PATENT DOCUMENT

Publication Number: US-10027185-B2
Application Number: US-201414502042-A
Country: US
Kind Code: B2

Title: Reducing the impact of an inductive energy transfer system on a touch sensing device

Abstract:
A transmitter device for an inductive energy transfer system can include a DC-to-AC converter operably connected to a transmitter coil, a first capacitor connected between the transmitter coil and one output terminal of the DC-to-AC converter, and a second capacitor connected between the transmitter coil and another output terminal of the DC-to-AC converter. One or more capacitive shields can be positioned between the transmitter coil and an interface surface of the transmitter device. A receiver device can include a touch sensing device, an AC-to-DC converter operably connected to a receiver coil, a first capacitor connected between the receiver coil and one output terminal of the AC-to-DC converter, and a second capacitor connected between the receiver coil and another output terminal of the AC-to-DC converter. One or more capacitive shields can be positioned between the receiver coil and an interface surface of the receiver device.

Claims:
What is claimed is: 
     
       1. A receiver device for an inductive energy transfer system, the receiver device comprising:
 a touch sensing device; 
 a receiver coil; 
 a first capacitor connected in series between the receiver coil and one input terminal of an AC-to-DC converter; 
 a second capacitor connected in series between the receiver coil and another input terminal of the AC-to-DC converter, wherein the first and second capacitors are matched to reduce an amount of noise the touch sensing device receives when the receiver coil is receiving energy inductively. 
 
     
     
       2. The receiver device as in  claim 1 , further comprising a first capacitive shield positioned adjacent to the receiver coil, wherein the capacitive shield reduces an amount of noise transferred to the receiver coil inductively to reduce an amount of noise received by the touch sensing device. 
     
     
       3. The receiver device as in  claim 2 , wherein the first capacitive shield comprises a distinct capacitive shield that is positioned between the receiver coil and an interface surface of the receiver device. 
     
     
       4. The receiver device as in  claim 3 , wherein the first capacitive shield is made of one of a paramagnetic material, a grounded pressure sensitive adhesive, and a grounded flexible printed circuit. 
     
     
       5. The receiver device as in  claim 2 , wherein the first capacitive shield is formed on a surface of an interface surface of the receiver device. 
     
     
       6. The receiver device as in  claim 5 , wherein the first capacitive shield comprises a conductive paint. 
     
     
       7. The receiver device as in  claim 1 , wherein the touch sensing device comprises a capacitive touch sensing device. 
     
     
       8. The receiver device as in  claim 1 , wherein the touch sensing device includes a differential integrator. 
     
     
       9. The receiver device as in  claim 8 , wherein the receiver device further comprises a processing device adapted to select a stimulation frequency for the touch sensing device based on the amount of noise transferred to the receiver device. 
     
     
       10. A portable electronic device comprising:
 a capacitive sensor; and 
 an inductive power receiver comprising:
 a receive coil comprising:
 a first output terminal; and 
 a second output terminal; 
 
 a load comprising:
 a first input terminal; and 
 a second input terminal; 
 
 a first resonant capacitor having a first capacitance and coupling the first output terminal of the receive coil to the first input terminal of the load; and 
 a second resonant capacitor having the first capacitance and coupling the second output terminal of the receive coil to the second input terminal of the load. 
 
 
     
     
       11. The electronic device of  claim 10 , further comprising:
 a housing enclosing:
 the capacitive sensor; and 
 the inductive power receiver; wherein 
 
 the electronic device further comprises a shield positioned between the housing and the receive coil. 
 
     
     
       12. The electronic device of  claim 11 , wherein the capacitive sensor comprises a touch-sensitive or force-sensitive sensitive interface. 
     
     
       13. The electronic device of  claim 11 , wherein the shield is disposed on an interior surface of the housing. 
     
     
       14. The electronic device of  claim 11 , wherein the load comprises a rechargeable battery. 
     
     
       15. An inductive power receiver comprising:
 a receive coil comprising:
 a first output terminal; and 
 a second output terminal; 
 
 a load comprising:
 a first input terminal; and 
 a second input terminal; and 
 
 a set of matched resonant capacitors coupling the first output terminal of the receive coil to the first input terminal of the load and the second output terminal of the receive coil to the second input terminal of the load; wherein 
 the set of matched resonant capacitors reduces common mode noise in the inductive power receiver when the receive coil is receiving energy. 
 
     
     
       16. The inductive power receiver of  claim 15 , wherein the load comprises a capacitive touch input sensor separated from the receive coil. 
     
     
       17. The inductive power receiver of  claim 16 , further comprising an electrically conductive shield positioned over the receive coil and configured to reduced common mode noise in the inductive power receiver when the receive coil is receiving energy. 
     
     
       18. The inductive power receiver of  claim 17 , wherein the electrically conductive shield comprises one or more cutouts. 
     
     
       19. The inductive power receiver of  claim 15 , wherein:
 the receive coil is surrounded in an enclosure configured to direct flux into the receive coil. 
 
     
     
       20. The inductive power receiver of  claim 15 , wherein the set of matched resonant capacitors comprises:
 a first resonant capacitor coupling the first output terminal of the receive coil to the first input terminal of the load; and 
 a second resonant capacitor coupling the second output terminal of the receive coil to the second input terminal of the load.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 62/005,822, filed May 30, 2014, entitled “Reducing the Impact of an Inductive Energy Transfer System on a Touch Sensing Device,” and U.S. Provisional Patent Application No. 62/044,991, filed Sep. 2, 2014, entitled “Reducing the Impact of an Inductive Energy Transfer System on a Touch Sensing Device,” the entireties of which are incorporated herein by reference as if fully disclosed herein. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to inductive energy transfer systems in electronic devices, and more particularly to techniques for reducing the impact of an inductive energy transfer system on a touch sensing device in an electronic device. 
     BACKGROUND 
     Many electronic devices include one or more rechargeable batteries that require external power to recharge from time to time. Often, these devices may be charged using a similar power cord or connector, for example a universal serial bus (“USB”) connector. However, despite having common connection types, devices often require separate power supplies with different power outputs. These multiple power supplies can be burdensome to use, store, and transport from place to place. As a result, the benefits of device portability may be substantially limited. 
     Furthermore, charging cords may be unsafe to use in certain circumstances. For example, a driver of a vehicle may become distracted attempting to plug an electronic device into a vehicle charger. In another example, a charging cord may present a tripping hazard if left unattended. 
     To account for these and other shortcomings of portable electronic devices, some devices include an inductive energy transfer device. The user may simply place the electronic device on an inductive charging surface of a charging device in order to transfer energy from the charging device to the electronic device. The charging device transfers energy to the electronic device through inductively coupling between a transmitter coil in the charging device and a receiver coil in the electronic device. In some situations, an inductive energy transfer device can adversely impact the operations of a touch sensing device in an electronic device that includes both a touch sensing device and an inductive energy transfer device. 
       FIG. 1  illustrates a simplified block diagram of a prior art transmitter device and a receiver device in an inductive energy transfer system. The charging device  102  (“transmitter device”) includes a transmitter coil  104  that couples inductively with a receiver coil  106  in the electronic device  108  (“receiver device”) to transfer energy from the transmitter device to the receiver device. At certain frequencies, noise produced by the transmitter device  102  can adversely impact a touch sensing device  110  in the receiver device  108  when a user touches an input surface for the touch sensing device  110  while the transmitter device is transferring energy to the receiver device (e.g., to charge the battery  112 ). The noise can overwhelm the measurements obtained by the touch sensing device and make it difficult to discern a touch measurement from the noise. The noise can reduce or effectively destroy the resolution of the touch sensing device. 
     For example, in some embodiments the touch sensing device is a capacitive touch sensing device that detects touch through changes in capacitance measurements. When the user touches the input surface of the touch device (e.g., with a finger  114 ), a parasitic capacitance exists between the finger and an earth ground  116 . A parasitic capacitance (represented by capacitor  122 ) also exists between the AC-to-DC converter  118  and the earth ground  116 . Common mode noise produced by the DC-to-AC converter  120  in the transmitter device  102  can couple to the receiver device through the parasitic capacitance C P . The common mode noise produces a noise signal I N  that produces a varying voltage across the capacitor  122 . The touch by the finger  114  is input with respect to the earth ground  116 , but the touch sensing device  110  measures capacitance C SIG  with respect to a device ground. Effectively, the varying voltage across the capacitor  122  interferes with the capacitive touch measurement and makes it difficult to discern the touch measurement from the noise. 
     SUMMARY 
     In one aspect, an inductive energy transfer system can include a transmitter device and a receiver device. The transmitter device can include a transmitter coil positioned adjacent to a first interface surface of the transmitter device and one or more capacitive shields positioned between the transmitter coil and the receiver device. The receiver device may include a receiver coil positioned adjacent to a second interface surface of the receiver device and one or more capacitive shields positioned between the receiver coil and the transmitter device. The second interface surface of the receiver device may be configured to mate with the first interface surface of the transmitter device. 
     In some embodiments, the capacitive shield is disposed on at least one surface of the interface surface. The capacitive shield can be made of any suitable material. As one example, the capacitive shield may be a conductive paint, such as a carbon paint. In other embodiments, the capacitive shield is configured as a separate component that is positioned adjacent to the interface surface. The separate component may be made of, for example, a paramagnetic material, a grounded pressure sensitive adhesive (PSA), or a grounded flexible printed circuit (FPC). 
     In another aspect, the transmitter device can include a DC-to-AC converter operably connected to the transmitter coil, a first capacitor connected in series between the transmitter coil and one output terminal of the DC-to-AC converter, and a second capacitor connected in series between the transmitter coil and another output terminal of the DC-to-AC converter. In one embodiment, the DC-to-AC converter is configured as a full bridge circuit and the first and second capacitors are substantially matched. A processing device can control the opening and closing of the switches in the DC-to-AC converter. 
     In another aspect, the receiver device can include an AC-to-DC converter operably connected to the receiver coil, a third capacitor connected in series between the receiver coil and one output terminal of the AC-to-DC converter, and a fourth capacitor connected in series between the receiver coil and another output terminal of the AC-to-DC converter. The receiver device can also include a touch sensing device. 
     Matching the capacitor values of the capacitors in the transmitter device, matching the capacitor values of the capacitors in the receiver device, using a full bridge circuit as a DC-to-AC converter in the transmitter device, including one or more capacitive shields in the transmitter device, and/or including one or more capacitive shields in the receiver device can reduce or cancel the amount of noise transferred from the transmitter device to the receiver device during energy transfer. Decreasing the amount of noise transferred to the receiver device reduces the impact that inductive energy transfer has on a touch sensing operation performed by the touch sensing device when the transmitter device is transferring energy inductively to the receiver device. 
     Differentially balanced signals can be produced when the capacitors in the transmitter device and in the receiver device are matched capacitors, and when a full bridge circuit is used as a DC-to-AC converter in the transmitter device. The differential balanced signals reduce or cancel common mode noise produced by the transmitter device, which decreases the impact inductive energy transfer has on the touch sensing device. 
     In another aspect, the receiver device can include a processing device that is adapted to select a stimulation frequency for the touch sensing device based on the amount of noise the touch sensing device receives when the receiver coil is receiving energy inductively. 
     And in yet another embodiment, a touch sensing device can select an optimum or desired stimulation frequency from two or more predetermined stimulation frequencies based on the amount of noise created by the inductive energy transfer system during energy transfer. A first sample can be taken by the touch sensing device at a first stimulation frequency, and a second sample can be taken by the touch sensing device at a second stimulation frequency. The first and second samples can be compared along with the noise received from the inductive energy transfer system. Based on the comparison, the optimum or desired stimulation frequency can be selected for the touch sensing device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention are better understood with reference to the following drawings. The elements of the drawings are not necessarily to scale relative to each other. Identical reference numerals have been used, where possible, to designate identical features that are common to the figures. 
         FIG. 1  illustrates a simplified block diagram of a prior art transmitter device and a receiver device in an inductive energy transfer system; 
         FIGS. 2 and 3  are perspective views of one example of an inductive energy transfer system; 
         FIG. 4  depicts a simplified cross-sectional view of the inductive energy transfer system taken along line  4 - 4  in  FIG. 3 ; 
         FIG. 5  illustrates a simplified block diagram of one example of the inductive energy transfer system  200  shown in  FIGS. 2-4 ; 
         FIG. 6  is a simplified schematic of an example differential integrator suitable for use in a touch sensing device; 
         FIG. 7  depicts a plot of the noise gain versus the stimulation frequency of the differential integrator  600  shown in  FIG. 6 ; 
         FIG. 8  is a flowchart of a method for selecting a stimulation frequency in a touch sensing device; 
         FIG. 9  illustrates a simplified schematic diagram of the example of the inductive energy transfer system  200  shown in  FIG. 5 ; and 
         FIG. 10A  depicts a simplified schematic diagram of an inductive energy transfer system that includes capacitive shields; 
         FIG. 10B  is a detail view of the parasitic capacitances in  FIG. 10A ; 
         FIG. 11  illustrates a simplified cross-section view of a first inductive energy transfer system that includes capacitive shields; 
         FIGS. 12-14  are plan views of an inductor coil and a capacitive shield suitable for use in a transmitter device or in a receiver device; 
         FIG. 15  depicts a simplified cross-section view of a second inductive energy transfer system that includes capacitive shields; and 
         FIGS. 16-17  are plan views of a capacitive shield formed on a surface of an interface surface that is suitable for use in a transmitter device or in a receiver device. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments described herein can reduce the effect an inductive energy transfer has on a touch sensing device in an electronic device. In one embodiment, the signals in the transmitter device and in the receiver device are differentially balanced signals. The differentially balanced signals may reduce or cancel the common mode noise produced by the transmitter device, which in turn can decrease the impact inductive energy transfer has on the touch sensing device. 
     In some embodiments, one or more capacitive shields may be included in the transmitter device and/or in the receiver device to further reduce or cancel the noise transferred from the transmitter device to the receiver device during inductive energy transfer, which in turn can further decrease the impact inductive energy transfer has on the touch sensing device. 
     A capacitive shield may be positioned between an inductor coil and an interface surface of the electronic device (e.g., between the transmitter coil and the transmitter interface surface). In some embodiments, the capacitive shield is disposed on at least one surface of the interface surface. The capacitive shield can be made of any suitable material. As one example, the capacitive shield may be a conductive paint, such as a carbon paint. In other embodiments, the capacitive shield is configured as a separate component that is positioned adjacent to the interface surface. The separate component may be made of, for example, a paramagnetic material, a grounded pressure sensitive adhesive (PSA), or a grounded flexible printed circuit (FPC). 
     In other embodiments, a first capacitive shield is formed on at least one surface of the interface surface, and a second capacitive shield is a separate component that is positioned between the inductor coil and the interface surface. The first and second capacitive shields can be made of any suitable material. As one example, the first capacitive shield may be a conductive paint (e.g., carbon paint) and the second capacitive shield made a paramagnetic material, a grounded PSA, or a grounded FPC. 
     Referring now to  FIG. 2 , there is shown a perspective view of one example of an inductive energy transfer system in an unmated configuration. The illustrated embodiment shows a transmitter device  202  that is configured to wirelessly pass energy to a receiver device  204 . The receiver device  204  can be any electronic device that includes one or more inductors, such as a portable electronic device or wearable communication device. 
     The wearable communication device, such as depicted in  FIG. 2 , may be configured to provide, for example, wireless electronic communication from other devices, and/or health-related information or data such as but not limited heart rate data, blood pressure data, temperature data, oxygen level data, diet/nutrition information, medical reminders, health-related tips or information, or other health-related data. A wearable communication device may include a strap or band to connect to secure the wearable communication device to a user. For example, a smart watch may include a band or strap to secure to a user&#39;s wrist. In another example, a wearable communication device may include a strap to connect around a user&#39;s chest, or alternately, a wearable communication device may be adapted for use with a lanyard or necklace. In still further examples, a wearable communication device may secure to or within another part of a user&#39;s body. In these and other embodiments, the strap, band, lanyard, or other securing mechanism may include one or more electronic components or sensors in wireless or wired communication with the communication device. For example, the band secured to a smart watch may include one or more sensors, an auxiliary battery, a camera, or any other suitable electronic component. 
     In many examples, a wearable communication device, such as the wearable communication device depicted in  FIG. 2 , may include a processor coupled with or in communication with a memory, one or more communication interfaces, output devices such as displays and speakers, one or more sensors, such as biometric and imaging sensors, and input devices such as one or more buttons, one or more dials, a microphone, and/or a touch sensing device. The communication interface(s) can provide electronic communications between the communications device and any external communication network, device or platform, such as but not limited to wireless interfaces, Bluetooth interfaces, Near Field Communication interfaces, infrared interfaces, USB interfaces, Wi-Fi interfaces, TCP/IP interfaces, network communications interfaces, or any conventional communication interfaces. The wearable communication device may provide information regarding time, health, statuses or externally connected or communicating devices and/or software executing on such devices, messages, video, operating commands, and so forth (and may receive any of the foregoing from an external device), in addition to communications. 
     Although the system  200  illustrated in  FIGS. 2 and 3  depicts a wristwatch or smart watch, any electronic device may be suitable to receive energy inductively from a transmitter device. For example, a suitable electronic device may be any portable or semi-portable electronic device that may receive energy inductively (“receiver device”), and a suitable dock device may be any portable or semi-portable docking station or charging device that may transmit energy inductively (“transmitter device”). 
     The transmitter device  202  and the receiver device  204  may each respectively include a housing  206 ,  208  to enclose electronic, mechanical and structural components therein. In many examples, and as depicted, the receiver device  204  may have a larger lateral cross section than that of the transmitter device  202 , although such a configuration is not required. In other examples, the transmitter device  202  may have a larger lateral cross section than that of the receiver device  204 . In still further examples, the cross sections may be substantially the same. And in other embodiments, the transmitter device can be adapted to be inserted into a charging port in the receiver device. 
     In the illustrated embodiment, the transmitter device  202  may be connected to a power source by cord or connector  210 . For example, the transmitter device  202  can receive power from a wall outlet, or from another electronic device through a connector, such as a USB connector. Additionally or alternatively, the transmitter device  202  may be battery operated. Similarly, although the illustrated embodiment is shown with the connector  210  coupled to the housing of the transmitter device  202 , the connector  210  may be connected by any suitable means. For example, the connector  210  may be removable and may include a connector that is sized to fit within an aperture or receptacle opened within the housing  106  of the transmitter device  202 . 
     The receiver device  204  may include a first interface surface  212  that may interface with, align or otherwise contact a second interface surface  214  of the transmitter device  202 . In this manner, the receiver device  204  and the transmitter device  202  may be positionable with respect to each other. In certain embodiments, the second interface surface  214  of the transmitter device  202  may be configured in a particular shape that mates with a complementary shape of the receiver device  204  (see  FIG. 3 ). The illustrative second interface surface  214  may include a concave shape that follows a selected curve. The first interface surface  212  of the receiver device  204  may include a convex shape following the same or substantially similar curve as the second interface surface  214 . 
     In other embodiments, the first and second interface surfaces  212 ,  214  can have any given shape and dimensions. For example, the first and second interface surfaces  212 ,  214  may be substantially flat. Additionally or alternatively, the transmitter and receiver devices  202 ,  204  can be positioned with respect to each other using one or more alignment mechanisms. As one example, one or more magnetic devices may be included in the transmitter and/or receiver devices and used to align the transmitter and receiver devices. In another example, one or more actuators in the transmitter and/or receiver devices can be used to align the transmitter and receiver devices. And in yet another example, alignment features, such as protrusions and corresponding indentations in the interface surfaces and/or housings of the transmitter and receiver devices, may be used to align the transmitter and receiver devices. The design or configuration of the interface surfaces, one or more alignment mechanisms, and one or more alignment features can be used individually or in various combinations thereof. 
       FIG. 4  illustrates a side cross-sectional view of the inductive energy transfer system taken along line  4 - 4  in  FIG. 3 . As discussed earlier, both the transmitter device  202  and the receiver device  204  can include electronic, mechanical, and/or structural components. For example, the receiver device  204  can include one or more processing devices, memory, a communication interface for wired and/or wireless communication, and a display, one or more input/output devices such as buttons, a microphone, and/or speaker(s). The illustrated embodiment of  FIG. 4  omits the electronic, mechanical, and/or structural components for simplicity. 
       FIG. 4  shows the example inductive energy transfer system in a mated and aligned configuration. The receiver device  204  includes one or more receiver coils having one or more windings. The receiver coil  400  may receive energy from the transmitter device  202  and may use the received energy to communicate with, perform, or coordinate one or more functions of the receiver device  204 , and/or to replenish the charge of a battery (not shown) within the receiver device  204 . In the illustrated embodiment, the receiver coil  400  includes sixteen windings arranged in two layers or rows. The receiver coil  400  can have a different number of windings arranged in one or more layers in other embodiments. 
     Similarly, the transmitter device  202  includes one or more transmitter coils having one or more windings. The transmitter coil  402  may transmit energy to the receiver device  204 . In the illustrated embodiment, the transmitter coil  402  includes twelve windings arranged in three layers. In other embodiments, the transmitter coil  402  can have a different number of windings arranged in one or more layers. 
     The transmitter device  202  can also include a processing device  404 . The processing device  404  can control one or more operations in the transmitter device  204 . For example, the processing device  404  can control the switching frequency of the DC-to-AC converter (not shown) and/or the amount of power applied to the transmitter coil  402 . 
     The transmitter and receiver coils can be implemented with any suitable type of inductor. Each coil can have any desired shape and dimensions. The transmitter and receiver coils can have the same number of windings or a different number of windings. Typically, the transmitter and receiver coils are surrounded by an enclosure to direct the magnetic flux in a desired direction (e.g., toward the other coil). The enclosures are omitted in  FIG. 4  for simplicity. 
     The receiver device  204  also includes a processing device  406  and a touch sensing device  408 . The processing device  406  can control one or more operations in the receiver device  204 . In one embodiment, the touch sensing device  408  may be operatively connected to a display  410  to detect a touch and/or force applied to the surface of the display. Additionally or alternatively, the touch sensing device  408  can be operatively connected to another input device such as a button and/or to a portion of the housing of the receiver device. 
     The processing devices  404 ,  406  can each be implemented as any electronic device capable of processing, receiving, or transmitting data or instructions. For example, a processing device can be a microprocessor, a central processing unit (CPU), an application-specific integrated circuit (ASIC), a digital signal processor (DSP), or combinations of multiple such devices. As described herein, the term “processing device” is meant to encompass a single processor or processing unit, multiple processors, multiple processing units, or other suitably configured computing element or elements. 
     Referring now to  FIG. 5 , there is shown a simplified block diagram of one example of the inductive energy transfer system  200  shown in  FIGS. 2-4 . The transmitter device  202  includes a power supply  500  operably connected to a DC-to-AC converter  502 . Any suitable type of a DC-to-AC converter may be used. For example, the DC-to-AC converter is constructed as a bridge circuit in the illustrated embodiment. The DC-to-AC converter  502  is operatively connected to a transmitter coil  504 . A first capacitor C P1  is connected in series between one output terminal  506  of the bridge circuit  502  and the transmitter coil  504 , and a second capacitor C P2  is connected in series between the other output terminal  508  of the bridge circuit  502  and the transmitter coil  504 . 
     The receiver device  204  can include a receiver coil  510  operably connected to an AC-to-DC converter  512 . Any suitable type of AC-to-DC converter may be used. For example, the AC-to-DC converter can be constructed as a diode bridge in one embodiment. A parasitic capacitance exists between the AC-to-DC converter  512  and earth ground  514 , and between the finger touching the touch sensing device  516  and the earth ground  514  (represented by capacitor  526 ). The capacitor C SIG  represents the capacitance to be measured between the finger and the touch sensing device  516 . 
     A third capacitor C S1  is connected in series between one output terminal (not shown) of the AC-to-DC converter  512  and the receiver coil  510 , and a second capacitor C S2  is connected in series between the other output terminal (not shown) of the AC-to-DC converter and the receiver coil. A load  518  is operably connected to the output of the AC-to-DC converter  512 . The load  518  is a rechargeable battery in one embodiment. A different type of load can be included in other embodiments. 
     The transmitter coil  504  and the receiver coil  510  together form a transformer  520 . The transformer  520  transfers power or energy through inductive coupling between the transmitter coil  504  and the receiver coil  510  (energy transfer represented by arrow  522 ). Essentially, energy is transferred from the transmitter coil  504  to the receiver coil  510  through the creation of a varying magnetic flux by the AC signal in the transmitter coil  504  that induces a current in the receiver coil  510 . The AC signal induced in the receiver coil  510  is received by the AC-to-DC converter  512  that converts the AC signal into a DC signal. In embodiments where the load  518  is a rechargeable battery, the DC signal is used to charge the battery. Additionally or alternatively, the transferred energy can be used to transmit communication signals to or from the receiver device (communication signals represented by arrow  524 ). 
     The frequency or rate at which the switches in the DC-to-AC converter  502  are opened and closed produces a given frequency of the AC signal applied to the transmitter coil. Opening and closing the switches oppositionally in the DC-to-AC converter  502  can cause the transmitter coil  504  to operate differentially in that the common mode noise is reduced or cancelled as measured across the transmitter coil  504  to earth ground. In other words, the voltage measured at the center of the transmitter coil should be zero or near zero. The switches are enabled and disabled oppositionally when switches  1  and  4  are closed and switches  2  and  3  are opened followed by switches  1  and  4  being opened and switches  2  and  3  closed. A processing device, such as processing device  404  in  FIG. 4 , can be adapted to control the opening and closing of the switches. 
     Additionally, the first and second capacitors C P1  and C P2  in the transmitter device  202  balance the transmitter device, and the third and fourth capacitors C S1  and C S2  in the receiver device  204  balance the receiver device. The first and second capacitors C P1  and C P2  can be matched capacitors. Similarly, the third and fourth capacitors C S1  and C S2  may be matched capacitors. With matched capacitors, the signals in the transmitter device and in the receiver device are differentially matched signals. The differential balanced signals reduce or cancel the common mode noise, which decreases the impact inductive energy transfer has on the touch sensing device  516 . As one example, the noise can be reduced to hundreds of millivolts compared to some prior art noise levels of five to ten volts. 
     The common mode noise can be defined as the voltage difference between the device chassis or ground and earth ground. The device chassis or ground references the capacitive touch sensing device  516 , while earth ground references the finger touching the touch sensing device  516  (and accordingly the capacitance C SIG  to be measured). In the differential embodiment shown in  FIG. 5 , the two sides of the full bridge  502  create opposing voltages between the device ground and the earth ground. The opposing voltages are depicted in  FIG. 5  by the direction of displacement current flow (see arrow paths  528 ,  530 ). 
     In some embodiments, the stimulation frequency of the touch sensing device may be selected when the common mode noise is reduced in the inductive energy transfer system. The stimulation frequency F STIM  is the frequency or rate at which the touch sensing device is charged and discharged.  FIG. 6  is a simplified schematic of an example differential integrator suitable for use in a touch sensing device. The inputs to the differential integrator  600  are operably connected to a switching device  602 . The switching device includes four switches S 1 , S 2 , S 3 , and S 4 . A capacitor C SIG  is operably connected to the switching device. C SIG  represents the capacitance or signal that is measured by the touch sensing device. 
     The switches S 5  and S 6  are closed when the differential integrator  600  is to be reset. The differential integrator  600  may be reset between each measurement in some embodiments. In other embodiments, multiple measurements are taken before the differential integrator  600  is reset. The measurements are added together when multiple measurements are taken before the differential integrator  600  is reset. 
     Only one of the four switches in the switching device  602  is closed when C SIG  is sampled. The four switches can close sequentially in the order of the switch number. Thus, switch S 1  closes and C SIG  is sampled a first time (all other switches are open). Next, switches S 1 , S 3 , S 4  are open, switch S 2  is closed, and C SIG  is sampled a second time. The switches S 1 , S 2 , S 4  are then open, switch S 3  is closed, and C SIG  is sampled a third time. Next, the switches S 1 , S 2 , S 3  are open, the switch S 4  is closed, and C SIG  is sampled a fourth time. 
     In one embodiment, the differential integrator is charged and discharged twice for each sample of C SIG .  FIG. 7  depicts a plot of the noise gain versus the stimulation frequency of the differential integrator  600  shown in  FIG. 6 . The plot  700  is produced when the differential integrator  600  is reset after a single sample of C SIG  (i.e., a single integration period). The plot  702  is generated when multiple integration cycles occur before the differential integrator is reset. Regions  704  in the plots  700 ,  702  represent charging of the differential integrator and regions  706  discharging of the differential integrator. Thus, a peak in the noise gain may occur at or near F STIM /2. 
     Plot  708  represents the voltage signal produced by the noise across the parasitic capacitance (represented by capacitor  526 ) in  FIG. 5 . The frequency at which the plot  708  occurs is the switching frequency of the DC-to-AC converter  502  in the transmitter device  202  (see  FIG. 5 ). Based on a known switching frequency, the stimulation frequency F STIM  can be selected to minimize the impact the inductive energy transfer has on the touch sensing device. Based on the switching frequency for the DC-to-AC converter  502 , the stimulation frequency F STIM  can be selected such that the samples of the touch sensing devices create nulls in the response. The magnitude of the noise gain of the touch sensing device should be sufficiently low so that the transfer of inductive energy does not significantly reduce the resolution of the touch sensing device. In the illustrated embodiment, the frequency of the inductive energy transfer is at the frequency F IET , a frequency that can occur between F STIM /2 and F STIM . In some embodiments, a range of frequencies can exist that provides sufficient attenuation to produce a desirable level of accuracy in the touch measurements. 
     Referring now to  FIG. 8 , there is shown a flowchart of a method for selecting a stimulation frequency in a touch sensing device. In some embodiments, the bandwidth of a null in the response of the touch sensing device can be sufficiently large to allow two or more stimulation frequencies for the touch sensing device. The touch sensing device can select the best stimulation frequency based on the amount of noise created by the inductive energy transfer system. The illustrated method is described in conjunction with two stimulation frequencies. Other embodiments can use more than two stimulation frequencies. 
     Initially, first sample can be taken by the touch sensing device at a first F STIM1  (block  800 ). A second sample can be taken by the touch sensing device at a second F STIM2  (block  802 ). The second F STIM2  is a different frequency than the first F STIM1 . Next, as shown in block  804 , the first and second samples can be compared along with the noise received from the inductive energy transfer system. Based on the comparison, the optimum or desired stimulation frequency can be selected for the touch sensing device (block  806 ). A processing device, such as processing device  406  in  FIG. 4 , may be adapted to perform the method of  FIG. 8 . The method can be performed at the beginning of the energy transfer process. Additionally or alternatively, the method may be performed periodically or at select times while a receiver device is receiving energy inductively (i.e., during the energy transfer process). 
     Referring again to  FIG. 5 , in some situations the parasitic capacitance between the transmitter coil and the receiver coil can be modeled as two capacitors C P1  and C P2  (see  FIG. 9 ), with one of the capacitors having a larger value than the other capacitor (e.g., C P1 &gt;C P2 ). In these situations, noise produced in the transmitter device  202  can couple to the receiver device  204  through the parasitic capacitance C P1  and C P2 . To reduce the amount of noise that is transferred to the receiver device through the parasitic capacitances, one or more capacitive shields can be included in the transmitter device and/or in the receiver device. 
       FIG. 10A  depicts a simplified schematic diagram of an inductive energy transfer system that includes capacitive shields. A first capacitive shield  1000  in a transmitter device  1002  may be positioned between the transmitter coil  504  and the receiver device  1004 . The first capacitive shield  1000  is electrically connected to ground  1008 . A second capacitive shield  1010  in the receiver device  1004  can be positioned between the receiver coil  510  and the transmitter device  1002 . The second capacitive shield  1010  is electrically connected to ground  1014 . 
     The first capacitive shield and the second capacitive shield are configured to reduce or block electric fields passing between the transmitter device and the receiver device. The first and second capacitive shields do not reduce or block the varying magnetic fields passing from the transmitter coil  504  to the receiver coil  510 . As described earlier, any suitable material or materials can be used to form a capacitive shield. As one example, a capacitive shield may be made of a carbon-based material. As other examples, a capacitive shield can be made of aluminum or a paramagnetic material. 
     The capacitive shields  1000 ,  1010  can create parasitic capacitances that can be controlled to increase the effectiveness of the shields.  FIG. 10B  is a detailed view of the parasitic capacitances in  FIG. 10A . Both the first capacitive shield  1000  and the second capacitive shield  1010  have a sheet resistance (Rs_tx and Rs_rx, respectively). In some embodiments, the sheet resistances Rs_tx and Rs_rx can be governed by the equation Rs_rx and Rs_tx&lt;&lt;1/(2π*f*max {Cp_rx, Cn_rx, Cp_tx, Cn_tx, Cs), where f is frequency, Cs is the capacitance between the two capacitive shields, Cp_tx is the capacitance coupling from the positive terminal of the transmitter coil  504  to the first capacitive shield  1000 , Cn_tx is the capacitance coupling from the negative terminal of the transmitter coil  504  to the first capacitive shield  1000 , Cp_rx is the capacitance coupling from the positive terminal of the receiver coil  510  to the second capacitive shield  1010 , Cn_rx is the capacitance coupling from the negative terminal of the receiver coil  510  to the second capacitive shield  1010 , Rx_tx is the total sheet resistance of the first capacitive shield  1000  to ground, and Rx_rx is the total sheet resistance of the second capacitive shield  1010  to ground. In some embodiments, coil-to-coil coupling (Cp 1 , Cp 2 ) should be smaller than the capacitance of the device to earth ground. For example, the coil-to-coil coupling can be 100× smaller than the capacitance of the device to earth ground. Other embodiments can use other difference magnitudes for the coil-to-coil coupling (Cp 1 , Cp 2 ). 
     Referring now to  FIG. 11 , there is shown a simplified cross-sectional view of an inductive energy transfer system that includes capacitive shields. A transmitter device  1100  includes a transmitter coil  1102  and a capacitive shield  1104  positioned between the transmitter coil  1102  and the receiver device  1106 . In one example embodiment, the capacitive shield  1104  can be a component included in the transmitter device  1100 . In another example embodiment, the capacitive shield  1104  can be a material that is disposed on or formed over at least one surface (interior and/or exterior surface) of the interface surface  1108  of the transmitter device  1100 . 
     The receiver device  1106  includes a receiver coil  1110  and a capacitive shield  1112  positioned between the receiver coil  1110  and the transmitter device  1100 . Similar to the first capacitive shield  1104 , the second capacitive shield  1112  can be a component included in the receiver device  1106 . In another example embodiment, the capacitive shield  1112  can be a material that is disposed on or formed over at least one surface of the interface surface  1114  of the receive device  1106 . 
     A capacitive shield may be a conductive paint, such as a carbon paint, that is formed on or over at least one surface (exterior and/or interior) of the interface surface. In other embodiments, the capacitive shield is configured as a separate component that is positioned adjacent to the interface surface. The separate component may be made of, for example, a paramagnetic material, a grounded PSA, or a grounded FPC. 
     Those skilled in the art will recognize that a capacitive shield can have any given shape and dimensions. For example, in some embodiments, the capacitive shield can extend across the interface surface of a transmitter and/or a receiver device. In the illustrated embodiment, the dashed lines in the region  1116  of the transmitter device  1100  depict the option of extending the first capacitive shield across the interface surface  1108 . 
       FIG. 12  is a plan view of an inductor coil and a first capacitive shield suitable for use in a transmitter device or in a receiver device. A capacitive shield  1200  is shown positioned over an inductor coil  1202 . In the illustrated embodiment, the capacitive shield  1200  has a shape and size that substantially matches the shape and size of the inductor coil  1202 . 
     In some embodiments, the capacitive shield  1200  may be configured as a separate component that is adjacent to an interface surface (e.g., surface  212  or  214  in  FIG. 2 ) of the transmitter device or receiver device. As one example, a capacitive shield can be formed as a distinct capacitive shield that corresponds to the shape of the inductor coil. The capacitive shield can be positioned between the inductor coil and an interior surface of the interface surface. Additionally or alternatively, the capacitive shield may be positioned over an exterior surface of the interface surface such that the interface surface is between the inductor coil and the capacitive shield. 
     The changing magnetic field used to transfer energy inductively can induce electric currents in the capacitive shield  1200 . These electric currents are known as eddy currents. Eddy currents flowing through the capacitive shield dissipates some of the energy as heat, which results in energy losses. To reduce these energy losses, the capacitive shield  1200  can include one or more gaps or breaks  1204  in the capacitive shield. The gap(s) prevent the eddy currents from flowing around the capacitive shield. Additionally or alternatively, in some embodiments, the capacitive shield  1200  may include one or more cutouts  1206  formed along at least one edge of the capacitive shield. The cutouts can reduce losses caused by eddy currents. 
     The gap(s) and/or the cutout(s) can have any given shape and dimensions. Additionally, the gaps(s) and/or cutout(s) can be positioned at any suitable location in the capacitive shield. 
     Referring now to  FIG. 13 , there is shown a plan view of an inductor coil and a second capacitive shield suitable for use in a transmitter device or in a receiver device. The capacitive shield  1300  is shown positioned over the inductor coil  1302 . The capacitive shield  1300  includes one or more gaps  1304  to reduce losses caused by eddy currents. Although not shown in  FIG. 13 , the capacitive shield  1300  may include one or more cutouts in addition to, or as an alternative to, the gap(s)  1304 . 
     Similar to the embodiment shown in  FIG. 12 , the capacitive shield  1300  is configured as a distinct component that is positioned adjacent to an interior and/or exterior surface of the interface surface of the transmitter device or receiver device. In the illustrated embodiment, the capacitive shield  1300  is formed in a shape that corresponds to the shape of the inductor coil  1302 , but is smaller in size compared to the inductor coil. Although shown centered with respect to the inductor coil, the capacitive shield  1300  may have any suitable alignment with respect to the inductor coil. 
     In another embodiment, the capacitive shield  1300  can be formed in a shape corresponding to the shape of the inductor coil  1302  and be larger in size compared to the inductor coil (see  FIG. 14 ). Moreover, as described earlier, the shape of the capacitive shield can have any given design and dimensions. As one example, the capacitive shield can be a rectangle shape positioned adjacent to a round inductor coil. 
     Referring now to  FIG. 15 , there is shown a simplified cross-section view of a second inductive energy transfer system that includes capacitive shields. A transmitter device  1500  includes a transmitter coil  1102  and a first capacitive shield  1502  positioned between the transmitter coil  1102  and the receiver device  1504 . In one example embodiment, the first capacitive shield  1502  can be a material that is disposed on or formed over at least one surface (interior and/or exterior surface) of the interface surface  1108  of the transmitter device  1500 . For example, the first capacitive shield may be a conductive paint, such as a carbon paint. 
     The transmitter device  1500  can include a second capacitive shield  1506  that is positioned between the first capacitive shield  1502  and the transmitter coil  1102 . The second capacitive shield can be made of any suitable material. As one example, the second capacitive shield may be a grounded PSA, such as an aluminized mylar, a carbon scrim, a copper foil PSA, pattern silver ink traces, or a graphite PSA. As another example, the second capacitive shield can be a grounded FPC, such as a patterned copper FPC, an indium tin oxide FPC, or a patterned carbon/silver FPC. The second capacitive shield  1506  can be electrically connected to a ground on a circuit element  1508 . The circuit element may be, for example, another FPC or a printed circuit board. The circuit element  1508  can be attached to a support structure  1510 . 
     The receiver device  1504  includes a receiver coil  1110  and a first capacitive shield  1512  positioned between the receiver coil  1110  and the transmitter device  1500 . Similar to the capacitive shield  1502  in the transmitter device  1500 , this first capacitive shield  1512  can be a material that is disposed on or formed over at least one surface (interior and/or exterior surface) of the interface surface  1114  of the receiver device  1504 . For example, the first capacitive shield  1512  may be a conductive paint, such as a carbon paint. 
     The receiver device  1504  can include a second capacitive shield  1514  that is positioned between the first capacitive shield  1512  and the receiver coil  1110 . The second capacitive shield can be made of any suitable material. Like the second capacitive shield  1506  in the transmitter device, the second capacitive shield  1514  may be a grounded PSA or a grounded FPC. The second capacitive shield  1514  can be electrically connected to a ground on a circuit element  1516 . The circuit element may be, for example, another FPC or a printed circuit board. The circuit element  1516  can be attached to a support structure  1518 . 
     Although not shown in  FIGS. 11 and 15 , those skilled in the art will recognize that additional layers or elements can be included in the transmitter device and/or the receiver device. As one example, the transmitter coil and/or receiver coil may be surrounded by an enclosure to direct the magnetic flux in a desired direction (e.g., toward the other coil). Additionally or alternatively, electrical components may be positioned between the interface surface and the second capacitive shield in the transmitter device and/or the receiver device. For example, one or more openings may be formed through the interface surface in the receiver device to permit biometric sensors, such as a PPG sensor, to sense or capture biometric data. Additionally or alternatively, additional electrical components may be connected to the circuit element  1508  and/or  1516 . 
       FIGS. 16-17  are plan views of a capacitive shield formed on a surface of an interface surface that is suitable for use in a transmitter device or in a receiver device. The material of the capacitive shield  1600  may be disposed over an interior surface of the interface surface  1602 , such that the capacitive shield  1600  is between the inductor coil and the interface surface. Additionally or alternatively, the capacitive shield  1600  may be formed over the exterior surface of the interface surface  1602 . As one example, a conductive paint, such as a carbon paint, may be formed over the interior surface and/or the exterior surface of the interface surface of the transmitter device and/or the receiver device. 
     The illustrated capacitive shield  1600  has a shape and size that corresponds to an inductor coil. Other embodiments, however, can configure the capacitive shield in any given shape or size. For example, the capacitive shield  1700  shown in  FIG. 17  may have a shape that corresponds to an inductor coil, but the capacitive shield can be larger in size than the inductive coil. Optionally, an area  1702  of the surface  1704  of the interface surface  1602  may not be covered by the capacitive shield  1700 , or the capacitive shield can cover the entire area of the surface  1704 . 
     Although not shown in  FIGS. 16 and 17 , the capacitive shield may include one or more gaps and/or cutouts to reduce eddy currents. The gap(s) and/or the cutout(s) can have any given shape and dimensions. Additionally, the gaps(s) and/or cutout(s) can be positioned at any suitable location in the capacitive shield. 
     As described herein, a transmitter device and/or a receiver device can each include one or more capacitive shields. A capacitive shield can be a separate component that is positioned between the inductor coil and the interface surface of the device. Additionally or alternatively, a capacitive shield may be formed on at least one surface of the interface surface. The capacitive shield can be formed on an interior surface of the interface surface, an exterior surface, or both the interior and exterior surfaces. The capacitive shield or shields can have any given shape, design, and size. 
     In some embodiments, mechanical constraints may not allow for full coil coverage on the receiver coil and/or the transmitter coil due to limited space. In such a situation, a larger shield on one device (e.g., transmitter device) and a smaller shield on the other device (e.g., receiver device) can be employed. The geometry of the smaller shield may be chosen to minimize the fringe field coupling. In other embodiments, the capacitive shields can be made to overhang the coils on both transmitter and receiver devices if space allows and this will decrease fringe field coupling and reduce noise further. 
     Various embodiments have been described in detail with particular reference to certain features thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the disclosure. And even though specific embodiments have been described herein, it should be noted that the application is not limited to these embodiments. In particular, any features described with respect to one embodiment may also be used in other embodiments, where compatible. Likewise, the features of the different embodiments may be exchanged, where compatible. For example, embodiments can include all of the components described herein. Alternatively, embodiments can include some of the components. As one non-limiting example, a transmitter device can open and close the switches oppositionally in the DC-to-AC converter and include a capacitive shield, but not include the matched capacitor values for capacitors C P1  and C P2 . Additionally, the components included in the transmitter device can be different from the components included in the receiver device. As one non-limiting example, a transmitter device can open and close the switches in the DC-to-AC converter oppositionally, matched capacitor values for capacitors C P1  and C P2 , and the capacitive shield. A receiver device can include the capacitive shield but not include matched capacitor values for capacitors C S1  and C S2 .

Metadata:
Filing Date: 20140930
Publication Date: 20180717
Grant Date: 20180717
Priority Date: 20140530
Inventors: MOYER, TODD K.
LIN, ALBERT
ZUBER, Wesley W.
PEREZ, YEHONATAN
ALVES, Jeffrey M.
BRZEZINSKI, MAKIKO K.
JOL, ERIC S.
THOMPSON, PAUL J.
Patel, Priyank D.
SAUER, Christian M.
GRAHAM, Christopher S.
HWANG, JIM C.
LEWIS-KRAUS, Micah
Assignee: APPLE INC
CPC Classifications: [{"code": "H02J50/70", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B15/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B15/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/90", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/70", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J7/025", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J5/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/70", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B15/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/90", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 53365742