Low consumption device for measuring a variation of a capacitance and associated method

A device for measuring a variation (ΔCX) of a capacitance (CX), comprising:

• a supply voltage (VCC).
• means for charging the capacitance (CX) on the basis of the supply voltage (VCC).
• means for discharging the capacitance (CX) into a reference capacitance (CS) in a fixed number of discharges (x),
• means for measuring a voltage (VS) across the terminals of the reference capacitance (CS).
• means for detecting a threshold of voltage (VTH) across the terminals of the reference capacitance (CS),
• characterized in that said device furthermore comprises:
• means for charging with current (IS) the reference capacitance (CS) on the basis of the supply voltage (VCC) for a duration (t), after the capacitance (CX) has been charged and discharged in a fixed number of discharges (x) into the reference capacitance (CS).
• a charge resistance (RC) for calibrating the current (IC), charging the reference capacitance (CS).
• means for:
• measuring the duration (t) with a temporal resolution (Δt), and
• computing the variation of this duration (t) with respect to a previously measured duration, this variation being representative of the variation (ΔCX) of the capacitance (CX).