Servo-controlled pendular micro-sensor

A method for providing an electrostatic return force between a mobile electrode and a fixed electrode for a micro-sensor measuring a physical quantity, said mobile electrode being integral with a pendular element sensitive to said physical quantity, comprising the step of applying to said electrodes a voltage having a zero mean value so as to impart to the electrodes an electrostatic return force opposing a force acting upon the electrodes by the physical quantity, wherein

• said voltage is a periodic voltage having a frequency higher than a cut-off frequency of the pendular element;
• wherein said method is for servo-controlling through electrostatic forces a pendular element of a micro-sensor including:
• at least one first and one second electrode pair each containing a mobile electrode integral with said pendular element, and a fixed electrode facing said mobile electrode, and
• a system for detecting the displacements of said pendular element providing a control signal for the servo-control operation to be achieved wherein a first control voltage and a second control voltage are respectively applied on said electrode pairs, wherein
• said first and second control voltages have the same frequency, and
• the difference of the squared respective amplitudes of said first and second control voltages is the product of a first term independent of said control signal by a second term proportional to said control signal.

A micro-sensor controlled through electrostatic forces, comprising:

• a pendular element disposed so as to respond to a force representative of a physical quantity to be measured;
• at least one first and one second electrode pair each including a mobile electrode associated with said pendular element and one fixed electrode facing each of said mobile electrodes;
• an assembly of switches in circuit with at least two d.c. voltage sources of opposite polarity;
• an integrating circuit whose input is received from said electrode pairs through said assembly of switches and whose output is applied to the input of a digital modulator of the sigma-delta type through a filter, said digital modulator providing a logic signal the mean value of which is modulated as a function of the output voltage of said integrating circuit;
• a digital circuit for sequencing and controlling said switch assembly to which is applied said logical signal, said digital circuit and said switch assembly being arranged for:
• (a) during electrostatic control phases of said pendular element:
• alternatively connecting at least one electrode of an electrode pair selected as a function of the value of said logic signal, to each of said d.c. voltage sources, and
• alternating the d.c. voltage source, connected to said at least one electrode of a selected electrode pair, several times during a control phase, or several times during several control phases;
• (b) during the phases of detection of the position of said pendular element, following each control phase:
• charging the capacitances of said electrode pairs through said source voltages, then simultaneously discharging said capacitances in said integrating circuit (67), with respective currents of opposite polarity.

A micro-sensor for measuring a physical quantity, comprising:

• at least one fixed electrode;
• a pendular element that is sensitive to the physical quantity to be measured;
• at least one mobile electrode movable with said pendular element and facing said at least one fixed electrode;
• and
• means for applying to said fixed and mobile electrodes a return voltage produced by an external voltage source, said return voltage being of zero mean value and producing at the electrodes an electrostatic return force opposing a force acting upon the electrodes by the physical quantity.