Method and circuit for detecting movements through micro-electric-mechanical sensors, compensating parasitic capacitances and spurious movements

A method for detecting a movement of a micro-electric-mechanical sensor having a fixed body and a moving mass, forming first and second detection capacitors, connected to a common node and to first and second detection nodes, respectively, and having a common detection rest capacitance and a capacitive unbalance following a movement of said moving mass;

• the method comprising:
• feeding said common node with a detection voltage;
• maintaining said first and the second detection node at a constant common mode voltage through a feedback voltage;
• detecting an output quantity related to said capacitive unbalance;
• and_feeding said common node with a compensating electric quantity, inversely proportional to said common detection rest capacitance in at least one predetermined interval.

A circuit for detecting movements through a micro-electric-mechanical sensor having a fixed body and a moving mass, forming first and second detection capacitors, connected to a common node and to first and second detection nodes, respectively and having a common detection rest capacitance;

• the circuit comprising:
• detection amplifying means, having inputs connected to said first and second detection capacitor, respectively and an output supplying an output voltage related to a voltage present on said common node;
• a feedback stage, connected to said first and second detection node and generating a feedback voltage, maintaining said first and second detection node at a constant common mode voltage;
• and
• a compensating stage, receiving said feedback voltage and feeding said common node with a compensating electric quantity, inversely proportional to said common detection rest capacitance in at least one predetermined interval.

A method for compensating for effects of spurious movements of an electro-mechanical sensor in a detection circuit, comprising:

• comparing capacitances of first and second detection capacitors formed between a moving mass of the electro-mechanical sensor and a fixed body of the sensor, wherein the moving mass is a common node of the first and second capacitors;
• measuring a common detection capacitance of the sensor;
• and
• introducing a compensation voltage, inversely proportionate to the common detection capacitance, to the common node of the sensor.

A device, comprising:

• an electro-mechanical sensor having a movable mass and a fixed body, configured to detect motion in a first axis and including first and second detection capacitors formed between the movable mass and the fixed body, the movable mass being a common node of the first and second capacitors;
• a first circuit, configured to compare capacitances of the first and second capacitors and provide an output voltage proportionate to a difference of the capacitances;
• and
• a second circuit, configured to supply a compensation voltage to the common node, inversely proportionate to a common capacitance of the sensor.

A method for operating an electro-mechanical sensor in a detection circuit, comprising:

• detecting a change in capacitance of first and second detection capacitors formed between a movable mass of the sensor and a fixed body of the sensor;
• providing, during the detecting step, an output value proportionate to a capacitive unbalance between the first and second detection capacitors;
• storing, during the detecting step, a value corresponding to a on detection capacitance of the sensor;
• and
• compensating, in the detection circuit, and during the detecting step, for changes in the common detection capacitance.