Reading device for capacitive sensing element

A reading device for capacitive sensing element, comprising:

• a differential capacitive sensing element comprising a common node and two non-common nodes;
• a charge-to-voltage conversion circuit comprising two input terminals and an output terminal, wherein the two input terminals are connected to the two non-common nodes, respectively, and the charge-to-voltage conversion circuit is configured to read a charge change of the differential capacitive sensing element and convert the charge change into a voltage signal;
• a modulation signal generator, connected to the common node of the differential capacitive sensing element, configured to output a modulation signal to the common node;
• a first offset capacitor with one end connected to one of the two non-common nodes;
• a second offset capacitor with one end connected to another one of the two non-common nodes;
• a demodulator connected to the output terminal of the charge-to-voltage conversion circuit and the phase-locked loop;
• a low-pass filter connected to the demodulator;
• a phase-locked loop, connected to the output terminal of the charge-to-voltage conversion circuit and the demodulator, configured to lock a phase of the modulation signal in response to a characteristic time delay inherent to the phase-locked loop, wherein the demodulator is configured to demodulate a combined signal comprising the locked modulation signal and the voltage signal.