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Features and Benefits

Integrated transmitter-receiver for 120kHz ASK transponders (tags)
Unique Parallel Antenna concept for maximum power efficiency.
No external quartz reference required. No zero modulation problems.
SO8 package and high level of integration for compact reader design
On chip decoding (Biphase and Manchester ASK) for fast system design and ease of use
Baudrate selectable On chip filtering for maximum sensitivity.
Open drain data and clock outputs for 2 wire serial communication
Power down mode available
Transparent ASK modulation for the downlink communication to the tag,including ON/OFF
keying (100%) and FDX-B20.

Applications

Portable tools and appliances, doorlocks ... and any RFID system requiring a large number
of readers for proximity Read and Write.

Ordering Information

Part No.

Temperature suffix

Package code

MLX90109

C (0癈 to 70癈)

DC (SOIC 8)

MLX90109

E (-40癈 to 85癈)

DC (SOIC 8)

Description

The MLX90109 is a single chip RFID transmitter-
receiver for the 125kHz range. It has been
conceived to realize a state of the art Read and
Write performance for minimum system cost, and
minimum power consumption.
An external L and C are connected as a parallel
resonant circuit, which will determine the carrier
frequency and the oscillator frequency of the reader.
This eliminates zero modulation effects, and avoids
the need for an external oscillator.
The antenna amplitude can be adjusted externally on
the fly. This allows straightforward modulation of the
antenna amplitude to write to the transponder.
The reader IC can easily be switched to power down
by setting the antenna amplitude to zero.
The MLX90109 can be configured to decode the
transponder signal on-chip. In this case the decoded
signal is available through a 2-wire interface of clock
and data. For minimum interface wiring, the
undecoded transponder signal can also be made
available on a single wire interface.

Functional Diagram

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MLX90109 Electrical Specifications

DC Operating Parameters T

= -40

C to 85

C, Fres = 125kHz, Lant = 73.6uH, Qant=17.3 , V

= 5V (unless otherwise specified)

Parameter

Symbol

Test Conditions

Min Typ Max

Units

Supply Voltage

VDD

4.5

5.5

Serial Resonance Freq.

SRF

100 125 150

kHz

Temperature drift

(

T)Fres

-1

Sensitivity

Vsens

VMODU = 1V

MODU voltage

VMODU

0.8

4.12

Amplitude Overshoot

Vos

VMODU=1V

.15

0.3

Antenna Amplitude

Vant

VMODU=1V
Calculated: Vant = VDD-VMODU+Vos

4.15

Power down voltage

VMODUpd

4.13

4.7

Power up voltage

VMODUpu

3.3

4.12

Power down Current

IDDpd

VMODU = 5V

Power down Pull up

RMODUpu

VMODU = 5V

100

Max. Operating Current

IDDmax

(1)

MODU = 1V, excluding IDDant (*)

Antenna Driver Current

Idriver

VMODU = 1V, Vos > 0.1V

Auto start up Idriver

Idriver_auto

By design : Idriver_auto = Idriver/2

AC Antenna Operating current

IDDant

Calculated: IDDant = 0.63*Idriver

8.6

Antenna Impedance

Zant

Calculated Zant = Vant / IDDant

0.5

Auto start up Zant

Zant_auto

Calculated Zant_auto = Vant / IDDant_auto

Filter Gain

Filter ripple

Filter 3db BW 2kbaud

SPEED = 1, By design

400 � 3.6k

Filter 3db BW 4kbaud

SPEED = 0, By design

800 - 7.2k

Output voltage DATA and CLOCK pin Vout

Isink = 2.5mA

0.4

Start up time

Tstartread

By design: time before ready to read

1024 Clock

periods

(*)Maximum operating current is slightly dependent on Iant. A good reference calculation is IDD = 1.3 +
Idriver/10

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1. Basic operating principles

The MLX90109 is a 125kHz reader IC designed for
use with a parallel LC antenna. This concept
requires significantly less current than traditional
serial antennas, for building up the same magnetic
field strength. The concept is limited to proximity
read/write basestations (less than 25cm range),
since the voltage amplitude (Vant) is limited by the
applied supply voltage.

Vant < VDD.

Antenna voltage definition

In order to use the driver FET as an ideal current
source, the voltage on the coil pin should remain
higher than 0.5V for up to 14mA driver current
(IDDant).
The voltage on the MODU pin (VMODU) controls
Vant, as follows:

Vant = VDD - VMODU + Vos

with Vos, the overshoot due to the inertia of the LC
antenna.
Because the overshoot can be as much as 300mV,
VMODU should be higher than 0.8V for correct
operation.

Power Down/Power On

By setting VMODU higher than Vpd (preferably to
VDD) the MLX90109 goes in power down. The
Antenna Voltage will fade to 0V.
When the antenna impedance is higher than Zant,
the MLX90109 powers on (POR) by pulling VMODU
below Vpu. The antenna Voltage will rise
proportionally to the applied voltage step. 1024
carrier periods after the POR the MLX90109 goes
from its power-on sequence to normal operating
mode with normal sensitivity.

Write operation

A sequence of power on / power down periods sets
the antenna voltage ON and OFF. This features
allows to simply realize an ON/OFF keying downlink
to the transponder.
Typically VMODU is toggled between 5V and 0.8V.
Antenna fade out is related with the antenna Q, start
up takes typically 3 carrier periods.
The MLX90109 can also be used to write to FDX-
B20 tags, which can not permit to loose clocks. In
tihis case we toggle VMODU between according to
the wanted modulation depth on the reader, without
allowing the antenna voltage to fade out completely.

See the section on `application information' further in
this document for more detailed information and
practical hints .

2. Functional blocks description

Oscillator

The oscillator frequency is locked on the antenna
frequency. The clock of the filter is derived from the
oscillator. In this way the filter characteristics are
locked to the transmission frequency. Consequently
the MLX90109 is not sensitive to zero modulation.

Amplitude detection

The AM signal generated by the tag is detected by
the amplitude demodulator of the transceiver. This
signal is filtered and amplified by an on-chip
switched capacitor filter before feeding it to the digital
decoder. The same signal is fed back to close the
control loop of the antenna voltage.

Filter settings

Block Diagram

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By setting the SPEED pin to VDD or to GND the
filtering characteristics are optimized for either
2kbaud or 4kbaud respectively.

Digital decoding

The MODE pin allows to define whether to issue
directly the filtered data stream on the DATA pin
(MODE floating), or to have the MLX90109 decoding
manchester (MODE = VSS) or biphase (MODE =
VDD) data. In the decoding mode the digital receiver
gets the filtered data stream and issues the tag data
on the DATA pin at the rising edge of the clock,
which is issued on the CLOCK pin. Both CLOCK
and DATA are open drain outputs and require
external pull-ups.
(*) Internally strapped to VDD/2

3. Reference docs:

EVB90109: Evaluation board and case study
with MLX90127 transponder
DVK90109: Development kit for advanced
system evaluation of 90109.
DS90125: Dedicated reader coils for MLX90109

4. System design parameters

The antenna driver FET is switched on as soon as
the antenna voltage drops below VDD, see graphical
representation below. The MLX90109 will inject
current into the antenna to guarantee an antenna
amplitude as set by the voltage on the MODU pin.

This operation is guaranteed as long as the voltage
swing guarantees the voltage on the COIL pin to
drop 100mV below VDD.
If Vant < 100mV the MLX90109 may not be able to
retrieve its clock.

Auto start up condition

Pulling VMODU, at power on, from 5V to less than
3.3V (VMODUpu) will set the driver FET on. The
voltage drop on the coil pin will be large enough
(Vant>100mV) to be coupled back into the
MLX90109, so as to close the feedback loop.
To obtain the required positive feedback to start up
the oscillation successfully Zant should be larger
than 1kOhm. This is the so-called `auto start-up
condition'.
If the antenna is (still) oscillating when VMODU is
pulled from 5V to less than 3.3V, the positive
feedback is not required, and the normal operating
conditions (Zant>500Ohm) apply. See application
notes for alternative start up methods, and
consequences for ON/OFF keying.

Currents

The MLX90109 is specified to drive maximum 14mA
antenna current (Idriver) in normal operation. (See

VSS

FLOAT (*)

VDD

SPEED

4kBaud

2kBaud

MODE

Biphase

No decoding Manchester

Graph:
Antenna voltage and Driver current during normal operation. VMODU=0.8V for VDD=5V. The
overshoot is visualized. The dashed curve shows the antenna voltage when the reader has been
powered down.

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the DVK90109 development kit for a current
measurement schematic).
The AC equivalent supply current (IDDant) can be
calculated:

IDDant = 2/

*sin(

) *Idriver

= 0.63*Idriver

with

the duty cycle which is typically 45%.

The current that the MLX90109 can inject each
oscillation onto the total antenna current is therefore
limited to 9mA in correctly designed reader base
stations.
For auto start up (see above) of the antenna the
maximum driver current is specified to maximum
7mA, or IDDant<4.5mA .

The actual antenna current that generates the
magnetic field can be calculated as

Iant

= Qant*IDDant

A typical coil quality factor (Qant) value is 23 (see
MLX90125), resulting in antenna currents of about
100mA for auto start up.

This current resonance of the parallel antenna allows
to build very low power reader base stations, as
opposed to serial antenna based version. Using
discrete power transistors, the serial antenna can
however leverage its voltage resonance to drive
bigger antenna's for long distance reading up to 1m,
whereas the MLX90109 is designed to drive
antennas of 1cm up to 15cm (6"). Maximum read
performances of up to 25cm (9") have been
demonstrated.

Voltages

The antenna voltage amplitude can easily be
calculated as

Vant

= VDD - VMODU+Vovershoot

Antenna Impedance.

Clearly the antenna impedance is an important
system design parameter for the MLX90109.

Zant

= Vant / IDDant

For IDDant<4.3mA (auto start up) and Vantmax =
4.2V, we find Zant should be 1kOhm.
A good approximation is

Zant

= Qant.Wres.Lant

with

Wres = 2*pi*Fres

From the above we find that

Iant

= Qant*IDDant

= Vant / (Wres*Lant)

The total number of ampere-turns

is then:

Nant * Iant ~ 1 / sqrt(Lant)

for Lant ~ Nant

Qant has no influence on Iant, it only reduces the
overall current consumption.

REMARK!
Mind that in reality the strong coupling with the tag
may drastically reduce the antenna impedance. This
is why the MLX90127 transponder can not be read at
0mm distance by the MLX90109 using the 18mm
MLX90125-CZA-A reader antenna coil with VMODU
= 0.8V. See the MLX90126 for a complete case
study with the MLX90127.

In practice the inductance values are matched with
standard capacitor values to realize the resonance
frequency (Fres). Below some typical values are
given for 125kHz.

For Vant = 4.4V the maximum antenna currents for
auto start up systems can be found in the table
below.
Remark that IDDant is 4mA if we match Qant such
that Zant = 1.1kOhm. However if we keep Qant
constant IDDant will further reduce for higher Lant.

Changing the MODU voltage, will change the
antenna voltage, and hence also the field strength.
This will be used to amplitude modulate for writing to
the transponder.
In the table above the antenna currents for VMODU
= 2.2V (Vant = 2.9V) and VMODU = 4.0V (Vant =
1.1V) are given.

Ctune

Lant

Qant (Zant=1.1k

)

Zant (Q=23)

12nF

135uH

2.4

15nF

108uH

2.0

18nF

90uH

1.6

22nF

74uH

1.3

30nF

54uH

1.0

Lant

Iant (Vant = 4.2V)

IDD (Qant=23)

135uH

1.7

108uH

2.2

90uH

2.6

74uH

3.1

54uH

100

4.3

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Also the current consumption (IDDant) is reduced by
reducing Vant. We will use this to artificially change
the impedance specification in some application
specific circumstances. (see READ: close coupling.)

5. Applications information: READ

Absolute minimum schematic

Power consumption

Noise suppression

Integrated decoding

Close coupling (impedance, frequency)

Absolute minimum schematic

The MLX90109 is a highly integrated reader IC. As
can be seen in the application schematic below only
two resistors (to set VMODU) are required, next to
the antenna inductance and tune capacitor.
The interface with the microcontroller can be realized
with 1 connection plus the supply lines. In this case
the MODE is left floating, and the integrated
decoding is not used.

Power consumption

If power consumption is not critical and the reader
does not have to be put in power down, the MODU
voltage can be strapped to the required level
(between 0.8V and 4.2V).
However the power consumption can be reduced in
between operations.

1) Supply from microcontroller IO port
The total maximum current consumption of the
MLX90109 plus the antenna is

IDDtot = IDDant + IDD90109 + IRmodu

With IRmodu, the trickle current through the
resistances R1 and R2, which can be chosen large

Lant

Iant (Vant = 3.0V)

Iant (Vant=1.1V)

135uH

108uH

90uH

74uH

54uH

Minimum Read Application schematic in black; Options in grey

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enough such that they can be neglected in this
calculation.

IDDant < 14mA

IDD90109 < 2mA

So if a 20mA port is available to supply the
transceiver it can easily be switched off.
Alternatively if no such port is available a switch in
the ground (VSS) can be added. This is not
recommended but in less critical application the
performance may be acceptable.
The antenna current can be further reduced as
explained

previously

(see

System

design

parameters: Antenna Impedance) such that even a
5mA port could be used.

2) VMODU >VMODUpd
By controlling the Voltage on the MODU pin the
device can be put to power down as described
previously (see Basic operating principles: Power
down / Power on).
Take into account that the trickle current from the
resistor tree R1-R2 is NOT switched off. During
power down this uA current may kill the lifetime of
the battery.

Noise cancellation

The entire read performance of a reader is linked
with its robustness versus noise. The IC design is
made to realize the best signal to noise ratios (SNR).
The resonant antenna is a natural band-pass filter,
which becomes more effective as Qr increases.
The MLX90109 has an internal first order filtering of
the envelope that changes according to the setting of
the SPEED pin to fit to the biphase and Manchester
data spectrum:

2kbaud:

400Hz to 3.6kHz

4kbaud:

800Hz to 7.2kHz

But even this filter only has a limited gain of 28dB,
such that noise should be avoided by carefull PCB
design and adding decoupling capacitance(s) on the
supply lines.

Most sensitive pins for noise injection (EMI) are
MODU and VDD. Since they directly determine
Vant, the noise will be considered to be AM data
from a transponder by the sampler.
Now, if the noise on both pins were identical it would
cancel itself, giving a very noise insensitive reader!
Adding C1 between MODU and VDD, together with
R1 and R2 yields a high pass filter with cut off
frequency at:

* (R1//R2) * C1

Typically the filter should short all noise in the data
spectrum, but for a lot of appliances it might be
beneficial to set it to less than the net frequency
(50Hz, 60Hz). For instance R1=100kOhm and
R2=19kOhm for setting MODU, with C1=220nF gives
a cut off frequency = 45Hz

Finally we want to draw your attention to the DATA
and CLOCK open drain drivers. These have been
dimensioned to drive strong loads. So take care to
use high ohmic (100kOhm) pull up resistances if the
loads are minimal.

Integrated decoding

The MLX90109 provides the option to have a
decoded output. This significantly reduces the
complexity of the microcontroller software.
The data is available when the clock output is high.
And the clock output has a 50% duty cycle if the data
is valid. When the noise level is stronger than the
signal level, for instance when no tag is present in
the reader field, the duty cycle will be random. When
using this feature to detect the presence of a tag,
allow some asymmetricity on the clock. The
sampling error may be 4us, so allow 8 or 12us of
margin.
Remark that when the MLX90109 picks up a
Manchester encoded signal when the MODE pin is
strapped to VSS (=biphase decoding), the clock will
also be asymmetric.

Close coupling

If a tag is coupled too strong, such that Zant drops to
500Ohms Vant can be reduced. This should be
evaluated case by case. See MLX90126 for a case
study of the 18mm reader coil with the MLX90127,
where at very close operating distances reading may
be less reliable.

The solution for this is to increase the voltage on the
MODU pin (VMODU), such that the current drawn by
the antenna is reduced. See the explanation of
theantenna impedance in the section of `System
design parameters'.

VMODU

0.8V

3.0V

4.0V

IDDant

8.8mA

4.4mA

2.2mA

Vant

4.4V

2.2V

1.1V (*)

(*) small amplitudes have smaller overshoot.

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Full Qualification of the write functionality is expected
by early 2003. The basic operating modes are
explained below.

6. Applications information: WRITE

ON/OFF keying (FDX-B100)

Schematic

Power on Boost

Noise suppression

Switching between Read and Write

The basic principle is to switch the voltage on MODU
between 0V and VDD. The antenna will reach its
maximum amplitude in less than 4 periods when
MODU is stepped down from VDD to VSS. Setting
the chip in power down (step Vmodu up to VDD) will
let the antenna fade out with a time constant=Qant/3.
An additional drain resistor on MODU operated by
the microcontroller can increase the fall time if
required.

7. Applications information: WRITE

20% to 60% modulation depth
(FDX-B20 to � B60)

Schematic

Power on Boost

Noise suppression

Switching between Read and Write

The writing is done identically to the ON/OFF keying
mode, but with an additional resistance R3 between
the microcontroller and MODU to set the `OFF level'.
An additional capacitor C3 can improve the edges on
VMODU.
Furthermore the falling edge on the transponder coil
can be improved by setting the reader in power down
for a few microseconds, and then turn it on again (to
avoid the tag to loose clocks when it modulation
resistance is ON). If this is done, capacitor C3 can
be dimensioned to guarantee a spike below 3V to
guarantee power on, with a target level of 4V for
instance.

Packaging Information

SOIC8 outline see further.
MLP10 package is being reviewed This could re-
duce the footprint from 5*7mm to 3*3mm.

ESD Precautions

Electronic semiconductor products are sensitive to
Electro Static Discharge (ESD).
Always observe Electro Static Discharge control pro-
cedures whenever handling semiconductor products

Reliability Information

Melexis devices are classified and qualified regar-
ding suitability for infrared, vapor phase and wave
soldering with usual (63/37 SnPb-) solder (melting
point at 183degC).
The following test methods are applied:

IPC/JEDEC J-STD-020A (issue April 1999)

Moisture/Reflow Sensitivity Classification
For Nonhermetic Solid State Surface Mount
Devices

CECC00802 (issue 1994)

Standard Method For The Specification of
Surface Mounting Components (SMDs) of
Assessed Quality

MIL 883 Method 2003 / JEDEC-STD-22 Test Method
B102

Solderability

For all soldering technologies deviating from above
mentioned standard conditions (regarding peak tem-
perature, temperature gradient, temperature profile
etc) additional classification and qualification tests
have to be agreed upon with Melexis.

The application of Wave Soldering for SMD's is allo-
wed only after consulting Melexis regarding assuran-
ce of adhesive strength between device and board.

For more information on manufacturabi-
lity/solderability see quality page at our website:

http://www.melexis.com/

3901090109

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Disclaimer

Devices sold by Melexis are covered by the warranty and patent indemnification provisions appearing in its
Term of Sale. Melexis makes no warranty, express, statutory, implied, or by description regarding the informati-
on set forth herein or regarding the freedom of the described devices from patent infringement. Melexis reser-
ves the right to change specifications and prices at any time and without notice. Therefore, prior to designing
this product into a system, it is necessary to check with Melexis for current information. This product is intended
for use in normal commercial applications. Applications requiring extended temperature range, unusual environ-
mental requirements, or high reliability applications, such as military, medical life-support or life-sustaining
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other services. � 2002 Melexis NV. All rights reserved.

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协谢械泻褌褉芯薪薪褘泄 泻芯屑锌芯薪械薪褌: MLX90109

协谢械泻褌褉芯薪薪褘泄泻芯屑锌芯薪械薪褌: MLX90109