MLX90109

125kHz RFID Transceiver

3901090109

Page 6 of 16

Data Sheet

Rev 011

Jun/12

6 Block Diagram

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

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:

:

400Hz to 3.6kHz

:

800Hz to 7.2kHz