Patent Publication Number: US-2022229084-A1

Title: Differential mems device and methods

Description:
The present application is a continuation of U.S. patent application Ser. No. 16/530,923 filed Aug. 2, 2019, now U.S. Pat. No. 11,255,871 issued Feb. 22, 2022, which claims benefit of U.S. Provisional Application No. 62/714,551 filed on Aug. 3, 2018, which are incorporated in its entirety herein. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to sensors. More specifically, the present invention relates to improving sensor performance with the use of multiple MEMS devices. 
     A constant challenge in the semiconductor space has been how to produce a high performance device for a low cost (low consumer price). An example of this is seen with microprocessors, where an Intel Core processor greatly outperforms an Intel Celeron processor, however is much more expensive. In the processor market, consumers often accept tradeoffs between processor performance and purchase price. 
     A similar challenge also applies in the case of sensors, e.g. MEMS-based sensors including accelerometers, magnetometers, gyroscopes, pressure sensors e.g. microphones, and the like. More particularly, the challenge is how to produce a high-performance MEMS for a low cost. There are differences in the sensor market, however, in that because it is a volume business, the price sensitivity is much higher. High performance MEMS devices are required at a low price. 
     In light of the above, what is desired are improved methods and apparatus to address the problem described above with reduced drawbacks. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention relates to sensors. More specifically, the present invention relates to improving sensor performance with the use of multiple MEMS devices. Low cost sensor devices (e.g. MEMS) intended for consumer applications, tend to have modest performance for parameters such as noise, temp coefficient, etc. In various embodiments, the performance of such lower-cost devices are greatly improved by using multiple sensors to make them suitable for applications requiring higher performance, such as for industrial applications 
     Embodiments of the present invention incorporate multiple MEMS devices into a single sensor device to improve performance of the sensor. The multiple MEMS devices may be oriented in orthogonal directions, in some embodiments, however may be in virtually any orientation with respect to each other. Further, the multiple MEMS devices may provide redundant data, that may be averaged or integrated to provide the sensor output; the multiple 
     MEMS devices may provide differential data, that may filter-out common mode movement or perturbation data; the multiple MEMS devices may provide combination of redundant and differential data; and the like. The MEMS devices may include accelerometers, gyroscopes, magnetometers. 
     According to one aspect of the invention, a sensor device is described. A system may include an initialization unit configured to simultaneously output a first initialization signal and a second initialization signal, in response to a master initialization signal, and a plurality of tri-axis MEMS sensors coupled to the initialization unit, wherein the plurality of tri-axis MEMS sensors comprises a first tri-axis MEMS sensor and a second tri-axis MEMS sensor, wherein the first tri-axis MEMS sensor is associated with a first spatial plane, wherein the second tri-axis MEMS sensor is associated with a spatial second plane, wherein the first spatial plane and the second spatial plane are not co-planar, wherein the first tri-axis MEMS sensor is configured to provide a first set of data in response to a physical perturbation, wherein the second tri-axis MEMS sensor is configured to provide a second set of data in response to the physical perturbation, wherein the first tri-axis MEMS sensor is configured to provide a first reply in response to the first initialization signal, wherein the second tri-axis MEMS sensor is configured to provide a second reply in response to the second initialization signal. An apparatus may include a controller coupled to the initialization unit and to the plurality of tri-axis MEMS sensors, wherein the controller is configured to provide the master initiation signal to the initialization unit, wherein the controller is configured to receive the first reply at a first time period, wherein the controller is configured to receive the second reply at a second time period, wherein the first time period and the second time period need not be identical, wherein the controller is configured to determine a latency between the first time period and the second time period, wherein the controller is configured to receive the first set of data and the second set of data, and wherein the controller is configured to determine motion data in response to the first set of data, to the second set of data, and to the latency. 
     According to another aspect of the invention, a sensor device is disclosed. A system may include a plurality of tri-axis MEMS sensors comprising a first tri-axis MEMS sensor and a second tri-axis MEMS sensor, wherein the first tri-axis MEMS sensor is associated with a first spatial plane, wherein the second tri-axis MEMS sensor is associated with a spatial second plane, wherein the first spatial plane and the second spatial plane are not co-planar, wherein the first tri-axis MEMS sensor is configured to provide a first interrupt in response to a physical perturbation, wherein the first tri-axis MEMS sensor is also configured to provide a first set of data in response to the physical perturbation, wherein the second tri-axis MEMS sensor is configured to provide a second interrupt in response to the physical perturbation, wherein the second tri-axis MEMS sensor is also configured to provide a second set of data in response to the physical perturbation. An apparatus may include a controller coupled to the plurality of tri-axis MEMS sensors, wherein the controller is configured to receive the first interrupt at a first time period, wherein the controller is configured to receive the second interrupt at a second time period, wherein the first time period and the second time period need not be identical, wherein the controller is configured to determine a latency between the first time period and the second time period, wherein the controller is configured to receive the first set of data and the second set of data, wherein the controller is configured to determine motion data in response to the first set of data, to the second set of data, and to the latency. 
     According to yet another aspect of the invention, a method for a sensor device is detailed herein. A technique may include simultaneously receiving in a first tri-axis MEMS sensor and a second tri-axis MEMS sensor an initialization signal, wherein the first tri-axis MEMS sensor is associated with a first spatial plane, wherein the second tri-axis MEMS sensor is associated with a spatial second plane, wherein the first spatial plane and the second spatial plane are not co-planar, outputting from the first tri-axis MEMS sensor a first reply in response to the initialization signal, and outputting from the second tri-axis MEMS sensor a second reply in response to the initialization signal. A process may include receiving in a controller the first reply at a first time period, receiving in the controller the second reply at a second time period, wherein the first time period and the second time period need not be identical, determining in the controller, a latency between the first time period and the second time period, outputting from the first tri-axis MEMS sensor a first set of data in response to a physical perturbation, and outputting from the second tri-axis MEMS sensor a second set of data in response to the physical perturbation. A method may include receiving in the controller the first set of data at a third time period, receiving in the controller the second set of data at a fourth time period, and determining in the controller motion data in response to the first set of data, to the second set of data, to the third time period, to the fourth time period and to the latency. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to more fully understand the present invention, reference is made to the accompanying drawings. Understanding that these drawings are not to be considered limitations in the scope of the invention, the presently described embodiments and the presently understood best mode of the invention are described with additional detail through use of the accompanying drawings in which: 
         FIG. 1  illustrates a configuration of embodiments of MEMS devices; 
         FIG. 2  illustrates another configuration of embodiments of MEMS devices; 
         FIG. 3  illustrates a block diagram of embodiments of various embodiments; 
         FIG. 4  illustrates another block diagram of embodiments of various embodiments; 
         FIG. 5  illustrates timing diagrams of embodiments of various embodiments; 
         FIG. 6  illustrates timing diagrams of embodiments of various embodiments; and 
         FIG. 7  illustrates a system block diagram of embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In various embodiments of the present invention, three-axis accelerometers provided by the inventors of the present invention are characterized by having low noise for X and Y axis since theses axis are typically sensed using in-plane motion. Data from the X and Y axis tend to have less parasitic noise, etc. compared to data from Z axis since this axis is typically sensed using out of plane motion. 
       FIG. 1  illustrates various embodiments of the present invention. In this figure, a sensor  100  is illustrated having multiple MEMS devices  110  (e.g. accelerometers) that are mounted substantially orthogonally  120  with respect to each other. This type of mounting provides lower noise data for the acceleration on the z-axis. In some embodiments, two or more MEMS devices may be mounted on a substrate, e.g. three, four, five, six, or the like, and may be used to sense the perturbation. In various embodiments of the present invention, post processing at a sensor-hub can perform many operations, including: selection of a particular data stream for each axis, merging of data from multiple sensors to compensate for effects of stress, temp coefficients, drift, etc. (e.g. averaging, integrating, differencing, etc.). 
       FIG. 2  illustrates a block diagram of embodiments of the present invention. More particularly  FIG. 2  illustrates a sensor  200  having three different pairs of sensors:  210 ,  220 , and  230 . As illustrated, pairs of sensors  210 ,  220  and  230  are substantially orthogonal with respect to each other and sensors (e.g.  212  and  214 ,  222  and  224 , and  232  and  234 ) are typically substantially parallel. In this embodiment, sets of differential data ( 240 ,  250  and  260 ) are obtained from pairs of sensors  210 ,  220  and  230 . As will be described below, a microcontroller, or the like receives data from pairs of sensors  210 ,  220  and  230  and determines physical perturbations based upon sets of differential data  240 ,  250  and  260 . 
       FIG. 3  illustrates an embodiment of the present invention. In this figure, a sensor  300  includes at least a first sensor  310  and a second sensor  320 , a clock  330  and a processing block  340 . Sensors  310  and  320  may be substantially orthogonal, substantially parallel, or skew with respect to each other. In this embodiment, data from the different sensors  310  and  320  that are to be merged or combined must be synchronized. An external clock or clock signal  350  is disclosed to provide a common clock to sensors  310  and  320 . The data  360  and  370  provided by sensors  310  and  320  are synchronized and provided to processing block  340  for processing. In one embodiment, sensors  310  and  320  can be synchronized at the system level. In various embodiments, the output data rate of clock  350  maybe increased (e.g. doubled) so that the synchronization between data  360  and  370  may be made more precise. 
       FIG. 4  illustrates an embodiment of the present invention. In this figure, a sensor  400  includes at least a first sensor  410  and a second sensor  420 , a self-test mechanism  430  and a processing block  440 . Sensors  410  and  420  may be substantially orthogonal, substantially parallel, or skew with respect to each other. In this embodiment, data from the different sensors  410  and  420  that are to be merged or combined must again be synchronized. In this embodiment, this is initiated by self-test or calibration mechanism  430 . In various embodiments, sensors  410  and  420  each have self-test mechanisms therein, that receive a self-test pulse or initiation command (e.g. via setting a register bit), and in response thereto, that generates a physical perturbation, e.g. a vibration or movement along one or more axes of interest therein. The self-generated perturbation or motion is then sensed by the other components within each respective sensor. The sensed motion waveforms  450  and  460  can be used to synchronize the data (e.g. multi-axis data) from the multiple sensors  410  and  420 . In some embodiments, the delay between initiation of the self-test process until when sensed data is output is known, based upon design specification, typically ahead of time. Accordingly, the synchronization can be performed more precisely. In some cases, the synchronization process may be performed once upon start up, at regular intervals, upon demand, or every time to establish time synchronization between multi-axis and multiple device data. As an example, during normal use of the device, a self-test process may be simultaneously performed. In such an example, a modulation or frequency for perturbation motion for the self-test may be different from than the frequency of the movement of the device while in normal use. Since the frequencies may be different, the device could verify synchronization based upon the self-test frequency of the self-test process, while at the same time obtaining perturbation data for the device at another frequency. 
     Various sensor devices including embodiments of the present invention may include: multiple sensor devices (e.g. MEMS devices, accelerometers, etc.), an aggregator, sensor hub, microcontroller unit (MCU) or application processor chip for performing the function of establishing and maintaining time synchronization between multiple axes and multiple sensor devices. 
       FIGS. 5 and 6  illustrate timing diagrams according to examples of embodiments. In the example in  FIG. 5 , the integrated device is subject to a physical perturbation A 1   500  at time TOA  510 . 
     In  FIG. 5 , T 11   520  represents the amount of time after A 1   500 , a first sensor puts sensed data into an output register, T 12   530  represents the amount of time after data is put into an output register until the first sensor puts out an interrupt signal, and T 13   540  represents the amount of time after the interrupt singal, until the MCU reads the sensed data from the first output reigster. Similarly, T 21   550  represents the amount of time after A 1 , a second sensor puts sensed data into an output register, T 22   560  represents the amount of time after data is put into an output register until the second sensor puts out an interrupt signal, and T 13   570  represents the amount of time after the interrupt singal, until the MCU reads the sensed data from the second output reigster. The sum of T 11   520 , T 12   530  and T 13   540  and the sum of T 21   550 , T 22   560  and T 23   570  are used to characterize a latency between the first output device and the second output device, such that the outputs can fused at time TOB  580  and be attributed to the same input perturbation at time TOA  510 . 
     In the example in  FIG. 6 , the use of the self-test function is illustrated while the device is in normal operation. In this example, the integrated device is subject to a physical perturbation A 1   600  at time TOA  610 . In  FIG. 6 , T 11   620  represents the amount of time after A 1   600 , a first sensor puts sensed data into a first output register, T 12   630  represents the amount of time after data is put into an output register until the MCU instructs the first sensor to perform a self-test, T 13   640  represents the amount of time after the self-test signal, until the first sensor responds to the self-test data, and T 14   650  represents the amount of time after the self-test data is responded, until data is read from the first ouput register. Similarly, T 21   660  represents the amount of time after A 1 , a second sensor puts sensed data into a second output register, T 22   670  represents the amount of time after data is put into an output register until the MCU instructs the second sensor to perform a self-test, T 23   680  represents the amount of time after the self-test signal, until the second sensor responds to the self-test data, and T 24   690  represents the amount of time after the self-test data is responded, until data is read from the second ouput register. 
     In various embodiments, in  FIGS. 6 , T 11   620 , T 12   630 , T 13   640  and T 14   650  and T 21   660 , T 22   670 , T 23   680  and T 24   690  are used to characterize a latency between the first output device and the second output device, such that the first output and the second output can be attributed to the same input perturbation or event at time TOA  610 . As an example, T 12   630  and T 13   640  may be summed and compared to the sum of T 22   670  and T 23   680 . In an ideal situation, these sums should be identical or substantially similar. If not, the difference may be used to adjust the data output latency between these sensors. In various embodiments, when data from more than two sensors are used, the differences between pairs of sensors can also be used to adjust data output latencies amoung the sensors. 
       FIG. 7  illustrates a functional block diagram of various embodiments of the present invention. More specifically,  FIG. 7  illustrates a system including embodiments of the present invention. In  FIG. 7 , a computing device  600  typically includes some or all of the following: an applications processor  610 , memory  620 , a touch screen display  630  and driver  640 , an image acquisition device  650 , audio input/output devices  660 , a power supply (e.g. battery) and the like. Additional communications from and to computing device may be provided by via a wired interface  670 , a GPS/Wi-Fi/Bluetooth interface  680 , RF interfaces  690  and driver  700 , and the like. Also included in various embodiments are physical sensors  710 . 
     In various embodiments, computing device  600  may be a hand-held computing device (e.g. Android tablet, Apple iPad), a smart phone (e.g. Apple iPhone, Google Nexus, Samsung Galaxy S), a portable computer (e.g. netbook, laptop, ultrabook), a media player, a reading device (e.g. Amazon Kindle), a wearable device (e.g. Apple Watch, Android watch, FitBit device, or other wearable device), appliances (e.g. washers, vacuum cleaners), autonomous or semi-autonomous vehicles, drones, or the like. 
     Typically, computing device  600  may include one or more processors  610 . Such processors  610  may also be termed application processors, and may include a processor core, a video/graphics core, and other cores. Processors  610  may be a processor from Apple (e.g. A9), Qualcomm (Snapdragon), or the like. In other embodiments, the processor core may be an Intel processor, an ARM Holdings processor such as the Cortex or ARM series processors, or the like. Further, in various embodiments, the video/graphics core may be an ARM processor, Imagination Technologies processor PowerVR graphics, an Nvidia graphics processor (e.g. 
     GeForce), or the like. Other processing capability may include audio processors, interface controllers, and the like. It is contemplated that other existing and/or later-developed processors may be used in various embodiments of the present invention. 
     In various embodiments, memory  620  may include different types of memory (including memory controllers), such as flash memory (e.g. NOR, NAND), pseudo SRAM, DDR 
     SDRAM, or the like. Memory  620  may be fixed within computing device  600  or removable (e.g. SD, SDHC, MMC, MINI SD, MICRO SD, CF, SIM). The above are examples of computer readable tangible media that may be used to store embodiments of the present invention, such as computer-executable software code (e.g. firmware, application programs), application data, operating system data or the like. It is contemplated that other existing and/or later-developed memory and memory technology may be used in various embodiments of the present invention. 
     In various embodiments, a touch screen display  630  and driver  640  may be provided and based upon a variety of later-developed or current touch screen technology including: resistive displays, capacitive displays, optical sensor displays, or the like. Additionally, touch screen display  630  may include single touch or multiple-touch sensing capability. Any later-developed or conventional output display technology may be used for the output display, such as TFT-LCD, OLED, Plasma, electronic ink (e.g. electrophoretic, electrowetting, interferometric modulating), or the like. In various embodiments, the resolution of such displays and the resolution of such touch sensors may be set based upon engineering or non-engineering factors (e.g. sales, marketing). In some embodiments of the present invention, a display output port, such as an HDMI-based port, DVI-based port, or the like may also be included. 
     In some embodiments of the present invention, image capture device  650  may be provided and include a sensor, driver, lens and the like. The sensor may be based upon any later-developed or convention sensor technology, such as CMOS, CCD, or the like. In various embodiments of the present invention, image recognition software programs are provided to process the image data. For example, such software may provide functionality such as: facial recognition, head tracking, camera parameter control, proximity detection, or the like. 
     In various embodiments, audio input/output  660  may be provided and include microphone(s)/speakers. In some embodiments of the present invention, three-wire or four-wire audio connector ports are included to enable the user to use an external audio device such as external speakers, headphones or combination headphone/microphones. In various embodiments, voice processing and/or recognition software may be provided to applications processor  610  to enable the user to operate computing device  600  by stating voice commands. Additionally, a speech engine may be provided in various embodiments to enable computing device  600  to provide audio status messages, audio response messages, or the like. 
     In various embodiments, wired interface  670  may be used to provide data transfers between computing device  600  and an external source, such as a computer, a remote server, a storage network, another computing device  600 , or the like. Such data may include application data, operating system data, firmware, or the like. Embodiments may include any later-developed or conventional physical interface/protocol, such as: USB, USB-C, Firewire, Apple Lightning connector, Ethernet, POTS, or the like. Additionally, software that enables communications over such networks is typically provided. 
     In various embodiments, a wireless interface  680  may also be provided to provide wireless data transfers between computing device  600  and external sources, such as computers, storage networks, headphones, microphones, cameras, or the like. As illustrated in  FIG. 8 , wireless protocols may include Wi-Fi (e.g. IEEE 802.11 a/b/g/n, WiMax), Bluetooth, IR, near field communication (NFC), ZigBee, ZWave, and the like. 
     GPS receiving capability may also be included in various embodiments of the present invention, however is not required. As illustrated in  FIG. 6 , GPS functionality is included as part of wireless interface  680  merely for sake of convenience, although in implementation, such functionality is currently performed by circuitry that is distinct from the Wi-Fi circuitry and distinct from the Bluetooth circuitry. 
     Additional wireless communications may be provided via RF interfaces  690  and drivers  700  in various embodiments. In various embodiments, RF interfaces  690  may support any future-developed or conventional radio frequency communications protocol, such as CDMA-based protocols (e.g. WCDMA), GSM-based protocols, HSUPA-based protocols, or the like. In the embodiments illustrated, driver  700  is illustrated as being distinct from applications processor  610 . However, in some embodiments, the functionality are provided upon a single IC package, for example the Marvel PXA330 processor, and the like. It is contemplated that some embodiments of computing device  600  need not include the RF functionality provided by RF interface  690  and driver  700 . 
       FIG. 7  also illustrates computing device  700  to include physical sensors  810 . 
     According to various embodiments, computing device  700  may include conventional components such as a microcontroller or processor  710 , a memory  720 , a (optional) display and driver  730 , a (optional) image input device  750 , an (optional) audio input or output device  760 , a communications interface  770  , a (optional) GPS/local interface  780 , an (optional) RF interface and driver  7900 , and the like. 
     In various embodiments of the present invention, physical sensors  810  are multi-axis Micro-Electro-Mechanical Systems (MEMS) based devices being developed by m-Cube, the assignee of the present patent application. Such sensors typically include very low power three-axis sensors (linear, gyro or magnetic); ultra-low jitter three-axis sensors (linear, gyro or magnetic); low cost six-axis motion sensor (combination of linear, gyro, and/or magnetic); ten-axis sensors (linear, gyro, magnetic, pressure); and various combinations thereof. As discussed above, multiple physical sensors  810  may be used and be orientated orthogonal to each other, and pairs of sensors  810  may be parallel to each other. The data from physical sensors  810  may include differential data. 
       FIG. 7  is representative of one computing device  700  capable of embodying the present invention. It will be readily apparent to one of ordinary skill in the art that many other hardware and software configurations are suitable for use with the present invention. Embodiments of the present invention may include at least some but need not include all of the functional blocks illustrated in  FIG. 7 . For example, in various embodiments, computing device  700  may lack one or more of the above functional blocks, such as image acquisition unit  750 , or 
     RF interface  790  and/or driver or GPS capability, a user input device (e.g. keyboard), or the like. Further, it should be understood that multiple functional blocks may be embodied into a single physical package or device, and various functional blocks may be divided and be performed among separate physical packages or devices. 
     Further embodiments can be envisioned to one of ordinary skill in the art after reading this disclosure. For example, in some embodiments, a sensor device including multiple sensors (e.g. MEMS devices) can be operated at higher output data rates to allow finer adjustment synchronization between the devices. 
     In other embodiments, combinations or sub-combinations of the above disclosed invention can be advantageously made. In some examples, multiple sensors may also provide redundancy for critical applications. If one sensor is damaged or does not provide appropriate data, in response to a physical perturbation, the sensed data from the remaining sensors may be used to compensate for the loss of the one sensor. In still other examples, environmental sensors, such as temperature, humidity, pressure, radiation sensors or the like may also be incorporated into a system, e.g. provided to the local processor. Such data may be used to compensate for temperature, temperature of coefficient offsets, temperature drift, radiation exposure of at least one, but not all MEMS devices, and the like. In other embodiments, instead of relyi  test functionality, the manufacturer or the user under specific conditions may provid  perturbation event, e.g. a knock, a drop, or the like. According to such embodiments, the time delay between the MCU receiving data from the different MEMS devices based upon the event can then be used to determine a latency between these sensors. Similar to the above examples, the latency may be used to better synchronize data received from these MEMS devices going forward in time. 
     The block diagrams of the architecture and flow charts are grouped for ease of understanding. However, it should be understood that combinations of blocks, additions of new blocks, re-arrangement of blocks, and the like are contemplated in alternative embodiments of the present invention. The examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims.