Detection circuit using a differential capacitive sensor with input-common-mode control in a sense interface

An interface circuit, for a detection circuit that includes a differential capacitive sensor, the interface circuit comprising:

• a first sense input and a second sense input configured for electrical connection to said differential capacitive sensor;
• a sense amplifier connected at input to said first sense input and said second sense input and configured to supply an output signal related to a capacitive unbalancing of said differential capacitive sensor;
• and
• a totally passive first common-mode control circuit connected to said first sense input and said second sense input, and configured to control a common-mode electrical quantity present on said first sense input and said second sense input, wherein said first common-mode control circuit comprises generating means for generating a balancing electrical quantity such as to balance said common-mode electrical quantity;
• said balancing electrical quantity being substantially equal in absolute value and opposite in sign to said common-mode electrical quantity.

An electronic device comprising:

• a processor;
• and
• a detection circuit coupled to the processor and including:
• a differential capacitive sensor having an input and differential first and second outputs;
• a first signal generator coupled to provide a read signal to the input of the differential capacitive sensor;
• and
• an interface circuit having a first sense input and a second sense input electrically connected to the first and second outputs of said differential capacitive sensor, respectively, said interface circuit including:
• a sense amplifier connected at input to said first sense input and said second sense input and configured to supply an output signal related to a capacitive unbalancing of said differential capacitive sensor;
• a passive first common-mode control circuit connected to said first sense input and said second sense input, and configured to control a common-mode electrical quantity present on said first sense input and said second sense input, wherein said first common-mode control circuit comprises first and second control capacitances coupled to the first and second sense inputs;
• and
• a second signal generator configured to provide a driving signal to the first and second control capacitances, the driving signal having a control amplitude variation opposite to a read amplitude variation of the read signal.

A method for reading a differential capacitive sensor through an interface circuit provided with a first sense input and a second sense input electrically connected to said differential capacitive sensor, comprising:

• providing a read signal to an input of the differential capacitive sensor;
• sensing a capacitive unbalancing of said differential capacitive sensor;
• generating an output signal related to said capacitive unbalancing;
• and
• controlling, using a passive first common-mode control circuit, a common-mode electrical quantity present on said first sense input and said second sense input, the controlling including providing a drive signal to a capacitive circuit coupled to the first and second sense inputs, the drive signal having a control amplitude variation opposite to a read amplitude variation of the read signal.