Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
  • G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
  • G01R27/26—Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric constants ; Measuring impedance or related variables
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
  • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
  • G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
  • G01D5/14—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage
  • G01D5/24—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying capacitance
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
  • G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
  • G01R27/26—Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric constants ; Measuring impedance or related variables
  • G01R27/2605—Measuring capacitance
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03K—PULSE TECHNIQUE
  • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
  • H03K17/94—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the way in which the control signals are generated
  • H03K17/945—Proximity switches
  • H03K17/955—Proximity switches using a capacitive detector
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03K—PULSE TECHNIQUE
  • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
  • H03K17/94—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the way in which the control signals are generated
  • H03K17/96—Touch switches
  • H03K17/962—Capacitive touch switches
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03K—PULSE TECHNIQUE
  • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
  • H03K17/94—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the way in which the control signals are generated
  • H03K17/965—Switches controlled by moving an element forming part of the switch
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03K—PULSE TECHNIQUE
  • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
  • H03K17/94—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the way in which the control signals are generated
  • H03K17/96—Touch switches
  • H03K2017/9602—Touch switches characterised by the type or shape of the sensing electrodes
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03K—PULSE TECHNIQUE
  • H03K2217/00—Indexing scheme related to electronic switching or gating, i.e. not by contact-making or -breaking covered by H03K17/00
  • H03K2217/94—Indexing scheme related to electronic switching or gating, i.e. not by contact-making or -breaking covered by H03K17/00 characterised by the way in which the control signal is generated
  • H03K2217/96—Touch switches
  • H03K2217/96058—Fail-safe touch switches, where switching takes place only after repeated touch
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03K—PULSE TECHNIQUE
  • H03K2217/00—Indexing scheme related to electronic switching or gating, i.e. not by contact-making or -breaking covered by H03K17/00
  • H03K2217/94—Indexing scheme related to electronic switching or gating, i.e. not by contact-making or -breaking covered by H03K17/00 characterised by the way in which the control signal is generated
  • H03K2217/96—Touch switches
  • H03K2217/9607—Capacitive touch switches
  • H03K2217/96071—Capacitive touch switches characterised by the detection principle
  • H03K2217/960725—Charge-transfer
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03K—PULSE TECHNIQUE
  • H03K2217/00—Indexing scheme related to electronic switching or gating, i.e. not by contact-making or -breaking covered by H03K17/00
  • H03K2217/94—Indexing scheme related to electronic switching or gating, i.e. not by contact-making or -breaking covered by H03K17/00 characterised by the way in which the control signal is generated
  • H03K2217/96—Touch switches
  • H03K2217/9607—Capacitive touch switches
  • H03K2217/960755—Constructional details of capacitive touch and proximity switches
  • H03K2217/960775—Emitter-receiver or "fringe" type detection, i.e. one or more field emitting electrodes and corresponding one or more receiving electrodes

Definitions

• the present invention generally relates to capacitance sensing, and more particularly relates to devices, systems and methods capable of detecting a measurable capacitance using switched charge transfer techniques.
• Capacitance sensors/sensing systems that respond to charge, current, or voltage can be used to detect position or proximity (or motion or presence or any similar information), and are commonly used as input devices for computers, personal digital assistants (PDAs), media players and recorders, video game players, consumer electronics, cellular phones, payphones, point-of-sale terminals, automatic teller machines, kiosks, and the like.
• Capacitive sensing techniques are used in applications such as user input buttons, slide controls, scroll rings, scroll strips, and other types of inputs and controls.
• One type of capacitance sensor used in such applications is the button-type sensor, which can be used to provide information about the proximity or presence of an input.
• touchpad-type sensor Another type of capacitance sensor used in such applications is the touchpad-type sensor, which can be used to provide information about an input such as the position, motion, and/or similar information along one axis (1-D sensor), two axes (2-D sensor), or more axes. Both the button-type and touchpad-type sensors can also optionally be configured to provide additional information such as some indication of the force, duration, or amount of capacitive coupling associated with the input. Examples of 1-D and 2-D touchpad-type sensor based on capacitive sensing technologies are described in United States Published Application- 2004/0252109 Al to Trent et al. and United States Patent No. 5,880,411, which issued to Gillespie et al. on March 9, 1999. Such 1-D and 2-D sensors can be readily found, for example, in input devices of electronic systems including handheld and notebook-type computers.
• a user generally operates a capacitive input device by placing or moving one or more fingers, styli, and/or objects, near the input device an in a sensing region of one or more sensors located on or in the input device. This creates a capacitive effect upon a carrier signal applied to the sensing region that can be detected and correlated to positional information (such as the position(s), proximity, motion(s), and/or similar information) of the stimulus/stimuli with respect to the sensing region.
• positional information can in turn be used to select, move, scroll, or manipulate any combination of text, graphics, cursors, highlighters, and/or any other indicator on a display screen.
• This positional information can also be used to enable the user to interact with an interface, such as to control volume, to adjust brightness, or to achieve any other purpose.
• capacitance sensors have been widely adopted, sensor designers continue to look for ways to improve the sensors' functionality and effectiveness. In particular, engineers continually strive to reduce the effects of spurious noise on such sensors.
• Many capacitive sensors for example, currently include ground planes or other structures that shield the sensing regions from external and internal noise signals. While ground planes and other types of shields held at a roughly constant voltage can effectively prevent some spurious signals from interfering with sensor operation, they can also reduce sensor resolution or increase parasitic effects, such as by increasing parasitic capacitance. Therefore, the performance of such devices is by no means ideal.
• a charge transfer process is executed for at least two executions.
• the charge transfer process includes applying a pre-determined voltage to at least one of the plurality of sensing electrodes using a first switch, applying a first guard voltage to the at least one guarding electrode using a second switch, sharing charge between the at least one of the plurality of sensing electrodes and a filter capacitance, and applying a second guard voltage different from the first guard voltage to the at least one guarding electrode.
• a voltage is measured on the filter capacitance for a number of measurements equal to at least one to produce at least one result to determine the measurable capacitance for proximity detection.
• a guarded capacitance detection scheme may be conveniently implemented using readily available components, and can be particularly useful in sensing the position of a finger, stylus or other object with respect to a capacitive sensor implementing button, slider, cursor control, or user interface navigation functions, or any other functions.
• FIG. IA is a flowchart of an exemplary technique for detecting capacitance using switched charge transfer techniques with guarding
• FIG. IB is a block diagram of an exemplary capacitive proximity sensor that includes guard circuitry;
• FIG. 1C is a timing diagram relating to an exemplary technique for operating the capacitive proximity sensor with guard circuitry of FIG. IB;
• FIGS. 2A-B are timing diagrams of exemplary guard signals that can be applied to guarding electrodes.
• FIGS. 3A-E are block diagrams of exemplary circuits that could be used to generate guard voltages of a guard signal
• FIGS. 4A-E are more detailed block diagrams of exemplary circuits that could be used to generate guard voltages of a guard signal.
• FIG. 5 is a schematic diagram of a proximity sensor device with an electronic system.
• a capacitance detection and/or measurement circuit can be readily formulated using two or more switches. Further, a guard signal with two or more guarding voltages can be applied to a guarding electrode using one or more additional switches and one or more passive electrical networks (which can be a simple wire or a complex network); this can be used to shield the sensor from undesired electrical coupling, thereby improving sensor performance. In a typical implementation, a charge transfer process is executed for two or more iterations.
• a pre-determined voltage is applied to a measurable capacitance using one or more of the switches and a first guarding voltage is applied to a guarding electrode with a second switch, the measurable capacitance then shares charge ' with a filter capacitance in the passive network and a second guarding voltage is applied to the guarding electrode.
• a plurality of applications of the pre-determined voltage and the associated sharings of charge influence the voltage on the filter capacitance.
• the voltage on the filter capacitance can be the voltage at a node of the circuit that indicates the voltage across the filter capacitance.
• the voltage on the filter capacitance can also be the voltage across the filter capacitance itself.
• the charge transfer process thus can be considered to roughly "integrate" charge onto the filter capacitance over multiple executions such that the "output" voltage of the filter capacitance is filtered.
• the charge transfer process may be done using only switches and passive elements such as resistances, capacitances, and/or inductances.
• the voltage on the filter capacitance (which is representative of the charge on the filter capacitance) is measured.
• One or more measurings can be used to produce one or more results and to determine the measurable capacitance.
• the measuring of the voltage on the filter capacitance can be as simple as a comparison of the voltage on the filter capacitance with a threshold voltage, or be as complex as a multi-step analog-to-digital conversion extracting charge from the filter capacitance and measuring the voltage multiple times.
• capacitive position sensors capable of detecting the presence or proximity of a finger, stylus, or other object can be readily formulated.
• various embodiments of the guard described herein can be readily implemented using only conventional switching mechanisms (e.g. signal pins of a control device) and passive components (e.g. one or more capacitors, resistors, inductors and/or the like), without the need for additional active electronics that would add cost and complexity.
• the various guarding techniques described herein can use similar components and methods as charge transfer sensing techniques. This, coupled with the ease of multi-channel integration, provide for highly efficient implementation of the guard. As a result, the various guarding schemes (and sensing schemes if desired) described herein may be conveniently yet reliably implemented in a variety of environments using readily-available and reasonably-priced components, as described more fully below.
• the method 800 uses switched charge transfer to detect measurable capacitances, and is particularly applicable to the detection of capacitances for object position detection.
• the technique suitably includes the broad steps of performing a charge transfer process with voltage guarding (step 801) for two or more times (as repeated by step 810) and selectively measuring a voltage on the filter capacitance to produce a result (step 824).
• the charge transfer process 801 includes applying a predetermined voltage to the measurable capacitance (step 802). Then, a first guard voltage is applied to a guarding electrode (step 804).
• the first guard voltage is preferably provided before the applying of the pre-determined voltage to the measurable capacitance ceases. Then; charge is shared by the measurable capacitance and a filter capacitance (step 806). “Sharing" charge in this context can refer to actively switching to couple the measurable capacitance and the filter capacitance, actively switching elsewhere in the system, otherwise directing the transfer of charge, or passively allowing the charge to transfer through impedance through quiescence or other inaction. Then, a second guard voltage is applied to the guarding electrode (step 808). The second guard voltage is different from the first guard voltage, and is preferably applied to the guarding electrode before the sharing of charge substantially ends.
• the charge transfer process repeats at least once (step 810) for at least two performances of the charge transfer process total, and may repeat many more times.
• the charge transfer process can repeat until the voltage on filter capacitance exceeds a threshold voltage, until the process 801 has executed for a pre-determined number of times, .and/or according to any other scheme.
• the first and second guard voltages are provided to shield from undesirable electrical coupling.
• Measurement of the voltage on the filter capacitance to produce a result can take place at any time, including before, after, and during the charge transfer process.
• none, one, or multiple measurements of the voltage on the filter capacitance 824 can be taken for each repetition such that the number of measurement results to the number of charge transfer processes performed can be of any ratio, including one-to-many, one-to- one, and many-to-one.
• the voltage on filter capacitance is measured when the voltage on the filter capacitance is substantially constant.
• One or more of the measurement results is/are used in a determination of the value of the measurable capacitance.
• the value of the measurable capacitance may take place according to any technique.
• the determination is made based upon the measurement(s) of the voltage on the filter capacitance (which is indicative of the charge on the filter capacitance), the values of known components in the system (e.g. the filter capacitance), as well as the number of times that the charge transfer process 801 was performed.
• the particular number of times that process 801 is performed may be determined according to a pre-determined value, according to the voltage across the filter capacitance crossing a threshold voltage, or any other factor as appropriate.
• Steps 802-808 and steps 824 can be repeated as needed (step 810).
• the measurable capacitance corresponding to each sensing electrode would typically be determined many times per second. This provides the ability to determine the proximity of objects near the sensor, as well as changes to that proximity, and thus facilitates use of the process in a- device for user input.
• the process can be repeated at a high rate for each sensing electrode each second to enable many determinations of the measurable capacitance per second.
• Process 800 may be executed in any manner.
• process 800 is executed by software or firmware residing in a digital memory, such as a memory located within or in communication with a controller, or any other digital storage medium (e.g. optical or magnetic disk, modulated signal transmitted on a carrier wave, and/or the like).
• a digital memory such as a memory located within or in communication with a controller, or any other digital storage medium (e.g. optical or magnetic disk, modulated signal transmitted on a carrier wave, and/or the like).
• Process 800 and its various equivalents and derivatives discussed above can also be executed with any type of programmed circuitry or other logic as appropriate.
• first and second guard voltages can be implemented with a variety of different techniques and devices.
• the guard voltages can be provided using switching mechanisms and passive components (e.g. one or more capacitors, resistors, inductors, and/or the like), without the need for additional active electronics that would add cost and complexity (although such active electronics, including DACs and followers, can be used to provide the proper guard voltages at low impedance).
• an exemplary capacitance sensor 100 suitably includes three sensing electrodes 112A-C and one guarding electrode 106.
• the sensing electrodes 112A-C are directly coupled to switches 116A-C, respectively.
• the sensing electrodes 112 A-C are also directly coupled with a filter capacitance (also "integrating capacitance” or “integrating filter”) 110 (Cp) through passive impedances 108A-C, respectively.
• the filter capacitance 110 is also shown directly coupled to a switch 118.
• the guarding electrode 106 is coupled to a guarding voltage generating circuit 104 that includes passive guarding network 105 and one or more switch(es) 114.
• Guarding voltage generating circuit 104 provides an appropriate guard signal (V G ) 103. Also shown in FIG. IB is stimulus 101 that is not part of capacitance sensor 100 and is detected by capacitance sensor 100. Stimulus 101 can be one or more fingers, styli, objects, and the like, even though one stylus is shown in FIG. IB.
• capacitance sensor 100 may include any number of sensing electrodes, guarding electrode, filter capacitances, passive impedances, switches, guarding voltage generating circuits, and ⁇ controllers as appropriate for Hie sensor. They can also -be in any ratio appropriate for the sensor; for example, the sensing electrodes may also be coupled to filter capacitance(s) with or without passive impedances in a many-to-one, one-to-many, one-to-one, or many-to- many configuration as allowable by the sensing scheme used. It should be noted that while FIG.
• IB shows switch(es) 114, 116A-C, and 118 all implemented using I/Os of a controller 102, that this is just one example embodiment, and that these and other switches could be implemented with a variety of different devices including discrete switches distinct from any controller.
• the sensor may use a passive guarding network that consists of a single wire or a more complex circuit network, or the sensor may also provide the guarding signal using a single switch or multiple switches (which may involve using one or many I/Os of a controller, a multiplexer, a digital-to-analog converter (DAC), etc., since each multiplexer or DAC includes multiple switches).
• DAC digital-to-analog converter
• a switch can be used in a multitude of ways to provide the guard signal, including closing the switch, opening the switch, or actuating it in some other manner (e.g. PWM and pulse coded modulating). Therefore, one can apply a voltage by closing a switch as well as by opening a switch, depending on how the circuit is laid out. Additional analog components may also be used (e.g. to buffer the output of the passive guarding network 105).
• the sensing electrodes 112A-C provide the measurable capacitances whose values are indicative of the changes in the electric field associated with stimulus 101.
• Each of the measurable capacitances represents the effective capacitance of the associated sensing electrode(s) 112A-C detectable by the capacitance sensor 100.
• the measurable capacitance represents the total effective capacitance from a sensing electrode to the local ground of the system.
• the measurable capacitance represents the total effective capacitance between the sensing electrode and one or more driving electrodes.
• the total effective capacitance can be quite complex, involving capacitances, resistances, and inductances in series and in parallel as defined by the sensor design and the operating environment.
• the measurable capacitance from the input can be modeled simply as a small variable capacitance in parallel with a fixed background capacitance.
• switches 114, 116A-C are controlled by a controller 102 (which can be a microprocessor or any other controller).
• controller 102 which can be a microprocessor or any other controller.
• guarding voltages can be generated to produce a guard signal 103 that is placed on guarding electrode 106 to shield the measurable capacitances from undesired effects of noise and other spurious signals during operation of sensor 100.
• Guarding electrode 106 is any structure capable of exhibiting applied guarding voltages comprising guard signal 103 to prevent undesired capacitive coupling with one or more measurable capacitances.
• FIG. IB shows guarding electrode 106 with a "comb"-type appearance, this appearance is shown for convenience of explanation, and guarding electrode 106 may exhibit any other form or shape, in any number of equivalent embodiments as applicable for the design of sensor 100.
• the sensing electrodes 112A-C may be laid out in some other pattern or have some other shape, and the shape of guarding electrode 106 can be laid out as appropriate.
• Guarding electrode 106 can also be routed around all or portions of a perimeter of a set of sensing electrodes to shield the set at least partially from the environment.
• Guarding electrode 106 can be routed behind at least a portion of the sensing electrodes to shield them from any electronics behind the sensing electrodes. Guarding electrode 106 can also be routed between sensing electrodes to shield them from each other. The guarding electrode does not need to extend the full length between sensing electrodes or cover the full sensing electrodes to offer a useful level of guarding. For example, guarding electrode 106 can parallel only portions of the sensing electrodes 112A-C, or interleave some or all of the sensing electrodes 112A-C.
• guarding electrode 106 may be routed around any areas where guarding electrode 106 may interfere with the capacitive coupling between the sensing electrodes 112A-C and any driving electrode(s), such as some regions between the sensing electrodes 112A-C and the driving electrode(s).
• capacitive coupling between guarding electrode 106 and measurable capacitances can be controlled through application of appropriate guarding voltages via switch(es) 114.
• a filter capacitance 110 is provided by one or more capacitors (such as any number of discrete capacitors) to accept charge transferred from sensing electrodes 112A-C.
• the capacitance of each filter capacitance 110 will typically be much greater - perhaps by only one to two orders of magnitude but often several orders of magnitude greater — than the capacitance of the measurable capacitances.
• Filter capacitance 110 may be designed to be on the order of several nanofarads, for example, when expected values of measurable capacitances are on the order of several picofarads or so. Actual values of filter capacitance 110 may vary, however, depending upon the particular embodiment.
• each sensing electrode 112A-C is coupled to a common filter capacitance 110 through an associated passive impedance 108 A-C.
• Alternate embodiments may use multiple filter capacitances and/or passive impedances for each measurable capacitance as appropriate. Alternate embodiments may also share a passive impedance and/or a filter capacitance between multiple measurable capacitances.
• passive impedances 108 A-C are typically provided by one or more non-active electronic components, such as any type of diodes, capacitors, inductors, resistors, and/or the like. Passive impedances 108 A-C are each generally designed to have an impedance that is large enough to prevent significant current bleeding into filter capacitance 110 during charging of measurable capacitance, as described more fully below. In various embodiments, impedances 108A-C may be on the order of a hundred kilo-ohms or more, although other embodiments may utilize widely different impedance values. Again, however, passive impedances 108A-C need not be present in all embodiments where charge sharing is otherwise implemented.
• Operation of sensor 100 suitably involves a charge transfer process and a measurement process facilitated by the use of one or more switches 116A-C, 118 while a guard signal 103 is applied using switch(es) 114.
• switches 114, 116A-C and/or 118 may be implemented with any type of discrete switches, multiplexers, field effect transistors and/or other switching constructs, to name just a few examples.
• any of switches 114, 116A-C, 118 can be implemented with internal logic/circuitry coupled to an output pin or input/output (I/O) pin of the controller 102, as shown in FIG. IB.
• I/O pins can also provide input functionality and/or additional switches.
• switch 118 can be implemented with I/O 119 that also connects to, or contains, input capability within controller 102.
• the input capability may be used in measuring the voltage on the filter capacitance 110 directly or indirectly, and might include a multiplexer, comparator, ⁇ hysteretic thresholds, CMOS threshold, or analog-to-digital converter.
• Such I/O pins are typically capable of switchably applying one or more logic values and/or a "high impedance" or "open circuit” value by using internal switches coupled to power supply voltages.
• the logic values may be any appropriate voltages or other signals.
• a logic “high” or “1” value could correspond to a "high” voltage (e.g. 5 volts), and a logic “low” or “0” value could correspond to a comparatively “low” voltage (e.g. local system ground, -5 volts or the like).
• the particular signals selected and applied can vary significantly from implementation to implementation depending on the particular controller 102, sensor configuration, and sensing scheme selected.
• a current source, a pull-up resistance, or a digital-to-analog converter (DAC) also could be used to provide the proper voltages, and may be external or internal to controller 102.
• controller 102 is a conventional digital controller comprised of any combination of one or more microcontrollers, digital signal processors, microprocessors, programmable logic arrays, integrated circuits, other controller circuitry, and/or the like.
• controller 102 can contain digital memory (e.g. static, dynamic or flash random access memory) that can be used to store data and instructions used to execute the various charge transfer processing routines for the various capacitance sensors contained herein.
• the only electrical actuation on the sensing electrodes 112A-C and their associated measurable capacitances that need take place during operation of sensor 100 involves manipulation of switches 114, 116A-C and 118; such manipulation may take place in response to configuration, software, firmware, or other instructions contained within controller 102.
• the charge transfer process which is typically repeated two or more times, suitably involves using a first switch to apply a pre-determined voltage (such as a power supply voltage, battery voltage, ground, or logic signal) to charge the applicable measurable capacitance ⁇ ), and then passively or actively allowing the applicable measurable capacitance ⁇ ) to share charge with any filter capacitance (e.g. 110) as appropriate.
• a pre-determined voltage such as a power supply voltage, battery voltage, ground, or logic signal
• Passive sharing can be achieved by charge transfer through an impedance such as a resistance
• active sharing can be achieved by activating a switch that couples the applicable measurable capacitance(s) to the appropriate filter capacitance(s).
• the pre-determined voltage is often a single convenient voltage, such as a power supply voltage, a battery voltage, a digital logic level, a resistance driven by a current source, a divided or amplified version of any of these voltages, and the like.
• the value of the pre-determined voltage is often known, and often remains constant; however, neither needs be the case so long as the pre-determined voltage remains ratiometric with the measurement of the voltage on the applicable filter capacitance (e.g. 110).
• a capacitance sensing scheme can involve resetting the filter capacitance to a reset voltage, and also involve measuring a voltage on the filter capacitance by comparing the voltage (as relative to the reset voltage) on one side of the filter capacitance with a threshold voltage (also as relative to the reset voltage).
• a threshold voltage also as relative to the reset voltage
• the threshold used to measure the change in voltage on the filter capacitance will be proportional to the change in voltage on the filter capacitance due to the charge shared from the measurable capacitance to the filter capacitance during the executions of the charge transfer process for a determination of the measurable capacitance.
• the threshold voltage can be ratiometric for a CMOS input threshold, for example (l/2)*(Vd d - GND).
• each switch 116A-C applies a pre-determined voltage with "charging pulses" 201 that typically have relatively short periods in comparison to' the RC time constants of impedances 108 A-C with the filter capacitance 110, and preferably have relatively short periods in comparison to the RC time constants of impedances 108 A-C with their associated measurable capacitances.
• charging pulses typically have relatively short periods in comparison to' the RC time constants of impedances 108 A-C with the filter capacitance 110, and preferably have relatively short periods in comparison to the RC time constants of impedances 108 A-C with their associated measurable capacitances.
• each charging pulse 201 additionally provides relatively brief durations of an "opposing" "discharging voltage” (a voltage that have a magnitude opposite that of the pre-determined voltage) before applying the pre-determined voltage.
• the discharging voltage can compensate for any current leaking through impedances 108 A-C during the charge transfer process; it is an optional feature that is not required in all embodiments. More than one level of voltage can be used in the pre-determined voltage in an execution or between executions, and this is also true for the opposing voltage. However, in many cases the pre-determined voltage and the opposing voltage (if used) will have substantially constant voltages.
• guarding electrode e.g. 106
• measurable capacitance e.g. associated with sensing electrodes 112A-C
• filter capacitance 110 e.g. 108 A-C
• passive impedance e.g. 108 A-C
• multiple measurable capacitances, passive impedances, and filter capacitances can be included in the system, and they can be operated in serially (at least partially or completely separate in time) or in parallel (at least partially or completely overlapping in time ).
• the measurable capacitance After applying the pre-determined voltage to the measurable capacitance, the measurable capacitance is allowed to share charge with filter capacitance. To allow measurable capacitance to share charge, no action may be required other than to stop applying the pre-determined voltage and pause for a time sufficient to allow charge to passively transfer. In various embodiments, the pause time may be relatively short (e.g. if the filter capacitance is connected directly to the measurable capacitance with a small resistance in series), or some delay time may occur (e.g. for charge to transfer through a larger resistance in series with the measurable capacitance, the filter capacitance, and reference voltage).
• allowing charge to transfer may involve stopping the application of the pre-determined voltage and actively actuating one or more switches associated with a controller to couple the measurable capacitance and the filter capacitance, and/or taking other actions as appropriate.
• charge sharing with the filter capacitance could occur in other embodiments using "sigma-delta” techniques; such as in a process whereby the filter capacitance is charged via a measurable capacitance and discharged by a "delta" capacitance (not shown), or vice versa.
• charge sharing with the filter capacitance could occur by actuating switches (not shown) that couple and decouple the measurable capacitance with the filter capacitance or that couple and decouple the filter capacitance with a power supply voltage.
• impedances such as those shown as 108 A-C shown in FIG. IB may not be present, may be augmented by passive or active elements, and/or may be replaced by passive or active elements as appropriate.
• a charge transfer process where sharing charge between the measurable capacitance and the filter capacitance occurs using one or more active components clearly indicates the beginning and the end of a sharing period with these actuations of the active component(s).
• a charge transfer process where the measurable capacitance is directly connected to one side of the filter capacitance, and the other side of the filter capacitance is coupled, by activating a switch, to a low impedance reference voltage also clearly indicates the beginning and ending of a sharing period.
• charge transfer processes that passively share charge have less clear denotations of the charge sharing periods.
• the charge sharing period can be considered to begin when the applying of the pre-determined voltage ceases; the charge sharing period must end at or before a subsequent charging pulse begins (for a subsequent execution of the charge transfer process) and at or before a reset of the filter capacitance (if a reset is used and indicates an end a set of charge transfer processes).
• the sharing period may end before a subsequent charging pulse and before any reset because current flow effectively stops when the voltages are similar enough that negligible charge is shared between the measurable capacitance and the filter capacitance; this will be the case when sufficient time has passed while the measurable capacitance and filter capacitance are coupled to each other.
• the measurement process may be performed at any point of the charge transfer process as appropriate for the sensor configuration and sensing scheme used, and the number of performances of the measurement process may be in any ratio with the performances of the charge transfer process as appropriate for the sensor configuration and sensing scheme used.
• the measurement process may take place after the sharing of the charge between the measurable capacitance and the filter capacitance brings the voltage on the filter capacitance to be within some percentage point from an asymptote, or the measurement process may take place every time a charge transfer process is performed.
• the measurement process may take place while the pre-determined voltage is applied (if the filter capacitance is properly prevented from charge sharing with the measurable capacitance at that time).
• the measurement process may take place only for a set number of repetitions of the charge transfer process, or only after a number of repetitions have already taken place.
• the measuring of the voltage on the filter capacitance can be as simple as a comparison of a voltage on the filter capacitance with a threshold voltage (such as in a "sigma-delta" scheme), or be as complex as a multi-step analog-to- digital conversion (such as when a known number of charge transfer processes are performed and then the voltage on the filter capacitance is read as a multi-bit value).
• Multiple thresholds can also be used, such as in an oscillator or other dual-slope sensing system where the voltage on the filter capacitance is driven between low and high thresholds, and in multi-bit ADCs where multiple thresholds are used to measure the voltage on the filter capacitance. One or more measurements can be taken, and stored if appropriate, to determine the measurable capacitance as applicable.
• a system without any shields or guards will be affected by the environment. Therefore, as discussed earlier, many capacitive sensors include ground planes or other structures that shield the sensing regions from external and internal noise signals. However, ground planes and other types of shields held at a roughly constant voltage are by no means ideal - they can increase the effects of parasitic capacitance (or other parasitic impedance and associated charge leakage) and reduce resolution or dynamic range. In contrast, a driven, low-impedance guard can provide similar shielding without significantly increasing the effect of parasitic capacitance or reducing resolution.
• the typical charge transfer sensing scheme will perform the charge transfer processes multiple times (and often hundreds of times or more) to generate the measurement(s) that are used for one determination of the measurable capacitance.
• This set of charge transfer processes that lead to the measurement(s) used for one determination varies between embodiments.
• the set can be between a reset state and a final-threshold-state for systems that charge to threshold(s); the set can be between an initial state and a final-read-state for systems that perform a set number of charge transfer processes and read one or more multi-bit voltage output(s); the set can be between the low and high thresholds for dual slope or oscillator systems; the set can also be the sample length of a digital filter for sigma-delta systems.
• This set of charge transfer processes defines a set where the overall guarding effect is considered, or "the course of executions of the charge transfer processes leading to the determination of the measurable capacitance.”
• a guard signal with proper guarding voltages can be applied.
• the applying of the predetermined charging voltage to the measurable capacitance lasts for some duration of time, and before this duration ends, a first guarding voltage similar to this pre-determined voltage can be applied to the appropriate guarding electrode. Since the pre-determined voltage is typically fairly constant, the first guarding voltage can often be a single, roughly constant voltage.
• the guard signal applied to the guarding electrode may be changed to a second guarding voltage similar to the voltage on the associated filter capacitance.
• Resetting of filter capacitance 110 can also be accomplished by simply coupling a switch on one side of the filter capacitance 110 to the appropriate power supply voltage.
• the voltage on the filter capacitance 110 may be reset to a pre-determined value by applying known voltages on both sides of the filter capacitance 110.
• filter capacitance 110 can comprise a ' network of capacitors instead of one single capacitor, and each capacitor in the network may be reset to a different voltage and controlled ' by one or more switches, such that resetting filter capacitance 110 may involve opening and closing a multitude of switches.
• charge transfer processes may be performed in synchrony or in series. Multiple similar charge transfer processes may be used, for example, to determine multiple measurable capacitances simultaneously or in sequence. Multiple similar charge transfer processes may also be used concurrently to obtain multiple determinations of the same measurable capacitance for a more accurate determination overall. Charge transfer processes that roughly oppose each other in effect may also be used to practice more complex measurement schemes. For example, a first charge transfer process may be used to charge a filter capacitance and a second charge transfer process may be used to discharge the same filter capacitance; one or more measurement(s) may be taken during the charge and discharge of the filter capacitance and used to determine the value of the measurable capacitance.
• guard signal 103 it is often more practical to apply a guard signal 103 to guarding electrode 106 that does not minimize charge transferred from the guarding electrode 106 to the filter capacitance 110 during a single execution of the charge transfer process, but does minimize the net transfer of charge during the set of charge transfer processes that eventually result in measurement(s) of the voltage on filter capacitance 110 that are used to determine the applicable measurable capacitance.
• This can be done with a guard signal 103 that causes charge transfer in a first direction between guarding electrode 106 and filter capacitance 110 during one or more executions of the charge transfer process, and causes charge transfer in a second direction opposite the first direction during other execution(s) of the charge transfer process.
• the end of the charge sharing period occurs when the applying of the pre-determined voltage begins in a switched time- constant system, such as the one shown in FIGS. IB-C; the end of the charge sharing period occurs when the measurable capacitance is decoupled from the filter capacitance or when the filter capacitance is decoupled from any reference voltage, such as in switched capacitance systems.
• the charge sharing period may be considered to continue only until a subsequent applying of the pre-determined voltage (when charge sharing can be considered to- end for -guarding purposes).
• the switching may be considered to define the end of the charge sharing period.
• FIGS. 2A-B Many changes can be made to the basic structures and operations shown in FIGS. 2A-B.
• the timing scheme 200 shown in FIG. 2A shows the first guard voltage is roughly constant and the second guard voltage as the one changing if such change were to occur.
• the guard voltage "swing" (difference between the first and second guard voltage aside from transition periods) matters more than the actual guard voltage values, the guard signal 103 can also be implemented with the first guard voltage changing instead of the second guard voltage, or both first and second guard voltages changing.
• the timing for the guard voltage changes have great flexibility.
• Circuit 104 can include any number of impedances and switches and utilize any number of reference sources as appropriate.
• each of the impedances shown in FIGS. 3A-D can. represent the impedance due to a single component or network of components.
• Active components in addition to switches, such as multiplexers, DACs, current sources, or OP-AMPS, can also be included in guard voltage generating circuit 104, but are not required and not used in most embodiments.
• This voltage of guard signal 103 could correspond to a reset voltage of a charge transfer process that is being guarded.
• the voltage of guard signal 103 s determined by the reference voltage 301 and the voltages across impedances 304, 306, and 308.
• This voltage of guard signal 103 could correspond to the voltage on a filter capacitance in a charge transfer process that is being guarded.
• switch 302 is open and switch 303 is closed, the voltage of guard signal 103 is driven to GND.
• This voltage of guard signal 103 could correspond to a pre-determined charging voltage of a charge transfer process that is being guarded.
• a configuration such as circuit 104A allows a guard voltage generating circuit that emulates the voltages associated with charge transfer processes utilizing a "switched time constant" technique, such as in FIGS IB-C.
• the impedance 304 could be configured to correspond with a filter capacitance formed from a network of components, and impedance 304 could be coupled to more than one voltage to accurately correspond to that of the matched filter capacitance. Note that a variety of reset voltages and charging voltages may be guarded though they may require different switching sequences or references voltages (e.g. Vd d and ground).
• impedances 304, 306, and 308 form an impedance divider with "common nodes" where impedance 306 connects to impedance 308 and where impedance 304 connects to impedance 306.
• impedances 306 and 308 form a different impedance divider with a common node where impedance 306 connects to impedance 308.
• guard voltage generating circuit 104B the passive guarding network is comprised of impedance 314.
• guard signal 103 is suitably switched by switch 312 between reference voltage 301 when switch 312 is closed; this voltage of guard signal 103 could correspond to a pre-determined charging voltage.
• Guard signal 103 suitably switches to a second voltage defined by the voltage across impedance 314 when switch 312 is open; this voltage of guard signal 103 could correspond to the voltage on a filter capacitance.
• Switch 313 could be closed to remove charge from impedance 314; this voltage of guard signal 103 can correspond to a reset voltage.
• impedance 314 a configuration as circuit 104B allows a guard voltage generating circuit that emulates the voltages associated with a charge transfer processes utilizing a sigma-delta version of the "switched time constant" technique.
• FIG. 3 C shows another embodiment of the guard voltage generating circuit 104C that includes a passive guarding network comprised of two impedances 324, 326 in series.
• Circuit 104C is driven by three switches 322, 323, and 325.
• switch 322 When switch 322 is closed and switches 323 and 325 are open, the guard signal 103 is the reference voltage 301; this voltage of guard signal 103 could correspond to a pre-determined charging voltage.
• switches 322 and 323 are open, and switch 325 is closed, the guard signal 103 is determined by the reference voltage 301 and the voltage across impedances 324, 326; this voltage of guard signal 103 could correspond to the voltage on a filter capacitance.
• FIG. 3D shows an embodiment of the guard voltage generating circuit 104D with a passive guarding network comprising two impedances 334 and 336 located in series with the reference voltage 301 and a switch 332 to ground (GND).
• guard signal 103 is suitably switched using switch 332.
• switch 332 When switch 332 is open, the guard signal 103 is determined by reference voltage 301 and the voltage across impedance 334; this voltage of guard signal 103 could correspond to a pre-determined voltage.
• switch 332 is closed, the guard signal 103 is determined by reference voltage 301 and the voltages across impedances 334 and 336; this voltage of guard signal 103 could correspond to an average voltage on a filter capacitance.
• the impedances 334 and 336 form an impedance divider that appropriately divides the reference voltage 301 as determined by the type and value of impedance components chosen. That is, impedances 334 and 336 suitably function as a "pull-up" component when switch 332 is open, and impedances 334 and 336 function as an impedance divider when switch 302 is closed.
• the impedance divider is a conventional voltage divider and- the- guard signal 103 when switch 332 closed is proportional to reference voltage 301 via the ratio of the resistance of impedance 336 to the sum of the resistances of impedances 334 and 336.
• circuit 104D allows a guard voltage generating circuit 104 for "switched voltage divider" type of guard signal 103.
• the output of circuit 104D can be further adapted, such as modulated in frequency, to produce a "pulse coded modulation" type of waveform for guard signal 103.
• guard voltage generating circuit 104 shown in FIGS. 3A-3E are but five examples of the various alternatives that can be used to determine Hie guard signal 103.
• an additional impedance could couple impedance 306 to another reference voltage in parallel with impedance 304 for circuit 104 A.
• impedance 314 of circuit 104B can be in parallel with switch 312 instead of switch 313.
• Switch 302 as implemented using I/O 402 is analogous to switch 118, and switch 303 as implemented using I/O 403 is analogous to switches 116A-C implemented using I/O 119 (FIG. IB).
• I/O 403 itself is analogous to I/O 119 (FIG. IB).
• the circuit 104F can thus be driven in a way to match the charge transfer process such that the guard signal 103 would roughly match the voltage 117 of a charge transfer sensing process as shown in FIGS. IB-C 5 and minimize charge transfer from the guarding electrode 106 to the filter capacitance 110 at all points of the charge transfer processes used for sensing.
• the example circuit 104G shown in FIG. 4B is an embodiment of the circuit 104B of FIG. 3B. Both switches 312 and 313 have been implemented using a single I/O 412, and the impedance 314 has been implemented as a network having a resistance 414 and capacitance 415.
• the example circuit 104G can be driven using something similar to a "one I/O sigrna delta" type "switched time constant" methodology.
• switch 313 of I/O 412 is opened (if it is not already open) and switch 312 of I/O 412 is closed to apply the reference voltage 301 (which is the pre-determined voltage), and then switch 312 of I/O 412 is opened to allow charge to share between any guarded capacitances in the system and capacitance 415.
• switch 312 of I/O 412 is closed, the capacitance 415 is charged through impedance 414.
• Closing switch 313 of I/O 412 discharges capacitance 415 through impedance 414.
• switch 322 of FO 422 is closed and switch 323 of I/O 422 is opened to apply the reference voltage 301 (which is the pre-determined voltage in the embodiment shown in FIG. 4C) to capacitance 424.
• switch 322 of I/O 422 is opened and switch 325 of I/O 425 is closed to allow charge to share between capacitances 424 and 426.
• This cycle of first closing switch 322 of I/O 422 and then opening switch 322 of I/O 422 and closing switch 325 of I/O 425 can be repeated synchronous with the charge transfer process used to detect proximity and measure the measurable capacitance.
• switch 323 of I/O 422 and switch 325 of I/O 425 can close to reset the charge on capacitance 426.
• the circuit 104G can thus be driven in a way to generate a guard signal 103 that has a first guard voltage that is the pre-determined voltage and a second guard voltage that is substantially constant within an execution of the charge transfer process but that rises from the reset voltage with ' each subsequent execution of the charge transfer process before reset.
• This guard signal 103 would then approximate the voltages of the measurable capacitance in a charge transfer process if the ratio of the fixed capacitance 424 to capacitance 426 is comparable to the ratio of the measurable capacitance to the filter capacitance.
• the example guard signal generating circuit 1041 shown in FIG. 4D is an embodiment of the circuit 104D shown in FIG. 3D.
• Impedance 334 has been implemented using resistance 434
• impedance 336 has been implemented using resistance 436
• switch 332 has been implemented using I/O 432.
• switch 332 of I/O 432 is open, the guard signal 103 approaches the reference voltage 301.
• switch 332 of I/O 432 is closed, the guard signal 103 is set to a voltage that is proportional to the reference voltage 301 by the ratio of resistance 436 to the sum of resistances 434 and 436.
• a guard signal 103 can be used to approximate the average swing of voltage associated with the measurable capacitance.
• sensing electrodes and/or guarding electrode(s) can be readily formed on a standard printed circuit board (PCB), so duplication of these elements is relatively inexpensive in a manufacturing sense.
• filter capacitance 110 may also be manufacturable in a PCB.
• none or one or more resistances, capacitances, and inductances may be formed on a PCB to provide impedances used in the guard voltage generating circuit 104, such as capacitance 404 and resistance 406 of circuit 104F.
• components such as filter ca ⁇ acitance(s) and/or passive impedance(s) and other impedances may be large enough or require tight enough tolerances to warrant discrete components in many embodiments.
• these components e.g. filter capacitance 110
• filter capacitance 110 may be implemented with one or more discrete capacitors, resistors, inductors, and/or other discrete components.
• FIG. 5 a block diagram is illustrated of an exemplary electronic system 10 that is coupled to a proximity sensor device 11.
• Electronic system 10 is meant to represent any type of personal computer, portable computer, workstation, personal digital assistant, video- game player, communication device (including wireless phones and messaging devices), media device, including recorders and players (including televisions, cable boxes, music players, and video players) or other device capable of accepting input from a user and of processing information.
• the various embodiments of system 10 may include any type of processor, memory or display.
• the elements of system 10 may communicate via a bus, network or other wired or wireless interconnection.
• the proximity sensor device 11 can be connected to the system 10 through any type of interface or connection, including I2C, SPI, PS/2, Universal Serial Bus (USB), Bluetooth, RP, IRDA, or any other type of wired or wireless connection to list several non-limiting examples.
• Proximity sensor device 11 includes a controller 19 and a sensing region 18.
• Proximity sensor device 11 is sensitive to the position of a stylus 114, finger and/or other input object within the sensing region 18 by measuring the resulting capacitance.
• "Sensing region” 18 as used herein is intended to broadly encompass any space above, around, in and/or near the proximity sensor device 11 wherein the sensor is able to detect a position of the object. In a conventional embodiment, sensing region 18 extends from the surface of the sensor in one or more directions for a distance into space until signal-to-noise ratios prevent object detection.
• proximity sensor device 11 suitably detects a position of stylus 14 by measuring the measurable capacitance associated with the plurality of electrodes and finger or other input object within sensing region 18, and using controller 9, provides electrical or electronic indicia of the position to the electronic system 10.
• the system 10 appropriately processes the indicia to accept inputs from the user, to move a cursor or other object on a display, or for any other purpose.
• the sensing technology can also vary in the type of information provided, such as to provide "one-dimensional" position information (e.g. along a sensing region) as a scalar, "two-dimensional" position information (e.g. horizontal/vertical axes, angular/radial, or any other axes that span the two dimensions) as a combination of values, and the like.
• the controller 19 sometimes referred to as a proximity sensor processor or touch sensor controller, is coupled to the sensor and the electronic system 10.
• the controller 19 measures the capacitance using any of the various techniques described above, and communicates with the electronic system.
• the controller 19 can perform a variety of additional processes on the signals received from the sensor to implement the proximity sensor device 11. For example, the controller 19 can select or connect individual sensing electrodes, detect presence/proximity, calculate position or motion information, and report a position or motion when a threshold is reached, and/or interpret and wait for a valid tap/stroke/character/button/gesture sequence before reporting it to the electronic system 10, or indicating it to the user.
• the controller 19 can also determine when certain types or combinations of object motions occur proximate the sensor.
• controller is defined to include one or more processing elements that are adapted to perform the recited operations.
• the controller 19 can comprise all or part of one or more integrated circuits, firmware code, and/or software code that receive electrical signals from the sensor, measure capacitance of the electrodes on the sensor, and communicate with the electronic system 10.
• the elements that comprise the controller 19 would be located with or near the sensor.
• some elements of the controller 19 would be with the sensor and other elements of the controller 19 would reside on or near the electronic system 100. In this embodiment minimal processing could be performed near the sensor, with the majority of the processing performed on the electronic system 10.
• the electronic system 10 could be a data input or output device, such as a remote control or display device, that communicates with a computer or media system (e.g., remote control for television) using a suitable wired or wireless technique.
• a computer or media system e.g., remote control for television
• the various elements (processor, memory, etc.) of the electronic system 10 could be implemented as part of an overall system, as part of the touch sensor device, or as a combination thereof.
• the electronic system 10 could be a host or a slave to the proximity sensor device 11.
• proximity sensor devices touch sensor devices
• proximity sensors proximity sensors
• touch pads touch pads
• position sensor devices position sensors
• object position are intended to broadly encompass absolute and relative positional information, and also other types of spatial- domain information such as velocity, acceleration, and the like, including measurement of motion in one or more directions.
• positional information may also include time history components, as in the case of gesture recognition and the like. Accordingly, proximity sensor devices can appropriately detect more than the mere presence or absence of an object and may encompass a broad range of equivalents.
• the mechanisms of the present invention are capable of being distributed as a program product in a variety of forms.
• the mechanisms of the present invention can be implemented and distributed as a proximity sensor program on a computer-readable signal bearing media.
• the- embodiments of the present invention apply equally regardless of the particular type of signal bearing media used to carry out the distribution. Examples of signal bearing media include: recordable media such as memory cards, optical and magnetic disks, hard drives, and transmission media such as digital and analog communication links.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Measurement Of Resistance Or Impedance (AREA)
• Position Input By Displaying (AREA)
• Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)
• Compression, Expansion, Code Conversion, And Decoders (AREA)
• Geophysics And Detection Of Objects (AREA)
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