MLX90109_06 Datasheet, PDF (5/15 Pages) Melexis Microelectronic Systems – 125kHz RFID Transceiver

6 Block Diagram
MLX90109
125kHz RFID Transceiver
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 V_DD 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 V_DD)
:
4kbaud (speed pin to V_SS)
:
400Hz to 3.6kHz
800Hz to 7.2kHz
3901090109
Rev 008
Page 5 of 15
Data Sheet
Jun/06