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Hello,
I am trying to understand how the ASK 125KHz RFID reader on page 140 of this pdf works (4.0 ASK READER SCHEMATIC, Page 134 of the document):
https://ww1.microchip.com/downloads/en/devicedoc/51115f.pdf
My understanding is that RFID data is modulated on a 125KHz carrier signal and the baseband frequency is 1-4KHz. My question is about the LP filter formed by C15 (0.0022uF) and R24(390K). When I calculate the cutoff frequency of this filter I get the value of around 180Hz which is well below the frequency of the RFID data and it filters the actual data.
Can someone please explain why these values are used?
Thanks,
Ahmad
I am trying to understand how the ASK 125KHz RFID reader on page 140 of this pdf works (4.0 ASK READER SCHEMATIC, Page 134 of the document):
https://ww1.microchip.com/downloads/en/devicedoc/51115f.pdf
My understanding is that RFID data is modulated on a 125KHz carrier signal and the baseband frequency is 1-4KHz. My question is about the LP filter formed by C15 (0.0022uF) and R24(390K). When I calculate the cutoff frequency of this filter I get the value of around 180Hz which is well below the frequency of the RFID data and it filters the actual data.
Can someone please explain why these values are used?
Thanks,
Ahmad
