Patent Description:
Electronics devices such as semiconductor chips frequently include movement detection devices such as accelerometers and gyroscopes. An accelerometer can detect acceleration of the electronics device in a specified direction and a gyroscope can detect a change in angle of the electronics device. Such measurement devices are usually manufactured using microelectromechanical systems (MEMS) technology.

<CIT> discloses a an electronics system comprising: a board that includes: a structural material; a thermal conduit on the structural material, the thermal conduit having a thermal conductivity that is higher than a thermal conductivity of the structural material; a thermal interface on the structural material, the thermal interface having a thermal heat transfer capacity that is higher than the thermal heat transfer capacity of the structural material and being attached to the thermal conduit; an electronics device mounted to the board at the thermal conduit, the thermal conduit forming a thermal path between the surface of the thermal interface and the electronics device; and a movement detection device in the electronics device; a system storage; and calibration data on the system storage, the calibration data including a first temperature of the movement detection device; a first output from the movement detection device recorded against the first temperature; and a second temperature of the movement detection device that is different than the first temperature; and a second output from the movement detection device recorded against the second temperature. While this teaching provides technical advances, improvements notable regarding the calibration process, remain desirable.

The invention provides an electronics system according to claim <NUM>.

The invention is described by way of examples with reference to the accompanying drawings, wherein:.

Output readings from movement detection devices, such as accelerometers and gyroscopes, can be affected by changes in temperature of the devices, thereby introducing temperature-dependent error in the output measurements. For example, an accelerometer at rest should provide an output measurement corresponding to gravitational acceleration; however when the accelerometer is subjected to different temperatures, the output measurement will be different due to error associated with the accelerometer being at a higher temperature. Because the output should not change while the accelerometer is at rest, that is, acceleration is still only gravity regardless of the temperature, it is possible to isolate the output measurement error associated with temperature by finding the difference (or "offset") between the erroneous measurement and the known baseline measurement (gravity in the case of an accelerometer). By conducting this measurement comparison at multiple temperatures, many data points are collected and an offset profile over a range of temperatures can be obtained. The collection of data associating temperatures with specific offset readings can be compiled for each movement detection device during the calibration process. The data can be stored as calibration data in a table for look up or extrapolation, or can be used to define a best fit function. The calibration data can be accessed by a virtual reality, augmented reality, or mixed reality system to obtain an adjusted measurement from a movement detection device given the temperature of the movement detection device and its initial "raw" measurement.

A calibration system and process that improves calibration accuracy is described herein. Known methods of calibrating movement detection devices involve contacting the movement detection device with a thermal probe to introduce heat by conduction or require actively blowing air across the movement detection device to adjust its temperature by convection. Both of these methods can cause the device to move so that a measurement taken from the device during calibration will include an error associated with temperature and an error associated with movement introduced by the measurement method. Because it is not possible to know how much movement is introduced by the measurement method, it is not possible to isolate the error associated with temperature. As a result, the error cannot be accurately removed from the raw output measurement of the device. In virtual, augmented, and mixed reality systems, the accuracy of a measurement taken by a device is critical for determining where to display virtual content to a user with respect to movement between the user and the real or virtual environment. Thus, there exists a need for a highly accurate calibration system and method in a virtual, augmented, or mixed reality device.

<FIG>, <FIG> illustrate an electronics system <NUM>, according to an embodiment of the disclosure. <FIG> is a top view of an example configuration of a board <NUM> in the electronics system <NUM>. <FIG> is a cross-sectional side view on <NUM>-<NUM> in <FIG>. <FIG> is a cross-sectional side view on <NUM>-<NUM> in <FIG>. The electronics system <NUM> includes a board <NUM> made up of multiple layers of different materials. The layers and various features disposed therein provide particular functions during calibration and use of an electronics device <NUM> (discussed with respect to <FIG> and <FIG>), such as a sensor or sensor suite, connected to the board <NUM>.

The board <NUM> is constructed from structural material <NUM>, such as FR4 dielectric, and a thermally and electrically conductive material, such as metal components <NUM>. Metal components <NUM> may include a copper material. The metal of the metal components <NUM> is more thermally conductive, and therefore has a higher thermal heat transfer capacity, than the structural material <NUM>. The metal of the metal components <NUM> is electrically conductive and the structural material <NUM> is electrically insulating.

Multiple layers of structural material <NUM> can be included in the board <NUM>. As shown in the example of <FIG>, two structural layers <NUM> and <NUM> can be provided. The metal components <NUM> are disposed between the layers of structural material <NUM>. For example, the metal components <NUM> can include first, second and third metal layers <NUM>, <NUM> and <NUM> separated by the first and second structural layers <NUM> and <NUM>. The board <NUM> further includes top and bottom insulating layers <NUM> and <NUM> that cover the first and third metal layers <NUM> and <NUM>. The top and bottom insulating layers <NUM> and <NUM> can include an electrically insulating solder resist material <NUM>.

The metal components <NUM> also include first and second sets of vias <NUM> and <NUM>, respectively. The first set of vias <NUM> connects portions of the first metal layer <NUM> to portions of the second metal layer <NUM>. The second set of vias <NUM> connects portions of the second metal layer <NUM> to portions of the third metal layer <NUM>. The metal layers <NUM>, <NUM> and <NUM> are thereby electrically and thermally connected to one another. The metal layers <NUM>, <NUM> and <NUM> together with the first and second sets of vias <NUM> and <NUM> form a thermal conduit of thermally conductive material that connect a first region <NUM> of the thermal conduit to a second region <NUM> of the thermal conduit.

Portions of the third metal layer <NUM> are isolated as metal lines <NUM> to function as traces for electrical signals. These metal lines <NUM> can be isolated from each other and from other metal components <NUM> such that each line is surrounded by non-conductive material, such as dielectric structural material <NUM> and insulating solder resist material <NUM>. One of skill in the art will appreciate that more or fewer than three metal lines <NUM> may be provided depending on the design of the electronic device <NUM> that is mounted to the board <NUM> at the second region <NUM>. The metal lines <NUM> may be disposed in one or more of the metal layers in the board <NUM>. Additionally, while the lines <NUM> are shown as exposed parts of the metal component <NUM>, portions of the metal lines <NUM> can also be coated with the insulating solder resist material <NUM>.

The metal components <NUM> further include a thermal interface <NUM>. The thermal interface <NUM> is an area of the third metal layer <NUM> at the first region <NUM> that has been exposed by removing a portion of the top insulating layer <NUM>. The thermal interface <NUM> is an upper surface <NUM> of third metal layer <NUM> that is exposed and is configured to contact part of an electronic device calibration station <NUM>. The upper surface <NUM> forms only a portion of an upper surface of the board <NUM>, with the remainder of the upper surface consisting of an upper surface of the structural layer <NUM> and insulating solder resist layer <NUM>.

Referring to <FIG> and <FIG> in combination, the first, second, and third metal layers <NUM>, <NUM>, <NUM> have an inner portion <NUM> and an outer portion <NUM>. The structural material <NUM> forms a plurality of barriers <NUM> that distinguish the inner portion <NUM> from the outer portion <NUM>. The barriers <NUM> act as thermal barriers to prevent heat from conducting from the inner portion <NUM> to the outer portion <NUM> of the second metal layer <NUM>, or at least substantially slow the transfer of heat so that the outer portion <NUM> is kept cooler than the inner portion <NUM>. Additional electronic components can be connected to the board <NUM>. Such components can be connected to the board <NUM> at the outer portion <NUM> to keep the components from experiencing high heat during the calibration process.

Referring to <FIG> and <FIG> in combination, it can be seen that the first, second, and third metal layers <NUM>, <NUM>, <NUM> also have connecting portions <NUM> that connect the inner portion <NUM> to the outer portion <NUM>. The connecting portions <NUM> ensure that the metal layers are electrically grounded such that there is an equal reference voltage between the inner portion <NUM> and the outer portion <NUM>.

Referring to <FIG> and <FIG> in combination, it can be seen that similar thermal barriers <NUM> are formed at one or more positions within the first, second and third metal layers <NUM>, <NUM> and <NUM> (<FIG>) and that each metal layer has respective portions <NUM> connecting inner and outer regions thereof. The barriers <NUM> prevent, or at least slow heat transfer from the inner portion <NUM> to the outer portion <NUM> to protect other components attached to the board <NUM> from experiencing high temperatures during the calibration of electronics device <NUM>.

Referring to <FIG> and <FIG>, the electronics system <NUM> further includes an electronics device <NUM> and a system storage <NUM>. The electronics device <NUM> is mounted to an upper surface of the board <NUM> through connections <NUM>. The electronics device <NUM> and the thermal interface <NUM> are within the barriers <NUM> that define the inner portion <NUM>. The electronics device <NUM> is mounted above the second region <NUM> of the thermal conduit described above.

The electronics system <NUM> further includes a board interface <NUM> that is attached to the board <NUM> and connected to the measurement devices in the electronics device <NUM>. The electronics device <NUM> includes a structural body <NUM> and a number measurement devices in the structural body <NUM>. The measurement devices include a temperature sensor <NUM> and two movement detection device in the form of an accelerometer <NUM> and a gyroscope <NUM>. Although two movement detection devices are used for purposes of this embodiment, it may be possible to implement aspects of the invention using only one measurement device. It may for example be possible to calibrate an electronics device having only a gyroscope or only an accelerometer. The structural body <NUM> may, for example, be a silicon or other semiconductor structural body that may be packaged using conventional packaging technologies. The temperature sensor <NUM>, accelerometer <NUM> and gyroscope <NUM> are connected through connectors <NUM> on an upper surface of the board <NUM> and metal lines <NUM> in the board <NUM> to the board interface <NUM>. Data traces from the temperature sensor <NUM>, accelerometer <NUM>, and gyroscope <NUM> are routed to a microprocessor <NUM> in the structural body <NUM> which serves as an input/output interface for the measurement devices. The system storage <NUM> serves to store calibration data received from the calibration station <NUM> that is associated with the accelerometer <NUM> and gyroscope <NUM>. The system storage <NUM> may, for example, include a solid-state memory. The system storage <NUM> is shown near the electronics device <NUM>, however, the system storage may be a remote storage, located on a cloud-based storage or on another area of the electronics device such that it is not in contact with the board <NUM>. One of skill in the art will appreciate that the system storage <NUM> may be located anywhere that is in communication with electronics device <NUM> to allow for data transfer between electronics device <NUM> and system storage <NUM>. The system storage <NUM> includes no calibration data immediately after the electronics system <NUM> has been assembled (that is, prior to undergoing calibration) but is uniquely associated with the electronics device <NUM> by enabling data to transfer between the electronics device <NUM> and the system storage <NUM>.

<FIG> further illustrates a calibration station <NUM> that is used to calibrate the accelerometer <NUM> and the gyroscope <NUM>. The calibration station <NUM> includes a frame <NUM>, a calibration computer <NUM>, a calibration computer interface <NUM>, a thermoelectric device <NUM>, a transformer <NUM> and an electric power connector <NUM>. The components of the calibration station <NUM> are mounted in a stationary position to one another via the frame <NUM>. A spacing between the calibration computer interface <NUM> and the thermoelectric device <NUM> is the same as a spacing between the board interface <NUM> and the thermal interface <NUM>. The calibration computer <NUM> is connected to the calibration computer interface <NUM> so that signals can transmit between the calibration computer <NUM> and the calibration computer interface <NUM>. Information from the microprocessor <NUM> can be accessed by the calibration station <NUM>. The calibration computer <NUM> is connected to the electric power connector <NUM> so that power can be provided through the electric power connector <NUM> to the calibration computer <NUM>. The thermoelectric device <NUM> is connected through the transformer <NUM> to the electric power connector <NUM>. The power can be provided by the electric power connector <NUM> through the transformer <NUM> to the thermoelectric device <NUM>. The transformer <NUM> reduces the voltage provided by the electric power connector <NUM> before providing power to the thermoelectric device <NUM>. The thermoelectric device <NUM> is preferably a reversible heat pump, such as a thermoelectric cooler, capable of providing heat into the board <NUM> or drawing heat out of the board <NUM>. The flexibility to achieve a wide range of temperatures on the board <NUM>, and thus at the electronics device <NUM>, can improve calibration accuracy of the electronic device <NUM>.

In use, the electronics system <NUM> is brought into contact with portions of the calibration station <NUM>. When the electronics system <NUM> and the calibration station <NUM> move relatively towards one another, the calibration computer interface <NUM> connects to the board interface <NUM> and can begin receiving data from the electronics device <NUM> at the same time that the thermoelectric device <NUM> comes into contact with the thermal interface <NUM>. In the embodiment described, the calibration computer interface <NUM> and the board interface <NUM> are wired interfaces that come into contact with one another to create a communication link and are releasable from one another to break the communication link. Data is received through a wired communication between the electronics system <NUM> and the calibration station <NUM>. In another embodiment, the calibration station <NUM> and the board may include wireless interfaces that create a wireless link for data transfer and the wireless link sis then broken.

Electric power is provided through the electric power connector <NUM> to the calibration computer <NUM>, which powers the calibration computer <NUM>. Electric power is also provided through the electric power connector <NUM> and the transformer <NUM> to the thermoelectric device <NUM>.

The entire electronics system <NUM> can begin calibration initially at room temperature, e.g. approximately <NUM>. The temperature sensor <NUM> (<FIG>) provides an output of the temperature to the calibration computer <NUM>. The accelerometer <NUM> and the gyroscope <NUM> simultaneously provide outputs to the calibration computer <NUM> that are associated with the output temperature from the temperature sensor <NUM>. Baseline outputs for the accelerometer and the gyroscope are either known because the device is at rest or are established at a reference temperature, such as at room temperature. These baseline outputs are used later in the calibration process to isolate errors in measurements ("offsets") that are associated with temperature changes of the sensors.

<FIG> illustrates that the calibration computer <NUM> is connected to the system storage <NUM> and records calibration data <NUM> in the system storage <NUM> as the calibration offsets are calculated. A first entry in a table of the calibration data <NUM> includes the initial temperature (in this example, <NUM>), an acceleration offset (calculated by finding the difference between the acceleration measurement at temperature and the known acceleration), and an angle offset (calculated by finding the difference between the gyroscope measurement at temperature and the known positional information) that are calculated for a given temperature sensor measurement using inputs from accelerometer <NUM> and gyroscope <NUM>, respectively.

The thermoelectric device <NUM> has an upper surface that is at a lower temperature than room temperature and a lower surface that is at a higher temperature than room temperature. Heat transfers from the high temperature, lower surface of the thermoelectric device <NUM> through the upper surface <NUM> of the thermal interface <NUM> into the thermal interface <NUM>. The heat transfer is primarily by way of conduction. The heat then conducts through the third metal layer <NUM> and first and second sets of vias <NUM> and <NUM> to the first and second metal layers <NUM> and <NUM>. The heat then conducts through the first, second and third metal layers <NUM>, <NUM> and <NUM> from the first region <NUM> nearest the heat source outward toward the second region <NUM>. The barriers <NUM> prevent or at least substantially retard transfer of heat from the inner portion <NUM> to the outer portion <NUM>.

Heating of the second region <NUM> causes its temperature to increase. Conduction of heat through the metal layers <NUM>, <NUM>, <NUM> and the thermal vias <NUM>, <NUM> happens rapidly while significantly slower conduction of heat occurs in the structural material layers <NUM>, <NUM>. Conduction through top metal layer <NUM> evenly distributes heat underneath electronics device <NUM> in the second region <NUM>. The increased temperature of the second region <NUM> causes heat transfer through conduction by connection <NUM> and through passive convection of air surrounding the electronics device <NUM>. This method of heating electronics device <NUM> closely mimics the field conditions that the electronic device <NUM> will experience. The temperature sensor <NUM> continues to detect the temperature of the electronics device <NUM>. The calibration computer <NUM> samples the temperature of the temperature sensor <NUM> on a predetermined interval, e.g. every five seconds, or more frequently for improved accuracy. The calibration computer <NUM> also samples outputs from the accelerometer <NUM> and the gyroscope <NUM> at the same time that the calibration computer <NUM> samples a temperature from the temperature sensor <NUM>. The calibration computer <NUM> then calculates and stores each temperature and each acceleration offset and each angle offset with the calibration data <NUM>. As described herein previously, each temperature is associated with an acceleration offset and an angle offset component within the measurement readings of the accelerometer and gyroscope, respectively. An offset profile can be obtained by measuring outputs of each sensor across a range of temperatures, each time subtracting the known value that the sensor should measure from the actual measurement to calculate error. Each temperature thus has a different acceleration offset and angle offset associated therewith, even though the accelerometer <NUM> and gyroscope <NUM> remain stationary from one measurement to the next. In some embodiments, multiple measurements are obtained at each temperature and an average offset is calculated for improved accuracy.

When sufficient data is collected, the calibration station <NUM> is removed from contact with the board <NUM>. The calibration computer interface <NUM> writes the collected calibration data to the system storage <NUM> and disconnects from the board interface <NUM>. The thermoelectric device <NUM> disengages from the thermal interface <NUM>. Heat convects and conducts from the electronics device <NUM> until the entire electronics device <NUM> returns to room temperature.

The calibration system and process described above do not require physical contact between the calibration station and the electronics device <NUM> and furthermore do not require forced convection across electronics device <NUM>. Rather, the electronics device <NUM> is heated by way of conduction through a permanent connection (connectors <NUM> and metal lines <NUM>) to the board <NUM> and by way of passive convection without the need for additional probe contact with or forced air blowing over the electronics device <NUM>. The electronics device <NUM> can thus be calibrated against temperature without disturbing the accelerometer <NUM> or the gyroscope <NUM>. This system and process allows for a more accurate offset calibration while mimicking real field conditions of the sensors on board electronics device <NUM>.

<FIG> illustrates the electronics system in conjunction with a field computer <NUM>, a field computer interface <NUM> and a controlled system <NUM>. The controlled system <NUM> may be, for example, a virtual reality, augmented reality, or mixed reality device. The field computer <NUM> is connected to the field computer interface <NUM>. The controlled system <NUM> is connected to the field computer <NUM>. The field computer <NUM> may, for example, be a computer that processes movement data of an augmented reality viewing system and the controlled system <NUM> may be a vision processing system of the viewing device. The field computer <NUM> is connected to the system storage <NUM> and has access to the calibration data <NUM>.

In use, the electronics system <NUM> is moved, e.g. in linear directions or rotational directions. The accelerometer <NUM> and the gyroscope <NUM> detect such movement of the electronics system <NUM>. The field computer <NUM> senses signals received from the temperature sensor <NUM>, accelerometer <NUM> and gyroscope <NUM>. The field computer <NUM> uses the temperature detected by the temperature sensor <NUM> to find a corresponding temperature in the calibration data <NUM>. The calibration data <NUM> may include the table with data as hereinbefore described or may include a formula, such as a linear regression, representative of the calibration data. The field computer <NUM> retrieves the acceleration offset and the angle offset in the calibration data <NUM> corresponding to the temperature measured by the temperature sensor <NUM>. The field computer <NUM> then adjusts the acceleration detected by the accelerometer <NUM> by the acceleration offset (acceleration = measured acceleration - acceleration offset). The field computer <NUM> also adjusts an angle measured by the gyroscope <NUM> by the angle offset corresponding to the temperature (adjusted angle = measured angle - angle offset). The field computer <NUM> then provides the adjusted acceleration and the adjusted angle to the controlled system <NUM>. The controlled system <NUM> utilizes the adjusted acceleration and the adjusted angle in one or more formulas. By way of example, the controlled system <NUM> adjusts placement of a rendered image in an augmented reality or mixed reality viewing device according to a placement formula that uses the adjusted acceleration and the adjusted angle received from the field computer <NUM>.

<FIG> illustrates an alternate embodiment wherein a thermal conduit is provided by any known heat spreader that can be built into a chip. In some embodiments, the heat spreader can be a heat pipe <NUM>. The heat pipe <NUM> has an evaporator end <NUM> and a condenser end <NUM>. The evaporator end <NUM> is located against or in close proximity to the thermal interface <NUM> and the condenser end <NUM> is located in close proximity to the electronics device <NUM>. In use, the thermal interface <NUM> heats a liquid in the heat pipe <NUM> and evaporates the liquid. The resultant vapor flows from the evaporator end <NUM> to the condenser end <NUM> and condenses. The resulting condensed liquid then flows through a wicking system from the condenser end <NUM> back to the evaporator end <NUM>.

<FIG> illustrate one type of thermal conduit consisting of a thermally conductive metal. The design in <FIG> is relatively inexpensive to manufacture. <FIG> illustrates a different type of thermal conduit in the form of a heat pipe. A heat pipe may transfer more heat, through flow, than thermally conductive metal but may be more expensive to manufacture. The thermal conduit provided by the thermally conductive metal in <FIG> and the thermal conduit provided by the heat pipe in <FIG> both have a thermal heat transfer capacity that is higher than a thermal heat transfer capacity of the structural material <NUM> of the board <NUM> and both form a thermal path between the surface of the thermal interface <NUM> and the electronics device <NUM>.

Claim 1:
An electronics system comprising:
a board (<NUM>) that includes:
a structural material (<NUM>);
a thermal conduit on the structural material (<NUM>), the thermal conduit having a thermal conductivity that is higher than a thermal conductivity of the structural material and having a first region (<NUM>), a second region (<NUM>), and a connecting portion (<NUM>, <NUM>) connecting the first region to the second region;
a thermal interface (<NUM>) on the structural material (<NUM>), the thermal interface having a thermal heat transfer capacity that is higher than the thermal heat transfer capacity of the structural material (<NUM>) and being attached to the first region (<NUM>) of the thermal conduit, the thermal interface (<NUM>) having a surface that is exposed for making temporary contact with a thermal device;
a field computer (<NUM>);
an electronics device (<NUM>) mounted to the board (<NUM>) at the second region (<NUM>) of the thermal conduit, the thermal conduit forming a thermal path between the surface of the thermal interface (<NUM>) and the electronics device (<NUM>); and
a movement detection device (<NUM>, <NUM>) in the electronics device (<NUM>);
a board interface (<NUM>) that is attached to the board (<NUM>) and connected to the movement detection device (<NUM>, <NUM>) in the electronics device (<NUM>);
a system storage (<NUM>); and
calibration data on the system storage (<NUM>), the calibration data including
a first temperature of the movement detection device (<NUM>, <NUM>);
a first output from the movement detection device (<NUM>, <NUM>) recorded against the first temperature; and
a second temperature of the movement detection device (<NUM>, <NUM>) that is different than the first temperature; and
a second output from the movement detection device (<NUM>, <NUM>) recorded against the second temperature, and
a field computer interface (<NUM>) connected to the board interface (<NUM>), the system storage (<NUM>) being connected through the field computer (<NUM>), the field computer interface (<NUM>) and the board interface (<NUM>) to the electronics device (<NUM>).