Image Number 3 for United States Patent #8130080.
The present invention relates to a switching device for generating a switch signal, a reading device with the switching device and a method for the communication between a reading device and a transponder (T). The switching device includes an antenna (4), which with the help of an adapter circuit (AN) is adapted to a given resistance, and a measuring bridge (1), which includes two voltage dividers connected in parallel. The resistance acts in one of the voltage dividers and in the case of a change of the resistance the measuring bridge (1) generates the switch signal. This means when a transponder reaches the detection range of a reading device having the switching device, an additional impedance is coupled in, which acts on the measuring bridge (1). This change is recognized and leads to the generation of the switch signal.