Electroacoustic device and acoustic equalization method

Abstract

To remove a resonance frequency from an acoustic band of a microphone.SOLUTION: An electronic acoustic device 12 comprises: a primary MEMS microphone 14 having a frequency response including a resonance frequency; a reference MEMS microphone 18 having the frequency response containing the resonance frequency; and an equalization module 22. The primary MEMS microphone and the reference MEMS microphone substantially simultaneously receive a common acoustic signal, and produce a transduced signal of the microphone and a transduced signal of the reference microphone. The resonance frequency of the reference MEMS microphone is different from the resonance frequency of the primary MEMS microphone. The equalization module equalizes the frequency response of the microphone based on the transduced signal of the primary MEMS microphone and the transduced signal of the reference MEMS microphone.SELECTED DRAWING: Figure 2A

Description

[Technical Field]

[0001] Multiple embodiments of the present invention relate to micro-electromechanical systems (MEMS). More specifically, at least some embodiments relate to frequency response equalization of MEMS transducers such as microphones. [Background technology]

[0002] The frequency response of a transducer, such as a microphone, is the frequency-specific output sensitivity of that transducer. Resonance occurs when a physical object or electronic circuit absorbs energy from an initial displacement or source, and sustains the resulting mechanical or electrical vibration without the action of additional force or energy. The frequency at which this vibration occurs is known as the resonant frequency. The resonant frequency of a microphone, when it appears in the acoustic band, can be potentially problematic because it can cause damage to the listener's ears and / or inaccurate reproduction of the perceived sound. Eliminating this resonance is essential for successful microphone performance.

[0003] MEMS microphones are micro-electromechanical devices used to convert sound pressure (e.g., speech) into electrical signals (e.g., voltage). MEMS microphones are widely used in wireless devices, portable devices, headsets, earpieces, speakers, and other audio interface devices or systems. Conventional capacitive MEMS microphones suffer from high power consumption (e.g., large bias voltage) and reliability when used in harsh environments (e.g., exposure to dust and / or water).

[0004] Piezoelectric MEMS are used to address the shortcomings of capacitive MEMS microphones. Piezoelectric MEMS microphones offer consistent listening performance with minimal power consumption (e.g., no bias voltage required), are robust, and resistant to water and dust contamination. Both conventional capacitive and piezoelectric MEMS microphones suffer from resonance problems in the acoustic band.

[0005] Previous attempts to eliminate or at least reduce resonance in MEMS microphones have involved several different approaches. Some solutions involve adding specific features to the microphone's structure to remove the resonant peak from the acoustic band. Other solutions involve multiband processing to address the frequency band near the resonance and compensate for the excess peak in the frequency response. Yet another solution is to push the resonant frequency out of the human-perceptible acoustic band by adjusting the microphone's packaging to correct the resonant frequency. Microphones can also be calibrated at the factory using, for example, pink noise to compensate for the peak by adding a fixed-frequency notch at the resonant frequency. However, none of these previous solutions provide a satisfactory way to remove the resonant frequency from the microphone's acoustic band once a particular microphone leaves the factory and unpredictable real-world noise is present. [Overview of the project]

[0006] According to at least one embodiment, an electroacoustic device is provided, which includes a microphone having a frequency response including a resonant frequency, a reference microphone having a frequency response including a resonant frequency, and an equalization module configured to equalize the frequency response of the microphone based on the converted signal of the microphone and the converted signal of the reference microphone, wherein the microphone and the reference microphone are configured to receive a common acoustic signal substantially simultaneously to generate the converted signal of the microphone and the converted signal of the reference microphone, and the resonant frequency of the reference microphone is different from the resonant frequency of the microphone.

[0007] In one example, the sensitivity of the microphone is higher than that of the reference microphone.

[0008] In other examples, the microphone and the reference microphone are micro-electromechanical system (MEMS) microphones.

[0009] In one example, the equalization module is further configured to equalize the frequency response of a microphone by filtering the microphone's frequency response with an equalization function. The equalization function is based on the converted signal of a reference microphone, which is generated in response to the reference microphone receiving a common acoustic signal.

[0010] In other examples, the equalization module is configured to equalize the frequency response of a microphone by estimating the power spectrum of the converted signal of a reference microphone, calculating the cross-correlation between the converted signal of the microphone and time-domain samples of the converted signal of the reference microphone, calculating the frequency-domain power spectrum estimate of the cross-correlation, and generating the transfer function of the microphone by dividing the frequency-domain power spectrum estimate of the cross-correlation by the power spectrum estimate of the reference microphone.

[0011] In one example, the equalization module is configured to equalize the frequency response of the microphone by determining a fitting polynomial of order N (N≧2) of the transfer function and calculating the reciprocal of the fitting polynomial to determine the equalization function of the microphone.

[0012] In other examples, the electroacoustic device further includes a packaging system for encapsulating a microphone, a reference microphone, and an equalization module.

[0013] In one example, the electroacoustic device further includes at least one rear cavity defined by the volume between the packaging system and the microphone and the reference microphone.

[0014] In other examples, at least one back cavity includes a first back cavity and a second back cavity, the first back cavity being acoustically isolated from the second back cavity.

[0015] In one example, the electroacoustic device further includes at least one port configured to receive a common acoustic signal, and at least one front cavity configured to allow the common acoustic signal to reach a microphone and a reference microphone substantially simultaneously through the at least one port.

[0016] In another example, at least one port includes a first port and a second port, and at least one front cavity includes a first front cavity and a second front cavity, the first port and the second port are configured to receive a common acoustic signal substantially simultaneously, the first front cavity is configured to allow the common acoustic signal to reach a microphone through the first port, and the second front cavity is configured to allow the common acoustic signal to reach a reference microphone through the second port.

[0017] In one example, the microphone and the reference microphone are located in the same place and on the same plane.

[0018] In other examples, the resonant frequency of the reference microphone is higher than the resonant frequency of the microphone.

[0019] In one example, the resonant frequency of the reference microphone is lower than the resonant frequency of the microphone.

[0020] In other examples, the equalization module is either an ASIC controller or a DSP controller.

[0021] According to at least one embodiment, an acoustic equalization method includes exciting a microphone and a reference microphone substantially simultaneously with a common acoustic signal to generate a converted signal of the microphone and a converted signal of the reference microphone, the microphone having a frequency response including a resonance frequency, the reference microphone having a frequency response including a resonance frequency, the resonance frequency of the reference microphone being different from the resonance frequency of the microphone, generating the converted signal of the reference microphone in response to the reference microphone receiving the common acoustic signal, and equalizing the frequency response of the microphone based on the converted signal of the microphone and the converted signal of the reference microphone.

[0022] In one example, the acoustic equalization method further includes estimating a transfer function of the microphone based on the converted signal of the microphone and the converted signal of the reference microphone.

[0023] In another example, estimating the transfer function of the microphone includes estimating a power spectrum of the converted signal of the reference microphone, calculating a cross-correlation of time-domain samples of the converted signal of the microphone and the converted signal of the reference microphone, calculating a frequency-domain power spectrum estimate of the cross-correlation, and generating the transfer function of the microphone by dividing the frequency-domain power spectrum estimate of the cross-correlation by the power spectrum estimate of the reference microphone.

[0024] In one example, the acoustic equalization method further includes determining an equalization function of the microphone based on the estimated transfer function, and filtering the frequency response of the microphone by the equalization function to equalize the frequency response of the microphone.

[0025] In other examples, determining the equalization function of the microphone includes determining a fitting polynomial of degree N (N≧2) of the transfer function and calculating the reciprocal of the fitting polynomial to determine the equalization function of the microphone.

[0026] In one example, the acoustic equalization method further includes reconstructing an adaptive filter with the coefficients of the equalization function so as to adaptively filter the converted signal of the microphone.

[0027] Further other aspects, embodiments and advantages of these exemplary aspects and embodiments are detailed below. The embodiments disclosed herein may be combined with other embodiments in any manner consistent with at least one of the principles disclosed herein, and references to "one embodiment", "some embodiments", "an alternative embodiment", "various embodiments", "one embodiment", etc. are not necessarily mutually exclusive, and are intended to indicate that the particular features, structures or characteristics described may be included in at least one embodiment. Even when such terms appear herein, they do not necessarily all refer to the same embodiment.

Brief Description of the Drawings

[0028] Various aspects of at least one embodiment are described below with reference to the accompanying drawings which are not intended to be drawn to scale. The drawings are included to provide an illustration and further understanding of the various aspects and embodiments, and are incorporated herein and constitute a part of this specification, but are not intended to define the limits of the present invention. In the drawings, the same or substantially the same components shown in the various drawings are each represented by the same reference numerals. For the sake of clarity, not all components are labeled in all the drawings.

[0029] [Figure 1] It is a block diagram of a microphone according to one embodiment. [Figure 2A] It is a cross-section of a microphone according to another embodiment. [Figure 2B]This is a cross-section of a microphone according to another embodiment. [Figure 3A] This is a cross-section of a microphone according to another embodiment. [Figure 3B] This is a cross-section of a microphone according to another embodiment. [Figure 4] This is a cross-section of a microphone according to another embodiment. [Figure 5] This is a functional block diagram of the equalization method according to another embodiment. [Figure 6] This is a set of frequency response graphs and a functional block diagram according to another embodiment. [Figure 7A] This is a cross-sectional view of a micro electromechanical system microphone having a flat cantilever beam according to another embodiment. [Figure 7B] This is a cross-sectional view of a micro-electromechanical system microphone array according to another embodiment. [Figure 8] This is a section layout of a cantilever beam piezoelectric microphone according to another embodiment. [Figure 9] This is a schematic diagram of a wireless device including a piezoelectric micro-electromechanical system microphone according to another embodiment. [Modes for carrying out the invention]

[0030] The aspects and embodiments described herein relate to frequency response equalization in MEMS transducers such as microphones. Among the technical problems of having microphone resonances in the acoustic band are high energy peaks / consumption that can damage the ear and / or electronic equipment, an intractable design trade-off between performance (e.g., sensitivity) versus resonant frequency for removing the resonant peak from the acoustic band, increased group delay at the resonant point (e.g., delay distortion of speech and / or acoustic signals), and manufacturing, packaging, and other variations that cause different resonant frequencies from component to component.

[0031] To address these technical issues, embodiments provided herein include an equalization method and an electroacoustic device for equalizing the frequency response of MEMS microphones, comprising a primary MEMS microphone and a reference MEMS microphone, packaging for encapsulating the primary and secondary microphones, and signal processing hardware (e.g., an ASIC). To benefit from the embodiments disclosed herein, the primary microphone and the reference microphone are of the same type, each having a different resonant frequency, and both microphones receive a signal that is converted substantially simultaneously. In one example, “same type” is understood to mean that both the primary microphone and the reference microphone have the same theoretical frequency response to the same / common acoustic excitation. The converted signal of the reference microphone is used to equalize the converted signal of the primary microphone, and more specifically, to equalize the resonant frequency of the primary microphone. Several examples include both microphones being MEMS microphones. However, it should be recognized that embodiments of the present invention are not limited to acoustic transducers (e.g., microphones) but can be adapted to other types of transducers, such as MEMS accelerometers or pressure transducers. An equalization method is given which includes exciting both the primary and secondary microphones with the same / common signal, performing spectral estimation of the converted signal, and finding the best polynomial fitting of the primary microphone's transfer function to generate an equalization function to remove the resonance peak of the primary microphone.

[0032] It is clear that the embodiments of the methods and apparatus described herein are not limited in their application to the details of configuration and arrangement described below or shown in the accompanying drawings. These methods and apparatus may be implemented in other embodiments and may be carried out or performed in various ways. Specific implementation examples are given herein for illustrative purposes only and are not intended to be limiting. Furthermore, the expressions and terms used herein are for illustrative purposes only and should not be considered limiting. The use herein of “includes,” “equips,” “has,” “contains,” and their variations means that they encompass the items and equivalents listed later, as well as additional items. References to “or” and “or else” are interpreted inclusively, and any item described using “or” and “or else” may refer to one, more than one, or all of the items described.

[0033] All microphones resonate with most microphones that have a very high Q factor (i.e., the ratio of the center frequency to the bandwidth of the resonator when subjected to a vibration-driving force), which can result in a peak of 10 times the midband sensitivity. Many microphones are condenser microphones, and the conventional solution to address the resonance peak / spike is to push the spike above 20 kHz, which is little or nowhere near perceptible to human hearing. However, pushing the resonance peak outside the acoustic band can have a significant negative impact on the microphone's sensitivity, sometimes by more than 20 dB.

[0034] Conventional solutions to improve the frequency response of microphones include adding structures to the microphone or its packaging to move the resonance peak out of the audible range, and calibrating the microphone at the factory. However, such solutions are not entirely adequate for improving the frequency response of microphones. This is because the frequency response changes over time due to various factors, including the aging of components and environmental influences. For example, the resonant frequency of a microphone may change as the physical structure of the microphone changes over time due to fluctuations in temperature, humidity, etc. When the resonant frequency changes, any previous calibrations are no longer optimal, and structures added to the microphone or its packaging can no longer eliminate the peak resonance as they did initially.

[0035] An ideal measurement from a microphone includes only the incoming acoustic signal without distortion or noise. Noise or signals that are not the acoustic signal picked up by the microphone will disrupt the microphone's estimation of the acoustic signal. The embodiments herein have the benefit of improving the estimation of the acoustic signal by a microphone (or other suitable transducer or sensor) even in the presence of any incoming energy (including noise).

[0036] The disclosed embodiments overcome the current limitations of the prior art by providing a MEMS microphone with high sensitivity and signal-to-noise (SNR) index with no trade-offs (i.e., no peaks) in the frequency response. The equalization method uses statistical signal processing. This processing is unknowable for the primary and reference microphones, is fast, and is suitable for operation in noisy environments. System-on-chip (SoC) embodiments of the MEMS microphones ensure precise acoustic excitation conditions and simple, inexpensive packaging due to shared ports and front and back cavities that are less sensitive to variations in the inherent MEMS manufacturing process. The embodiments also include system-in-package (SiP) implementation examples in which each microphone is manufactured by a separate process.

[0037] Figure 1 is a block diagram of an electroacoustic device 2. The electroacoustic device 2 includes a primary microphone 4, a primary preamplifier 6, a reference microphone 8, a reference preamplifier 10, and an equalization module 11. In one embodiment, the equalization module 11 is a digital signal processor (DSP) or a DSP controller. In another embodiment, the equalization module 11 is one of a microcontroller, an ASIC controller, or a general-purpose central processing unit (CPU). The electroacoustic device 2 includes a package (not shown in Figure 1) that encloses each of the primary microphone 4, primary preamplifier 6, reference microphone 8, reference preamplifier 10, and the equalization module 11. An example includes an electroacoustic device 2 implemented as an SoC or SiP.

[0038] The primary preamplifier 6 is electronically coupled to the primary microphone 4 and configured to amplify the converted signal output by the primary microphone 4. Similarly, the reference preamplifier 10 is electronically coupled to the reference microphone 8 and configured to amplify the converted signal output by the reference microphone 8. The equalization module 11 is electronically coupled to the primary preamplifier 6 and the reference preamplifier 10 and configured to receive the converted signals from the primary microphone 4 and the reference microphone 8.

[0039] To perform the equalization method and technique disclosed herein, the primary microphone 4 and the reference microphone 8 are configured to receive the same elastic signal, each having a different resonant frequency. In one embodiment, the resonant frequency of the reference microphone 8 is higher than that of the primary microphone 4. In another embodiment, the resonant frequency of the reference microphone 8 may be lower than that of the primary microphone 4. It is understood that the equalization method and technique disclosed herein are applicable to both embodiments in which the reference microphone 8 has a higher resonant frequency than that of the primary microphone 4, and embodiments in which the reference microphone 8 has a lower resonant frequency than that of the primary microphone 4.

[0040] In a given example, the primary microphone 4 has a lower resonant frequency than the reference microphone 8, and also has higher sensitivity than the reference microphone 8. In this case, the resonance in the primary microphone may negatively affect the usefulness of the primary microphone's bandwidth. The frequency responses of the primary microphone 4 and the reference microphone 8 after their respective first resonant peaks may be more complex than the frequency responses before their respective first resonant peaks, which have a steep decline and rise in sensitivity and higher-order resonant peaks. In this scenario, the acoustic and environmental condition measurements attempted with the lower-frequency reference microphone are all performed in a region of the frequency response with many features and a non-flat sensitivity response, so the reference microphone becomes less suitable to serve as a "clean" reference compared to a reference microphone with a lower resonant frequency response. Therefore, in a given example, a reference microphone with a first peak higher than that of the primary microphone in its frequency response is desirable.

[0041] Figure 2A is a cross-section of the electroacoustic device 12. The electroacoustic device 12 includes a primary MEMS microphone 14, a primary microphone preamplifier 16, a reference MEMS microphone 18, a reference preamplifier 20, an equalization module 22, a substrate 24, packaging 26, a back cavity 28, a front cavity 30, and a port 32. In one embodiment, the substrate 24 is made of silicon. In another embodiment, the substrate 24 is a printed circuit board (PCB). The primary microphone 14 is supported by a support 19. In some examples, the support 19 is made of silicon and bonded to the substrate 24. The substrate 24 is also made of silicon. Similarly, the reference microphone 18 is supported by a support 21. In some examples, the support 21 is made of silicon and bonded to the substrate 24. The substrate 24 is also made of silicon. In one example, the primary microphone 14 and the reference microphone 18 are constructed on a silicon die pieceped from a silicon wafer. In other examples, the primary MEMS microphone 14, primary microphone preamplifier 16, reference MEMS microphone 18, reference preamplifier 20, and equalization module 22 are all manufactured as chips mounted on a substrate 24.

[0042] The rear cavity 28 is enclosed within the packaging 26 and defined by the volume enclosed between the substrate 24 and the internal components. For the sake of brevity, the relevant descriptions from Figure 1 of similar components (e.g., preamplifiers 16 and 6) are not repeated as they are applicable to the embodiments described in Figure 2A and thereafter.

[0043] The electroacoustic device 12 is configured to receive the acoustic signal 13 at port 32. The acoustic signal 13 is then guided into the front cavity 30 and further into the rear cavity 28, where it is reflected and reaches both the reference microphone 18 and the primary microphone 14 substantially simultaneously. Here, the phrase "substantially simultaneously" is understood to mean ideally at the same time. In practical terms, it is virtually impossible for acoustic waves to reach two sensors in the same location and on the same plane at exactly the same time (i.e., simultaneously). Therefore, the electroacoustic device 12 is designed to guide the incoming acoustic signal to both microphones as precisely as possible simultaneously or substantially simultaneously. By ensuring that both microphones encounter and convert the incoming signal substantially simultaneously, the converted signal from the reference microphone 18 can be used to remove the resonance peak of the primary microphone 14.

[0044] The rear cavity 28 supports the operation and performance of the primary microphone 14 and the reference microphone 18 in several ways. Firstly, the rear cavity 28 finalizes the frequency response; that is, the size of the rear cavity 28 ultimately defines the resonant frequencies of the primary microphone 14 and the reference microphone 18. Secondly, as a result, the rear cavity 28 also determines other key performance parameters such as the sensitivity and noise / SNR of each microphone.

[0045] Each component depicted in Figure 2A is constructed within the same SoC manufacturing process, with both microphones 14 and 18 having different sensitivities and frequencies while using the same process layer. The electroacoustic device 12 may include one or more ASICs for amplification, signal conditioning, and equalization modules 22.

[0046] As shown in Figure 2A, the electroacoustic device 12 includes two SoC devices, namely a reference microphone 18 and a primary microphone 14. However, the electroacoustic device may include more than two SoC devices (not shown). For example, in addition to the reference microphone 18 and the primary microphone 14, an additional microphone may be provided.

[0047] Figure 2B is a cross-section of an electroacoustic device 34 having a first front cavity 36 and a second front cavity 38. A first port 36a is provided near the first front cavity 36 to guide acoustic energy into the first front cavity 36. A second port 38b is provided near the second front cavity 38 to guide acoustic energy into the second front cavity 38. For the sake of brevity, explanations of elements with the same number as those in Figure 2A are omitted. In some examples, the primary microphone 14 and the reference microphone 18 are each constructed from a piezoelectric material formed on the top of a silicon substrate. As shown in Figure 2B, the electroacoustic device 34 includes a silicon material that forms a layer bonding the microphones 14, 18 to the base substrate 24. The base substrate 24 may be a silicon substrate or a printed circuit board (PCB) substrate. In one example, “bonding” means connection, contact and / or support. Furthermore, the silicon divider 40 is used to separate the first cavity 36 from the second cavity 38. Providing a separate front cavity for each microphone helps to acoustically isolate the primary microphone 14 so that it does not interact with the reference microphone 18.

[0048] Figure 3A is a cross-section of an electroacoustic device 42 having a first back cavity 44 and a second back cavity 46 separated by a divider 48. In some examples, the divider 48 is made of silicon. In other examples, the divider is made from the same material as the packaging and becomes part of the packaging 26. For the sake of brevity, explanations of elements with the same number common to Figures 2A and 2B are omitted. Providing a separate back cavity for each microphone helps to acoustically isolate the primary microphone 14 so that it does not interact with the reference microphone 18.

[0049] Figure 3B is a cross-section of an electroacoustic device 50 having a first back cavity 44 and a second back cavity 46 separated by a divider 48, and a first front cavity 36 and a second front cavity 38 separated by a divider 40. For the sake of brevity, explanations of elements with the same number common to Figures 2A and 2B are omitted. Providing separate front cavities in addition to the separate back cavities for each microphone helps to acoustically isolate the primary microphone 14 so that it does not interact with the reference microphone 18.

[0050] Figure 4 is a cross-section of an electroacoustic device 52 having a single back cavity 54 enclosed by a packaging 56. The electroacoustic device 52 includes a primary MEMS microphone 58 and a primary preamplifier 60, a reference microphone 62 and a reference preamplifier 64, and an equalization module 66. While Figure 4 depicts the primary MEMS microphone 58 and the reference microphone 62 as diaphragm piezoelectric microphones, in other embodiments, the electroacoustic device may alternatively include a cantilever piezoelectric microphone. Furthermore, the type of microphone used in the electroacoustic device 52 is not limited to diaphragm piezoelectric microphones and cantilever piezoelectric microphones. Each microphone in the electroacoustic device 52 is provided with a separate front cavity and port. The primary microphone 58 is provided with a front cavity 68 and a port 70. Similar to the embodiments described above, the port 70 is configured to guide incoming acoustic waves into the front cavity 68 to interact with the primary microphone 58. Similarly, the reference microphone 62 is provided with a front cavity 72 and a port 74, and the port 74 is configured to direct the same incoming acoustic waves into the front cavity 72 and interact with the reference microphone 62.

[0051] In a given embodiment, the primary microphone 58 and the reference microphone 62 are each constructed in a different manufacturing process and housed on two different chips, each integrated at the packaging level. In one embodiment, this integration is part of constructing the electroacoustic device 52 as a SiP. An example of the electroacoustic device 52 includes two or more ASICs for amplification purposes; that is, at least one is included for the primary microphone 58, and a second ASIC is included for the reference microphone 62, signal conditioning, and equalization module 66. The packaging structure may be similar for both microphones, but in a given embodiment, modifications may be necessary to suit the respective ASIC chips and design details.

[0052] Any of the electroacoustic devices disclosed herein, including electroacoustic devices 2, 12, 34, 42, 50, and 52, utilize an equalization method to remove resonance peaks in the frequency response of a MEMS microphone. Figure 5 shows such an acoustic equalization method 76.

[0053] The equalization method 76 begins with an acoustic wave or excitation 78. The acoustic excitation is passed to at least two MEMS microphones as a common elastic excitation. As an example, as shown in Figure 5, the at least two microphones include a primary MEMS microphone 80 and a reference MEMS microphone 82 (however, the equalization method described is applicable to any of the electroacoustic devices described herein).

[0054] In operation 84 of Method 76, the converted signal from a reference microphone 82 having a higher resonant frequency than the primary microphone 80 in this example is processed to estimate the power spectrum of the converted signal. In at least one embodiment, the power spectrum is used to estimate the spectrum S 22 To generate this, the power spectrum is obtained by calculating the Fast Fourier Transform (FFT) of the transformed signal. It is understood that other techniques may be applied to estimate the power spectrum of the transformed signal. For example, the Welch estimation or other techniques that do not use FFT (e.g., the Goertzel filter algorithm) may be applied to estimate the power spectrum of the transformed signal. In another example, a Kalman filter may be used instead of FFT to extract the microphone transfer function estimate.

[0055] In operation 86 of Method 76, the cross-correlation R of time-domain samples generated from the converted signals of the primary microphone 80 and the reference microphone 82 is 12 This is obtained. Next, the cross-correlation R 12 Frequency domain power spectrum estimation S 12 This is calculated.

[0056] In operation 88, cross-correlation R 12Power spectrum estimation S 12 is divided by the power spectrum estimation S 22 of the reference sensor, and the transfer function estimation T 12 of the primary microphone 80 is generated.

[0057] In operation 90, a polynomial of degree N is fitted to the quotient of the transfer function estimation T 12 . Here, N ≥ 2.

[0058] Once the polynomial is obtained, the method 76 proceeds to operation 92. Here, the reciprocal of the polynomial T 12 -1 is calculated as the equalization function of the primary microphone 80. A predetermined embodiment utilizes least squares fitting of the coefficients to the frequency points of the transfer function estimation T 12 in operation 92. In one example, the degree N is 3, and at least four frequency points are used such that there is sufficient rank to solve for the curve.

[0059] In operation 93, the frequency response of the primary microphone 80 is filtered by the inverse polynomial T 12 -1 , and at 96, the equalized frequency response of the primary microphone 80 is generated. In operation 93, the coefficients obtained by operation 92 are passed to operation 93. Operation 93 includes a fetch procedure that retrieves the coefficients and reprograms / updates the filter function N with such coefficients. Thus, operation 93 provides a reconfigurable adaptive filter using the coefficients of the equalization function N. The adaptive filter then continuously processes and filters the converted signal generated by the primary microphone.

[0060] As a result of performing the equalization method 76, the influence of noise on the estimation of the transfer function of the primary microphone 80 can be reduced. In a given example, the power spectrum estimation algorithm used in the equalization method 76 uses the accumulation and averaging of FFTs of signal samples, which is equivalent to improving noise immunity. This is because the noise variance is reduced by averaging, making it possible to extract a "clean" transfer function.

[0061] Figure 6 shows a set of frequency response graphs 94, 100, 102, 106, and a functional block diagram 104. Before equalization (e.g., by applying method 76), the frequency response of the primary microphone 97 and the frequency response of the reference microphone 98 are presented in the first frequency response graph 94. The lowest resonant frequency, i.e., the fundamental frequency f0, is represented by the peak in each frequency response of graph 94. It is noteworthy that, as shown in graph 100, the reference microphone has a substantially flat frequency response at the fundamental frequency of the primary microphone. Graphs 94 and 100 represent the frequency responses without equalization. Graph 100 is an enlarged view of the first frequency response graph 94. Thus, the condition for the frequency response of the reference microphone is that the frequency response may be monotonic around the resonance of the reference microphone (i.e., there is no up or down near the resonance of the primary microphone, and the sensitivity may slope (increase or decrease)).

[0062] Graph 102 corresponds to the first frequency response graphs 94 and 100. Graph 102 shows the frequency responses of two microphones in the same package (e.g., primary microphone 80 and reference microphone 82). These frequency responses are processed by an equalization module 104 (e.g., having the same or similar function as the equalization module 11 in Figure 1) to produce the equalized frequency response shown in Graph 106. Here, both frequency responses are generally flat at the fundamental frequency of the primary microphone.

[0063] Figure 7A shows a cross-sectional view of one implementation example of a piezoelectric microelectromechanical system (MEMS) microphone 108. Microphone 108 is a piezoelectric MEMS cantilever microphone usable in any of the electroacoustic devices 2, 12, 34, 42, 50, and 52 described herein. Microphone 108 includes a substrate 110. The substrate 103 is optionally made of silicon. The substrate 1110 has two side walls 105 arranged to extend perpendicular to the length of the cantilever. Two further end walls (not shown) complete the cavity on the opposite side, touching the side at a right angle, and further structures described in relation to Figure 7B below may be present on the underside of the cavity. These walls are preferably approximately 108 to 500 micrometers thick. A piezoelectric film layer 111 forms a cantilever beam 116 over the cavity. At least one of the side walls 105 defines an anchor region 113. The anchor region is preferably approximately 10⁸ to 500 micrometers thick. The anchor region 113 is the area to which the piezoelectric film layer 111 is bonded and supported to one of the side walls. The microphone 108 optionally includes an insulating layer 109 disposed on the surface of the substrate 110. The insulating layer is optionally silicon dioxide. As a result of the piezoelectric film layer 111 being supported by the substrate 110 in the anchor region 113, the piezoelectric film layer 111 is cantilevered and extends between a fixed end 114 and a free end 112. At least one electrode (not shown) is arranged on the piezoelectric film layer. This arrangement preferably includes a number of electrodes arranged above and below the piezoelectric film layer, and in some arrangement examples, a number of electrodes arranged between the layers. The piezoelectric film layer and electrodes together form a cantilever beam 116. As can be seen, although the beam is shown to have a rectangular shape, other shapes may also be used. The microphone 108 includes at least one electrode that may be disposed on the piezoelectric film layer 111. This electrode is positioned on the cavity side of the piezoelectric layer, or on the other side of the piezoelectric layer away from the cavity. The electrode can be optionally positioned adjacent to the anchor region 113. The insulating layer 109 provides insulation between the electrode positioned on the cavity side of the piezoelectric film layer and the silicon substrate 110.

[0064] Figure 7B shows a cross-sectional view of another microphone array 130. As can be seen, this is an exemplary embodiment for illustrative purposes, and microphones may be contained in various different arrays. As shown, the microphone 108 of Figure 7A is placed inside a cap 133. The cap may be flexible or rigid and may be any suitable material such as a metallic material. This cap, together with a substrate 135 (e.g., a printed circuit board), provides a seal that allows only air to flow in and out of the array through the sound inlet 131. The substrate 135 may be any suitable material. The cap 133 also mitigates electromagnetic interference. As described herein, sound waves enter this array, causing a bend in the cantilever beam 116 and resulting in a voltage due to the piezoelectric effect. The array 130 includes at least one solder pad 137, and this microphone array may be soldered to external devices not shown herein. This microphone array further includes an application-specific integrated circuit chip / die ("ASIC") 139. The MEMS microphone is electrically connected by wire bonding 141. Although not shown, it can be seen that wire bonding may be connected to one or more electrodes of the microphone described herein.

[0065] Figure 7B is a cross-sectional view of the array 130, and as described in relation to other embodiments disclosed herein, one or more solder pads 137, substrate 135, MEMS microphone 108, ASIC 139, and cap 133 extend into the plane of the paper in a three-dimensional manner.

[0066] Figure 8 shows the layout of section 108 of a cantilever beam piezoelectric microphone, including a first set of cantilever beams 120 and a second set of cantilever beams 122. The first set of beams 120 corresponds to a primary microphone (e.g., primary microphone 58), and the second set of beams 122 corresponds to a reference microphone (e.g., reference microphone 62). The triangular tabs formed by beams 120, 122 and the material between them are each piezoelectric materials. When the piezoelectric material moves or bends due to sound waves encountering the material, the voltage is modified in accordance with the amount of such movement or bending. Specifically, the triangular sections include a metal layer that causes the change, and this change is picked up by electrodes. In some examples, all four triangular sections of the first set of beams 120 are coupled together (i.e., electrically connected) to function as a single microphone, and all four triangular sections of the second set of beams 122 are coupled together to function as a single microphone. In other examples, one or more individual triangular sections are separately coupled to an equalization module to operate as separate microphones, thereby including two or more microphones according to a given embodiment. For example, an electroacoustic device may include three microphones, two of which may be made from at least two of a first set of beams 120. The length and / or size of each cantilever beam may be modified to produce different desired resonant frequencies. In one example, the beam length is increased to lower its resonant frequency.

[0067] Figure 9 is a schematic diagram of a wireless device 150 according to one embodiment. The wireless device 150 is, for example, a portable telecommunications device such as a mobile cellular telephone. The wireless device 150 includes an electroacoustic device 170 described herein in relation to Figures 1 to 6, and may include one or more of the following: a baseband system 152, a transceiver 154, a front-end system 156, one or more antennas 158, a power management system 160, a memory 162, a user interface 164, and a battery 166. The electroacoustic device 170 may supply signals to an acoustic codec 168. The acoustic codec 168 can encode analog sound into digital signals or decode digital signals into analog. The acoustic codec 168 may transmit signals to the user interface 164. The user interface 164 transmits signals to the baseband system 152. The transceiver 154 generates RF signals for transmission and processes incoming RF signals received from the antennas.

[0068] The transceiver 154 assists in conditioning the signals transmitted to and / or received from the antenna 158.

[0069] Antenna 158 may include antennas used for a wide variety of types of communication. For example, antenna 158 may include antennas for transmitting and / or receiving signals associated with a wide variety of frequencies and communication standards.

[0070] The baseband system 152 is coupled to a user interface to facilitate the processing of various user inputs and outputs, such as voice and data. The baseband system 152 provides a digital representation of the transmit signal to the transceiver 154, which processes this to generate the RF signal for transmission. The baseband system 152 also processes the digital representation of the receive signal provided by the transceiver 154. As shown in Figure 9, the baseband system 152 is coupled to a memory 162 to facilitate the operation of the wireless device 150.

[0071] Memory 162 can be used for a wide variety of purposes, such as storing data and / or instructions, in order to facilitate the operation of the wireless communication device and / or to provide storage for user information.

[0072] The power management system 160 provides a certain number of power management functions for wireless devices.

[0073] The power management system 160 receives battery voltage from the battery 166. The battery 166 may be any suitable battery for use in wireless devices, including, for example, a lithium-ion battery.

[0074] The embodiments provided herein are applicable to both diaphragm microphones and cantilever microphones, although other geometric shapes may be more suitable for specific applications (e.g., bridge / clamp and clamp beam). Those skilled in the art will understand how the principles and techniques disclosed herein may be applied to other types of microphones besides diaphragm microphones and cantilever microphones.

[0075] While the embodiments described herein are based on MEMS microphones, it should be understood that the principles and techniques described herein are also applicable to other types of transducers. For example, the embodiments herein may be adapted and used for equalizing the frequency responses of pressure sensors, force sensors, and imaging sensors (where the common excitation signal replaces the common acoustic wave described above). The advantage of the devices, systems, and methods described herein lies in the fact that the given solutions are applicable to a wide range of sensors and transducers, particularly when there is little or no control over what the incoming stimulus is. For example, unlike pink noise generated in a lab to calibrate MEMS microphones, real-world MEMS microphones are often out of calibration and / or never encounter the exact type of noise simulated in a lab. By intentionally using a reference transducer with a higher or lower frequency response than the primary transducer, the techniques given herein enable the equalization of the frequency response of the primary transducer while keeping the resonant frequency within the bandwidth of the primary transducer.

[0076] While several aspects of at least one embodiment have been described above, it should be understood that those skilled in the art will readily recall various modifications, alterations, and improvements. Such modifications, alterations, and improvements are intended to be part of this disclosure and to be within the scope of the invention. Therefore, the above description and drawings are merely illustrative, and the scope of the invention should be determined by the appropriate configuration of the appended claims and their equivalents.

Claims

1. It is an electroacoustic device, A microphone having a frequency response that includes the resonant frequency, A reference microphone having a frequency response including the resonant frequency, Equalization module and Includes, The aforementioned microphone and the aforementioned reference microphone are configured to receive a common acoustic signal substantially simultaneously and generate the converted signal of the aforementioned microphone and the converted signal of the aforementioned reference microphone. The resonant frequency of the reference microphone is different from the resonant frequency of the microphone. The equalization module is configured to equalize the frequency response of the microphone based on the converted signal of the microphone and the converted signal of the reference microphone. The aforementioned equalization module further, To estimate the power spectrum of the converted signal from the aforementioned reference microphone, The process involves calculating the cross-correlation between time-domain samples of the converted signal from the aforementioned microphone and the converted signal from the aforementioned reference microphone, To calculate the frequency domain power spectrum estimation of the aforementioned cross-correlation, The frequency domain power spectrum estimation of the cross-correlation is divided by the power spectrum estimation of the converted signal of the reference microphone to generate the transfer function of the microphone. An electroacoustic device configured to equalize the frequency response of the microphone.

2. The electroacoustic device according to claim 1, wherein the sensitivity of the microphone is higher than the sensitivity of the reference microphone.

3. The electroacoustic device according to claim 1, wherein the microphone and the reference microphone are each micro-electromechanical system (MEMS) microphones.

4. The equalization module is further configured to equalize the frequency response of the microphone by filtering the frequency response of the microphone with an equalization function, The electroacoustic device according to claim 1, wherein the equalization function is based on the converted signal of the reference microphone, which is generated in response to the reference microphone receiving the common acoustic signal.

5. The aforementioned equalization module further, The process involves determining the fitting polynomial of the order N (N ≥ 2) of the aforementioned transfer function, The equalization function of the microphone is determined by calculating the reciprocal of the fitting polynomial. The electroacoustic device according to claim 1, configured to equalize the frequency response of the microphone by means of...

6. The electroacoustic device according to claim 1, further comprising a packaging system for sealing the microphone, the reference microphone, and the equalization module.

7. The electroacoustic device of claim 6, further comprising at least one back cavity defined by the volume between the packaging system, the microphone, and the reference microphone.

8. The aforementioned at least one back cavity includes a first back cavity and a second back cavity, The electroacoustic device according to claim 7, wherein the first rear cavity is acoustically isolated from the second rear cavity.

9. At least one port configured to receive the aforementioned common acoustic signal, At least one front cavity configured to allow the common acoustic signal to reach the microphone and the reference microphone substantially simultaneously through the at least one port, The electroacoustic device according to claim 1, further comprising:

10. The aforementioned at least one port includes a first port and a second port, The aforementioned at least one front cavity includes a first front cavity and a second front cavity. The first port and the second port are configured to receive the common acoustic signal substantially simultaneously. The first front cavity is configured to allow the common acoustic signal to reach the microphone through the first port. The electroacoustic device of claim 9, wherein the second front cavity is configured to allow the common acoustic signal to reach the reference microphone through the second port.

11. The electroacoustic device according to claim 1, wherein the microphone and the reference microphone are located at the same location and on the same plane.

12. The electroacoustic device according to claim 1, wherein the resonant frequency of the reference microphone is higher than the resonant frequency of the microphone.

13. The electroacoustic device according to claim 1, wherein the resonant frequency of the reference microphone is lower than the resonant frequency of the microphone.

14. The electroacoustic device according to claim 1, wherein the equalization module is either an ASIC controller or a DSP controller.

15. A method for acoustic equalization, The method involves exciting a microphone and a reference microphone substantially simultaneously with a common acoustic signal to generate a converted signal of the microphone and a converted signal of the reference microphone, wherein the microphone has a frequency response including a resonant frequency, the reference microphone has a frequency response including a resonant frequency, and the resonant frequency of the reference microphone is different from the resonant frequency of the microphone. The reference microphone generates a converted signal in response to receiving the common acoustic signal, Equalizing the frequency response of the microphone based on the converted signal of the microphone and the converted signal of the reference microphone, Estimating the transfer function of the microphone based on the converted signal of the microphone and the converted signal of the reference microphone. Includes, Estimating the transfer function of the aforementioned microphone is To estimate the power spectrum of the converted signal from the aforementioned reference microphone, The process involves calculating the cross-correlation between time-domain samples of the converted signal from the aforementioned microphone and the converted signal from the aforementioned reference microphone, To calculate the frequency domain power spectrum estimation of the aforementioned cross-correlation, The estimated frequency domain power spectrum of the cross-correlation is divided by the estimated power spectrum of the converted signal of the reference microphone to generate the estimated transfer function of the microphone. A method of acoustic equalization, including the following.

16. The equalization function of the microphone is determined based on the estimated transfer function, The frequency response of the microphone is filtered using the equalization function to equalize the frequency response of the microphone. The acoustic equalization method of claim 15, further comprising:

17. The acoustic equalization method of claim 16, further comprising reconstructing an adaptive filter by coefficients of the equalization function in order to adaptively filter the converted signal from the microphone.

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