Patent Application
20180139551
The invention relates to an audio transducer, such as a speaker to transduce an electrical audio signal into acoustic sound or a receiver to transduce an acoustic sound into an electrical audio signal. This invention furthermore relates to a micro speaker optimized for high acoustic output and located within a small volume of a mobile device, such as a mobile phone, a tablet, a gaming device, a notebook or similar device. As the physical volume within these mobile devices is very limited and as the audio transducer has to fit into the housing of the mobile device together with other modules having rectangular shapes, the micro speaker quite often must be constructed having a rectangular form factor.
When maximizing the performance of a speaker by means of output power, linearity and robustness, limitations given by the design of the speaker need to be taken into account. Using the electrical interface as a driver to drive the membrane and as a sensor to sense the actual position of the membrane at the same time is well-known and used in several sophisticated class D amplifiers that model the loudspeaker based on static as well as dynamically gathered parameters through the electrical interface. Some prior art speakers comprise a sensor to sense the position of the membrane in the speaker. The sensor signal may be used to track the actual deflection of the membrane and to avoid deflections that are too large. Such large deflections may cause the membrane to touch the housing of the speaker or the top plate of the magnet located beneath the membrane, both of which result in a distorted sound being emitted from the speaker. The sensor signal may be fed into the amplifier that amplifies the audio signal being fed into the voice coil of the speaker in order to avoid such large deflections of the membrane.
In some prior art speakers, a sensor comprises a second coil layer wound over the whole height of the voice coil that drives the membrane to generate sound. The magnetic flux of the magnet system of the speaker induces a membrane voltage in both coils based on the position of the coil in relation to the magnet system which is not equally distributed over the moving range of the coils. This type of sensor has the disadvantage that the second coil adds cost and technical complexity to the speaker and that the second coil increases the weight of the moving part of the speaker, thereby reducing the acoustic sound output power of the speaker.
Another sensor in prior art loudspeakers uses laser light to measure the varying distance of the membrane. This type of sensor is only used for large speakers and it increases the costs and technical complexity of the speaker substantially.
It is an object of the invention to have an audio transducer for mobile devices without the disadvantages of known transducers. A new audio transducer for mobile devices, in particular for a micro speaker, comprises a sensor for sensing the position of the membrane using the capacitance between a membrane plate and a top plate, which is part of the magnetic system of the speaker. An advantage of this new sensor is that mechanical elements already part of the speaker are used to form a capacitor which capacitance changes with the position of the membrane within the speaker. This helps to keep the weight of the moving parts of the speaker low and the quality of sound emitted high. Further details and advantages of such an audio transducer will become apparent in the following description and the accompanying drawings.
The foregoing and other aspects, features, details, utilities, and advantages of the present invention will be apparent from reading the following description and claims, and from reviewing the accompanying drawings.
Further embodiments of the invention are indicated in the figures and in the dependent claims. The invention will now be explained in detail by the drawings. In the drawings:
Various embodiments are described herein to various apparatuses. Numerous specific details are set forth to provide a thorough understanding of the overall structure, function, manufacture, and use of the embodiments as described in the specification and illustrated in the accompanying drawings. It will be understood by those skilled in the art, however, that the embodiments may be practiced without such specific details. In other instances, well-known operations, components, and elements have not been described in detail so as not to obscure the embodiments described in the specification. Those of ordinary skill in the art will understand that the embodiments described and illustrated herein are non-limiting examples, and thus it can be appreciated that the specific structural and functional details disclosed herein may be representative and do not necessarily limit the scope of the embodiments, the scope of which is defined solely by the appended claims.
Reference throughout the specification to “various embodiments,” “some embodiments,” “one embodiment,” or “an embodiment,” or the like, means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases “in various embodiments,” “in some embodiments,” “in one embodiment,” or “in an embodiment,” or the like, in places throughout the specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. Thus, the particular features, structures, or characteristics illustrated or described in connection with one embodiment may be combined, in whole or in part, with the features, structures, or characteristics of one or more other embodiments without limitation given that such combination is not illogical or non-functional.
Speaker 1 comprises a magnet system 5 with four magnets 6 arranged on the rectangular sides of the rectangular speaker 1 and a magnet 7 arranged in the center of speaker 1. Magnet system 5 furthermore comprises magnetic field guiding means 8 comprising top plate 9 fixed to magnet 7, ring plate 10 fixed to magnets 6, and pot plate 11 fixed to magnets 6 on the side opposite to ring plate 10. Field guiding means 8 guides and focuses the magnetic field of magnets 6 and 7 in an air gap 12, into which air gap 12 voice coil 3 is arranged in the assembled speaker 1.
Prior art micro speaker 1 further comprises frame 13 to assemble and align membrane 2 with magnet system 5. Voice coil 3 fixed to membrane 2 fits into air gap 12. Frame 13 typically is made from a molded plastic to enable the complex surface with openings to enable airflow and fixation of further parts of speaker 1. The ends of leads 4 of voice coil 3 are soldered with a contact pad, not shown in
The relevant parts of a first embodiment of the invention is shown in
The layered construction of membrane 22 is shown in the enlarged view of
In an embodiment, upper face-sheet layer 30 of membrane 22 is comprised of an aluminum foil while lower face-sheet layer 32 is comprised of a flexible circuit 36 that serves two functions. The flexible circuit 36 both stiffens membrane 22 similar to the function of an aluminum foil, and supports the electronic components of sensor 23. Flexible circuit 36 comprises a gate area 38 electrically separated from a ground area 40. The sensor 23 further comprises field effect transistor 42 and Ohmic resistor 44.
As show in
Top plate 30 is also connected to electrical ground 46. Together top plate 30 and gate area 38 of the flexible circuit 36 form a capacitor that changes its capacity based on the distance between gate area 38 and the top plate 30, and thus can be used to measure the position of membrane 22 within speaker 20.
The electrical connections for the components of sensor 23 and the leads 32, 34 for voice coil 3 to the stationary frame holding speaker 20 are not shown in the
Flexible circuit 36 in
Spider arms 48, 50, 52, 54 are also used to carry the electrical connections for sensor 23 and voice coil 3. In an embodiment shown in
The function of the sensor 23 is as follows. Gate area 38 connected to gate G of field effect transistor 42 is charged via resistor 44 with a very small current defined by the high Ohmic resistance of resistor 44. The distance between gate area 38 and top plate 30 connected to electrical ground 46 changes fast as membrane 22 moves with a frequency in the acoustic area (20 Hz to 20 kHz). As a result, electric potential on gate G changes equivalent to the movement of membrane 22 and modulates the current flow between drain D and source S of the field effect transistor 42. The graph of
In principle it would be possible to use the complete lower face-sheet layer 32 as a gate area, but it is advantageous to shield gate area 38 with ground area 40 and upper face-sheet layer 30 against electromagnetic interference. This not only improves the quality of sensor signal 60, but is essential that the waveform of the signal strongly correlates with the actual displacement of the membrane. Any corruption of the signal (e.g., spurious impulses from a display driver in a mobile phone) will lead to under- or overestimation of the actual position of the membrane. It is furthermore advantageous to insert the electronic components of the sensor 23 into membrane 22 in order to prevent the high impedance area of gate area 38 getting covered by electromagnetic noise in one of the spider arms.
Gate area 72 and ground area 74 are electrically created on a flexible circuit 76, which means that there needs to be a low resistive electrical connection between the top plate 70 and the flexible circuit 76 holding the electronics. The lower face-sheet layer of membrane 66 is a single layer, for example, of aluminum foil, which acts as shielding and needs to be connected to electrical ground as well. This connection can be easily achieved when the micro speaker 62 is connected to a Class AB amplifier because one of the connections of voice coil 3 will be connected to electrical ground through the amplifier.
In the micro speaker 62 depicted in
Speakers according to further embodiments of the invention could comprise two or four or even more gate areas of sensors to measure the movement of different parts of the membrane. The lower face-sheet layer of a membrane could be realized in another way than with a flexible circuit.
Speakers according to further embodiments of the invention could comprise a gate area with a fixed doped dielectric material like in electret microphones. This provides the advantage that there would be no need for resistor 44.
It is noted above that the lower face-sheet layer of membrane 66 can be connected to electrical ground 46 through the connections of voice coil 3 when the micro speaker 62 is connected to a Class AB amplifier. In that instance, the capacitive sensor 64 will be shielded by the lower face-sheet layer of membrane 66, the voice coil 3 and the top plate 70. The shielding is not perfect, however, because the resistance between the grounding connections are in the range of the voice coil impedance. Nevertheless, the shielding is sufficient to raise the signal-to-noise ratio of the sensor signal by several decibels.
In mobile applications, however, it is more common to use Class D amplifiers, in which case there is no ground signal because both connections to the speaker are switched. Thus, an alternative method to minimize the impact of highly transient high power signals within the mobile device environment is required.
The conductive layer 84 can also be made of aluminum or other conductive material. Further, the conductive layer 84 may be part of the lower face-sheet layer 82, which might be simply folded during the process of attaching the voice coil 3 to the membrane 66. Additionally, the conductive layer 84 may be a conductive color, paint or other coating applied to the inner side of the voice coil 3. It is desirable for the conductive layer 84 to have a low resistance and be as thin as possible to have minimal intrusion into the air gap 12 and thus minimal loss to the sensitivity of the performance of the micro speaker 62′.
The circuit described above and depicted in the figures may be particularly useful in frequency ranges greater than 1 Hz but not as practical in lower frequencies due to the high-pass behavior of the impedance converting component.
Where operation at very low frequencies is desired, a sensor circuit that can detect capacitance change rates down to 0 Hz is desirable. One such a circuit may employ frequency modulation of an oscillator in the RF region, which is not limited by a low cutoff frequency.
Different methods for readout of sensor capacitance at 0 Hz exist, including an oscillator principle, time constant measurement, a Schering Bridge and charging the capacitance with known charge. Example implementations of these methods, especially using a microcontroller, are described in Milosavljević, V., Mihajlović, Ž., Rajs, V., Živanov, M. (2011, September) Solution of Capacitive Touch Panel for Robust Industrial and Public Usage, Proceedings of the XV International Scientific Conference on Industrial Systems, Sep. 14-16, 2011, Novi Sad, Serbia, pp. 140-144.
In closing, it should be noted that the invention is not limited to the above mentioned embodiments and exemplary working examples. Further developments, modifications and combinations are also within the scope of the patent claims and are placed in the possession of the person skilled in the art from the above disclosure. Accordingly, the techniques and structures described and illustrated herein should be understood to be illustrative and exemplary, and not limiting upon the scope of the present invention. The scope of the present invention is defined by the appended claims, including known equivalents and unforeseeable equivalents at the time of filing of this application.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2016/081395 | 5/9/2016 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62158772 | May 2015 | US |
