Transponder with a frequency detector for protection of security-related data during contactless inductive communication, and an integrated circuit therefor

An integrated circuit for a transponder constructed to provide contactless inductive communication with a base station, wherein the transponder comprises an antenna resonant circuit adapted to receive a modulated HF signal supplied by the base station and to supply said signal to signal processing means, the integrated circuit comprising:

• signal processing means for processing a received modulated HF signal and for supplying a data signal and a clock signal, the data signal comprising data contained in the modulated HF signal and the frequency of the clock signal being derived from the frequency of the HF signal,
• data processing means arranged to receive the data signal and the clock signal and adapted to process the data signal, the processing speed of the data processing means being dependent upon the clock signal and the data processing means being arranged to receive reset information for terminating the processing of the data signal,
• a frequency detector arranged to receive the clock signal, to compare the frequency of the clock signal with at least a first limit frequency and to generate the reset information and to supply the reset information to the data processing means if the frequency of the clock signal is lower than the limit frequency;
• wherein the integrated circuit is adapted to activate a high-security mode in the transponder during which the transponder processes security-related data and a second limit frequency that is higher than the first limit frequency is defined by the frequency detector.

transponder for the contactless inductive communication with a base station, comprising:

• an antenna resonant circuit adapted to receive a modulated HF signal supplied by the base station;
• signal processing means for processing the received modulated HF signal from the antenna resonant circuit and for supplying a data signal and a clock signal, the data signal comprising data contained in the modulated HF signal and the frequency of the clock signal being derived from the frequency of the HF signal;
• data processing means arranged to receive the data signal and the clock signal and adapted to process the data signal, the processing speed of the data processing means being dependent upon the clock signal and the data processing means being arranged to receive reset information for terminating the processing of the data signal,
• a frequency detector arranged to receive the clock signal, to compare the frequency of the clock signal with at least a first limit frequency and to generate the reset information and to supply the reset information to the data processing means so as to terminate the processing of the data signal by the data processing means if the frequency of the clock signal is lower than the limit frequency.