Communication method of contactless ID card and integrated circuit used in communication method

An integrated circuit comprising:

• a buffer circuit having an input terminal to receive an input data signal of said integrated circuit, a first output terminal, and a second output terminal to output the same signal as that of
• said first output terminal thereof
• a low-pass filter circuit having an input terminal and an output terminal, said first output terminal of said buffer circuit being connected to said input terminal of said low-pass filter circuit;
• a latch circuit having a first input terminal, a second input terminal, and an output terminal, said output terminal of said low-pass filter circuit being connected to said first input terminal of said latch circuit;
• and
• a pulse generating circuit having an input terminal and an output terminal to provide said latch circuit with an edge trigger to drive said latch circuit, said second output terminal of said buffer circuit being connected to said input terminal of said pulse generating circuit, said output terminal of said pulse generating circuit being connected to said second input of said latch circuit,
• wherein said latch circuit is configured so that an output of said pulse generating circuit may be inputted thereto through said second terminal thereof performing as a clock input terminal, to be driven at one of a rising edge and a falling edge of an original waveform of said input data signal,
• wherein said integrated circuit is configured to be used in a communication method for transmitting information by a waveform combined with either a first waveform or a second waveform, using a first waveform and a second waveform,
• wherein said combined plurality of waveform patterns has transitions of any one of rising edges and falling edges in approximately equi-intervals,
• wherein said combined plurality of waveform patterns keeps a constant duty independently of said data signals to be communicated, and
• wherein in such a case that an observation is made of said combined waveform which is filtered by a low-pass filter at timing of said transitions, different logic levels can be monitored as to said first waveform and said second waveform.

An integrated card system with employment of an amplitude modulation, wherein:

• a transition of an internal clock occurs in synchronism with rising edge timing of a modulation signal,
• an internal logic circuit is operated in synchronism with the transition of said internal clock,
• said integrated card system is configured to execute a communication method for transmitting information by a waveform combined with either a first waveform or a second waveform, using a first waveform and a second waveform,
• said combined plurality of waveform patterns has transitions of any one of rising edges and falling edges in approximately equi-intervals,
• said combined plurality of waveform patterns keeps a constant duty independently of data signals to be communicated,
• in such a case that an observation is made of said combined waveform which is filtered by a low-pass filter at timing of said transitions, different logic levels can be monitored as to said first waveform and said second waveform,
• said first waveform represents one level of data signal and said second waveform represents another level of data having at center portions thereof, a transition of any one of a rising edge and a falling edge, and
• for data communication carried out by employing said first waveform and said second waveform, said data communication is performed in such a manner that said one transition does not occur except for at center portions of the waveform patterns.