| 摘要 |
A combined seat heater and capacitive occupancy sensor comprises a heating element (10) connected between a first (21) and a second (22) node, and a capacitive sensing network connected to the heating element to apply an oscillating voltage thereto and to derive the capacitive load of the heating element. A common mode choke (16) connects the first and second node to a third (23) and fourth (24) node, respectively. The capacitive sensing network comprises an oscillator (28), AC-coupled to the third and/or the fourth node to drive oscillating voltage into that node, and a transimpedance amplifier (32), which has a first input to receive the oscillating voltage as reference voltage and a second input operatively connected to the heating element. The transimpedance amplifier maintains a voltage on its second input equal to the reference voltage by driving a current into the second input. An output signal (44) indicates the AC component of the current driven into the second input.
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