PATENT DOCUMENT

Publication Number: US-7671837-B2
Application Number: US-35502206-A
Country: US
Kind Code: B2

Title: Scrolling input arrangements using capacitive sensors on a flexible membrane

Abstract:
Scrolling input arrangements are presented including: a flexible membrane; a number of capacitive sensors mechanically integrated with the flexible membrane, the capacitive sensors radially disposed with respect to a first axis that is perpendicular with respect to the flexible membrane; an integrated circuit mechanically coupled with the flexible membrane and electronically coupled with the capacitive sensors, the integrated circuit configured to process a number of electronic signals from the capacitive sensors to provide a scrolling function; and a connection region on the flexible membrane for electronically coupling the scrolling input arrangement with an electronic device. In some embodiments, the capacitive sensors are configured with a plate element having a first surface area and a trace element having a second surface area such that the first surface area and second surface area comprise a sensor surface area, wherein the sensor surface areas for the capacitive sensors is substantially equal in size.

Claims:
1. A scrolling input arrangement comprising:
 a flexible membrane; a plurality of capacitive sensors mechanically integrated with the flexible membrane, the plurality of capacitive sensors radially disposed with respect to a first axis that is perpendicular with respect to the flexible membrane; 
 an integrated circuit mechanically coupled onto an integrated circuit region of the flexible membrane and electronically coupled with the plurality of capacitive sensors, the integrated circuit configured to process a plurality of electronic signals from the plurality of capacitive sensors to provide a scrolling function; and 
 a connection region on the flexible membrane for electronically coupling the scrolling input arrangement with an electronic device. 
 
   
   
     2. The arrangement of  claim 1  wherein each of the plurality of capacitive sensors is configured with a plate element having a first surface area and a trace element having a second surface area such that the first surface area and second surface area comprise a sensor surface area, wherein the sensor surface areas for the plurality of capacitive sensors is substantially equal in size. 
   
   
     3. The arrangement of  claim 1  wherein the integrated circuit includes logic for calibrating the plurality of capacitive sensors in response to a changing positive temperature gradient. 
   
   
     4. The arrangement of  claim 3  wherein the changing positive temperature gradient is approximately 4.degree. C./ms within a range of approximately 0.degree. C. to 60.degree. C. 
   
   
     5. The arrangement of  claim 2  further comprising:
 a plurality of switches mechanically integrated with the flexible membrane, the plurality of switches configured for providing a plurality of selection functions wherein at least one of the plurality of switches is approximately co-located with the first axis. 
 
   
   
     6. The arrangement of  claim 1  wherein the flexible membrane is a polyimide film. 
   
   
     7. The arrangement of  claim 6  wherein the flexible membrane has a thickness of approximately 0.21 millimeters. 
   
   
     8. The arrangement of  claim 6  wherein the flexible membrane is further configured with a plurality of anti-rotation elements for securing the flexible membrane against a rotational force. 
   
   
     9. The arrangement of  claim 1  wherein the plurality of capacitive sensors includes at least 16 sensors. 
   
   
     10. A low-profile scrolling input assembly comprising:
 a scrolling input arrangement for providing a scrolling function, the scrolling input arrangement having a top surface and a bottom surface, the scrolling input arrangement comprising, a flexible membrane; 
 a plurality of capacitive sensors mechanically integrated with the flexible membrane, the plurality of capacitive sensors radially disposed with respect to a first axis that is perpendicular with respect to the flexible membrane; 
 an integrated circuit mechanically coupled onto an integrated circuit region of the flexible membrane, the integrated circuit electronically coupled with the plurality of capacitive sensors, the integrated circuit configured to process a plurality of electronic signals from the plurality of capacitive sensors to provide a scrolling function; 
 a connection region on the flexible membrane for electronically coupling the integrated circuit with a device; 
 a backing plate for providing mechanical support for the scrolling input arrangement, the backing plate mechanically coupled with the bottom surface; and 
 a cover plate for providing protecting the top surface, the cover plate configured to provide a low-friction surface to receive a user input. 
 
   
   
     11. The assembly of  claim 10  further comprising:
 a plurality of switches mechanically integrated with the flexible membrane, the plurality of switches configured for providing a plurality of selection functions. 
 
   
   
     12. The assembly of  claim 11  wherein at least one of the plurality of switches is approximately co-located with the first axis. 
   
   
     13. The assembly of  claim 11  wherein the backing plate further comprises a plurality of actuator nubs for actuating the plurality of switches. 
   
   
     14. The assembly of  claim 10  wherein the cover plate further comprises a plurality of actuator nubs for actuating a plurality of switches mechanically integrated with the flexible membrane. 
   
   
     15. The assembly of  claim 10  wherein the integrated circuit includes logic for calibrating the plurality of capacitive sensors in response to a changing positive temperature gradient. 
   
   
     16. The assembly of  claim 15  wherein the changing positive temperature gradient is approximately 4.degree. C./ms within a range of approximately 0.degree. C. to 60.degree. C. 
   
   
     17. The assembly of  claim 10  further comprising a plurality of anti-rotation elements for securing the assembly against a rotational force. 
   
   
     18. A method of calibrating a plurality of capacitive sensors in response to a changing positive temperature gradient, comprising:
 establishing a baseline, the baseline comprising a first minimum function of a signal from each of the plurality of capacitive sensors; 
 scanning the plurality capacitive sensors; and 
 if more than eight of the plurality of capacitive sensors exceeds a threshold value, determining a thermal drift of the plurality of capacitive sensors, the thermal drift corresponding to a second minimum function of a signal from each of the plurality of capacitive sensors, and for each of the plurality of capacitive sensors, calculating an updated baseline based on the baseline and the thermal drift such that the plurality of capacitive sensors is calibrated. 
 
   
   
     19. The method of  claim 18  wherein the threshold value is selected to avoid a noise floor of the plurality of capacitive sensors. 
   
   
     20. The method of  claim 18  wherein the scanning the plurality of capacitive sensors frequency is conducted at a frequency of approximately three megahertz. 
   
   
     21. The flexible membrane of  claim 1 , wherein the membrane comprises a polyimide film. 
   
   
     22. The flexible membrane of  claim 1 , wherein the membrane has a thickness less than approximately 0.50 millimeters.

Description:
PRIORITY CLAIM TO PROVISIONAL APPLICATION 
   A claim for priority is hereby made under the provisions of 35 U.S.C. § 119 for the present application based upon U.S. Provisional Application No. 60/714,609, filed on Sep. 6, 2005. 

   BACKGROUND 
   As modern electronic devices have continued to evolve, size reduction has become a preeminent design consideration. Indeed, shrinking device profiles have made pocket electronics possible while preserving robust processing capability. Much progress has been made in shrinking electronic components like integrated circuits. However, mechanical support systems have sometimes lagged behind electronic advances. At least one reason for this lag is that many mechanical structures are limited by strength to weight considerations. Thus, while a miniaturized circuit may consume ever shrinking profiles, a mechanical structure may be limited to a minimum size in order to achieve structural stability. In some examples, structural stability may include unwanted inefficiencies. 
   For example,  FIG. 1  is an illustrative cross-sectional representation of a scrolling device portion  100 . Embodiments of this device are described in detail in U.S. patent application Ser. No. 10/188,182 entitled, “TOUCH PAD HANDHELD DEVICE,” and in U.S. patent application Ser. No. 10/643,256 entitled, “MOVABLE TOUCH PAD WITH ADDED FUNCTIONALITY,” which are hereby incorporated by reference. Scrolling device portion  100  includes a cover  104  that provides a protection for the device. An adhesive layer  108  mechanically couples cover  104  with printed circuit board (PCB)  112 . PCB  112  may provide structural support for electronic components like, for example, a capacitive sensor (not shown), an integrated circuit  128 , a switch  120  and a connection pad  116 . PCB&#39;s  112  structural rigidity provides at least some durability to the device, but its use is not without some inherent disadvantages. 
   For example, PCB&#39;s may be limited to a minimum thickness. Minimum thickness is due to structural requirements that may, in some examples, be unavoidable. Further, because a PCB is rigid, applications may, in some examples, require that features like integrated circuit  128 , switch  120 , and connection pad  116  be co-located with the PCB. Co-location requirements may add to the device stack height further limiting size reductions. Still further, co-location of associated electronic components, like a switch, for example, may ultimately lead to device failure due to cracked soldering or components as a result of stresses imparted on the PCB during switch cycling. Still further, PCB rigidity may result in some loss of tactile responsiveness of an electronic component like a switch, for example. Therefore scrolling input arrangements using capacitive sensors on a flexible membrane are presented herein. 
   As may also be appreciated, capacitive sensors such as those described above generally may respond undesirably in rapidly changing temperature conditions. For example, in a rapidly heating environment, both the environment as well as an input pointer such as a finger may cause an increase in capacitance signals on sensors. In current designs, if recalibration is conducted while a finger is present, the unit may “calibrate out” the finger. Thus, either the unit remains with an incorrect calibration or it does not respond to the finger. Thus, methods of calibrating a plurality of capacitive sensors in response to rapidly changing positive temperature gradients are presented herein. 
   SUMMARY 
   The following presents a simplified summary of some embodiments of the invention in order to provide a basic understanding of the invention. This summary is not an extensive overview of the invention. It is not intended to identify key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some embodiments of the invention in a simplified form as a prelude to the more detailed description that is presented below. 
   Scrolling input arrangements are presented including: a flexible membrane; a number of capacitive sensors mechanically integrated with the flexible membrane, the capacitive sensors radially disposed with respect to a first axis that is perpendicular with respect to the flexible membrane; an integrated circuit mechanically coupled with the flexible membrane and electronically coupled with the capacitive sensors, the integrated circuit configured to process a number of electronic signals from the capacitive sensors to provide a scrolling function; and a connection region on the flexible membrane for electronically coupling the scrolling input arrangement with an electronic device. In some embodiments, the capacitive sensors are configured with a plate element having a first surface area and a trace element having a second surface area such that the first surface area and second surface area comprise a sensor surface area, wherein the sensor surface areas for the capacitive sensors is substantially equal in size. In some embodiments, the integrated circuit includes logic for calibrating the plurality of capacitive sensors in response to a changing positive temperature gradient. In some embodiments, the changing positive temperature gradient is approximately 4° C./ms within a range of approximately 0° C. to 60° C. In some embodiments, the arrangement further includes: a number of switches mechanically integrated with the flexible membrane, the switches configured for providing a number of selection functions wherein at least one of the switches is approximately co-located with the first axis. 
   In other embodiments, low-profile scrolling input assemblies are presented including: a scrolling input arrangement for providing a scrolling function, the scrolling input arrangement having a top surface and a bottom surface, the scrolling input arrangement including, a flexible membrane; a number of capacitive sensors mechanically integrated with the flexible membrane, the capacitive sensors radially disposed with respect to a first axis that is perpendicular with respect to the flexible membrane; an integrated circuit mechanically coupled with the flexible membrane, the integrated circuit electronically coupled with the capacitive sensors, the integrated circuit configured to process a plurality of electronic signals from the capacitive sensors to provide a scrolling function; a connection region on the flexible membrane for electronically coupling the integrated circuit with a device; a backing plate for providing mechanical support for the scrolling input arrangement, the backing plate mechanically coupled with the bottom surface; and a cover plate for providing protecting the top surface, the cover plate configured to provide a low-friction surface to receive a user input. In some embodiments, assemblies further include: a number of switches mechanically integrated with the flexible membrane, the switches configured for providing a number of selection functions. In some embodiments, the backing plate further includes a number of actuator nubs for actuating the switches. In some embodiments, assemblies further include a number of anti-rotation elements for securing the assembly against a rotational force. 
   In other embodiments, methods of calibrating a number of capacitive sensors in response to a changing positive temperature gradient are presented including: establishing a baseline, the baseline comprising a first minimum function of a signal from each of the plurality of capacitive sensors; scanning the plurality capacitive sensors; and if more than eight of the plurality of capacitive sensors exceeds a threshold value, determining a thermal drift of the plurality of capacitive sensors, the thermal drift corresponding to a second minimum function of a signal from each of the capacitive sensors, and for each of the capacitive sensors, calculating an updated baseline based on the baseline and the thermal drift such that the capacitive sensors are calibrated. In some embodiments, the threshold value is selected to avoid a noise floor of the capacitive sensors. In some embodiments, scanning the capacitive sensors frequency is conducted at a frequency of approximately three megahertz. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
       FIG. 1  is an illustrative cross-sectional representation of a scrolling device portion; 
       FIG. 2  is an illustrative representation of a scrolling input arrangement in accordance with an embodiment of the present invention; 
       FIG. 3  is an illustrative representation in exploded as well as cross-section views of a scrolling input assembly in accordance with an embodiment of the present invention; 
       FIG. 4  is an illustrative representation of a scrolling input arrangement in accordance with an embodiment of the present invention; 
       FIG. 5  is an illustrative representation in exploded as well as cross-section views of a scrolling input assembly in accordance with an embodiment of the present invention; and 
       FIG. 6  is an illustrative flowchart of a method of calibrating a plurality of capacitive sensors in accordance with an embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   The present invention will now be described in detail with reference to a few embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present invention. 
   Various embodiments are described hereinbelow, including methods and techniques. It should be kept in mind that the invention might also cover articles of manufacture that includes a computer readable medium on which computer-readable instructions for carrying out embodiments of the inventive technique are stored. The computer readable medium may include, for example, semiconductor, magnetic, opto-magnetic, optical, or other forms of computer readable medium for storing computer readable code. Further, the invention may also cover apparatuses for practicing embodiments of the invention. Such apparatus may include circuits, dedicated and/or programmable, to carry out tasks pertaining to embodiments of the invention. Examples of such apparatus include a general-purpose computer and/or a dedicated computing device when appropriately programmed and may include a combination of a computer/computing device and dedicated/programmable circuits adapted for the various tasks pertaining to embodiments of the invention. 
     FIG. 2  is an illustrative representation of a scrolling input arrangement  200  in accordance with an embodiment of the present invention. In particular, scrolling input arrangement  200  includes a flexible membrane  204 . In some embodiments, flexible membrane  204  is a polyimide film. Flexible membrane  204  provides distinct advantages over prior solutions. For example, flexible membrane  204  provides a reduction in thickness over printed circuit boards (PCB) while still providing adequate structure for electronic components. In some embodiments, flexible membrane  204  may have a thickness of approximately 0.21 millimeters where typical PCB applications have a thickness of approximately 0.50 millimeters. Flexible membrane  204  provides further advantage by allowing associated electronic components and connectors to be disposed away from an arrangement stack comprised of capacitive elements. Allowing associated electronic components and connectors to be disposed away from an arrangement stack may thus provide a thinner cross-sectional profile of scrolling input arrangement  200  as well as provide mechanical shock insulation for associated electronic components. In this manner, a smaller, more durable arrangement may be realized. 
   In some instances, flexible membrane  204  may provide for increased tactile feedback efficiency. Tactile feedback efficiency is a measurement of a user&#39;s ability to discern a tactile change. Thus, when tactile feedback efficiency is high, a user is more readily able to discern a tactile change. In one example, a switch or plurality of switches may be co-located with flexible membrane  204 . When those switches are actuated, a user may more readily discern a tactile change (e.g. a “click”) over prior art solutions because of flexible membrane&#39;s  204  physical properties. As a further advantage, tactile specificity may result because of flexible membrane&#39;s  204  physical properties. That is, because of flexible membrane&#39;s  204  elasticity, unintentional actuation of switches may be reduced or avoided altogether. This may allow for more switches to be placed closer together while avoiding inadvertent actuation of neighboring switches. 
   As can be appreciated, flexible membrane  204  may be cut or formed into any number of shapes in accordance with user preferences. The illustrated shape is provided for clarity and should not be construed as limiting. Mechanically integrated with flexible membrane  204  are a variety of electronic components. Mechanical integration of capacitive sensors, for example, may be accomplished by gluing, bonding, molding, or any other method known in the art without departing from the present invention. A number of capacitive sensors  208  may be radially disposed with respect to axis  202 , which is perpendicular with respect to flexible membrane  204 . Capacitive sensors  208  may also be mechanically integrated with top surface of flexible membrane  204 . In some embodiments, 16 capacitive sensors are utilized. Capacitive sensors  208  may be mechanically integrated with flexible membrane  204  in any manner well-known in the art. Each capacitive sensor includes a plate element  210  and a trace element (not shown). A plate element is one plate in a capacitor and is mechanically integrated with flexible membrane  204 . Trace elements (not shown) may also be mechanically integrated with flexible membrane  204 . Trace elements provide for electronic communication between capacitive sensors  208  and integrated circuit (IC) region  212 . An IC provides processing capability for capacitive sensors  208 . IC processing will be discussed in further detail below for  FIG. 6 . Any number of IC&#39;s may be mechanically coupled with flexible membrane  204  without departing from the present invention. Mechanical coupling of integrated circuits, for example, may be accomplished by gluing, bonding, molding, or any other method known in the art without departing from the present invention. 
   As can be appreciated, for each capacitive sensor, the sum of the surface area of its corresponding plate element and the surface area of its corresponding trace element is the sensor surface area. In some embodiments, the sensor surface area for all capacitive sensors is substantially equal in size. Thus, where a longer trace element is required due to location constraints, a corresponding smaller surface area of the plate element results. Thus, plate elements may not match exactly in some embodiments. At least one reason for matching sensor surface areas is so that sensing will be uniform across the arrangement. As can be appreciated, where matching sensor surface areas is not practicable, adjustments for each sensor may be made algorithmically thus calibrating each sensor to its particular configuration. 
   Scrolling input arrangement  200  may further include ground pad  220  for electronically connecting with a ground source. Ground shielding  232  may be incorporated in some embodiments to provide for electronic isolation of capacitive sensors  208 . Ground shielding may be mechanically integrated with flexible membrane  204  in any manner well-known in the art. A connection region  216  may be utilized for electronically coupling the arrangement  200  with an associated electronic device. In some examples, the electronic device is an IPOD™. Any number of connectors may be mechanically integrated with flexible membrane  204  without departing from the present invention. 
   Still further, in some embodiments, flexible membrane  204  may be configured with anti-rotation elements  228 . Anti-rotation elements provide rotational stability for flexible membrane  204 . In this example, anti-rotation elements are embodied as cut-outs that mate with a matching surface. In other embodiments, through holes  224  may be provided to allow actuator nubs disposed on one side of scrolling input arrangement  200  to reach electronic elements disposed on an opposite side of scrolling input arrangement  200 . As can be appreciated, anti-rotation elements and through holes may be configured in any manner in accordance with user preferences without departing from the present invention. 
     FIG. 3  is an illustrative representation in exploded as well as cross-section views of a scrolling input assembly  300  in accordance with an embodiment of the present invention. Scrolling input assembly  300  includes a scrolling input arrangement  312  such as those described above for  FIG. 2 . Scrolling input assembly  300  further includes cover plate  304 . Cover plate  304  may provide protection for the top surface of scrolling input arrangement  312 . Cover plate  304  may also provide a low-friction surface to receive user input from, for example, a finger or stylus. Referring to cross-sectional illustration, cover plate  304  may be configured with an actuator nub  316  for actuating a switch  318 . Switch  318  may be electronically coupled with a processor or IC to provide selection functions individually or in combination. As can be appreciated, through holes  311  (see also  FIG. 2 ) provide access for actuator nub  318 . Cover plate  304  may be composed of any suitable material that does not interfere with capacitive sensing. In some embodiments thermoplastic is utilized to create a cover plate. It should be noted that the figures provided herein are for illustrative purposes only and should not be construed to provide precise dimensions. 
   In some embodiments, scrolling input assembly  300  may include a center button  308  that may actuate switch  310 . Switch  310  may be electronically coupled with a processor or IC to provide selection functions. Backing plate  314  may be mechanically coupled with the bottom surface of scrolling input arrangement  312  to provide structural support. Backing plate  314  may also provide a grounding surface in some embodiments. 
     FIG. 4  is an illustrative representation of a scrolling input arrangement  400  in accordance with an embodiment of the present invention. In particular, scrolling input arrangement  400  includes a flexible membrane  404 . In some embodiments, flexible membrane  404  is a polyimide film. Flexible membrane  404  provides distinct advantages over prior solutions. For example, flexible membrane  404  provides a reduction in thickness over printed circuit boards (PCB) while still providing adequate structure for electronic components. In some embodiments, flexible membrane  404  may have a thickness of approximately 0.21 millimeters where typical PCB applications have a thickness of approximately 0.50 millimeters. Flexible membrane  404  provides further advantage by allowing associated electronic components and connectors to be disposed away from an arrangement stack comprised of capacitive elements. Allowing associated electronic components and connectors to be disposed away from an arrangement stack may thus provide a thinner cross-sectional profile of scrolling input arrangement  400  as well as provide mechanical shock insulation for associated electronic components. In this manner, a smaller, more durable arrangement may be realized. 
   In some instances, flexible membrane  404  may provide for increased tactile feedback efficiency. Tactile feedback efficiency is a measurement of a user&#39;s ability to discern a tactile change. Thus, when tactile feedback efficiency is high, a user is more readily able to discern a tactile change. In one embodiment, switch  420  may be mechanically integrated with flexible membrane  404 . When switch  420  actuated, a user may more readily discern a tactile change (e.g. a “click”) over prior art solutions because of flexible membrane&#39;s  404  physical properties. As a further advantage, tactile specificity may result because of flexible membrane&#39;s  404  physical properties. That is, because of flexible membrane&#39;s  404  elasticity, unintentional actuation of switches may be reduced or avoided altogether. This may allow for more switches to be placed closer together while avoiding inadvertent actuation of neighboring switches. In other embodiments, a flexible membrane  404  may include a center region  424  for mechanically integrating center switch  428  such that the center switch is approximately co-located with axis  402 . As noted above for  FIG. 2 , electronic components (e.g. switches) need not be co-located with capacitive sensors. In some embodiments, however, some advantages may be realized by co-locating some electronic components with capacitive sensors such as ease of manufacture or assembly. 
   As can be appreciated, flexible membrane  404  may be cut or formed into any number of shapes in accordance with user preferences. The illustrated shape is provided for clarity and should not be construed as limiting. Mechanically integrated with flexible membrane  404  are a variety of electronic components. A number of capacitive sensors  408  may be radially disposed with respect to axis  402  and mechanically integrated with top surface of flexible membrane  404 . In some embodiments, 16 capacitive sensors are utilized. Capacitive sensors  408  may be mechanically integrated with flexible membrane  404  in any manner well-known in the art. Each capacitive sensor includes a plate element  410  and a trace element (not shown). A plate element is one plate in a capacitor and is mechanically integrated with flexible membrane  404 . Trace elements (not shown) may also be mechanically integrated with flexible membrane  404 . Trace elements provide for electronic communication between capacitive sensors  408  and integrated circuit (IC) region  412 . An IC provides processing capability for capacitive sensors  408 . IC processing will be discussed in further detail below for  FIG. 6 . Any number of IC&#39;s may be mechanically integrated with flexible membrane  404  without departing from the present invention. 
   As can be appreciated, for each capacitive sensor, the sum of the surface area of its corresponding plate element and the surface area of its corresponding trace element is the sensor surface area. In some embodiments, the sensor surface area for all capacitive sensors is equivalent. Thus, where a longer trace element is required due to location constraints, a corresponding smaller surface area of the plate element results. Thus, plate elements may not match exactly in some embodiments. At least one reason for matching sensor surface areas is so that sensing will be uniform across the arrangement. As can be appreciated, where matching sensor surface areas is not practicable, adjustments for each sensor may be made algorithmically thus calibrating each sensor to its particular configuration. 
   Finally, a connection region  416  may be utilized for electronically coupling the arrangement  400  with an associated electronic device. In some examples, the electronic device is an IPOD™. Any number of connectors may be mechanically integrated with flexible membrane  404  without departing from the present invention. 
     FIG. 5  is an illustrative representation in exploded as well as cross-section views of a scrolling input assembly  500  in accordance with an embodiment of the present invention. Scrolling input assembly  500  includes a scrolling input arrangement  512  such as those described above for  FIG. 4 . Scrolling input assembly  500  further includes cover plate  504 . Cover plate  504  may provide protection for the top surface of scrolling input arrangement  512 . Cover plate  504  may also provide a low-friction surface to receive user input from, for example, a finger or stylus. Cover plate  504  may be composed of any suitable material that does not interfere with capacitive sensing. In some embodiments thermoplastic is utilized to create a cover plate. It should be noted that the figures provided herein are for illustrative purposes only and should not be construed to provide precise dimensions. 
   In some embodiments, scrolling input assembly  500  may include a center button  508  that may actuate switch  510  on scrolling arrangement  512 . Switch  510  may be electronically coupled with a processor or IC to provide selection functions. Backing plate  514  may be mechanically coupled with the bottom surface of scrolling input arrangement  512  to provide structural support. Backing plate  514  may also provide a grounding surface in some embodiments. In still other embodiments, grounding plate  514  may be configured with actuator nub  516  for actuating switch  520  on scrolling input arrangement  512 . In some embodiments, actuator nub  516  may be co-compression molded. 
     FIG. 6  is an illustrative flowchart of a method of calibrating a plurality of capacitive sensors in accordance with an embodiment of the present invention. As noted above, current designs may fail to properly calibrate in environments experiencing rapid temperatures changes. In one example, embodiments may be configured to respond to a temperature change of approximately 4° C./ms within a range of approximately 0° C. to 60° C. Thus, at a first step  604 , a baseline is established. A baseline may be established by assuming a current baseline and then scanning a plurality of capacitive sensors and tracking a lower edge of that scan to find a current sample. A minimum function of the current sample and the current baseline will provide a new current baseline for use with methods described herein. 
   At a next step  608 , capacitive sensors are scanned. As can be appreciated, responsiveness of a system is determined at least in part by the frequency with which samples are taken. For example, if a capacitive sensor is scanned more often, then the accuracy of the sample is likely to be much higher than if the capacitive sensor is scanned less often. Processing power and power consumption are two factors which account for a selection of sample frequency. In some embodiments described herein capacitive sensors are scanned at a frequency of approximately three megahertz. Once capacitive sensors are scanned at a step  608 , the method determines whether more than eight capacitive sensors have a count change greater than two. The selection of number of capacitive sensors corresponds to a likely change in sensor not attributable to a finger. That is, it is assumed, in this example, that a finger generally covers no more than eight capacitive sensors at any one time. In this manner, the method is determining whether a change in sensor is attributable to a change in ambient. A change in counts corresponds to a change in temperature. The selection of how many counts (i.e. threshold value) corresponds to a count high enough to avoid the noise floor of the sensor while still providing a count responsive to rapid changes. As can be appreciated by one skilled in the art, a noise floor of a sensor is generally sensor dependent. That is, for any given sensor, a noise floor may be specified by the manufacturer in accordance with manufacturing parameters. Thus, when more than eight capacitive sensors are scanned that have a count change greater than two, the method then calculates thermal drift at a step  616 . 
   Thermal drift corresponds to a change in baseline attributable to change in ambient temperature. In one embodiment, thermal drift is a minimum function of the signals of all capacitive sensors. Once thermal drift is found, that value is added to each capacitive sensor signal value at a step  620  thus creating a new baseline for each capacitive sensor signal value. The method continues to a step  624  continuing to a step  608  to scan all capacitive sensors. If the method, at a step  612  determines that eight or more capacitive sensors do not have a count change greater than two, the method continues to a step  624  continuing to a step  608  to scan all capacitive sensors. 
   While this invention has been described in terms of several embodiments, there are alterations, permutations, and equivalents, which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and apparatuses of the present invention. For example, although embodiments described herein provide for 16 capacitive sensors, more or fewer sensors may be utilized depending on user preferences and system requirements without departing from the present invention. Further, while scanning frequency has been described as approximately three megahertz, higher and lower frequencies may be employed without departing from the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, and equivalents as fall within the true spirit and scope of the present invention.

Metadata:
Filing Date: 20060214
Publication Date: 20100302
Grant Date: 20100302
Priority Date: 20050906
Inventors: FORSBLAD LARRY
HOTELLING STEVE
LYNCH BRIAN
LYON BENJAMIN
MOOLSINTONG JAN
WEBER DOUG
ZADESKY STEVE
Assignee: APPLE INC
CPC Classifications: [{"code": "H03K17/9622", "inventive": true, "first": true, "tree": "[]"}, {"code": "H03K2217/960755", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03K17/9622", "inventive": true, "first": true, "tree": "[]"}, {"code": "H03K2217/960755", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 37829277