MEMS speaker device with an electronic test circuit

A method, comprising:

• testing a microelectromechanical system speaker device, the testing including:
• operating at least one elementary unit in a first operating period and a second operating period with a driving device, said elementary unit including a membrane, a top plate, and a bottom plate, the membrane being arranged between the top plate and the bottom plate and forming a first capacitor and a second capacitor, respectively with the top plate and with the bottom plate, the operating including:
• moving the membrane into a first position, in which the membrane is close to the bottom plate in the first operating period;
• and
• moving the membrane into a second position, in which the membrane is close to the top plate during a second operating period;
• after the first operating period that corresponds to the membrane being in the first position, generating a first measurement signal that is proportional to a capacitance of a first one of said first and second capacitors;
• after the second operating period that corresponds to the membrane being in the second position, generating a second measurement signal that is proportional to the capacitance of said first one of said first and second capacitors;
• and
• detecting a mobility of the membrane in a direction of the top plate or the bottom plate that forms said first one of said first and second capacitors, said detecting the mobility including:
• comparing said first and second measurement signals with a first electrical reference quantity;
• and
• detecting that, if the capacitance is from the first capacitor, the first measurement signal does not exceed the first electrical reference quantity and the second measurement signal exceeds said first electrical reference quantity.

A system, comprising:

• a microelectromechanical system speaker, including:
• a membrane;
• a first plate;
• and
• a second plate, the membrane being between the first plate and the second plate, the membrane forming a first capacitor with the first plate;
• a driving circuit configured to move the membrane in to a first position or a second position, the membrane being closer to the first plate in the first position, the membrane is closer to the second plate in the second position;
• and
• a test circuit including:
• a measuring circuit configured to generate a first measurement signal that is proportional to a capacitance of the first capacitor in response to the membrane being moved in to the first position by the driving circuit, and generate a second measurement signal that is proportional to a capacitance of the first capacitor in response to the membrane being moved in to the second position by the driving circuit;
• and
• a comparator circuit configured to determine whether the first and second measurement signals exceeds an electrical reference quantity, the comparator circuit configured to detect that, if the capacitance is from the first capacitor, the first measurement signal does not exceed the electrical reference quantity and the second measurement signal exceeds the electrical reference quantity.