Kasakachda,
See i dont worry of what the filters are or stuffs like that.What I look into the ckt. is that it uses the Op-amps to pass signal voltages ,from a specific I/p that you provide.Next it compares with the provided 5V supply accompanied with diff. Resistor values,as you can see to just modify it O/P's of the individual OPamps to rectify its Final O/p stage of the Recieving stage of RFID reader.
For more information on RFID, you can check my blog:--
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