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MLX90108B

64bit Read Only Transponder

Melexis Microelectronic Systems  

MLX90108

64bit Read Only Transponder

General Description

The MLX90108 is a 64 bit Read Only (RO)

transponder. The integrated tune capacitance

and the external coil form a resonant LC antenna

that absorbs part of the electromagnetic energy

radiated by the transceiver LC antenna.

Physically, a magnetic coupling occurs between

the transceiver, also referred to as "reader", and

transponder antennas

To amplitude modulate (AM) the RF carrier, the

transponder damps the electromagnetic field by

switching a resistor in parallel with its coil. This

way the transponder repetitively transmits its 64

bit-identification code (ID) to the reader base

station.

Frequency tuning

Tuning and buffer capacitors are integrated to

optimize total system cost.

The 80pF integrated tuning capacitor is +/-20%

accurate from batch to batch. A spread of max

+/-2.5% is guaranteed across a full batch, which

is typically 200k dice.

Clock Extractor:

Master clock is taken from the carrier frequency

which is picked up on the coil. Depending on the

options, the carrier frequency is divided by

16(8kBaud: PSK only), 32(4kbaud) or

64(2kbaud)to generate the bit rate.

VDD regulator:

Supply voltage is taken from the AC voltage

induced in the coil. Overvoltage protection is

done by current clamping.

POR level

When the transponder is placed in an external

radio frequency (RF) field of appropriate

frequency and amplitude, the internal power

supply (VDD) can build up as charge on the

integrated buffer capacitance. The modulation

resistor is switched on and off as soon as VDD

has reached the Power On Reset (POR) level.

When the modulation resistor is switched on, the

LC circuit is no longer tuned, therefore no energy

is taken from the field, and VDD drops due to

internal consumption. Hence, by switching the

modulation resistor on and off, it is possible to

oscillate around the POR level. This

phenomenon is referred to as hiccuping.

The modulation resistor is switched off when the

transponder drops below the POR level.

Block diagram

VDD

Coil

CTUNE

GND

Clock

extractor

MLX90108

VDD

Divider by

64, 32 or 16

AC

+

VDD

regulator

Sequencer

CBUFFER

Memory

Array

Modulator

Data encoder

Sensitivity level

The minimum electromagnetic force (e.m.f.)

needed to avoid hiccuping is defined by Vacsens.

At this level the power supply will not drop below

the POR level while the modulation resistance is

switched on during modulation.

Modulator

The modulator consists of a modulation resistor

that is switched in parallel with the resonant LC

circuit (antenna). The MLX90108 offers different

encoding schemes and AM modulation

techniques, which are discussed below, each

optimized for maximum operating and reading

distance under different field conditions.

EEPROM

The Identification code is written in EEPROM

during wafer test. After POR the device will read

out the data periodically. Data retention is

guaranteed as specified (Tret, Ncyc).

MLX90108 64bit Read Only Transponder

Page 3 of 6

Rev1.6 5-Feb-01

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