I am Planning to Implement Card sniffing with NFC Front Chip !
Can I Utilize Comparator for card presence detection system senses the card by measuring the decay time of a transmitter signal after it has been turned off. When a card is in the field of the transmitter, power transfer occurs, and with more current the voltage on the transmitter output increases. The closer the card is to the reader the higher the voltage will be from the not present state. Measuring the decay of this signal by a comparator creates a simple A/D, since effectively the voltage is what is being measured