Abstract:
The present disclosure relates to a microphone, and more particularly, to a microphone capable of improving a signal-to-noise ratio (SNR) by receiving a sound pressure through at least two acoustic sensing modules. 
     According to an exemplary form of the present disclosure, a microphone includes first and second acoustic sensing modules including a diaphragm vibrated by a sound pressure introduced from the outside and a fixed membrane spaced apart from the diaphragm, and a signal processing module receiving first and second capacitance signals from each of the first and second acoustic sensing modules and removing and outputting noises included in the first and second capacitance signals based on the first and second capacitance signals.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Korean Patent Application No. 10-2015-0121846, filed on Aug. 28, 2015, the entire contents of which is incorporated herein by reference. 
     FIELD 
     The present disclosure relates to a microphone, and more particularly, to a microphone capable of improving a signal-to-noise ratio (SNR) by receiving a sound pressure through at least two acoustic sensing modules. 
     BACKGROUND 
     A microphone which has been widely used in mobile devices, acoustic devices, vehicles, or the like senses a sound, that is, a sound wave, and converts the sound into a physical value or an electrical value. The converted signal is processed to be a signal which may be captured by a person or a machine. 
     Since the microphone receives a natural signal such as the sound wave, analog signal processing is essentially performed for signal conversion. Performance of a circuit for processing an analog signal may directly affect the overall performance of the microphone. In particular, the microphone receives a wide frequency range of a signal due to its characteristics and therefore noise characteristics are very important. 
     The microphone has a thin film applied with a pressure due to the sound pressure and thus an interval between two electrodes is changed. As a result, since capacitance is changed, the microphone converts a change amount of the capacitance into a voltage output using a buffer and outputs a digital signal. The typical microphone receives a single input signal and therefore outputs power supply noise and noise included in a bias voltage through the buffer as they are, such that sensitivity of the microphone may deteriorate. As a result, a high sensitivity microphone may show inappropriate performance. 
     Further, a signal-to-noise ratio (SNR) of the existing microphone applied to a vehicle is not good, such that customer dissatisfaction with a speech recognition rate or handsfree performance has been raised. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
     SUMMARY 
     The present disclosure has been made in an effort to provide a microphone capable of processing a signal by receiving a sound pressure through at least two acoustic sensing modules. 
     Further, the present disclosure has been made in an effort to provide a microphone capable of increasing an output signal and improving a signal-to-noise ratio. 
     An exemplary form of the present disclosure provides a microphone including: first and second acoustic sensing modules including a diaphragm vibrated by a sound pressure introduced from the outside and a fixed membrane spaced apart from the diaphragm, and a signal processing module receiving first and second capacitance signals from each of the first and second acoustic sensing modules and removing and outputting noises included in the first and second capacitance signals based on the first and second capacitance signals. 
     The signal processing module may include an amplifier amplifying the first and second capacitance signals and removing the noises included in the first and second capacitance signals to output an output signal. 
     The amplifier may include: a non-inverting input terminal connected to the first acoustic sensing module and receiving the first capacitance signal including noise from the first acoustic sensing module, an inverting input terminal connected to the second acoustic sensing module and receiving the second capacitance signal including noise from the second acoustic sensing module, and an output terminal removing the noises included in the first and second capacitance signals and amplifying the first and second capacitance signals to output an output signal. 
     Each of the first and second capacitance signals may be determined by at least one of sensitivities and capacitances of the first and second acoustic sensing modules, a sound pressure, noise, and a bias. 
     The sensitivity of the first acoustic sensing module and the sensitivity of the second acoustic sensing module may be equal to each other, and the capacitance of the first acoustic sensing module and the capacitance of the second acoustic sensing module may be equal to each other. 
     The output signal may be generated by performing a subtraction operation on the first capacitance signal and the second capacitance signal. 
     Another form of the present disclosure provides a microphone, including: first and second acoustic sensing modules outputting first and second capacitance signals for capacitance changed by a sound pressure introduced from the outside, and a signal processing module receiving the first and second capacitance signals from each of the first and second acoustic sensing modules and including an amplifier amplifying the first and second capacitance signals to output an output signal, in which the amplifier may include a non-inverting input terminal electrically connected to the first acoustic sensing module and receiving the first capacitance signal from the first acoustic sensing module, an inverting input terminal electrically connected to the second acoustic sensing module and receiving the second capacitance signal from the second acoustic sensing module, and an output terminal removing the noises included in the first and second capacitance signals and amplifying and outputting the first and second capacitance signals from which the noises are removed. 
     According to a form of the present disclosure, it is possible to remove the noise introduced from the outside by receiving the sound pressure through the at least two acoustic sensing modules. 
     Further, according to a form of the present disclosure, it is possible to improving the speech recognition rate or the handsfree performance by increasing the output signal and improving the signal-to-noise ratio. 
     Further, the effects which may be obtained or predicted by the exemplary form of the present disclosure will be directly or implicitly disclosed in the detailed description of the exemplary forms of the present disclosure. That is, various effects which are predicted by the exemplary forms of the present disclosure will be disclosed in the detailed description to be described below. 
    
    
     
       DRAWINGS 
         FIG. 1  is a diagram schematically illustrating a microphone. 
         FIG. 2  is a diagram illustrating a first acoustic sensing module. 
         FIG. 3  is a circuit diagram illustrating the microphone. 
         FIG. 4  is a diagram illustrating a simulation result of the microphone. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, an operation principle of a microphone according to an exemplary form of the present disclosure will be described with reference to the accompanying drawings. However, the following illustrated drawings and the detailed description to be described below relate to one exemplary form among several exemplary forms for effectively describing features of the present disclosure. Therefore, the present disclosure is not limited to only the following drawings and the description. 
     In describing exemplary forms of the present disclosure, well-known functions or constructions will not be described in detail since they may unnecessarily obscure the understanding of the present disclosure. Further, the following terminologies are defined in consideration of the functions in the present disclosure, and may be construed in different ways by the intention of users and operators or practice. Therefore, the definitions thereof should be construed based on the contents throughout the specification. 
     Further, for efficiently describing the technical core features of the present disclosure, terms will be appropriately changed, integrated, or separately used in the following exemplary forms to be clearly understood by those skilled in the art, but the present disclosure is never limited thereto. 
     Hereinafter, an exemplary form of the present disclosure will be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a diagram schematically illustrating a microphone. 
     Referring to  FIG. 1 , a microphone  50  includes a first acoustic sensing module  100 , a second acoustic sensing module  200 , and a signal processing module  300 . 
     The first acoustic sensing module  100  and the second acoustic sensing module  200  are vibrated by a sound pressure depending on an acoustic signal input from the outside to generate an electrical signal. 
     The first acoustic sensing module  100  and the second acoustic sensing module  200  may be an acoustic sensing module using a microelectromechanical systems (MEMS) technology. 
     The first acoustic sensing module  100  and the second acoustic sensing module  200  include a fixed membrane  160  and a diaphragm  130  which form a capacitor. When the sound pressure depending on the acoustic signal is applied to the diaphragm  130  from the outside, an interval between the fixed membrane  160  and the diaphragm  130  is changed and capacitance of the capacitor is changed correspondingly. In this case, the first acoustic sensing module  100  and the second acoustic sensing module  200  output a varying capacitance signal to the signal processing module  300 . 
     A structure of the first acoustic sensing module  100  will be described with reference to  FIG. 2 . 
     The signal processing module  300  is connected to the first acoustic sensing module  100  and the second acoustic sensing module  200 . The signal processing module  300  receives a first capacitance signal from the first acoustic sensing module  100  and receives a second capacitance signal from the second acoustic sensing module  200 . The signal processing module  300  amplifies and outputs the first capacitance signal and the second capacitance signal and therefore may sense the sound pressure from the outside. 
     The signal processing module  300  may be an application specific integrated circuit (ASIC). 
     The signal processing module  300  will be described in more detail with reference to  FIG. 3 . 
       FIG. 2  is a diagram illustrating a first acoustic sensing module. 
     Referring to  FIG. 2 , the first acoustic sensing module  100  includes a substrate  110 , the diaphragm  130 , and the fixed membrane  160 . 
     The substrate  110  may be made of silicon and is provided with a through hole  115 . 
     An oxide film  120  is disposed on the substrate  110 . That is, the oxide film  120  may be disposed between the substrate  110  and the diaphragm  130 . 
     The diaphragm  130  is disposed on the oxide film  120  and covers the through hole  115  formed on the substrate  110 . A portion of the diaphragm  130  is exposed through the through hole  115 , and the portion of the diaphragm  130  exposed through the through hole  115  is vibrated by the sound pressure introduced from the outside. 
     The diaphragm  130  may have a circular shape and includes a plurality of slots  135 . The slot  135  is disposed on the through hole  115 . 
     A first pad  140  is disposed on the diaphragm  130 . The first pad  140  is connected to the signal processing module  300 . 
     A support layer  150  is disposed at an edge portion of the diaphragm  130  and supports the fixed membrane  160 . The support layer  150  is provided with a contact hole  155  for exposing the first pad  140 . 
     The fixed membrane  160  is spaced apart from the diaphragm  130 . The fixed membrane  160  includes a plurality of air inlets  165 . The fixed membrane  160  is fixedly disposed on the support layer  150 . Here, the fixed membrane  160  may be made of polysilicon or metal. 
     An air layer is formed between the fixed membrane  160  and the diaphragm  130 . The fixed membrane  160  and the diaphragm  130  are spaced apart from each other at a predetermined distance. The sound pressure is introduced through the air inlet  165  formed on the fixed membrane  160  to stimulate the diaphragm  130 , such that the diaphragm  130  is vibrated. In this case, the interval between the fixed membrane  160  and the diaphragm  130  is changed and the capacitance between the diaphragm  130  and the fixed membrane  160  is changed correspondingly. The so-changed capacitance signal is output to the signal processing module  300  through the first pad  140  connected to the diaphragm  130  and a second pad  170  connected to the fixed membrane  160 . 
     The second pad  170  is disposed on the fixed membrane  160 . The second pad  170  is connected to the signal processing module  300 . 
     Meanwhile, a structure of the second acoustic sensing module  200  is the same as that of the first acoustic sensing module  100  described in  FIG. 2 , and therefore a description thereof will be omitted. 
       FIG. 3  is a circuit diagram illustrating the microphone. 
     Referring to  FIG. 3 , the signal processing module  300  may be an amplifier  300  amplifying and outputting the first and second capacitance signals input from the first acoustic sensing module  100  and the second acoustic sensing module  200 . 
     The amplifier  300  includes a non-inverting input terminal  320 , an inverting input terminal  330 , and an output terminal  350 . 
     The non-inverting input terminal  320  is connected to the first acoustic sensing module  100  and receives the first capacitance signal from the first acoustic sensing module  100 . 
     The first capacitance signal may be determined by at least one of sensitivity of the first acoustic sensing module  100 , capacitance of the first acoustic sensing module  100 , a sound pressure, noise, and a bias. In this case, the noise may be noise generated from the outside. 
     That is, the first capacitance signal may be determined by the following Equation 1.
 
Δ V   1   =−k   1   C   1 ( V   B   +V   N )Δ P   S   [Equation 1]
 
     In the above Equation 1, ΔV 1  represents the first capacitance signal, k 1  represents a sensitivity constant of the first acoustic sensing module  100 , C 1  represents the capacitance of the first acoustic sensing module  100 , V N  represents the noise, V B  represents the bias, and ΔP S  represents the sound pressure. 
     The inverting input terminal  330  is connected to the second acoustic sensing module  200  and receives the second capacitance signal from the second acoustic sensing module  200 . 
     The second capacitance signal may be determined by at least one of sensitivity of the second acoustic sensing module  200 , the capacitance of the second acoustic sensing module, a sound pressure, noise, and a bias. 
     That is, the second capacitance signal may be determined by the following Equation 2.
 
Δ V   2   =−k   2   C   2 ( −V   B   +V   N )Δ P   S   [Equation 2]
 
     In the above Equation 2, ΔV 2  represents the second capacitance signal, k 2  represents a sensitivity constant of the second acoustic sensing module  200 , C 2  represents the capacitance of the second acoustic sensing module  200 , V B  represents the bias, V N  represents the noise, and ΔP S  represents the sound pressure. 
     The first capacitance signal and the second capacitance signal may include noise as can be confirmed by the above Equations 1 and 2. 
     The output terminal  350  removes the noises included in the first capacitance signal and the second capacitance signal, and amplifies the first capacitance signal and the second capacitance signal without noise to output an output signal. 
     The output signal may be determined by the following Equation 3.
 
 V   0   =ΔV   1   −ΔV   2   [Equation 3]
 
     In the above Equation 3, V O  may represent the output signal, ΔV 1  may represent the first capacitance signal, and ΔV 2  may represent the second capacitance signal. 
     In this case, the first acoustic sensing module  100  and the second acoustic sensing module  200  use the same acoustic sensing module, and therefore the capacitance of the first acoustic sensing module  100  may be equal to that of the second acoustic sensing module  200  and the sensitivity of the first acoustic sensing module  100  may be equal to that of the second acoustic sensing module  200 . 
     Therefore, the output signal may be determined by the following Equation 4.
 
 V   0 =−2 kC   0   V   B   ΔP   S   [Equation 4]
 
     In the above Equation 4,V O  may represent the output signal, k may represent an initial sensitivity constant, C 0  may represent an initial capacitance, V B  may represent the bias, and ΔP S  may represent the sound pressure. 
     Therefore, the signal processing module  300  may remove noise and output the amplified output signal as can be confirmed by the above Equation 4. 
       FIG. 4  is a diagram illustrating a simulation result of the microphone  50 . 
     Referring to  FIG. 4 , the signal processing module  300  receives a first capacitance signal  410  including noise from the first acoustic sensing module  100 , and receives a second capacitance signal  420  from the second acoustic sensing module  200  including noise. The signal processing module  300  may remove noises from the first capacitance signal  410  and the second capacitance signal  420  and amplify the signals without noises to output output signals  430  and  440 . 
     While this disclosure has been described in connection with what is presently considered to be practical exemplary forms, it is to be understood that the disclosure is not limited to the disclosed forms, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.