Patent ID: 7907897
Filing Date: 2011-03-15
Classification: G06K

Abstract:
1. A data carrier for contactless communication with a base station by means of an electromagnetic field generated by the base station, having an antenna coil connected to a first coil terminal and to a second coil terminal, in which antenna coil an antenna signal can be induced in operation by the electromagnetic field, and having modulation means for modulating the electromagnetic field, during successive load periods and off-load periods, with transmission data to be communicated to the base station, the electromagnetic field being load-modulated during the load periods by modifying a value of an impedance of a modulation load that is connected at least indirectly to the first coil terminal and the second coil terminal, and having detection means for detecting an item of energy information that characterizes the energy content of the antenna signal, and having comparator means for comparing the detected item of energy information that characterizes the energy content of the antenna signal with a preset item of energy information and for emitting an item of comparison information that gives a distance at which the data carrier is situated from the base station and having modification means for modifying a ratio of the duration of a load period to the duration of a succeeding off-load period as a function of the item of comparison information that gives the distance at which the data carrier is situated from the base station; wherein the modulation means are designed to modulate the electromagnetic field with a subcarrier signal, the sum of the duration of the load period and the duration of the succeeding off-load period corresponding to the length of one cycle of the subcarrier signal and wherein the ratio of the duration of the load period to the duration of the succeeding off-load period is modified such that the sum of the duration of the load period and the duration of the off-load period is kept constant and equal to the length of one cycle of the subcarrier signal.