Semiconductor integrated circuit, a contactless information medium having the semiconductor integrated circuit, and a method of driving the semiconductor integrated circuit

A contactless information medium comprising:

• a power generation circuit which receives an ASK-modulated carrier from outside the contactless information medium and generates AC power;
• a rectifier circuit which rectifies the AC power generated by the power generation circuit to DC power;
• a reference voltage generation circuit which outputs a reference voltage;
• a regulator circuit which includes an input terminal for receiving the DC power, a control terminal, and an output terminal, regulates the DC power so as not to exceed a voltage value determined from a voltage value received by the control terminal, and outputs the regulated DC power from the output terminal;
• and
• a reference voltage changing circuit which changes the reference voltage in correspondence to voltage change of the DC power, the changed reference being input to the control terminal.

A method for driving a semiconductor integrated circuit which includes a regulator circuit for outputting DC power so as not to exceed a voltage value determined from a voltage value received by a control terminal, the method comprising:

• a reception step in which a carrier having been ASK-modulated by digital data is received by an antenna coil;
• a rectification step in which the carrier is received and AC power which is generated at two ends of the antenna coil is rectified;
• and
• a value discrimination step in which the digital data piggybacked on the carrier is discriminated by inputting the DC power into the regulator circuit and latching a pulse signal which is obtained by differentiating an output of the regulator circuit, wherein
• a value of a voltage input into the control terminal is changed in correspondence to voltage change of the DC power.