Microelectromechanical device having an oscillating mass, and method for controlling a microelectromechanical device having an oscillating mass

A microelectromechanical device, comprising:

• a body;
• a movable mass, elastically connected to the body and oscillatably movable with respect to the body according to a degree of freedom;
• a driving device coupled to the movable mass so as to form a microelectromechanical loop and configured to keep the movable mass in oscillation with a steady operating frequency in a normal operating mode;
• and
• a start-up device activatable in a start-up operating mode and configured to compare a current oscillation frequency of a first signal correlated to oscillation of the movable mass with a reference frequency and to selectively transfer energy to the movable mass by providing the movable mass with a forcing signal packet, based on a comparison between the current oscillation frequency and the reference frequency, wherein:
• the start-up device is configured to provide the movable mass with one forcing signal packet in response to determining that the current oscillation frequency is outside an acceptable range including the reference frequency;
• the driving device is configured to provide the first signal having the current oscillation frequency;
• the start-up device comprises a start-up stage and an oscillator configured to provide a second signal having the reference frequency;
• the start-up stage is coupled to the driving device and to the oscillator for receiving respectively the first signal and the second signal and is moreover configured to compare the current oscillation frequency with the reference frequency;
• and
• the start-up stage comprises:
• a first counter coupled to the driving device and configured to receive the first signal;
• a second counter coupled to the oscillator and configured to receive the second signal;
• an enable circuit configured to enable the first counter when a counting value stored in the second counter is lower than a control value, and a disabling value when the control value is reached;
• and
• a counting comparator, configured to fetch the control value from the second counter and a final counting value from the first counter, when the second counter reaches the control value, and to compare the control value and the final counting value.

A system, comprising:

• a body;
• a mass coupled to the body, and movable with respect to the body;
• a driver capacitively coupled to the movable mass and configured to provide a signal to the movable mass so as to maintain oscillation movement of the movable mass, relative to the body, at a stable frequency;
• and
• a start-up circuit configured to supply a first quantity of energy to the movable mass, and to determine, following the supply of the first quantity of energy, whether the movable mass is oscillating with sufficient energy to continue in stable oscillation controlled by the driver, wherein:
• the start-up device is configured to compare a current oscillation frequency of a first signal correlated to oscillation of the movable mass with a reference frequency;
• the start-up device is configured to provide the movable mass with one forcing signal packet in response to determining that the current oscillation frequency is outside an acceptable range including the reference frequency;
• the driving device comprises a PLL circuit;
• and
• the start-up stage is configured to disable the PLL circuit when the current oscillation frequency is outside the acceptable range relative to the reference frequency and to enable the PLL circuit otherwise.

A method, comprising:

• sending an activation signal to a device that includes a mass that is configured to oscillate with respect to a body;
• in response to the activation signal, supplying a first quantity of energy to the movable mass;
• after supplying the first quantity of energy, determining whether the movable mass is oscillating with sufficient energy to continue in stable oscillation;
• resetting first and second counters;
• while supplying the first quantity of energy to the movable mass, incrementing the first counter at a rate that corresponds to the current oscillating frequency of the movable mass;
• while supplying the first quantity of energy to the movable mass, incrementing the second counter at a rate that corresponds to a reference frequency, until the second counter reaches a threshold value;
• and
• when the second counter reaches the threshold value, stopping the supplying the first quantity of energy to the movable mass and stopping the incrementing the first counter, and
• wherein the determining comprises, after stopping the supplying, comparing a value reached by the first counter with the threshold value.