Matched Beamforming Microphone Array

Abstract

The disclosure relates to a system, comprising a first circuit board comprising a control circuitry configured to control a beamforming array of microphones, and multiple second circuit boards attached to the first circuit board, each one of the multiple second circuit boards mounting a microphone of the array of microphones.

Claims

1. A system comprising: a first circuit board comprising control circuitry configured to control a beamforming array of microphones, and multiple second circuit boards attached to the first circuit board, each one of the multiple second circuit boards mounting a microphone of the beamforming array of microphones.

2. The system of claim 1, wherein the multiple second circuit boards are electronically coupled to the first circuit board using at least one of a pin header or a cable.

3. The system of claim 1, wherein, for each one of the multiple second circuit boards, the respective microphone is soldered to the respective one of the multiple second circuit boards.

4. The system of claim 1, wherein, a respective at least one acoustically-active element is attached to each one of the multiple second circuit boards, and wherein the respective at least one acoustically-active element is selected from the group comprising: an acoustic mesh; a sound guide; a sealing; and a bezel of the microphone.

5. The system of claim 1, wherein at least two of the microphones of the beamforming array of microphones have a different acoustic configuration.

6. A method comprising: mounting, to each second circuit board of a plurality of second circuit boards, at least one microphone using soldering points, upon the mounting, applying one or more heat shocks to the soldering points, to trigger a reflow process of the soldering points, upon applying of the one or more heat shocks, performing an acoustic characterization of the microphones, selecting a subset of the plurality of second circuit boards based on the acoustic characterization, the subset comprising multiple second circuit boards of the plurality of second circuit boards, and forming a beamforming array of microphones based on the microphones attached to the subset of the plurality of second circuit boards.

7. The method of claim 6, wherein the forming of the beamforming array of microphones comprises: attaching the multiple second circuit boards of the subset to a first circuit board, the first circuit board comprising control circuitry configured to control the beamforming array of microphones.

8. The method of claim 7, wherein the attaching of the multiple second circuit boards of the subset to a first circuit board comprises: electronically coupling the multiple second circuit boards to the first circuit board via a connection which does not require or generate heat during fabricating the connection.

9. The method of claim 6, wherein the subset of second circuit boards is selected based on a match between the acoustic characterization of the microphones.

10. The method of claim 6 further comprising attaching, to each second circuit board of the plurality of second circuit boards, at least one acoustically-active element.

11. The method of claim 10, wherein the acoustic characterization is performed upon attaching the at least one acoustically-active element.

12. The method of claim 10, wherein different ones of the plurality of second circuit boards have different acoustically-active elements attached thereto, and wherein selecting is based on a type of the acoustically-active elements.

13. The method of claim 10, wherein the acoustically-active elements are selected from the group comprising: an acoustic mesh; a sound guide; a sealing; and a bezel of the microphone.

14. A system comprising: a first circuit board comprising control circuitry configured to control a beamforming array of microphones, and a plurality of second circuit boards attached to the first circuit board, each one of the multiple second circuit boards to receive a corresponding microphone of the beamforming array of microphones.

15. The system of claim 14, wherein the plurality of second circuit boards is electronically coupled to the first circuit board using at least one of a pin header or a cable.

16. The system of claim 14, wherein, for each one of the plurality of second circuit boards, the respective microphone is soldered to the respective one of the plurality of second circuit boards.

17. The system of claim 14, wherein, a respective at least one acoustically-active element is attached to each one of the plurality of second circuit boards, and wherein the respective at least one acoustically-active element is selected from the group comprising: an acoustic mesh; a sound guide; a sealing; and a bezel of the microphone.

18. The system of claim 14, wherein at least two microphones of the beamforming array of microphones have a different acoustic configuration.

19. The system of claim 14, wherein each microphone of the beamforming array of microphones is a micro-electro-mechanical system (MEMS) microphone.

20. The system of claim 19, wherein each MEMS microphone is omni-directional.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG. 1 schematically illustrates an MA and an associated control circuitry according to various examples.

[0033] FIG. 2 schematically illustrates a 2-axis polar plot of an MA's directivity according to various examples.

[0034] FIG. 3A schematically illustrates frequency responses of an MA according to various examples.

[0035] FIG. 3B schematically illustrates frequency responses of an MA according to various examples.

[0036] FIG. 4 schematically illustrates a system of a first circuit board and three second circuit boards having each a microphone according to various examples.

[0037] FIG. 5 is a perspective view a possible structural implementation of a system of a first circuit board and four second circuit boards each having a microphone attached thereto according to various examples.

[0038] FIG. 6 is a cross-section view of the system of FIG. 5.

[0039] FIG. 7 is a flowchart of a method for fabricating an MA according to various examples.

DETAILED DESCRIPTION OF EMBODIMENTS

[0040] The above-described characteristics, features, and advantages of this disclosure, as well as the manner in which they will be achieved, will become clearer and more clearly understood in connection with the following description of the examples, which will be described in detail in conjunction with the drawings.

[0041] Hereinafter, various examples will be described with reference to preferred examples with reference to the drawings. In the figures, similar reference characters designate the same or similar elements. The figures are schematic representations of various examples of the disclosure. Elements shown in the figures are not necessarily drawn to scale. Rather, the various elements shown in the figures are reproduced in such a way that their function and general purpose will be understood by those skilled in the art.

[0042] Hereinafter, a 2-step assembly process for an MA will be described. Firstly, multiple sub-assemblies are formed, each sub-assembly including a respective circuit board and one or more microphones are attached thereto. The one or more microphones are attached to the respective circuit board using soldering points. After triggering a reflow process of the soldering points, by using one or more heat shocks, an acoustic characterization of the microphones of the multiple sub-assemblies can be implemented. Based on the acoustic characterization, it is possible to select a subset of the sub-assemblies for forming the MA. In particular, the MA can be built from such microphones that have matching acoustic characterization.

[0043] FIG. 1 illustrates aspects relating to the MA 200. The MA 200 includes multiple microphones and control circuitry 81. For example, the multiple microphones 201, 202, 203 can be MEMS microphones. MEMS microphones have an omnidirectional directivity. This means that they respond equally to sounds no matter which direction they come from. Multiple microphones or in particular, MEMS microphones can be configured in a phase-array to form a directional response or a beam pattern. Such an array can be called MA. The MA can be configured to be more sensitive to sound which comes from one or more specific directions than to sound which comes from other directions. Different array configurations are possible, for example, broadside summing arrays or differential endfire arrays, which can have e.g. different spatial and frequency responses advantageous for particular applications.

[0044] The control circuitry 81 may be, for example, implemented by an integrated circuit, a microcontroller, or as a Field Programable Gate Array (FPGA) and may be configured to implement a beamforming algorithm. Based on a combination of the signals received from each microphone 201-203, a directivity of the reception sensitivity can be implemented. For example, a weighted combination would be conceivable, considering amplitude and a phase of the signals received from each microphone 201-203. Also, a non-weighted summing would be conceivable. In other scenarios, it is possible that the control circuitry 81 is configured to forward the audio signals received from each microphone 201-203 to a further processing circuitry located off-chip (e.g., a vehicle head unit of a vehicle). It is also possible that the control circuitry 81 encodes the audio signals received from the microphones 201-203, for example, prior to forwarding. It would be possible that the control circuitry 81 is configured to act as a communication interface, for example, for communicating on a vehicle bus system.

[0045] For example, the MA is a broadside array and includes three microphones 201, 202, 203 as shown in FIG. 1. In a broadside MA, a line of microphones is arranged perpendicular to the preferred direction of sound waves—having a high reception sensitivity. The microphones or elements of the MA are positioned with an equidistant spacing between each other. Higher numbers of microphones in broadside arrays can achieve greater attenuation of sound from the sides of the MA.

[0046] FIG. 2 shows a 2-axis polar plot of a directional sensitivity of the MA of FIG. 1. Directional sensitivity describes the pattern in which the output level of the microphone or array changes when the sound source changes position in an anechoic space. Individual MEMS microphones can have an omnidirectional sensitivity. This entails that the microphones are equally sensitive to sound coming from all directions, regardless of the orientation of the microphone. For an omnidirectional microphone, a 2-axis polar plot of the microphone's response looks the same (e.g., a circle) regardless of whether the microphones port is oriented in the x-y, x-z, or y-z plane. In the polar plot, the front of the array, as the on-axis direction, is the direction of the desired audio pickup and is labeled as 0°. The rear of the array is at 180° and the sides refer to the space in between, centered on 90° and 270°. The polar plot is normalized to the 0° response level.

[0047] In FIG. 3A, frequency responses 300 of an MA are shown. In particular, a normalized frequency response of a broadside beamformer at different incident angles is illustrated. A broadside beamformer has a flat frequency response, on-axis, since the signals from two microphones receiving the same signal are simply summed up (not shown in FIG. 2). Off-axis, FIG. 2 clearly shows the nulls in the response.

[0048] Upon applying a heat-shock (e.g., to trigger a reflow process of soldering points), the frequency response 300 shifts by an offset 301 in frequency (full line vs. dashed line in FIG. 3A). The frequency offset 301 can vary depending on multiple circumstances and it has been observed that it is not always easy to control the magnitude of the offset 301 during assembly.

[0049] While FIG. 3A shows a frequency offset 301, in other examples, a level offset of the frequency response 300 may be observed, cf. FIG. 3B, offset 302.

[0050] According to various examples, a selection of the microphones that are used to form an MA is made after applying the heat-shock. This post-heat-shocked selection is facilitated by a 2-step assembly using sub-assemblies including respective circuit boards mounting the microphones. A respective system forming a microphone module is illustrated in FIG. 4.

[0051] In FIG. 4, a system 80 of a first circuit board 90 and four second circuit boards 101-104 having each a microphone 201, 202, 203, 204 is illustrated. The circuit board 101 and the microphone 201 forms a sub-assembly 71; the circuit board 102 and the microphone 202 forms a sub-assembly 72; the circuit board 103 and the microphone 203 forms a sub-assembly 73; and the circuit board 104 and the microphone 204 forms a sub-assembly 74.

[0052] Each sub-assembly 71-74 may also include one or more acoustically-active elements (not shown in FIG. 4).

[0053] The circuit board 101, for example, a printed circuit board, PCB is mounted to the circuit board 90 or for example, a PCB using one or more physical mounting features 95. The circuit board 102 is mounted to the circuit board 90 using one or more physical mounting features 96. The circuit board 103 is mounted to the circuit board 90 using one or more physical mounting features 97. The circuit board 104 is mounted to the circuit board 90 using one or more physical mounting features 98. For example, a pin-socket connection may be used for the physical mounting features 95-98. For example, a clip-on mounting may be used for the physical mounting features 95-98.

[0054] Illustrated in the example of FIG. 4 is a scenario in which, in addition to the physical mounting features 95-98, the circuit boards 101-103 are also electrically connected using electrical connections 91-94. In some examples, the electrical connections 91-94 and the physical mounting features 95-98 may be implemented by the same structural features.

[0055] The system 80 includes a number of 4 sub-assemblies 71-74, as a general rule, a larger or smaller count of sub-assemblies may be used.

[0056] According to various examples, multiple sub-assemblies including the sub-assembly 71-74 may be formed by attaching one or more microphones on respective circuit boards. Then, the appropriate sub-assembly 71-74 having matched acoustic characteristics of the respective microphones 201-203 may be selected; and the circuit boards 101-104 can be subsequently attached to the circuit board 90. The control circuitry 81 can then control the operation of the formed MA.

[0057] FIG. 5 is a perspective view of a possible structural implementation of the system 80 of FIG. 4, including a first circuit board 90 and four second circuit boards 101, 102, 103, 104 each having a microphone 201, 202, 203, 204 attached thereto according to various examples.

[0058] The first circuit board 90 can include parts such as power supply filtering capacitors and connectors for signal and power distribution. The first circuit board 90 can be described as a motherboard. The first circuit board 90 includes the control circuitry 81 combining signals from each one of the microphones 201-204. For example, the microphones are MEMS microphones.

[0059] The multiple second circuit boards 101, 102, 103 are electronically and mechanically coupled to the first circuit board 90 via connections 91-98 implemented by metallic pins, more specifically, a pin header that engage into a corresponding socket 99. This plug-and-socket connection does not require or generate heat to form the engagement and electrical connection. Another possible electronic connection would include a cable connection, e.g., combined with a clip-on connection for establishing a mechanical engagement.

[0060] For example, the audio signals can be transmitted from each microphone 201-204 to the control circuitry 81 via the electronic connection as discussed above.

[0061] For each one of the multiple second circuit boards 101-104, the respective microphone 201-204 is soldered to the respective one of the multiple second circuit boards 101-104. The microphones can be surface mounted components. The microphones can be soldered in a reflow oven. Thereby, a heat shock can be applied to trigger the reflow process.

[0062] In one example of the system 80, at least two of the multiple second circuit boards 101-104 have a different acoustic configuration of the microphones 201-204. For example, at least two of the multiple second circuit boards 101-104 have different acoustic channels attached to the microphones 201-204. Alternatively or additionally, one or more other acoustically-active elements may vary between the sub-assembly 71-74, e.g., the type and/or placement with respect to the microphone 201-204. Details with respect to such acoustically-active elements are illustrated in connection with FIG. 6.

[0063] FIG. 6 is a detailed cross-section of the first and second circuit board attached to each other according to various examples. This perspective shows multiple acoustically-active elements. One or more acoustically-active elements can be included in each sub-assembly 71-74, e.g., attached to the respective microphone 201-204. The acoustically-active element can be selected from the group comprising: an acoustic mesh 400; a sound guide 500; a sealing 401; and/or a bezel 501 of the microphone 201. The sound guide 500 implements the acoustic channel.

[0064] FIG. 7 shows an example of a method 3000 for a method for fabricating a matched MA. For example, it would be possible to fabricate the system 80 according to FIG. 4 or FIG. 5 using the method 3000. Optional boxes are illustrated with dashed lines.

[0065] The method 3000 includes mounting 3005, to each second circuit board of a plurality of second circuit boards, at least one microphone 201 using soldering points.

[0066] Upon mounting, the method includes applying 3015 one or more heat shocks to the plurality of second circuit boards, thereby triggering a reflow process of the soldering points.

[0067] Upon applying of the one or more heat shocks, the method includes performing 3020 an acoustic characterization of the microphones of the plurality of second circuit boards.

[0068] One or more acoustic characteristics can be determined for the microphones. For instance, a frequency response can be measured for each microphone. For instance, a minimum position and/or maximum position of the frequency responses could be determined.

[0069] The method further includes selecting 3025 a subset of the plurality of second circuit boards comprising multiple second circuit boards based on the acoustic characterization. In particular, the subset of second circuit boards can be selected based on a match between the acoustic characterization of the microphones of the plurality of second circuit boards. For example, a frequency offset between the frequency positions of minimums or maximums in the frequency responses could be considered.

[0070] The method also includes forming 3030 an MA based on the subset of the plurality of second circuit boards. The forming of the MA can include attaching the multiple second circuit boards of the subset to a first circuit board, the first circuit board comprising a control circuitry configured to control the MA. The forming of the MA can include electrically connecting the microphones to the control circuitry on the first circuit board.

[0071] This method enables making a selection on microphones already soldered on the second circuit board, after the reflow heat shock. In this way, the frequency responses of the microphones can be matched accurately, as the effect of frequency response change due to soldering is eliminated.

[0072] The attaching of the multiple second circuit boards of the subset to a first circuit board at 3030 can include electronically coupling the multiple second circuit boards to the first circuit board via a connection which does not require or generate heat during fabricating the connection. This prevents influences on the frequency response due to heat.

[0073] The method 3000 can further include attaching 3010, to each second circuit board of the plurality of second circuit boards, at least one acoustically-active element. The acoustic characterization can be performed upon attaching the at least one acoustically-active element. Elements attached to the second circuit board, like for example an acoustic mesh, can have an effect on the single channel frequency response. The selection process can be done once all the raw materials are attached to the sub-assembly of the second circuit boards. Performing the acoustic characterization after the attaching of the acoustically active elements ensures that all influences on the acoustic behavior of the second circuit boards including all elements are taking into account. This further improves the matching and the performance of the MA.

[0074] It is possible that the selecting 3025 depends on a type of acoustically-active elements attached 3010 to the second circuit boards. For example, it would be possible to select 3025 for a given MA such sub-assemblies that include the same types of acoustically-active elements. It would also be possible to select sub-assemblies that include complimentary types of acoustically-active elements, e.g., different acoustic channels, etc.

[0075] In some scenarios, it would even be possible that two or more MAs are formed, by selecting multiple subsets, each subset being associated with sub-assemblies of different types of acoustic channels or other acoustic characteristics. For example, a first MA could be formed having sub-assemblies, where a first type of acoustic channel is attached to the respective microphones and the second MA could be formed using the same first circuit board where a second type of acoustic channel is attached to the respective microphones.

[0076] Although the invention has been shown and described with respect to certain preferred embodiments, equivalents and modifications will occur to others skilled in the art upon the reading and understanding of the specification. The present invention includes all such equivalents and modifications and is limited only by the scope of the appended claims.

[0077] For example, above, scenarios have been described in which a single microphone is mounted to each second circuit board. As a general rule, it would be possible that multiple microphones mounted to each second circuit board. Still, a post-heat-exposure selection can be possible.

[0078] Furthermore, scenarios have been shown in which a single MA is implemented on the first circuit board. It would be possible that multiple MAs are implemented on the first circuit board, for example, using different acoustic channels or hardware filters for the respective microphones. Here, it would be possible that the microphones of each MA are individually matched based on the acoustic characteristics; or it would even be possible that the microphones are matched across multiple MAs.