Patent Publication Number: US-2022236299-A1

Title: Microelectromechanical acceleration sensor system

Description:
CROSS REFERENCE 
     The present application claims the benefit under 35 U.S.C. § 119 of German Patent Application No. DE 10 2021 200 764.3 filed on Jan. 28, 2021, which is expressly incorporated herein by reference in its entirety. 
     FIELD 
     The present invention relates to a microelectromechanical acceleration sensor system and an electronic device including a microelectromechanical acceleration sensor system. 
     BACKGROUND INFORMATION 
     So-called in-ear headphones that are worn wirelessly directly in the ear are a very significant technology trend right now. In one possible technical specific embodiment, these in-ear headphones have multiple microphones and acceleration sensors. The acceleration sensors must be operable in such a way that measured signals of the sensors do not generate perceptible tones. Due to their high performance and good signal-to-noise ratio, sigma-delta analog-to-digital converters (SD-ADCs) are increasingly used in this field. In sigma-delta analog-to-digital converters, the development of an undesirable so-called idle tone behavior is a known problem, however, in the case of which oscillations that may be significantly above the general noise background signal of the sensor and may generate a tone that is audible for the human ear may be measurable when an idle signal, i.e., a signal having a disappearing signal intensity, is applied in the noise power spectrum of the SD-ADC. 
     SUMMARY 
     It is an object of the present invention to provide an improved microelectromechanical acceleration sensor system and an electronic device including a microelectromechanical acceleration sensor system. 
     This object may be achieved by the microelectromechanical acceleration sensor system and by the electronic device in accordance with example embodiments of the present invention. Advantageous embodiments of the present invention are disclosed herein. 
     According to one aspect of the present invention, a microelectromechanical acceleration sensor system including a microelectromechanical acceleration sensor element for detecting acceleration values acting on the acceleration sensor element, a sigma-delta analog-to-digital converter for converting the analog output signals of the acceleration sensor element into digital output signals of the sensor system, and a first signal generator element and a second signal generator element are provided, the first signal generator element being connected between the acceleration sensor element and the analog-to-digital converter and being configured to apply a predetermined signal value to the output signals of the acceleration sensor element, the signal value of the first signal generator element corresponding to an acceleration value that is greater than the average gravity acceleration, and the second signal generator element being connected in a signal processing direction downstream from the analog-to-digital converter and being configured to correct the digital output signals of the analog-to-digital converter by the signal value of the first signal generator element. 
     In this way, the technical advantage may be achieved that an improved microelectromechanical acceleration sensor system may be provided, in which an idle tone of a sigma-delta analog-to-digital converter may be prevented. Via a first signal generator element a signal value that corresponds to an acceleration value that is greater than the average gravity acceleration is applied to the output signals of an acceleration sensor element of the microelectromechanical acceleration sensor system. By applying the above-mentioned signal value to the output signals of the acceleration sensor element it is achieved that in the resting position of the acceleration sensor system, in which merely the gravity acceleration acts on the acceleration sensor system, it is prevented that a zero signal is output by the acceleration sensor element to the analog-to-digital converter. By applying the signal value to the output signals of the acceleration sensor element, signals that are different from zero at any given time are output to the analog-to-digital converter, so that an idle tone of the analog-to-digital converter is prevented that occurs only if the analog-to-digital converter is in an idle state, in which a zero signal acts on the analog-to-digital converter. Due to the fact that the signal value is greater than the average gravity acceleration, it is ensured in any resting position of the acceleration sensor system that signals that are different from zero act on the analog-to-digital converter. 
     According to one specific embodiment, the signal value corresponds to twice the gravity acceleration. 
     In this way, the technical advantage may be achieved that the signals acting on the analog-to-digital converter have a preferably large distance to the zero signal, so that it may be ensured with increased reliability that the analog-to-digital converter is not in the idle state and thus does not produce an idle tone. 
     According to one specific embodiment of the present invention, the first signal generator element is configured to apply the predetermined signal value exclusively to the output signals of the acceleration sensor element that correspond to the zero signal. 
     In this way, the technical advantage may be achieved that a precise analog-to-digital conversion may be achieved in that the output signals are exclusively applied if an idle tone is to be suspected from the analog-to-digital converter. For the output signals of the acceleration sensor element that are different from zero no application takes place. In this way, errors due to application may be prevented, thus contributing to an increased precision of the acceleration sensor system. 
     According to one specific embodiment of the present invention, the acceleration sensor element is designed as a three-dimensional acceleration sensor element including three measuring channels, the first signal generator element being configured to apply the signal value to the output signals of each measuring channel of the acceleration sensor element and the second signal generator element being configured to correct the digital output signals of the analog-to-digital converter by the signal value for each measuring channel. 
     In this way, the technical advantage may be achieved that for any arbitrary position of the acceleration sensor system an application of the predetermined signal value to the particular output values of the acceleration sensor element is made possible and it may thus be prevented for any position of the acceleration sensor system that the analog-to-digital converter produces an idle tone in the idle state. 
     According to one specific embodiment of the present invention, the signal value includes for each measuring channel of the acceleration sensor a partial signal value, each partial signal value corresponding to an acceleration value that is greater than the average gravity acceleration in a direction in space of the particular measuring channel and the partial signal values of different measuring channels having different values. 
     In this way, the technical advantage may be achieved that for each measuring channel of the acceleration sensor element an application of the predetermined partial signal value to the particular output values is made possible and it may thus be ensured that an idle tone of the analog-to-digital converter, as a result of a zero signal acting on it, may be prevented in any arbitrary position or orientation of the acceleration sensor system. 
     According to one specific embodiment of the present invention, the first signal generator element and the second signal generator element are designed as evaluation circuits, in particular as application-specific integrated circuits (ASICs). 
     In this way, the technical advantage may be achieved that a technically simple implementation of the first and the second signal generator elements is made possible. 
     According to one specific embodiment of the present invention, the acceleration sensor element is designed as a capacitive acceleration sensor element. 
     In this way, the technical advantage may be achieved that a technically robust and precise acceleration sensor element may be provided. 
     According to one specific embodiment of the present invention, the sensor system further includes a capacitance-to-voltage converter, the capacitance-to-voltage converter being connected between the first signal generator element and the analog-to-digital converter and being configured to convert the capacitive output signals of the acceleration sensor element into voltage signals. 
     In this way, the technical advantage may be achieved that a precise processing of the output signals of the capacitive acceleration sensor element is made possible. 
     According to one specific embodiment of the present invention, the sensor system is employable as a microphone. 
     In this way, the technical advantage may be achieved that a preferably wide use of the sensor system according to the present invention is made possible. 
     According to a second aspect of the present invention, an electronic device including a microelectromechanical acceleration sensor system according to one of the preceding specific embodiments is provided. 
     In this way, the technical advantage may be achieved that an electronic device including a microelectromechanical acceleration sensor system having the above-mentioned technical advantages may be provided. The electronic device may be an in-ear headphone, for example. 
     Exemplary embodiments of the present invention are elucidated based on the figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic illustration of a microelectromechanical acceleration sensor system according to one specific embodiment. 
         FIG. 2  shows a schematic illustration of an electronic device including a microelectromechanical sensor system according to one specific embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENT 
       FIG. 1  shows a schematic illustration of a microelectromechanical acceleration sensor system  100  according to one specific embodiment of the present invention. 
       FIG. 1  shows a sequence diagram of a microelectromechanical acceleration sensor system  100  according to the present invention. In the shown specific embodiment, microelectromechanical acceleration sensor system  100  includes a microelectromechanical acceleration sensor element  101 , a sigma-delta analog-to-digital converter  103 , a first signal generator element  105 , a second signal generator element  107 , and a capacitance-to-voltage converter  109 . First signal generator element  105  is connected between microelectromechanical acceleration sensor element  101  and sigma-delta analog-to-digital converter  103 . Second signal generator element  107  is connected in a signal processing direction D downstream from sigma-delta analog-to-digital converter  103 . In contrast, capacitance-to-voltage converter  109  is connected between first signal generator element  105  and sigma-delta analog-to-digital converter  103 . 
     In the shown specific embodiment, microelectromechanical acceleration sensor element  101  is designed as a capacitive acceleration sensor element and is configured to detect accelerations of microelectromechanical acceleration sensor system  100  and to output corresponding capacitance signals as output signals to first signal generator element  105 . 
     First signal generator element  105  is configured to apply a predetermined signal value to the output signals of acceleration sensor element  101 . In this case, the predetermined signal value corresponds to an acceleration value that is greater than the average gravity acceleration. By applying the predetermined signal value to the output signals of acceleration sensor element  101  it is achieved that in the case of a resting position of microelectromechanical acceleration sensor system  100 , in which microelectromechanical acceleration sensor system  100  is not accelerated and in which the gravity acceleration exclusively acts on microelectromechanical acceleration sensor system  100 , the output signals of acceleration sensor element  101  have a value different than zero. 
     The output signals of acceleration sensor element  101  acted on by the predetermined signal value are transferred from first signal generator element  105  to capacitance-to-voltage converter  109 . Capacitance-to-voltage converter  109  is configured to convert the capacitive output signals of capacitive acceleration sensor element  101  into voltage signals. The voltage signals converted by capacitance-to-voltage converter  109  are subsequently forwarded to sigma-delta analog-to-digital converter  103 . 
     Sigma-delta analog-to-digital converter  103  is configured to convert the analog output signals of acceleration sensor element  101  into digital output signals of microelectromechanical acceleration sensor system  100 . Sigma-delta analog-to-digital converter  103  is configured to carry out the analog-to-digital conversion of the output signals of acceleration sensor element  101  according to a sigma-delta modulation of the analog output signals. In the present specific embodiment, sigma-delta analog-to-digital converter  103  may be a conventional sigma-delta analog-to-digital converter from the related art. 
     By applying the predetermined signal value to the output signals of acceleration sensor element  101  via first signal generator element  105 , the signals of acceleration sensor element  101  acting on sigma-delta analog-to-digital converter  103  as input signals have a value different from zero at any given time. Even in the resting position of acceleration sensor system  100 , in which acceleration sensor system  100  is not accelerated and the gravity acceleration exclusively acts on acceleration sensor system  100 , the signals acting on sigma-delta analog-to-digital converter  103  have a value different from zero. The signals acting on sigma-delta analog-to-digital converter  103  have as their minimum value at least one difference value between the average gravity acceleration acting on microelectromechanical acceleration sensor system  100  in the resting position and the predetermined signal value that is greater than the average gravity acceleration according to the present invention. As a result of the input signals that are different from zero at any given time and that act on sigma-delta analog-to-digital converter  103  it may be prevented that sigma-delta analog-to-digital converter  103  switches into the idle state, in which exclusively zero signals act on sigma-delta analog-to-digital converter  103 . By preventing sigma-delta analog-to-digital converter  103  from switching into the idle state as a result of the zero signals acting on it, it is moreover prevented that an idle tone is produced by sigma-delta analog-to-digital converter  103 . Since an idle tone of this type is disturbing to a use of microelectromechanical acceleration sensor system  100  in an in-ear headphone, for which an undesirable noise formation is to be avoided, an improved microelectromechanical acceleration sensor system  100  may be provided. 
     With the aid of second signal generator element  107 , the output signals of acceleration sensor element  101  converted by sigma-delta analog-to-digital converter  103  into digital signals are corrected by the signal value applied by first signal generator element  105 . The digital output signals output by microelectromechanical acceleration sensor system  100  thus do not have an additional signal value, so that in the not accelerated resting position of microelectromechanical acceleration sensor system  100 , same correctly outputs an acceleration value of zero. The measurement precision of microelectromechanical acceleration sensor system  100  is thus not impaired by the output signals of acceleration sensor element  101  being applied via first signal generator element  105  and the acceleration values output by microelectromechanical acceleration sensor system  100  correspond to those acceleration values measured by acceleration sensor element  101 . The application of the predetermined signal value to the output signals of acceleration sensor element  101  via first signal generator element  105  is used exclusively to prevent an idle tone by sigma-delta analog-to-digital converter  103 . 
     According to one specific embodiment, the predetermined signal value of first signal generator element  105  corresponds to twice the gravity acceleration. Alternatively thereto, the predetermined signal value may correspond to any other arbitrary multiple of the gravity acceleration. 
     According to one specific embodiment, acceleration sensor element  101  is designed as a three-dimensional acceleration sensor element including three measuring channels. In this specific embodiment, first signal generator element  105  is configured to apply a corresponding signal value to the output signals of each measuring channel of acceleration sensor element  101 . Second signal generator element  107  is correspondingly configured to correct the digital output signals of sigma-delta analog-to-digital converter  103  by the corresponding signal value for each measuring channel of the three-dimensional acceleration sensor element. 
     According to one specific embodiment, the signal values, which are applied to the output signals of each measuring channel of acceleration sensor element  101 , may have different values. Alternatively thereto, the signal values, which are applied to the output signals of each measuring channel of acceleration sensor element  101 , may have an identical value. 
     According to one specific embodiment, first and second signal generator elements  105 ,  107  may be designed as application-specific integrated circuits (ASICs). 
     According to one specific embodiment, microelectromechanical acceleration sensor system  100  is employable as a microphone. In particular, microelectromechanical acceleration sensor system  100  may be used in an in-ear headphone. 
     According to one specific embodiment, first signal generator element  105  may be designed to apply the predetermined signal value to any output values of acceleration sensor element  101 . Alternatively thereto, first signal generator element  105  may be designed to apply a corresponding signal value exclusively to output signals of acceleration sensor element  101  that correspond to the zero signal. Second signal generator element  107  may have a similar design for the purpose of correcting the signal values of first signal generator element  105  for all output signals of sigma-delta analog-to-digital converter  103  or of carrying out a correction of this type exclusively for the output signals of sigma-delta analog-to-digital converter  103  that correspond to the zero signal of acceleration sensor element  101 . 
       FIG. 2  shows a schematic illustration of an electronic device  200  including a microelectromechanical sensor system  100  according to one specific embodiment. 
     In the shown specific embodiment, electronic device  200  includes in addition to acceleration sensor system  100  a control unit  201 , which is connected to acceleration sensor system  100  via data technology and is configured to process the sensor values of acceleration sensor system  100 . The electronic device may be a consumer electronic device, for example. For example, the electronic device may be an in-ear headphone. The present invention is, however, not intended to be limited thereto.