Non-contact IC card system and non-contact IC card

A non-contact IC card system comprising:

• a reader/writer and a non-contact IC card, wherein at least one of said reader/writer and said non-contact IC card includes:
• a filter for converting a reception signal including a plurality of carriers different in frequency from each other into a binary signal by comparing said reception signal with a reference value and further for extracting a carrier with a desired frequency by comparing a pulse width of the converted binary signal with a width of a reference pulse feedbacked to vary in accordance with a variation of said pulse width of the converted binary signal.

A non-contact IC card which receives power supply from a reader/writer and conducts data transmission/reception to/from said reader/writer, comprising:

• an AM demodulating circuit for converting a reception signal being a carrier AM-modulated by transmission data into a binary signal by comparing said reception signal with a reference value and further for detecting said transmission data by comparing a pulse width of the converted binary signal with a width of a reference pulse feedbacked to vary in accordance with a variation of said pulse width of the converted binary signal.

A non-contact IC card which receives power supply from a reader/writer and conducts data transmission/reception to/from the reader/writer, comprising:

• a filter for converting a reception signal including a plurality of carriers different in frequency from each other into a binary signal by comparing said reception signal with a reference value and further for extracting a carrier with a desired frequency by comparing a pulse width of the converted binary signal with a width of a reference pulse feedbacked to vary in accordance with a variation of said pulse width of the converted binary signal.