(12) United States Patent
`Philipp et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 8,749,251 B2
`Jun. 10, 2014
`
`US008749251B2
`
`(54) PROXIMITY SENSOR
`
`O O
`(75) Inventors: t Philipp (H): Kevin
`noad, Chicester (GB)
`(73) Assignee: Atmel Corporation, San Jose, CA (US)
`(*) Notice:
`Subject to any disclaimer, the term of this
`patent 1s is: sisted under 35
`U.S.C. 154(b) by 569 days.
`(21) Appl. No.: 13/116,764
`(22) Filed:
`May 26, 2011
`
`(65)
`
`Prior Publication Data
`
`9/2002 Philipp
`6.452,514 B1
`10/2002 Philipp
`6,466,036 B1
`8, 2006 Lee
`7,091,727 B2
`7.245,131 B2 * 7/2007 Kurachi et al. ............... 324f663
`7,567,088 B2
`7/2009 Yoshida
`7,663,607 B2
`2/2010 Hotelling
`7,714,595 B2
`5/2010 Fujiwara
`7,797,115 B2
`9/2010 Tasher
`2. R:
`38: Sin
`8,031,094 B2 10/2011 Hotelling
`8,031,174 B2 10/2011 Hamblin
`8,040.326 B2 10/2011 Hotelling
`8,049,732 B2 11/2011 Hotelling
`8,179,381 B2
`5/2012 Frey
`2003. O132763 A1
`7, 2003 Ellenz
`2006/0170411 A1* 8, 2006 Kurachi et al. ............... 324,132
`(Continued)
`
`Otelling
`
`- 4 W
`
`US 2011 FO242O51A1
`
`Oct. 6, 2011
`
`FOREIGN PATENT DOCUMENTS
`
`Related U.S. Application Data
`(63) Continuation of application No. 12/179,769, filed on
`Jul. 25, 2008, now Pat. No. 7,952,366.
`(60) Provisional application No. 60/952,053, filed on Jul.
`26, 2007.
`(51) Int. Cl.
`GOIR 27/26
`G08B I3/08
`(52) U.S. Cl.
`USPC ........................................ 324/663; 340/545.4
`(58) Field of Classification Search
`USPC .................... 324/663, 658, 649, 600; 702/57;
`340/545.4, 545.2, 545.1, 541, 540:
`381/74.
`See application file for complete search history.
`
`(2006.01)
`(2006.01)
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`5,730,165 A
`6,452.494 B1
`
`3/1998 Philipp
`9, 2002 Harrison
`
`6, 2005
`1536314 A2
`EP
`W. WO 201 5. A1 539.
`
`OTHER PUBLICATIONS
`U.S. Appl. No. 61/454,936, filed Mar. 21, 2011, Myers.
`(Continued)
`
`Primary Examiner — Hoai-Ain DNguyen
`(74) Attorney, Agent, or Firm — Baker Botts LLP
`
`ABSTRACT
`(57)
`In one embodiment, a method includes monitoring detection
`by a sensing element of a key touch on a touch screen; deter
`mining an amount of time that has elapsed since the sensing
`element last detected a change of capacitance indicative of a
`key touch on the touch screen; and, if the amount of time that
`has elapsed exceeds a predetermined time duration, then ini
`tiating a particular function of an apparatus.
`
`20 Claims, 10 Drawing Sheets
`
`
`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1001, IPR2021-01161 Page 1 of 21
`
`

`

`US 8,749,251 B2
`Page 2
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`2012fO243719 A1
`
`9/2012 Franklin
`
`OTHER PUBLICATIONS
`
`2006, O25O142
`2007.0062739
`2007/0076897
`2008/0047764
`2008/O147350
`2008, O246723
`2009/0027O68
`2009/0225,044
`2009/0315854
`2012fO242588
`2012fO242592
`2012fO243151
`
`11, 2006
`3, 2007
`4, 2007
`2, 2008
`6, 2008
`10, 2008
`1/2009
`9, 2009
`12, 2009
`9, 2012
`9, 2012
`9, 2012
`
`
`
`Abe
`Philipp
`Philipp
`Lee et al. ................... 178/1806
`Jean .........
`TO2,150
`Baumbach .................... 345,156
`Philipp
`Jeon et al. ..................... 345,173
`Matsuo
`Myers
`Rothkopf
`Lynch
`
`U.S. Appl. No. 61/454,950, filed Mar. 21, 2011, Lynch.
`U.S. Appl. No. 61/454,894, filed Mar. 21, 2011, Rothkopf.
`UK Intellectual Property Office, Search Report for GB 0813682.2,
`Nov. 4, 2008.
`Datasheet “QT100-Charge Transfer IC.” Quantum Research Group,
`2006.
`Datasheet "QT 110-Touch Sensor IC.” Quantum Research Group,
`2004.
`
`* cited by examiner
`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1001, IPR2021-01161 Page 2 of 21
`
`

`

`U.S. Patent
`US. Patent
`
`Jun. 10, 2014
`Jun. 10, 2014
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`Sheet 1 of 10
`Sheet 1 of 10
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`US 8,749,251 B2
`US 8,749,251 B2
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`Petitioner STMICROELECTRONICS, INC.,
`
`EX. 1001,1PR2021-01161 Page 3 of21
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`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1001, IPR2021-01161 Page 3 of 21
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`

`

`U.S. Patent
`US. Patent
`
`Jun. 10, 2014
`Jun. 10, 2014
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`Sheet 2 of 10
`Sheet 2 of 10
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`US 8,749,251 B2
`US 8,749,251 B2
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`Petitioner STMICROELECTRONICS, INC,
`
`EX. 1001,1PR2021-01161 Page 4 of21
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`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1001, IPR2021-01161 Page 4 of 21
`
`

`

`U.S. Patent
`US. Patent
`
`Jun. 10, 2014
`Jun. 10, 2014
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`Sheet 3 of 10
`Sheet 3 of 10
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`US 8,749,251 B2
`US 8,749,251 B2
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`
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`Petitioner STMICROELECTRONICS, INC,
`
`EX. 1001,1PR2021-01161 Page 5 of21
`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1001, IPR2021-01161 Page 5 of 21
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`

`

`U.S. Patent
`US. Patent
`
`Jun. 10, 2014
`Jun. 10, 2014
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`Sheet 4 of 10
`Sheet 4 of 10
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`US 8,749,251 B2
`US 8,749,251 B2
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`
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`Petitioner STMICROELECTRONICS, INC,
`
`EX. 1001,1PR2021-01161 Page 6 of21
`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1001, IPR2021-01161 Page 6 of 21
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`

`

`U.S. Patent
`
`Jun. 10, 2014
`
`Sheet 5 of 10
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`US 8,749,251 B2
`
`
`
`III
`
`P- override (reload auto off delay)
`O - switch output off (toff burst time + 50ms)
`C - sensor recalibration
`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1001, IPR2021-01161 Page 7 of 21
`
`

`

`U.S. Patent
`
`Jun. 10, 2014
`
`Sheet 6 of 10
`
`US 8,749,251 B2
`
`QT102 Active High Output
`
`53
`51
`49
`47
`45
`43
`RC
`Divisor 41
`39
`(K)
`,
`
`35
`33
`21
`29
`2
`
`2.5
`
`3
`
`4 4.5
`3.5
`VDD(volts)
`
`5
`Fig. 13
`
`QT102 Active Low Output
`
`
`
`RC
`Divisor
`(K)
`
`2
`
`2.5
`
`5
`4 4.5
`3.5
`3
`VDD(volts)
`Fig. 14
`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1001, IPR2021-01161 Page 8 of 21
`
`

`

`U.S. Patent
`
`Jun. 10, 2014
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`Sheet 7 of 10
`
`US 8,749,251 B2
`
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`Petitioner STMICROELECTRONICS, INC,
`
`EX. 1001,1PR2021-01161 Page 9 0f21
`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1001, IPR2021-01161 Page 9 of 21
`
`
`
`
`

`

`U.S. Patent
`
`Jun. 10, 2014
`
`Sheet 8 of 10
`
`US 8,749,251 B2
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`Petitioner STMICROELECTRONICS, INC,
`
`EX. 1001,1PR2021-01161 Page 10 0f21
`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1001, IPR2021-01161 Page 10 of 21
`
`
`
`
`

`

`U.S. Patent
`
`Jun. 10, 2014
`
`Sheet 9 of 10
`
`US 8,749,251 B2
`
`SENSE
`ELECROE
`
`
`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1001, IPR2021-01161 Page 11 of 21
`
`

`

`U.S. Patent
`
`Jun. 10, 2014
`
`Sheet 10 of 10
`
`US 8,749,251 B2
`
`
`
`.
`
`-
`E
`
`Fig. 19
`
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`
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`
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`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1001, IPR2021-01161 Page 12 of 21
`
`

`

`US 8,749,251 B2
`
`1.
`PROXMITY SENSOR
`
`RELATED APPLICATIONS
`
`This application is a continuation under 35 U.S.C. S 120 of
`U.S. patent application Ser. No. 12/179,769, filed 25 Jul.
`2008, which claims the benefit under 35 U.S.C. S 119(e) of
`U.S. Provisional Patent Application No. 60/952,053, filed 26
`Jul. 2007.
`
`TECHNICAL FIELD
`
`This disclosure generally relates to proximity sensors.
`
`BACKGROUND
`
`5
`
`10
`
`15
`
`25
`
`Capacitive position sensors have recently become increas
`ingly common and accepted in human interfaces and for
`machine control. For example, in the fields of portable media
`players it is now quite common to find capacitive touch con
`trols operable through glass or plastic panels. Some mobile
`telephones are also starting to implement these kinds of inter
`faces.
`Many capacitive touch controls incorporated into con
`Sumer electronic devices for appliances provide audio or
`visual feedback to a user indicating whether a finger or other
`pointing object is present or approaches Such touch controls.
`A capacitive sensing microprocessor may typically be com
`prised in touch-controlled devices which are arranged to pro
`30
`vide an “on” output signal when a finger is adjacent to a
`sensor and an “off” output signal when a finger is not adjacent
`to a sensor. The signals are sent to a device controller to
`implement a required function dependent on whether a user's
`finger is in proximity with or touching an associated touch
`control.
`Some touch-controlled devices remain “on” or “active'
`despite the user having moved away from the device or a
`particular function no longer being required. This results in
`the device consuming a large amount of power which is not
`efficient.
`
`35
`
`40
`
`OVERVIEW
`
`Particular embodiments provide a sensor for determining
`the presence of an object comprising: a sensing element; a
`capacitance measurement circuit operable to measure the
`capacitance of the sensing element; and a control circuit
`operable to determine whether an object is in proximity with
`the sensor based on a measurement of the capacitance of the
`sensing element, the control circuit further being operable to
`provide an output signal to control a function of an apparatus
`when it is determined that an object has not been in proximity
`with the sensor for a predetermined time duration.
`The control circuit may be configured so that the predeter
`mined time duration is selectable from a number of different
`predefined time durations.
`The control circuit may include a time input terminal and
`the predetermined time duration may selectable from the
`number of different predefined time durations according to a
`Voltage applied to the time input terminal.
`The control circuit may include a delay multiplier terminal
`and be configured so that a selected one of the number of
`different predefined time durations is multiplied by a multi
`plication factor according to a Voltage applied to the delay
`multiplier terminal so as to provide the predetermined time
`duration.
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`The control circuit may be configured so that the predeter
`mined time duration is programmable by a user to provide a
`user-selected time duration.
`The sensor may comprise a resistor-capacitor (RC) net
`work coupled to the control circuit and the predetermined
`time duration may depend on a time constant of the RC
`network.
`The control circuit may include a delay multiplier terminal
`and be configured so that the user-selected time duration is
`multiplied by a multiplication factor according to a Voltage
`applied to the delay multiplier terminal to provide the prede
`termined time duration.
`The control circuit may be configured such that the provi
`sion of the output signal to control a function of an apparatus
`after the predetermined time duration may be overridden so
`the output signal is not provided when it is determined that an
`object has not been in proximity with the sensor for a prede
`termined time duration. For example, the control circuit may
`be operable to receive an override pulse and on receipt of the
`override pulse to retrigger the predetermined time duration to
`So as to extend the time before the output signal to control a
`function of an apparatus is provided.
`The control circuit may be configured such that the provi
`sion of the output signal to control a function of an apparatus
`after the predetermined time duration may be overridden so
`the output signal is provided before it is determined that an
`object has not been in proximity with the sensor for a prede
`termined time duration. For example, the control circuit may
`be operable to receive an override pulse and on receipt of the
`override pulse to provide the output signal to control a func
`tion of an apparatus.
`The sensor may be configured to perform a recalibration
`when the sensor is powered up, when an object is determined
`to be in proximity with the sensor for more than a timer
`setting, and/or when an override is released.
`The control circuit may be configured such that the output
`signal is toggled between a high state and a low state when an
`object is determined to be in proximity with the sensor.
`The function of an apparatus controlled by the output sig
`nal may be a switch-off function.
`The capacitance measurement circuit may employ bursts
`of charge-transfer cycles to acquire measurements.
`The capacitance measurement circuit may be configured to
`operate in one of more than one acquisition modes depending
`on the output signal, for example a low-power mode or a fast
`mode.
`The capacitance measurement circuit and the control cir
`cuit may be comprised in a general purpose microcontroller
`under firmware control.
`The capacitance measurement circuit and the control cir
`cuit may be comprised within a six-pin integrated circuit chip
`package. Such as an SOT23-6.
`Particular embodiments provide an apparatus including a
`sensor as described above.
`Particular embodiments provide a method for controlling a
`function of an apparatus comprising: determining whetheran
`object is in proximity with a sensor based on a measurement
`of the capacitance of a sensing element and providing an
`output signal to control the function of the apparatus when it
`is determined that an object has not been in proximity with the
`sensor for a predetermined time duration.
`The function of the apparatus controlled by the output
`signal may be a Switch-off function.
`Particular embodiments provide a sensor for determining
`the presence of an object comprising: a sensing element, a
`capacitance measurement circuit operable to measure the
`capacitance of the sensing element, and a control circuit
`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1001, IPR2021-01161 Page 13 of 21
`
`

`

`US 8,749,251 B2
`
`3
`operable to determine whether an object is in proximity with
`the sensor based on a measurement of the capacitance of the
`sensing element, the control circuit also being operable to
`provide an output signal to control a function of an apparatus
`based on an object not being in proximity with the sensor and 5
`the output signal being produced after a predetermined time
`duration.
`
`4
`FIG. 20 schematically shows a pin diagram for an imple
`mentation of the chip shown in FIG. 1 in an SOT23-6 pack
`age.
`
`DESCRIPTION OF EXAMPLE EMBODIMENTS
`
`Particular embodiments may be implemented in an inte
`grated circuit chip providing a proximity sensor function. The
`integrated circuit chip may thus be incorporated into a device
`or apparatus to provide and control a proximity sensor func
`tionality for the device or apparatus in particular embodi
`ments. For the purposes of explanation, a specific integrated
`circuit chip providing the functionality of an example
`embodiment will be described further below. The chip will in
`places be referred to by product name QT 102. However, it
`will be appreciated that the QT 102 chip is merely a specific
`example application of an example embodiment. Particular
`embodiments need not be implemented in a chip in this way,
`and furthermore, particular embodiments may be provided in
`conjunction with all. Some or none of the additional features
`of the QT102 chip described further below.
`Before turning specifically to the QT 102 chip embodi
`ment, a Summary is provided.
`It is known that a touch sensitive sensor may comprise a
`sensor element, such as an etched copper electrode mounted
`on a PCB substrate, and a control circuit for measuring a
`capacitance of the sensor element to a system reference
`potential. The sensor element may be referred to as a sense
`electrode. The capacitance of the sense electrode is affected
`by the presence of nearby objects, such as a pointing finger.
`Thus the measured capacitance of the sense electrode, and in
`particular changes in the measured capacitance, may be used
`to identify the presence of an object adjacent the sense elec
`trode. The control circuit may be configured to provide an
`output signal, e.g. by setting an output logic level as high or
`low, indicating whether or not an object is deemed to be
`adjacent the sense electrode. A controller of a device in which
`the touch sensitive sensor is implemented may receive the
`output signal and act accordingly.
`There are various known technologies for measuring
`capacitance of a sense electrode in a capacitive touch sensor.
`Particular embodiments may be implemented in conjunction
`with any of these technologies or measurement circuits. For
`example, the fundamental principles underlying the capaci
`tive sensors described in U.S. Pat. No. 5,730,165, U.S. Pat.
`No. 6,466,036, and U.S. Pat. No. 6,452,514 could be used.
`In particular embodiments, the control circuit of the sensor
`can determine whetheran objectora user's finger is no longer
`in proximity with the sensor and based on a predetermined
`time duration, the control circuit can produce an output signal
`automatically to prevent the capacitance measurement circuit
`from continually measuring changes in capacitance due to,
`for example, the perceived presence of an object in proximity
`with the sensor.
`Therefore, the control circuit is able to deactivate, turn-off,
`orpower down the capacitance measurement circuit where an
`apparatus has inadvertently been left on or with the erroneous
`perception that a user is still present. This may, for example,
`be referred to as an “auto-off feature. The signal for prevent
`ing the capacitance measurement circuit from continually
`measuring changes in capacitance may be referred to as an
`auto-off signal. The capacitance measurement circuit and the
`auto-off control circuit may be comprised in a general-pur
`pose microcontroller under firmware control, for example,
`such as the QT102 chip described further below.
`As described in Section 3.5 of the below numbered sec
`tions, and in conjunction with the drawings, the control circuit
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`10
`
`Reference is now made by way of example to the accom
`panying drawings in which:
`FIG. 1 schematically shows sense electrode connections
`for an example chip for implementing an auto-off function in
`15
`particular embodiments;
`FIG. 2 schematically represent an application of drift com
`pensation in the chip of FIG. 1;
`FIG. 3 schematically shows a basic circuit configuration
`for providing a 15 minute auto switch-off function in an active
`high output implementation of particular embodiments;
`FIG. 4 schematically shows a series of fast mode bursts on
`the SNSK pin of the chip shown in FIG. 1 where in an on
`condition;
`FIG. 5 schematically shows a series of low-power mode
`bursts and a switch to fast mode power bursts on the SNSK pin
`of the chip shown in FIG. 1 when switching from an off
`condition to an on condition;
`FIG. 6 schematically shows use of an output configuration
`resistor Rop to configure the chip of FIG. 1 to have an active
`high or an active low output;
`FIG. 7 schematically shows an example circuit configura
`tion for the chip shown in FIG. 1 with the output connected to
`a digital transistor,
`FIG. 8 schematically shows an example circuit configura
`tion for the chip shown in FIG. 1 configured to provide a
`predefined auto-off delay:
`FIG.9 schematically shows an example circuit configura
`tion for the chip shown in FIG. 1 configured to provide a
`programmable auto-off delay;
`FIG. 10 schematically shows an example pulse applied to
`the chip shown in FIG. 1 to override an auto-off delay;
`FIG. 11 schematically shows another example pulse
`applied to the chip shown in FIG. 1 to override an auto-off
`delay;
`FIG. 12 schematically shows example voltage levels for 45
`the chip shown in FIG. 1 in overriding of an auto-off delay;
`FIGS. 13 and 14 schematically show typical values of RC
`divisor Kas a function of supply voltage VDD for the chip
`shown in FIG. 1 with active high output and active low output
`respectively;
`FIG. 15 schematically shows typical curves of auto-off
`delay as a function of timing resistor value for different
`capacitor values and different Supply Voltages for an active
`high output configuration;
`FIG. 16 schematically shows typical curves of auto-off 55
`delay as a function of timing resistor value for different
`capacitor values and different Supply Voltages for an active
`low output configuration;
`FIG. 17 schematically shows an example application of the
`chip shown in FIG. 1 in an active low output configuration 60
`driving a PNP transistor with an auto-off time of 3.33 hours:
`FIG. 18 schematically shows another example application
`of the chip shown in FIG. 1 in an active high output configu
`ration driving a high impedance with an auto-off time of 135
`seconds;
`FIG. 19 schematically shows an implementation of the
`chip shown in FIG. 1 in an SOT23-6 package; and
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`5
`of the sensor may be implemented by different methods—for
`example, the auto-off signal output may be produced auto
`matically after different predetermined time durations to
`effect powering down the capacitance measurement circuit
`due to no presence of the user; the control circuit may be
`programmed by a user so that it may power down an apparatus
`based on a user-selected time duration; the control circuit
`output signals may be overridden, for example, to extend time
`durations before an apparatus is turned-off or to immediately
`turn-off an apparatus when a user is no longer present.
`The sensor of particular embodiments may be useful in
`various applications, for example in kitchen appliances, light
`Switches, headsets, and other electronic consumer devices.
`For example, a coffee machine incorporating a sensor of
`particular embodiments may be programmed to power-down
`after a time period of, say, 30 minutes, where the coffee
`machine has been left on inadvertently. This will beneficially
`conserve energy use and minimize the possibility of damage
`or accidents caused by the coffee machine or glass
`container(s) overheating.
`Aspects of the QT102 chip referred to above will now be
`described in the following numbered sections.
`The numbered sections may be considered to relate gener
`ally to features of the QT 102 chip as follows: Section
`1—Overview (including 1.1 Introduction, 1.2 Electrode
`Drive, 1.3 Sensitivity, 1.3.1 Introduction, 1.3.2 Increasing
`Sensitivity, 1.3.3 Decreasing Sensitivity, 1.4 Recalibration
`Timeout, 1.5 Forced Sensor Recalibration, 1.6 Drift Compen
`sation, 1.7 Response Time, 1.8 Spread Spectrum). Section
`2—Wiring and Parts (including 2.1 Application Note, 2.2 Cs
`Sample Capacitor, 2.3 Rs Resistor, 2.4 Power Supply, PCB
`Layout, 2.5 Wiring). Section 3 Operation (including 3.1
`Acquisition Modes, 3.1.1 Introduction, 3.1.2 OUT Pin"On”
`(Fast Mode), 3.1.3 OUT Pin “Off” (Low Power Mode), 3.2
`Signal Processing, 3.2.1 Detect Integrator, 3.2.2 Detect
`Threshold, 3.3 Output Polarity Selection, 3.4 Output Drive,
`3.5 Auto Off Delay, 3.5.1 Introduction, 3.5.2 Auto Off
`Predefined Delay, 3.5.3 Auto Off User-programmed Delay,
`3.5.4 Auto Off Overriding the Auto Off Delay, 3.5.5 Con
`figuring the User-programmed Auto-off Delay, 3.6 Examples
`40
`of Typical Applications). Section 4-Specifications (includ
`ing 4.1 Absolute Maximum Specifications, 4.2 Recom
`mended Operating Conditions, 4.3 AC Specifications, 4.4
`Signal Processing, 4.5 DC Specifications, 4.6 Mechanical
`Dimensions, 4.7 Moisture Sensitivity Level (MSL)).
`1 Overview
`1.1 Introduction
`The QT 102 is a single key device featuring a touch
`on/touch off (toggle) output with a programmable auto
`switch-off capability.
`The QT 102 is a digital burst mode charge-transfer (QT)
`sensor designed specifically for touch controls; it includes
`hardware and signal processing functions to provide stable
`sensing under a wide variety of changing conditions. In
`examples, low cost, non-critical components are employed
`for configuring operation.
`The QT 102 employs bursts of charge-transfer cycles to
`acquire its signal. Burst mode permits power consumption in
`the microampere range, dramatically reduces radio frequency
`(RE) emissions, lowers Susceptibility to electromagnetic
`interference (EMI), and yet permits good response time.
`Internally the signals are digitally processed to reject impulse
`noise, using a "consensus’ filter which in this example
`requires four consecutive confirmations of a detection before
`the output is activated.
`The QT Switches and charge measurement hardware func
`tions are all internal to the QT 102.
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`1.2 Electrode Drive
`FIG. 1 schematically shows the sense electrode connec
`tions (SNS, SNSK) for the QT102.
`For improved noise immunity, it may be helpful if the
`electrode is only connected to the SNSK pin.
`In examples the sample capacitor Cs may be much larger
`than the load capacitance (CX). E.g. typical values for CX are
`5 to 20 pF while Cs is usually 1 or 2 to 50 nF. (Note: Cx is not
`a physical discrete component on the PCB, it is the capaci
`tance of the touch electrode and wiring. It is shown in FIG. 1
`to aid understanding of the equivalent circuit.)
`Increasing amounts of CX destroy gain, therefore it is
`important to limit the amount of load capacitance on both
`SNS terminals. This can be done, for example, by minimizing
`trace lengths and widths and keeping these traces away from
`power or ground traces or copper pours.
`The traces and any components associated with SNS and
`SNSK will become touch sensitive and so may need to be
`considered to help in limiting the touch-sensitive area to the
`desired location.
`A series resistor, Rs, may be placed in line with SNSK to
`the electrode to suppress electrostatic discharge (ESD) and
`Electromagnetic Compatibility (EMC) effects.
`1.3 Sensitivity
`1.3.1 Introduction
`The sensitivity of the QT 102 is a function of such things as:
`the value of Cs
`electrode size and capacitance
`electrode shape and orientation
`the composition and aspect of the object to be sensed
`the thickness and composition of any overlaying panel
`material
`the degree of ground coupling of both sensor and object
`1.3.2 Increasing Sensitivity
`In some cases it may be desirable to increase sensitivity; for
`example, when using the sensor with verythick panels having
`a low dielectric constant. Sensitivity can often be increased by
`using a larger electrode or reducing panel thickness. Increas
`ing electrode size can have diminishing returns, as high Val
`ues of CX will reduce sensor gain.
`The value of Cs also has an effect on sensitivity, and this
`can be increased in value with the trade-off of slower response
`time and more power. Increasing the electrode's Surface area
`will not substantially increase touch sensitivity if its diameter
`is already significantly larger in Surface area than the object
`being detected. Panel material can also be changed to one
`having a higher dielectric constant, which will better help to
`propagate the field.
`Ground planes around and under the electrode and its
`SNSK trace may lead to high CX loading and destroy gain.
`Thus in some cases the possible signal-to-noise ratio benefits
`of ground areas may be more than negated by the decreased
`gain from the circuit, and so ground areas around electrodes
`may be discouraged in some circumstances. Metal areas near
`the electrode may reduce the field strength and increase CX
`loading and so it may be helpful if these are avoided if pos
`sible. It may be helpful to keep ground away from the elec
`trodes and traces.
`1.4 Recalibration Timeout
`If an object or material obstructs the sense electrode the
`signal may rise enough to create a detection, preventing fur
`ther operation. To help reduce the risk of this, the sensor
`includes a timer which monitors detections. If a detection
`exceeds the timer setting (known as the Max On-duration) the
`sensor performs a full recalibration. This does not toggle the
`output state but ensures that the QT 102 will detect a new
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`US 8,749,251 B2
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`7
`touch correctly. The timer is set to activate this feature after
`~30 seconds. This will vary slightly with Cs.
`1.5 Forced Sensor Recalibration
`
`The QT102 has no recalibration pin; a forced recalibration
`is accomplished when the device is powered up, after the
`recalibration timeout or when the auto-off override is
`released.
`
`However, supply drain is low so it is a simple matter to treat
`the entire IC as a controllable load; driving the QT102’s VDD
`pin directly from another logic gate or a microcontroller port
`will serve as both power and “forced recal(ibration)”. The
`source resistance of most CMOS gates and microcontrollers
`are low enough to provide direct power without problems.
`1.6 Drift Compensation
`Signal drift can occurbecause ofchanges in Cx and Cs over
`time. It may be helpful if drift is compensated for, otherwise
`false detections, nondetections, and sensitivity shifts may
`follow.
`
`Drift compensation is schematically shown in FIG. 2. Drift
`compensation is performed by making a reference level track
`the raw signal at a slow rate, but only while there is no
`detection in effect. It may be helpful if the rate of adjustment
`is performed relatively slowly, otherwise there may be a risk
`that legitimate detections may be ignored. The QT102 drift
`compensates using a slew-rate limited change to the reference
`level; the threshold and hysteresis values are slaved to this
`reference.
`
`Once an object is sensed, the drift compensation mecha-
`nism ceases since the signal is legitimately high, and there-
`fore should not cause the reference level to change (as indi-
`cated in FIG. 2 during the period between the vertical dotted
`lines).
`The QT102’s drift compensation is “asymmetric”; the ref-
`erence level drift-compensates in one direction faster than it
`does in the other. Specifically,
`it compensates faster for
`decreasing signals than for increasing signals. It may be help-
`ful if increasing signals are not compensated for quickly,
`since an approaching finger could be compensated for par-
`tially or entirely before approaching the sense electrode.
`However, an obstruction over the sense pad, for which the
`sensor has already made full allowance, could suddenly be
`removed leaving the sensor with an artificially elevated ref-
`erence level and thus become insensitive to touch. In this
`
`the sensor will compensate for the object’s
`latter case,
`removal more quickly, for example in only a few seconds.
`With relatively large values of Cs and small values of Cx,
`drift compensation will appear to operate more slowly than
`with the converse. Note that the positive and negative drift
`compensation rates are different.
`1.7 Response Time
`The QT102’s response time is dependent on burst length,
`which in turn is dependent on Cs and Cx. With increasing Cs,
`response time slows, while increasing levels of Cx reduce
`response time.
`1.8 Spread Spectrum
`The QT102 modulates its internal oscillator by 17.5 per-
`cent during the measurement burst. This spreads the gener-
`ated noise over a wider band reducing emission levels. This
`also reduces susceptibility since there is no longer a single
`fundamental burst frequency.
`2 Wiring and Parts
`FIG. 3 schematically shows a basic circuit configuration
`for an implementation of particular embodiments.
`2.1 Application Note
`Although not necessarily relevant to particular embodi-
`ments, for completeness, reference may be made to Applica-
`tion Note AN-KDO2 (“Secrets of a Successful QTouchTM
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`Design”), included herein in its entirety by reference, and
`downloadable from the Quantum Research Group website,
`for information on example construction and design methods.
`Go to http://www.qprox.com, click the Support tab and then
`Application Notes.
`2.2 Cs Sample Capacitor
`Cs is the charge sensing sample capacitor. The required Cs
`value depends on the thickness of the panel and its dielectric
`constant. Thicker panels require larger values of Cs. Typical
`values are 1 or 2 nF to 50 nF depending on the sensitivity
`required; larger values of Cs may demand higher stability and
`better dielectric to ens