX90121: Scope
This application note is a design guide to increase the output power of the MLX90121.
Power boosting is introduced to improve the reading range of tags. The reading range of a tag
can in general be limited by two factors:
A first factor is the strength of the transmitted field. A tag needs a minimum field in order to
operate. The required field could be quite high for microprocessor cards.
A second limitation is the sensitivity of the reader. When the tag is powered it is normally able to
modulate. However the coupling to the reader can be low (this is the case for sensitive tags).
Hence the reader might be unable to recover the return signal of the tag.
In both cases reading distance can be gained by increasing the readers’ output power. In case
one this is straightforward. In case two, where the reading distance is limited by the read
sensitivity, the reading distance increases because of a larger return signal coming from the tag
as a result of an increased carrier.
In the document below, design issues about power boosting of the MLX90121 will be discussed
into some detail and different implementations will be considered. There are two parts in this
document: a first part describing the boost output stage that delivers the necessary output
power. A second part explains how to make the adaptation of the receiver part to cope with the
increased antenna signals.
1. Power boost with external MOSFET
1.1. Application schematic
+ 12V
+ 5V
L3
Vdd
L1
TP2
Mlx90121
TX
13.56MHZ
L4
TP1
R1
OUT
TP3
C2
L2
L5
C3
C4
M1
C1
R2
D1
MOD
MOD
RMOD
TX-GND
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Application Note
Transceiver RFID 13.56MHz MLX90121
Cookbook
1.2. Recommended Components
Reference
R1
R2
C1
C2
C3
Value
10 ohms
680 ohms
330pF
10nF or 100nF
68pF
C4
5-50
variable
680nH
270nH
560nH
3.3 H
2.2 H
IRFD110
1N4148
See text
L1
L2
L3
L4
L5
M1
D1
RMOD
Comments
5% or better
5% or better
50Volts NPO
50 Volts X7R
100Volts
NPO
pF 100Volts
See note 1
See note 1
See note 1
See note 1
See note 1
See note 2
See note 3
3 to 6 ohms
Notes:
Inductors should be carefully selected.
Standard through hole types available from
Farnell or Radiospares work well for this
application.
IRFD 110, IRFU110, IRFR110 can be
interchanged. Manufacturer is International
Rectifier.
Any fast silicon diode will work. A peak
current of about 300mA will circulate trough
the diode. It may be replaced by a Schottky.
1.3. Theory of operation and design guidelines
L2 forms a series resonant network with M1 gate capacitance. However, it is not possible to
drive directly such a network with the MLX90121 output stage because it will draw too much
current. Therefore, we mistune it with C1, sufficiently to keep the current requirements in line
with the MLX90121 internal power transistor safety area while maintaining enough voltage swing
at TP1 to drive correctly the gate of the external power transistor, M1. L1 and R1 provide the
necessary DC bias to the MLX90121 internal power transistor. R1 is again selected to maintain
the current drain within acceptable limits. R2 provides a DC return path and dampens the
resonance. It has a critical role, along with R1, in avoiding spurious oscillations.
L3 provides the DC bias for the power transistor. L4, C3, C4, L5 form an impedance matching
network that converts the 50 ohms load into about 150 ohms seen from the drain of M1. Since
M1 operates as a pulse generator, this impedance transformation is only theoretical. However,
this ratio gives the best results. In this application note, the component values for this network
have been selected to provide a Q of about 4. This reduces the peak to peak voltage at TP3 and
permits the use of standard components. In order to comply with EMC radiation limits, it might
prove necessary to increase the network Q, and in that case, higher voltage ratings for C3 and
C4 will be required. For instance, with a Q of 7, the peak to peak voltage will easily reach 200
Volts at TP3. If you need to use a different impedance transformation network, you can use this
link to compute component values: http://rfengineer.cc/match1.htm .
RMOD should be selected to provide an adequate modulation depth in the low modulation index
mode. Its value will be dependent on the external power transistor supply voltage. With a 12
volts supply voltage, a value of 6 ohms gives good results. At 15 volts, the modulation depth
increases a lot, so a lower value should be used for RMOD.
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Application Note
Transceiver RFID 13.56MHz MLX90121
Cookbook
1.4. Waveforms at selected test points
All waveforms are recorded with the transmitter loaded with a pure resistive 50Ohms load.
1.4.1. Waveform at TP1
1.4.2. Waveform at TP2
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Application Note
Transceiver RFID 13.56MHz MLX90121
Cookbook
1.4.3. Waveform at TP3
1.4.4. Waveform at output
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Application Note
Transceiver RFID 13.56MHz MLX90121
Cookbook
1.4.5. Transient performance at output with 100% modulation
1.4.6. Output transient performance, low index modulation
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Application Note
Transceiver RFID 13.56MHz MLX90121
Cookbook
1.5. Performance summary
Output power: 20 volts peak to peak min into 50 ohms, which is 7.07 volts rms or 1 watt
with a 12 volts supply. The power supply voltage can be increased to 15 volts and the
output voltage goes up to 26 volts peak to peak, that is 9.2 volts rms or 1.6 watts.
Total current drain from 5 volts MLX 90121 supply: 60 mA or less.
Total current drain from 12 volts supply: 0.2 amps or less.
Power dissipation of MLX90121 internal transistor (simulated): 80 milli-watts or less.
Power dissipation of M1 (simulated): 200 milli-watts or less.
Please note that all these values apply to room temperature conditions ( 25°C )
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Application Note
Transceiver RFID 13.56MHz MLX90121
Cookbook
2. Receiver part
The antenna swing, depending on the transmitted power, varies from 7 to 9V RMS. As the RX
input of the chip can only cope with a limited voltage swing some measures have to be taken to
limit that swing. There are two different solutions possible.
The first solution requires less hardware and is suited for the situation whereby the reading
distance is limited by the field and not by the receiver sensitivity (the case of power hungry
micro-processor cards). In that case one can afford to attenuate the receiver signal somewhat.
This is the solution requiring only two extra resistors.
In case the reading distance is limited by the receiver sensitivity, one cannot afford to lose any
sensitivity at the RX input. Then the use of an external detector that is capacitively coupled with
the RX input should be used. This is the solution requiring somewhat more extra hardware.
2.1. Solution 1: Attenuation of the RX input.
Here we just use a T type of resistive attenuator to reduce the input swing at the TX pin. This
setup will reduce the sensitivity of the receiver part with about 9dB.
MLX 90121
R1
R3
RX IN
TX OUT
R2
External Power stage
2.2. Recommended components
Reference
R1
R2
R3
Value
Comments
1.2 K ohms
680 ohms
1.2 K ohms
390119012109
Notes:
For higher attenuation decrease R2, for less
attenuation increase R2. Leave the values
of R1 and R3 unchanged
Page 12 of 37
Rev.001
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Application Note
Transceiver RFID 13.56MHz MLX90121
Cookbook
2.3. Solution 2: External detector.
The antenna signal is coupled in with C1, R1 makes a low impedance reference to ground. D1
does the envelope modulation. R2 and C2 are the decay resistor and the smoothing cap
respectively. The envelope signal, that has a DC level which is at the peak level of the carrier, is
capacitively coupled to the RX input of the MLX90121. The resistor R3 assures a proper biasing
of the MLX90121 internal circuitry. This solution needs more components, but does not
introduce any receiver attenuation.
VDD
+ 5 Volts
R3
C1
D1
MLX 90121
C3
RX IN
R1
R2
C2
TX OUT
External Power stage
2.4. Recommended Components:
Notes:
Reference
R1
R2
R3
C1
C2
C3
D1
Value
1.5 K ohms
22 K ohms
27 K ohms
100nF
100pF
2.2nF
BAT 48
390119012109
Comments
50 Volts X7R
50 Volts NPO
50 Volts X7R
Schottky
With the exception of R3, all components
values, proposed here should be considered
as a good starting point. Depending on the
exact application, the modulation type, etc..,
further optimization is possible.
R3 is used to set the DC level at the input of
the MLX 90121. There is an internal current
source in the chip that normally sets the
decay time constant when the internal
detector is used. The value of R3 is
therefore fully optimized and should not be
changed.
Page 13 of 37
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Application Note
Transceiver RFID 13.56MHz MLX90121
Cookbook
3. Remarks about PCB layout.
Good RF layout techniques should be used when designing a printed circuit board. It is best to
avoid long traces, especially where high frequencies are present. Although not represented on
the schematics, a good decoupling is required. It should be placed as close as possible to the
cold ends (power supply side) of the coils that provide the DC bias to MOSFETS drains. A
100nF X7R type in parallel with a 10µF solid tantalum is the recommended decoupling network.
An additional RF choke and capacitor may be required to comply with applicable EMC stand.
390119012109
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Application Note
Transceiver RFID 13.56MHz MLX90121
Cookbook
C. A 1 Watt 5 volts power booster for the MLX90121: Scope
For some applications, single supply operation is a must. In this document, a 1 Watt power
booster for the MLX90121, that requires only a single 5 volts power supply, is described. Only
standard CMOS high speed logic is required to generate the drive signal to the power stage,
which is in fact a high power CMOS inverter. Furthermore, the output matching circuit can be
reduced to a bare minimum of two components, reducing circuit complexity and cost.
1. Application schematic
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390119012109
Page 15 of 37
Rev.001
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7 ?
Application Note
Transceiver RFID 13.56MHz MLX90121
Cookbook
1.1. Recommended Components:
Reference
Value
R1,R2,R3,R4 See text
R5, R6
4.7 ohms
R7
R8
See text
2.2 K ohms
R9, R10
C4
IC1
IC2, IC3
Q1, Q2, Q3
L1
C1
Comments
5%
better
or
Notes:
5%
or
better
10 K ohms
5%
or
better
5-50
pF 100Volts
variable
74 AC 08
74 AC 04
FDC 6327C
FAIRCHILD
130 nH
See note 1
1 nF
See note 2
Minimum current raring: 1 Amp.
Recommended component is COILCRAFT
“Maxi Spring” part number 132-11SM.
Use only a very low loss capacitor. Current
rating is the same as L1. A MICA capacitor
is recommended. (Cornell Dubilier, Arco ). If
you prefer ceramic, you can purchase low
loss RF ceramic power caps from ATC.
2. Theory of operation and design guidelines
2.1. Theory of operation.
In order to reduce the current drain to a minimum, we do not use the power stage of the
MLX90121. Instead, we take advantage of the clock output (XBUF, pin 8). From this point, we
generate two independent drive signals that will be used by the final power inverter formed by
the complementary pair Q1, Q2. Components R1, R2, R3, R4, are used to define the duty cycle
of the signals applied to the gates of the PMOS transistor Q1 and the NMOS transistor Q2,
respectively. This configuration creates a non-overlapping gate drive for the transistors Q1 and
Q2, avoiding excessive power dissipation. By adjusting independently the duty cycle of the drive
signal applied to each gate, we can fine tune the amplifier to obtain the best power efficiency.
Three 74AC04 gates are connected in parallel to generate for each power FET the gate drive.
Use of the 74AC family is required as it has enough fan-out to directly drive the gates of Q1 and
Q2 that have a fairly large capacitance. ( about 330 pF )
R5 and R6 are connected in series with the gates. This reduces slightly the overall efficiency,
but it avoids parasitic oscillations. The optimal resistor value is layout dependent; some kind of
fine tuning could be required.
The output matching circuit is implemented by L1 and C1. Together, they form a low- to high
impedance converter. L1 and C1 must have very low losses. L1 sees an AC current of about 2
Amps peak-peak. When substituting the recommended L1 from Coilcraft by some other
component, you have to take care of its current rating. The same holds true for C1.
In order to meet applicable electromagnetic compatibility standards, an additional low pass filter
maybe required.
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Application Note
Transceiver RFID 13.56MHz MLX90121
Cookbook
Modulation in 100% mode is achieved by using a special output pin ( RES, pin 18) of the
MLX90121 from which modulation pulses can be recovered. For info on how to configure the
MLX90121 to do this, please contact Melexis. These pulses are applied to the 74AC08 gate to
key the carrier on and off. R10 is a pull up resistor that makes sure that when the RES pin goes
to a high impedance state, the carrier from XBUF still drives the amplifier. R9 is a pull down
intended to make sure that when the carrier is off, the DC voltage at the output antenna
connector is 0 volts. Please note that the antenna output is DC coupled. This is not a problem
since most RFID antennas have a DC blocking cap somewhere in the signal path. To check the
signal power on a dummy load ( 50 ohms resistor ), one must insert a DC blocking capacitor in
series with the output. Two high quality plastic film 47 nF capacitors placed in parallel will do the
job.
Low index modulation is achieved by means of an additional power MOSFET Q3. Since the
normal output power stage of the MLX90121 is unused, the RMOD output is pulled-up with
resistor R8 to Vcc, generating a modulation signal. The value of the pull up resistor has to be
kept low enough so that capacitance does not become a problem. A value of 2.2 K gives good
results. Two 74AC04 inverter gates are used to drive the gate of Q3 and provide the proper
signal polarity. The value of R7 will be layout dependent. One should start to experiment with a
value of 1 ohm. A tight tolerance is required (1% or better). The power rating of R7 should be no
less than 500 milliwatts.
2.2. Fine tuning of the circuit.
If you plan to use your own layout, some adjustments may be required. The trickiest point is to
set the correct value for the duty cycle of each gate. In the first place, one should replace R1,
R2, R3, and R4 by two multi turn potentiometers. The lowest possible value must be used for
the pot. High ohmic values will dramatically increase the rise and fall times, because of the
74AC04 gate input capacitance. We suggest to use a 2K pot from the BOURNS 3296W series.
To adjust the duty cycle, remove R5 and R6 from the board, tie the PMOS gate to VCC (+ 5
volts) through a 1K resistor, tie the NMOS gate to GND trough a 1K resistor, and adjust the duty
cycle for each gate to 80%/20% and 20%/80% respectively. Remove the two 1K resistors, put
back in place R5 and R6. Monitor at the same time the duty cycle at each gate, the output
voltage on an adequate dummy 50 ohms load, and the power supply current. Increase little by
little the duty cycle on each gate until the output voltage stops increasing. Go back a little to
make sure that you have the best power efficiency. Check the current drain, the power output,
and verify Q1 and Q2 power dissipation. Although the FDC6327C case is rated for 1 Watt at
25°C, we recommend having no more than 0.5 Watts total power dissipation for Q1, Q2.
The logic circuits may have slightly different characteristics, depending on their manufacturer. It
is better to use only one manufacturer for all the gates. In case of substitution, check again the
duty cycle settings.
Use adequate decoupling whenever possible. Place decoupling caps close to the power pins of
each IC. Use good quality caps, some ceramic caps have unacceptable ESR values. Most
manufacturers provide models and/or simulation tools that let you examine the frequency
characteristics of their products. Since we have very fast edges in the circuit, it will be necessary
to have a combination of several capacitors to have a proper decoupling at all the frequencies of
interest. A low ESR tantalum cap will provide the general low frequency decoupling. For each IC
power pin, a 100 nF in parallel with a 100 pF is a good combination. Additionally, the use of RF
chokes to isolate the different supply rails is highly recommended. These chokes should have
390119012109
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Application Note
Transceiver RFID 13.56MHz MLX90121
Cookbook
the highest possible resistive component, since this is the best way to prevent ringing and
“communication” between the circuits via the supply rails.
Note:
One should plan in advance adequate test points for the gate drive signals. The best is to have
test points where you can plug the scope probe head directly, thereby insuring the best possible
monitoring. Using a standard probe ground attachment is NOT an acceptable option. Inductance
does matter a lot. If you cannot use specific probe head inserts, the following trick may work.
Take a piece of small gage rigid wire. Form a coil spring around the scope probe head where
you will find in general the ground connection. Twist both ends on a SHORT length (less than
1.5 centimeters). Solder directly on the ground plane close to the pcb trace you want to monitor
the resulting ground attachment. The only requirement is to have planned a plated through hole
in the middle of the pcb trace with a drill diameter large enough to accommodate the probe tip
pin. Be careful to not break the probe tip!
It is recommended to have the antenna close to the transmitter, by preference on the same
board. If this is not possible a 50Ohm coax cable may be used, but care must be taken to the
cable length as matching is not a perfect 50Ohm. Performance might then be cable length
dependent.
2.3. Printed circuit board layout issues.
The track length between R5, R6 should be kept to an absolute minimum. The same holds true
for the tracks that go from the 74AC04 gates to these resistors. If some length cannot be
avoided, the trace should be as wide as possible. The width of a 0805 resistor is a minimum.
One must always remember that in this application, stray inductors and ringing are the enemies.
If too much ringing occurs at the power MOSFETS gates, they may turn on simultaneously. This
will affect severely the amplifier efficiency or even destroy it. Use of large ground plane is an
absolute necessity. However, it is better to think and plan in advance where the return currents
will flow. We are not in the microwave range of frequencies, and it is perfectly acceptable to
insert slits in the ground plane in order to channel the return currents paths, and create areas
where the ground plane is quiet.
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Application Note
Transceiver RFID 13.56MHz MLX90121
Cookbook
D. MLX90121: Support of different modulation modes: Scope
This application note is a guide to read transponders with the MLX90121 that use non-standard
ISO14443 or 15693 modulation formats.
The different formats described in this application note are the following:
Base band communication: i.e. communication without sub-carrier
Applications with a sub-carrier of 212 kHz
Decoding the different modulation types does not require any specific hardware. It only requires
a different register configuration setting of the MLX90121.
1. Base band communication:
This application note is divided in four parts:
1. Low Data Rates:
2. Medium Data Rates:
3. High Data Rates:
4. Very High Data Rates:
up to 40 kb/s.
around 100 kb/s.
around 200 kb/s.
over 400 kb/s.
1.1. Low data rates:
1.1.1. Configuration:
Address
0
1
3
12
Register
AnalogConfig
PowerState
DigitalConfig
LTC
Data
0x27
0x01
0x09
0x01
The encoder has to be programmed according
(DecoderTimeRef) is not used.
to
the
application. The
decoder
With this configuration the chip is in ASK configuration with a higher comparator threshold to
avoid glitches. The result is a pulse on DOUT at each field edge.
1.1.2. Screen captures:
The following captures show the MLX10111 in direct mode. The response is a Bi-phase coded
signal at 4 kb/s.
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Transceiver RFID 13.56MHz MLX90121
Cookbook
Channel 1: RF Tag response
Channel 2: DOUT (MLX90121)
Figure 1: Byte transmission
Channel 1: RF Tag response
Channel 2: DOUT (MLX90121)
Figure 2: Zoom to one bit
Typical pulse duration is 6µs.
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Cookbook
The following captures show an ASIC in base band mode. The response is a Manchester coded
signal at 26.5 kb/s.
Channel 1: RF Tag response
D15: DOUT (MLX90121)
Figure 3: Block reading
Channel 1: RF Tag response
D15: DOUT (MLX90121)
Figure 4: Block reading, zoom in
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Cookbook
Because of the differentiating character of the receiver, it generates pulses at the rising and
falling edges of the modulation signal. Typical pulse duration is 7µs. By software, the complete
signal can be properly decoded.
Note: it is not possible to decode NRZ (Non Return to Zero) coded signals.
1.2. Medium Data Rates
1.2.1. Configuration
Address
0
1
3
12
Register
AnalogConfig
PowerState
DigitalConfig
LTC
Data
0x37
0x01
0x09
0x00
The encoder has to be programmed accordingly to the application. The decoder
(DecoderTimeRef) is not used.
With this configuration the chip is in ASK configuration. The result is a pulse on DOUT at each
field edge.
1.2.2. Screen captures:
The following capture shows the MLX10111 replying in BPSK at about 106 kb/s.
Channel 1: RF Tag response
D15: DOUT (MLX90121)
Figure 5: Pattern response at 104 kb/s
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Cookbook
Here also the receiver chain shows its differentiating character. The phase shifts can be very
easily extracted out of the pulse pattern as shown in previous scope screen capture.
Note: it is not possible to decode NRZ (Non Return to Zero) coded signals.
1.3. High Data Rates:
1.3.1. Configuration:
Address
0
1
3
12
Register
AnalogConfig
PowerState
DigitalConfig
LTC
Data
0x23
0x01
0x0B
0x00
The encoder has to be programmed accordingly to the application. The decoder
(DecoderTimeRef) is not used.
With this configuration the chip is in FM configuration. The low pass filters and gain blocks have
been added.
1.3.2. Screen capture:
The following capture shows the MLX10111 replying in BPSK at about 212 kb/s.
Channel 1: RF Tag response
D15: DOUT (MLX90121)
Figure 6: Pattern response at 208 kb/s
Here again phase shifts can be easily recovered from the digital signal at Dout.
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Transceiver RFID 13.56MHz MLX90121
Cookbook
1.4. Very High Data Rates
1.4.1. Configuration
Address
0
1
3
12
Register
AnalogConfig
PowerState
DigitalConfig
LTC
Data
0x27
0x01
0x0B
0x00
The encoder has to be programmed accordingly to the application. The decoder
(DecoderTimeRef) is not used.
With this configuration the chip is in FM configuration.
1.4.2. Screen captures:
The following captures show the MLX10111 replying in BPSK at about 424 kb/s and 848 kb/s.
Channel 1: RF Tag response
D15: DOUT (MLX90121)
Figure 7: Pattern response at 434 kb/s
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Cookbook
Channel 1: RF Tag response
D15: DOUT (MLX90121)
Figure 8: Pattern response at 833 kb/s
Here again phase shifts can be easily recovered from the digital signal at Dout.
Note: For frequencies > 800 kHz, the digital output starts to be distorted. Still the signal can be
decoded.
2. Applications with a sub-carrier of 212 KHz:
2.1. Configuration:
Address
0
1
3
12
Register
AnalogConfig
PowerState
DigitalConfig
LTC
Data
0x27
0x01
0x09
0x00
The encoder has to be programmed accordingly to the application or the chip can be used in
direct mode. The decoder (DecoderTimeRef) is not used.
With this configuration the chip is in ASK configuration, high baud rate.
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Transceiver RFID 13.56MHz MLX90121
Cookbook
2.2. Screen captures:
The following captures show the MLX10111 response and the MLX90121 digital output.
Channel 1: RF Tag response
D15: DOUT (MLX90121)
Figure 9: Reception example
Channel 1: RF Tag response
D15: DOUT (MLX90121)
Figure 10: Bit ‘1’
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Cookbook
Channel 1: RF Tag response
D15: DOUT (MLX90121)
Figure 11: Zoom on the subcarrier
The sub-carrier envelope can be easily recovered from the Dout output of the MLX90121.
3. Conclusion
The MLX90121 supports ISO standard 14443A/B and 15693 protocols. In addition, its high
versatility allows for handling of other custom protocol, like base band modulation and
modulation at a 212 kHz sub-carrier.
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Transceiver RFID 13.56MHz MLX90121
Cookbook
E. Progressive field increase for the MLX90121: Scope
This application note is a design guide to provide a means of controlling the radio frequency field
intensity when a command is sent to a tag. It has been found that some RFID tags do not
operate properly when the field intensity reaches its maximum in a very short time. In order to
solve this issue, we propose a universal solution, applicable to both the standard and power
boosted version, where the characteristics of the progressive field increase sequence can be
parameterized under software control to achieve the desired performance.
1. Standard design (200 mW @ 5 Volts)
1.1. Application schematic
+ 5V
Q1
C5
R2
R1
Field Increase
Control Line
M1
Vdd
C1
L1
Mlx90121
OUT
TX
L2
13.56MHZ
C2
L3
C3
C4
MOD
MOD
RMOD
TX-GND
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Transceiver RFID 13.56MHz MLX90121
Cookbook
1.2. Recommended Components:
Reference Value
R1
470 ohms
R2
M1
Q1
C5
Comments
5%
or
better
2.2 Kohms
5%
or
better
BS 170 or PMBF PHILIPS
170
FZT 949
ZETEX
4.7 F
Tantalum
Note:
Other components values do not differ from
the
standard
recommended
reader
schematic.
1.3. Theory of operation and design guidelines:
When M1 is switched on, it delivers about 10 milliamps of base current to Q1. Hence Q1 is
switched on. To progressively increase the field intensity and therefore obtain a smooth start–up
sequence, it is possible to apply short pulses to the gate of M1 and therefore gradually increase
the output stage supply voltage and hence the radio frequency field intensity.
In the application software (available on request with the MLX90121 demo board), we have
implemented a special command which gives control over 5 parameters for the radio frequency
field intensity. To understand their utility, we shall refer to the following timing diagram of the
signal applied to the gate of M1 during a typical RFID tag transaction:
T1 T2
T3
T4
T5
T1 adjusts the pulse width. T2 controls the duty cycle. T3 controls the duration of the smooth
power supply ramp up. With these three parameters, the smooth start procedure can be fine
tuned, adjusted to a specific design, different values of the power stage supply decoupling
capacitor, etc…
The main voltage regulator of the application board has a response time to the current surge
during the field increase. Because of that, the maximal field intensity is not immediately reached.
In order to provide an optimal communication performance during the transaction with the tag,
an additional delay T4 is introduced, so that no modulation is applied to the radio frequency field
before the end of the main power supply voltage regulator settling.
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Transceiver RFID 13.56MHz MLX90121
Cookbook
After the end of the transaction with the tag, the gate of M1 goes low, effectively switching off
the power stage supply. However, since the power stage uses a large decoupling capacitor ( C5
on above schematic), it will take a long time before its charge is dissipated if the carrier drive
inside the MLX90121 is shut-off at the same time. To remedy this situation, T5 introduces a
delay between the instant at which M1 and Q1 are switched off, and the moment where the
MLX90121 internal carrier drive signal is also switched off. During the time T5, the power stage
is still driven, and discharges C5 rapidly. At the expiration of the T5 delay, one should send the
carrier off command to the MLX 90121 to end the RFID transaction.
An additional note about capacitor C5: Optimal would be to use a high quality ceramic or plastic
film capacitors. Unfortunately, such components are bulky and may be also hard to find. A solid
tantalum capacitor will do the job. However, its transient performance will be much worse, and
this will severely affect the cleanliness of the output stage supply voltage during the initial ramp
up phase. Experimenting with T1, T2 and T3 should yield an acceptable performance.
1.4. Oscilloscope screen captures
1.4.1. Overview of complete sequence
Channel one is the RF signal at the antenna connector.
Channel two is the power supply voltage of the power stage.
D3 is the command line of the MLX90121
D4 is the control line of M1 of this application schematic.
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Cookbook
1.4.2. Detail of start up sequence:
1.4.3. Detail of main voltage regulator settling effect:
As can bee seen on this screen capture, the main voltage regulator takes about 300
microseconds to recover from the initial current surge. Therefore, we have adjusted the value of
T4 accordingly, so that the first modulation pulse does not occur before this time.
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Transceiver RFID 13.56MHz MLX90121
Cookbook
1.4.4. End of RFID transaction:
On this first screen capture, we have adjusted T5 so that the carrier off command is issued to
the MLX90121 1 millisecond after M1 is switched off. The continued carrier drive on the output
power stage discharges its filtering capacitor, C5, during that time.
On the following screen capture, one can see what happens when the carrier off command is
sent to the MLX 90121 immediately after the output power stage supply has been switched off:
The supply voltage remains high for a very long time since in principle, there is not current drain.
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Transceiver RFID 13.56MHz MLX90121
Cookbook
2. Power booster configuration ( 1 Watt @ 12 Volts )
For the description of the MLX90121 12V power booster, we refer to the corresponding
application note.
2.1. Application schematic
+ 12V
Q1
C5
R4
+ 5V
R3
Field Increase
Control Line
M2
L3
L1
TP2
Mlx90121
Vdd
TX
TP1
R1
13.56MHZ
TP3
OUT
L5
L4
C2
L2
C3
C4
M1
C1
D1
R2
MOD
MOD
RMOD
TX-GND
2.2. Recommended Components
Notes:
Reference Value
R3
1.2 Kohms
R4
M2
Q1
C5
Comments
5%
or
better
2.2 Kohms
5%
or
better
BS 170 or PMBF PHILIPS
170
FZT 949
ZETEX
4.7 F
Tantalum
390119012109
Other component’s values do not differ from
the passive matching power boost reader
schematic.
Since the 5 volts supply line is not
controlled, the MLX90121 internal power
transistor is energized. Therefore, during the
discharge time T5, when the booster power
supply is completely switched off, the
antenna signal will not be completely zero
because some capacitive feed through will
occur from the output stage of the
MLX9012. The antenna signal during this
period amounts to less than 400 millivolts
into 50 ohms load. After T5, the carrier will
be switched off inside the MLX90121 which
will remove any antenna signal.
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Transceiver RFID 13.56MHz MLX90121
Cookbook
F. A modulation index switch for the MLX90121: Scope
This application note is a design guide to adjust the modulation depth of the MLX 90121. In the
low modulation index mode, the ISO 14443 standard requires a typical modulation depth of 11
%, whereas the ISO 15693 standard requires 15 %. In order to make a multipurpose reader, one
should be able to switch between these two modulation indexes. Two different designs will be
considered. The first one is the standard application schematic with 200 mW output power @ 5
Volts. The second is the 1 Watt power booster described in the corresponding application note.
1. Standard design (200 mW @ 5 Volts)
1.1. Application schematic
+ 5V
Vdd
L1
C1
Mlx90121
OUT
TX
L2
13.56MHZ
L3
C3
C2
C4
MOD
MOD
RMOD
RINDEX
TX-GND
M1
INDEX CONTROL LINE
1.2. Recommended Components:
Reference Value
RMOD
12 ohms
RINDEX
51 ohms
M1
BS 170 or PMBF
170
390119012109
Comments
1%
or
better
1%
or
better
Note:
Other components values do not differ from
the
standard
recommended
reader
schematic.
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Transceiver RFID 13.56MHz MLX90121
Cookbook
1.3. Theory of operation and design guidelines
When M1 is switched on, it places RINDEX in parallel to RMOD, thereby effectively reducing the
modulation depth. RMOD should be selected to achieve the typical modulation depth for the ISO
15693 standard (15 %) with M1 switched off. RINDEX should be selected to reach the typical
modulation depth of the ISO 14443 standard (11 %) with M1 switched on. The index control line,
that is the gate of M1, should be driven by a dedicated micro controller line under appropriate
software control.
1.4. Waveforms at the antenna connector
1.4.1. ISO 15693, M1 switched off
Modulation depth according to scope cursors measurements: m = (Y2-Y1) / (Y2+Y1) = 14.1 %
1.4.2. ISO 14443, M1 switched on:
Modulation depth according to scope cursors measurements: m = (Y2-Y1)/(Y2+Y1) = 11.5 %
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Transceiver RFID 13.56MHz MLX90121
Cookbook
2. Power booster configuration (1 Watt @ 12 Volts)
For the description of the 12V power booster we refer to the corresponding application note.
2.1. Application schematic
+ 12V
+ 5V
L3
Vdd
L1
TP2
Mlx90121
TX
TP1
R1
13.56MHZ
TP3
OUT
L4
C2
L2
L5
C3
C4
M1
C1
R2
D1
MOD
MOD
RMOD
RINDEX
TX-GND
M2
Index Control Line
2.2. Recommended Components:
Notes:
Reference Value
RMOD
7.5 ohms
RINDEX
27 ohms
M1
BS 170 or PMBF
170
390119012109
Comments
1%
or
better
1%
or
better
Other component’s values do not differ from
the passive matching power boost reader
schematic.
Values for RMOD and RINDEX are valid
only for a 12 Volts booster stage supply.
Other supply voltages will require different
values for RMOD and RINDEX.
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Transceiver RFID 13.56MHz MLX90121
Cookbook
2.3. Waveforms at the antenna connector
2.3.1. ISO 15693, M2 switched off:
Modulation depth according to scope cursors measurements: m = (Y2-Y1)/(Y2+Y1) = 16.36 %
2.3.2. ISO 14443, M1 switched on
Modulation depth according to scope cursors measurements: m = (Y2-Y1)/(Y2+Y1) = 11.31 %
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