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  1. #1
    Junior Member level 2
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    May 2020
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    RFID Transponder transmission and reception working

    I am reading about RFID systems and designs. And I stumbled upto this Digikey article -

    I am really confused with Figure 5 in that article.

    In the above IC Diagram, I am really confused with Pin 2, Pin 4 Pin 14. How does these three pins work?

    How is the transmission TX from pin 2 and pin 4 happening? And how is the information at pin 14 received?

    Doesn't pin 14 receive whatever pin 2 sends? - I agree when some passive RF Antenna is bought nearby, RX plays a role. But I am not clear on how this IC functions in proper operating conditions.

    Request you to explain how the pins 2, 4 and 14 work during RF Transmission and reception and how the values are selected.

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  2. #2
    Super Moderator
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    betwixt's Avatar
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    Jul 2009
    Aberdyfi, West Wales, UK
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    Re: RFID Transponder transmission and reception working

    A bit over simplified but this will give you the general idea:

    In RFID systems, the transmitter sends pulses at the chosen frequency, it also monitors the amplitude of pulses it sends.
    The 'tag' uses the induced voltage in it's receive antenna to power itself and it also switches an additional load on or off across the antenna to change its impedance.

    In the schematic the transmit oscillator sends the pulses across pins 2 and 4. It monitors the voltage at pin14. Once powered up, the IC inside the tag pulses the additional load on and off to carry data. The voltage monitor on pin 14 sees the load on the transmit antenna changing it's amplitude in sympathy with the load placed on it by the tag. This is converted back to data.

    It might be easier to visualize it as the primary and secondary of a transformer. As the load on the secondary changes it causes an increase or decrease in current in the primary. Substitute the RFID transmitter for the primary and the tag for the secondary. You can see that by monitoring the current on one side of the magnetic field you can tell if the other side is drawing power from it and how that power is changing to carry data.

    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.

    1 members found this post helpful.

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