MLX90109 데이터 시트보기 (PDF) - Melexis Microelectronic Systems

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MLX90109

125kHz RFID Transceiver

Melexis Microelectronic Systems  

MLX90109

125kHz RFID Transceiver

6. Block Diagram

VDD

VDD

COIL

GND

Peak

Detector

clock

Loop Gain

Oscillator

MODU

Band-pass

Filter

MLX90109

Comparator

Digital

Decoder

SPEED MODE

DATA

CLOCK

7. General Description

7.1. Loop Gain Oscillator

The oscillator frequency is locked on the antenna resonance frequency. The clock is derived from the oscillator. In this way,

its characteristics are locked to the transmission frequency. As the antenna is used to determine the carrier frequency, the

antenna is always perfectly tuned to resonance. Consequently the MLX90109 is not sensitive to zero modulation (the so-

called “zero modulation” is the phenomena whereby the tag does modulate properly, but no amplitude modulation can be

observed at the reader coil).

7.2. Peak Detector

The peak detector of the transceiver detects the AM signal generated by the tag. This signal is filtered and amplified by an

on-chip switched capacitor filter before feeding the digital decoder. The same signal is fed back to close the loop of the

antenna voltage.

7.3. Band-Pass Filter

By setting the SPEED pin to VDD or to GND, the filtering characteristics are optimized for either 2 or 4 kbaud. The MLX90109

makes an internal first-order filtering of the envelope that changes according to the setting of the SPEED pin, to fit the

Biphase and Manchester data spectrum:

2kbaud (speed pin to VDD) :

4kbaud (speed pin to VSS) :

400Hz to 3.6kHz

800Hz to 7.2kHz

REVISION 011 - JUNE 19, 2017

3901090109

Page 7 of 17

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