Capacitive occupant detection system with improved isofix discrimination

A capacitive sensing device for a seat occupancy detection and classification system, including:

• a capacitive sensor that includes a plurality of electrically conductive antenna electrodes that are mutually galvanically separate from each other, the plurality of electrically conductive antenna electrodes comprising at least a first antenna electrode and at least a second antenna electrode that are arranged to mainly cover distinct portions of a seat cushion, wherein said first antenna electrode is arranged to mainly cover a central portion of the seat cushion and wherein said second antenna electrode comprises two electrode members, wherein said two electrode members are galvanically connected to each other and wherein each electrode member covers one side region of the seat cushion such that the first antenna electrode is arranged between the two electrode members of the second antenna electrode;
• an impedance measurement circuit, comprising:
• a signal voltage source that is configured for providing, with reference to a ground potential, a periodic electrical measurement signal at an output port, and
• at least one sense current measurement means that is configured to measure complex sense currents with reference to a reference voltage,
• wherein the impedance measurement circuit is electrically connected to said capacitive sensor such that each antenna electrode of the plurality of antenna electrodes is electrically connectable to the output port for receiving the electrical measurement signal,
• wherein a complex sense current is being generated by the provided periodic measurement signal in an antenna electrode of the plurality of antenna electrodes when it is connected to the signal voltage source output port,
• and
• a signal processing unit that is configured:
• to determine, with reference to the ground potential, a complex impedance of a connected antenna electrode from a measured complex sense current through the connected antenna electrode, and
• to provide output signals that are representative of the determined complex impedances.