Patent ID: 7783254

Claim:
A signal processing circuit for a contactless communicating communication partner device comprising: a transmitted signal path between a transmitted signal input and a transmission coil connection; a filter stage that is coupled to the transmitted signal input, the filter stage having a resonant frequency in a range of frequency values, the range of frequency values being determined by a center frequency, an upper limiting frequency and a lower limiting frequency where the center frequency is defined as the sum of an operating frequency and a modulation frequency, where the upper limiting frequency is defined as the sum of the operating frequency and of substantially half of the modulation frequency and where the lower limiting frequency is defined as the sum of the center frequency and of the negative of substantially half of the modulation frequency; a matching stage coupled to the filter stage; and a received-signal path between a received signal output and the transmission coil connection where the received-signal path branches off to the received signal output from a branch point situated in a region on the transmitted signal path that is isolated from an input side of the filter stage by a component of the filter stage and that is isolated from an output side of the matching stage by a component of the matching stage.