MEMS microphone and method for self-calibration of the MEMS microphone

1. A method for recalibrating a capacitively operating MEMS microphone,

wherein the BIAS voltage present at a MEMS microphone is increased step by step in order to ascertain the present pull-in voltage VP a and the corresponding pull-in capacitance CP a or the change in capacitance associated with the present increase in the bias voltage at a pull-in point of the MEMS microphone,

wherein from the deviation of the present pull-in point from the values of a first pull-in point, said values being determined after an end test and stored in an internal memory of the MEMS microphone, and the values CS 1 , VS 1 of a first operating point and a recalibrated bias voltage VS new is determined and set in order thereby to bring a sensitivity of the MEMS microphone closer again to a desired sensitivity of the MEMS microphone originally set at the first operating point.

2. The method according to claim 1 ,

wherein the end test is carried out directly after the production of the MEMS microphone, comprising

ascertaining the first pull-in voltage VP 1 ,

setting the operating point in accordance with the desired sensitivity of the MEMS microphone by varying the bias voltage at a first operating voltage VS 1 ,

ascertaining the first pull-in capacitance CP 1 of the MEMS microphone at the first pull-in voltage VP 1 and the first operating capacitance CS 1 at the first operating voltage VS 1 or alternatively the corresponding changes in the observed value, the change in capacitance associated with the present increase in the bias voltage at the pull-in point,

storing the values CS 1 , VS 1 , CP 1 and VP 1 in an internal memory of the MEMS microphone,

wherein a first recalibration is carried out after the installation of the MEMS microphone in a circuit environment.

3. The method according to claim 2 , wherein the recalibrated bias voltage VS new is calculated according to the formula

VS new =VS 1 −( VP 1 −VP 2 )+( CP 1 −CP 2 )*( VP 3 −VP 2 )/( CP 1 −CP 2 ).

4. The method according to claim 2 , wherein the recalibration is carried out repeatedly, wherein the values CS 1 , VS 1 , CP 1 and VP 1 determined after the end test are used in each case as reference.

5. The method according to claim 1 , wherein the desired sensitivity and also the values for the first operating point and the first pull-in point are determined in a defined acoustic environment.

6. The method according to claim 1 ,

wherein the MEMS microphone carries out a recalibration

automatically according to specific rules depending on the acoustic or thermal stress loading of the MEMS microphone, or

automatically when a specific time interval has elapsed, or

if the recalibration is initiated manually by a user, or

after every restart of the device in which the microphone is installed.

7. The method according to claim 1 , wherein both in the end test and during the recalibration the bias voltage is increased in steps until the pull-in point is reached, and wherein the respective capacitance or change in capacitance is determined during each step, wherein, when the pull-in point is reached, the capacitance of the MEMS microphone reaches a high value or makes a jump and the values used and stored as pull-in voltage VP a and pull-in capacitance CP a or change in pull-in capacitance are the last values in each case before the pull-in point is reached.

8. A MEMS microphone with self-calibration device,

comprising a capacitively operating MEMS sensor, to which a bias voltage is able to be applied, and

comprising an ASIC connected to the MEMS sensor,

wherein the ASIC is designed for the following steps

a) carrying out a step by step increase in the bias voltage,

b) determining the change in capacitance or the capacitance that forms in each case at the MEMS sensor,

c) ascertaining a present pull-in point by way of the capacitance measurement,

d) storing the measurement values for bias voltage and associated capacitance or change in capacitance at a first pull-in point ascertained at an earlier first measurement of the MEMS sensor in an internal memory,

e) carrying out an algorithm for calculating a recalibrated bias voltage VS new using the presently determined measurement values and the already stored measurement values measured at the first pull-in point,

f) applying the recalibrated BIAS voltage VS new to the MEMS microphone.