Patent Application
20170048623
This application relates to micro electro mechanical system (MEMS) acoustic devices.
Achieving acceptable ultrasonic signal-to-noise ratio (SNR) levels has been challenging in relation to a number of applications. Operating a microphone so as to have an adequate response curve over a frequency range including ultrasonic frequencies has also proved challenging. The problems of previous approaches have resulted in some user dissatisfaction.
In one or more embodiments, a microelectromechanical systems (MEMS) acoustic device includes a first MEMS transducer and a second MEMS transducer. The first MEMS transducer includes a first diaphragm and a first back plate. At least one of the first diaphragm and the first back plate has a first dimension. The second MEMS transducer includes a second diaphragm and a second back plate. At least one of the second diaphragm and the second back plate has a second dimension. A magnitude of the second dimension is less than a magnitude of the first dimension.
In one or more embodiments, a device includes a first microelectromechanical systems (MEMS) transducer, a second MEMS transducer and a summing device. A first dimension of the first MEMS transducer is predefined to configure the first MEMS transducer to have a first resonance frequency. A second dimension of the second MEMS transducer is predefined to configure the second MEMS transducer to have a second resonance frequency different than the first resonance frequency. The summing device is coupled to the first MEMS transducer and the second MEMS transducer and provides an output representing a combination of information from the first MEMS transducer and the second MEMS transducer.
The foregoing summary is illustrative and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the following drawings and the detailed description.
For a more complete understanding of the disclosure, reference should be made to the following detailed description and accompanying drawings wherein:
In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols identify similar components. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and make part of this disclosure.
As used herein, relative terms, such as “inner,” “interior,” “outer,” “exterior,” “top,” “bottom,” “front,” “back,” “upper,” “upwardly,” “lower,” “downwardly,” “vertical,” “vertically,” “lateral,” “laterally,” “above,” and “below,” refer to an orientation of a set of components with respect to one another; this orientation is in accordance with the drawings, but is not required during manufacturing or use.
The present disclosure describes acoustic devices that include two or more MEMS transducers. The present disclosure further describes acoustic devices which include a first MEMS transducer having a first resonance frequency and a second MEMS transducer having a second resonance frequency different from the first resonance frequency by design. The term “resonance frequency” as used herein refers to a frequency or range of frequencies at which signals oscillate with relatively greater amplitude due to configuration of a device, circuitry, environment, or a combination thereof, such that an amplitude of oscillation at the resonance frequency is greater than an amplitude of oscillation at frequencies other than the resonance frequency.
In the present disclosure, the terms “audible frequency range” and “ultrasonic frequency range” are used. It is to be understood that an “audible frequency range” will vary between subjects (e.g., humans, animals, or other receivers). For example, humans collectively have a human-audible frequency range within a range of about 10 Hertz (Hz) to about 20 kilohertz (kHz), while specific human individuals may have a smaller (and even significantly smaller) audible frequency range within the human-audible frequency range. Thus, references to an audible frequency range herein are intended to be helpful in understanding the concepts described, and are not limiting to one specific range of frequencies. As used herein, the term “ultrasonic frequency range” encompasses frequency ranges of acoustic frequencies above the human-audible frequency range such as, for example, acoustic frequencies above 20 kHz, acoustic frequencies in a range of 20 kHz to 100 kHz, acoustic frequencies in a range of 20 kHz to 2 megahertz (MHz), acoustic frequencies in a range of 50 kHz to 500 kHz, or any other acoustic frequency range above the human-audible frequency range. It should be understood that in some embodiments, an acoustic device may be configured for individuals with hearing capabilities that do not extend to 20 kHz, and an ultrasonic frequency range would accordingly be above an audible frequency range of those individuals.
In one or more embodiments, an acoustic device incorporates a first MEMS transducer for signals in an audible frequency range and a second MEMS transducer for signals in an ultrasonic frequency range. Accordingly, a frequency response of the acoustic device can be improved to be sensitive to audible frequencies and ultrasonic frequencies. In one or more embodiments, the first MEMS transducer is designed to have a resonance frequency in the audible frequency range, and the second MEMS transducer is designed to have a resonance frequency in the ultrasonic frequency range. In one example, the first resonance frequency is designed to be 15 kHz and the second resonance frequency is designed to be 50 kHz. In one or more embodiments, the first MEMS transducer is designed to have a first resonance frequency in the ultrasonic frequency range, such that a frequency response curve of the first MEMS transducer is relatively flat across portions of, or all of, the audible frequency range, and the second MEMS transducer is designed to have a second resonance frequency in the ultrasonic frequency range, where the second resonance frequency is greater than the first resonance frequency. In one example, the first resonance frequency is 30 kHz and the second resonance frequency is 70 kHz.
In one or more embodiments, an acoustic device includes a first MEMS transducer having a first size and a second MEMS transducer having a second size. The term “size” refers to one or more dimensions (e.g., length, width, thickness, area, circumference, radius or volume) of a diaphragm, a back plate, and/or a chamber of a MEMS transducer. In one or more embodiments, an area of the diaphragm and an area of the back plate of the first MEMS transducer is greater than an area of the diaphragm and an area of the back plate of the second MEMS transducer, respectively. This difference in the areas of the diaphragms and the back plates of the first and the second MEMS transducers can result in different resonance frequencies of the first and the second MEMS transducers. For example, the smaller size of the second MEMS transducer results in a resonance frequency that is greater than the resonance frequency of the larger first MEMS transducer.
In one or more embodiments, ultrasonic performance of acoustic devices used in applications such as proximity detection, gesture recognition, activity detection, pen input, and so on, can be improved by including a second MEMS transducer, and may further be improved by combining the advantages of the second MEMS transducer with other ultrasonic performance boosting techniques.
As will be seen from the following discussions related to example embodiments of the present disclosure, MEMS devices can be used as ultrasonic transmitters by leveraging MEMS and package resonances (which can be tuned to ultrasonic frequencies) to maximize output. An ultrasonic MEMS transmitter in conjunction with a dual-band MEMS architecture as discussed herein additionally provides for improvements in (1) ultrasonic sensing, (2) ultrasonic transmission, and (3) ultrasonic proximity detection.
Further, an ability to selectively designate MEMS transducers as transmitters or receivers, combined with multiple MEMS die in a package or multiple MEMS dies on a single substrate, provides for a configurable MEMS architecture for configuration for multiple uses cases. Examples of use cases include enhanced ultrasonic sensing using the MEMS transducers as receivers tuned for ultrasonic signal acquisition, enhanced ultrasonic transmission using the MEMS transducers as transmitters for maximum output/range, and proximity detection with a single package (and/or a single MEMS die with multiple transducers) that can transmit and receive ultrasonic signals for near range proximity.
The component 105 includes a charge pump 106 and a summing amplifier 108. In one or more embodiments, the charge pump 106 is a direct current (DC) to DC voltage converter. The charge pump 106 is coupled to the first MEMS transducer 102 and the second MEMS transducer 104. In one or more embodiments, the first MEMS transducer 102 and second MEMS transducer 104 can be coupled to separate charge pumps, instead of the same charge pump 106. The charge pump 106 provides power to charge and maintain the first MEMS transducer 102 and the second MEMS transducer 104 at a bias voltage (e.g., the variable capacitances of the first MEMS transducer 102 and the second MEMS transducer 104 are charged to a particular bias voltage in the absence of diaphragm movement). A voltage V1 at an output of the first MEMS transducer 102 varies as the capacitance of the first MEMS transducer 102 changes responsive to incident acoustic signals, and a voltage V2 at an output of the second MEMS transducer 104 varies as the capacitance of the second MEMS transducer 104 changes responsive to incident acoustic signals. In other words, the output voltages V1 and V2 vary over time as the capacitances of the respective first MEMS transducer 102 and second MEMS transducer 104 vary with the incident acoustic signals, and thus diaphragm movement is translated into an alternating current (AC) signal superimposed over the bias voltage. The output voltages V1 and V2 are provided to the summing amplifier 108. In one or more embodiments, the output voltages V1 and V2 may be filtered or buffered prior to being provided to the summing amplifier 108 (e.g., to filter out ripple from the charge pump, or to average out unwanted noise).
The summing amplifier 108 adds the voltage outputs V1 and V2 of the first and the second MEMS transducers 102 and 104, respectively, and outputs a summed output voltage Vs. The summing amplifier 108 can include, for example, a summing operational amplifier, an instrumentation amplifier, a differential amplifier, or two or more thereof. In one or more embodiments, the summing amplifier 108 can have unity gain. The output voltage Vs of the summing amplifier 108 is provided to a controller 110 (e.g., shown by way of example as a system on chip (SoC)). In one or more embodiments, the controller 110 can be implemented, without limitation, using a microprocessor, a multi-core processor, a digital signal processor, an ASIC, a field programmable gate array (FPGA), or other control device and associated circuitry. In one or more embodiments, the component 105 can include an analog to digital converter (ADC) to digitize the summed output voltage Vs. Alternatively, the controller 110 can include an ADC to digitize the summed output voltage Vs. The digitized summed output voltage can be processed by the controller 110. For example, in one or more embodiments, processing carried out by the controller 110 can include identifying a word or phrase, or identifying an ultrasonic frequency pattern. In one or more other embodiments, processing can further include, without limitation, filtering, determining impulse response, sampling and signal reconstruction, frequency analysis, and power spectrum estimation.
The first MEMS transducer 102 includes a first diaphragm and a first back plate. Similarly, the second MEMS transducer 104 includes a second diaphragm and a second back plate. In one or more embodiments, the first back plate and the second back plate are coupled to the summing amplifier 108, while the first diaphragm and the second diaphragm are coupled to the charge pump 106. In one or more other embodiments, the first back plate and the second back plate are coupled to the charge pump 106, while the first diaphragm and the second diaphragm are coupled to the summing amplifier 108.
In one or more embodiments, surface areas of the first back plate and the first diaphragm of the first MEMS transducer 102 are approximately the same. In one or more other embodiments, the surface area of the first back plate can be different from the surface area of the first diaphragm. In one or more embodiments, surface areas of the second back plate and the second diaphragm of the second MEMS transducer 104 are approximately the same. In one or more other embodiments, the surface area of the second back plate can be different from the surface area of the second diaphragm.
In one or more embodiments, the surface areas of the first back plate and the first diaphragm of the first MEMS transducer 102 are substantially greater by design than surface areas of, respectively, the second back plate and the second diaphragm of the second MEMS transducer 104; such as, for example two to three times greater.
In general terms, when a MEMS transducer is positioned within an acoustic device, the acoustic device has a geometric front volume defined between a first side of the transducer (closest to the diaphragm) and a portion of the acoustic device that includes a port corresponding to the transducer (such as a printed circuit board with a port hole faced by the transducer in a bottom port configuration, or such as a housing with a port hole faced by the transducer in a top port configuration). Thus, the front volume is a function of a surface area of the first side of the transducer facing the port (in either the top port configuration or the bottom port configuration). The acoustic device also has a geometric back volume defined between an opposite second side of the transducer (closest to the back plate) and a portion of the acoustic device opposite the port corresponding to the transducer (e.g., a side of the housing (e.g., a can) of the acoustic device in the bottom port configuration or in the printed circuit board in the top port configuration). A resonance frequency of the transducer is inversely related to a ratio of the front and back volumes. Because the front volume is a function of the surface area of the first side of the transducer, and because generally the surface area of the first side of the transducer is defined in large part by the sizes of the back plate and the diaphragm within the transducer, the front volume is a function of the surface areas of the back plate and the diaphragm. Thus, for a defined distance between the transducer and the port, a decrease in the surface areas of the back plate and the diaphragm will result in a decrease in the front volume and a corresponding increase in the resonance frequency.
Referring back to
In addition to being related to a relationship between the front and back volumes, the resonance frequency of a MEMS transducer is a function of a thickness of the diaphragm. In particular, the resonance frequency of the MEMS transducer can increase with an increase in the thickness of the diaphragm. In one or more embodiments, the first MEMS transducer 102 and the second MEMS transducer 104 may have similar surface areas but different diaphragm thicknesses, resulting in different respective resonance frequencies. In one or more embodiments, the diaphragm of the second MEMS transducer 104 is thicker than the diaphragm of the first MEMS transducer 102, such that the resonance frequency of the second MEMS transducer 104 is in the ultrasonic frequency range, while the resonance frequency of the first MEMS transducer 102 is in the audible frequency range.
The component 205 includes a first charge pump 206 and a second charge pump 207, which can be similar in design and operation to the charge pump 106 of
The component 205 further includes a first amplifier 208, a second amplifier 209, an adder 210, a first filter 214, and a second filter 216. An output of the first MEMS transducer 202 is coupled to the first amplifier 208, while an output of the second MEMS transducer 204 is coupled to the second amplifier 209. An output of the first amplifier 208 is coupled to the first filter 214, and an output of second amplifier 209 is coupled to the second filter 216. Outputs of the first filter 214 and the second filter 216 are coupled to the adder 210. An output of the adder 210 is coupled to a controller 212 (e.g., shown by way of example as a system on chip (SoC)). In one or more embodiments, the controller 212 can be implemented, without limitation, using a microprocessor, a multi-core processor, a digital signal processor, an ASIC, an FPGA, or other control device and associated circuitry.
The adder 210 can be similar to the summing amplifier 108 discussed above in relation to
The first amplifier 208 and the second amplifier 209 amplify signals received from the first MEMS transducer 202 and the second MEMS transducer 204, respectively.
One or both of the first filter 214 and the second filter 216 may filter unwanted noise from the respective received signals. In one or more embodiments, one or both of the first filter 214 and the second filter 216 filter out signal information in frequencies not in a range of interest. For example, if it is desired that signals received from the first amplifier 208 are to be limited to human-audible frequencies, the first filter 214 may filter out ultrasonic frequencies. For another example, if it is desired that signals received from the second amplifier 209 are to be limited to ultrasonic frequencies, the second filter 216 may filter out human-audible frequencies. For a further example, the first filter 214 may filter out frequencies below a human-audible range, and/or the second filter 216 may filter out frequencies above an ultrasonic frequency of interest. Thus, the first filter 214 and the second filter 216 may include lowpass, highpass, bandpass, or bandstop filters, or any combination thereof. In one or more embodiments, one or both of the first filter 214 and the second filter 216 may average or integrate received signals over specified time periods, such as to reduce noise. In one or more embodiments, one or both of the first filter 214 and the second filter 216 may be omitted.
The adder 210 sums or adds the two filtered signals together to generate a summed signal provided to the controller 212.
Similarly as discussed with respect to the first MEMS transducer 102 and the second MEMS transducer 104 in
Although the foregoing discussion was with respect to two MEMS transducers, additional MEMS transducers may be included in an acoustic device according to the present disclosure, to further shape a desired frequency response.
Also in
It is to be understood that the acoustic devices of
Although illustrated in
Although described above with respect to receiving incident signals, any of the MEMS transducers (e.g., any of the first MEMS transducers 102, 202, 404 or the second MEMS transducers 104, 204, 406) may be used alternatively or additionally to transmit signals. For example, with respect to
While the shape of each of the first and the second MEMS transducers 404 and 406 shown in
As used herein, the terms “approximately,” “substantially,” “substantial” and “about” are used to describe and account for small variations. When used in conjunction with an event or circumstance, the terms can refer to instances in which the event or circumstance occurs precisely as well as instances in which the event or circumstance occurs to a close approximation. For example, when used in conjunction with a numerical value, the terms can refer to a range of variation less than or equal to ±10% of that numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. For example, two numerical values can be deemed to be “substantially” the same if a difference between the values is less than or equal to ±10% of an average of the values, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%.
Additionally, amounts, ratios, and other numerical values are sometimes presented herein in a range format. It is to be understood that such range format is used for convenience and brevity and should be understood flexibly to include numerical values explicitly specified as limits of a range, but also to include all individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly specified.
It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.).
As used herein, the singular terms “a,” “an,” and “the” may include plural referents unless the context clearly dictates otherwise.
It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations).
Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.”
While the present disclosure has been described and illustrated with reference to specific embodiments thereof, these descriptions and illustrations do not limit the present disclosure. It should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the present disclosure as defined by the appended claims. The illustrations may not be necessarily drawn to scale. There may be distinctions between the artistic renditions in the present disclosure and the actual apparatus due to manufacturing processes and tolerances. There may be other embodiments of the present disclosure which are not specifically illustrated. The specification and drawings are to be regarded as illustrative rather than restrictive. Modifications may be made to adapt a particular situation, material, composition of matter, method, or process to the objective, spirit and scope of the present disclosure. All such modifications are intended to be within the scope of the claims appended hereto. While the methods disclosed herein have been described with reference to particular operations performed in a particular order, it will be understood that these operations may be combined, sub-divided, or re-ordered to form an equivalent method without departing from the teachings of the present disclosure. Accordingly, unless specifically indicated herein, the order and grouping of the operations are not limitations of the present disclosure.
This application claims the benefit of and priority to U.S. Provisional Patent Application 62/203,048 filed Aug. 10, 2015 to Qutub et al., titled “Dual Band MEMS Microphone,” the contents of which are incorporated herein by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62203048 | Aug 2015 | US |
