Detecting capacitive faults and sensitivity faults in capacitive sensors

A capacitive sensor, comprising:

• a first conductive structure;
• a second conductive structure that is counter to the first conductive structure, wherein the second conductive structure is movable relative to the first conductive structure, wherein the second conductive structure is capacitively coupled to the first conductive structure to form a first capacitor having a first capacitance that changes with a change in a distance between the first conductive structure and second conductive structure, wherein the first capacitor comprises a first terminal coupled to a bias supply voltage and a second terminal coupled to a first DC voltage set by a bias resistive circuit;
• a third conductive structure that is counter to the first conductive structure, wherein the third conductive structure is movable relative to the first conductive structure, wherein the third conductive structure is capacitively coupled to the first conductive structure to form a second capacitor having a second capacitance that changes with a change in a distance between the first conductive structure and third conductive structure, wherein the second capacitor comprises a first terminal coupled to the bias supply voltage and a second terminal coupled to a second DC voltage set by the bias resistive circuit;
• a common mode buffer configured to receive the first DC voltage, the second DC voltage, and a reference voltage, and generate a differential signal based on a difference between a common mode voltage of the first DC voltage and the second DC voltage and the reference voltage;
• a signal generator configured to apply a first electrical signal step at an input or at an output of the first capacitor and at an input or at an output of the second capacitor to induce a first voltage transient response in the first DC voltage and to induce a second voltage transient response in the second DC voltage, respectively;
• and
• a diagnostic circuit configured to detect a fault in the capacitive sensor by measuring a first time constant of the differential signal that corresponds to the first and the second voltage transient responses and detect the fault based on the first time constant.