CA1110727A - Laminated capacitive touch-pad - Google Patents
Laminated capacitive touch-padInfo
- Publication number
- CA1110727A CA1110727A CA311,806A CA311806A CA1110727A CA 1110727 A CA1110727 A CA 1110727A CA 311806 A CA311806 A CA 311806A CA 1110727 A CA1110727 A CA 1110727A
- Authority
- CA
- Canada
- Prior art keywords
- touch
- pad
- electrodes
- layer
- electrode
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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- Electronic Switches (AREA)
- Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A laminated capacitive touch-pad having a thin film touch-plate electrode deposited upon a first (exterior) surface of a first, relatively thin dielectric layer and having spaced transmitter and receiver electrodes deposited upon a second surface of the first layer within the out-line of and opposite to the touch electrode, with a relatively thick backing layer of dielectric material laminated upon the second surface to provide a total thickness, as measured between the furthest opposed surfaces of the first and second layers, as required for high voltage insulation purposes and to provide additional impact strength.
The touch, transmitter and receiver electrodes may be of thin film construction.
A laminated capacitive touch-pad having a thin film touch-plate electrode deposited upon a first (exterior) surface of a first, relatively thin dielectric layer and having spaced transmitter and receiver electrodes deposited upon a second surface of the first layer within the out-line of and opposite to the touch electrode, with a relatively thick backing layer of dielectric material laminated upon the second surface to provide a total thickness, as measured between the furthest opposed surfaces of the first and second layers, as required for high voltage insulation purposes and to provide additional impact strength.
The touch, transmitter and receiver electrodes may be of thin film construction.
Description
~ 2~ RD-9454 The present invention relates to capacitive touch-pads and, more particularly, to a novel laminated capacitive touch-pad providing greater dielectric coupling between touch plate and transmit and receive electrodes, thus greatly enhancing the ratio of desired coupling capacitance to parasitic coupling capacitance between transmit and receive electrodes while ;~, maintaining required high voltage insulation parame-ters and facilitating a greater total dielectric thickness ~hich is required in some applications.
Touch-pads capable of changing capacitance, when ap-proached or contacted, are well known. Capacitive touch-pads are often used in high voltage environments where relatively thick dielectrics are required for safety purposes; the value of a parasitic capacity between a pair of spaced transmitting and receiving electrodes r fabricated upon a first surface of -' a relatively thick dielectric substrate, often approaches the capacitance value between each of the electrodes and a touch-pad electrode fabricated upon the remaining surface of the substrate, whereby erroneous signals are frequently generated.
The problem is compounded when arrays of discrete touch-pad devices are utilized; the separation distance between each device -in the array and all other adjacent devices must be relatively greater to prevent additional parasitic capacitance, and the - associated signal leakage attributable thereto, from totally masking the desired change in signal when the touch electrode is approached and/or contacted. A capacitive touch-pad having a relatively large ratio of desired coupling capacity to parasitic ~.~.6~;~7 capacity, yet r~taining a relatively thick dielectric for safety reasons in high voltage environments, i5 desirable.
Brief Descri tion o~_the Invention A laminated capacitive touch-pad, i.n accordance wi~h the invention, has a first, relatively thin clielec~ric layer having a conductive touch electrode fabricated upon an exterior surface thereof and has a transmitting electrode and a receiving elec-trode fabricated, within the outline of the touch pad, upon the remaining substrate surface. A second layer o~ dielectric material, of relatively greater thickness with respect to the thickness of the first layer, is laminated against the surface of the first layer bearing the spatially ~eparated transmitting and receiving elec~rodes to achieve a total dielectric thickness as required for safety reasons, while having a dielectric thickness between the touch electrode and the transmitting and receiving electrodes o relatively small dimension to cause the touch-pad capacity to be relatively greater than the parasitic capacity between transmitting and receiving ele~trodes, thereby preventlng erroneous signal generation, even when a pl~rality of the laminated capacitive touch~pads are arrayed wi~h relatively small separation dlstances therebetween.
In a preferred embodiment of the invention, the electrodes are fabricated by thin film deposition techniques; the receiving and ~ransmitting electrode leads are of the thin film type and are integrally fabricated with the electrodes. Thlck film leads and electrodes may also be utilized.
Accordingly, it is one object of the present invention to provide a novel capacitive touch-pad having a relatively large dielectric thickne9s whlle minimizing parasitic capacitance e~ects.
It is another ob~ect of the present invention to provide ,.
_, R~-945~
a novel capacitive ~ouch pad havlng lamina~ed dielectric lsyers, It is a further object of the preseant inventlon to prQ-~ide a laminated capacitive touch-pad having ~hin ilm electrodes.
~hese and other objects of the present invention will become apparent upon consideration of the following detailed description and accompanying drawings.
Figures la and lb are respectively plan and sect:ional views of a prior art capacltive touch pad; and Figures 2a and 2b are respectively plan and sectional views of a laminated capacitive touch-pad in accordance with the prirlciple~ o the present invention.
etaile~ Descripti n o~ ~he Present Invention ; 15 Referring ini.tially to Figures la and lb, a prior art capaci~ive touch-pad 10 comprises a dielectric substra~e 11, upon a fron~, or outwardly-facing, ~urface lla on which is fabricated a touch electrode 12 of conductive or semiconductive material and having a preselected boundary, hereln illustrated as'being of rectangular shape, A pair of electrodes 14 and 15, commonly referred to as a transmitting electrode and a r~ceiving electrode, respectively, are :~abricated of a conduct-. ive or semiconductive material upon the remaining, inwardly-facing surface llb of ~he substrate, Both transmi~ing and receiving electrodes 14 and lS are typically o substantially smaller area than, and are positloned substantially within the boundaries of, the area of touch electrode 12, The closest points between transmitting and recaiving electrode~ 14 and lS are se~ara~ied by a preselected di~tance ~, while each of lelectrode~
14 and 15 are 3eparated from ~ouch electrode 12 by a preselccted .D-~54 , dielectric thicknes~ T, derived in accordance with the insula-tion characteristics to be achieved, Each of transmi~ting and receiving electrodes 14 and 15 has an associated conductive lead wire 16 and 17, respectlvely, coupleld to a polnt thereon for connection of the touch-pad to known circu'~try (not shown for purposes of simplicity) configured to drive the transmitting electrode with a pPriodically varying waveform an~ to recognize :~ a change in the peak amplitude of that waveform at the receiving :~ electrode a~ the effective serie~ coupling impedance between transmitting and receiving electro~es varies when touch elec- ;;
trode 12 is approached and/or contacted.
In situations where relatively large values of dielectric thickness T are required, to pro~ect personnel contacting touch electrode 12 from high voltages present in apparatus adjacent substrate rear surface llb, the relative magn-Ltude of a para-sitic capacity Cp (between the facing surfaces of the trans-mitting and receiving electrodes 14 and 15 separated by the relatively small distance D), approaches the magnitude of the :~ desired 6eries capacity C (C=CaCb/(Ca+Cb) between electrodes 14 a~d 15 via touch electrode 12, Similarly, when arrays of a plurality of such touch-pads are posltioned with relatlvely close spacing, the ~ransmitting electrode of one touch-pad is positioned relatively close to the receiving electrode of an :~
adjacent touch-pad, whereby the magnitude of the pad-to-pad parasitic capacities approach the magnitude of electrod~
capacity through the substrate. These and other parasitic ~.apacities cause relatively large coupling between transmitting and receiving electrodes leading to the generation of erroneous signals which are not always easily lden~ifled or rejected, The coupl~ng problem is even more severe where the value o the 7~Y
, touch-pad capacitor C is small due to increasingly greater dLelectric thickness T, In many circum~tances, dielectric thickness and the distance separating individual touch-pad~ of an array are configured, in high density arra~s, such that device and parasitic capa.citances are su~stantially equal and allow a signal, introduced into the transmittlng electrode 14, to have substantial equal coupling to r~ceiving electrode 15 through either the parasitic or the intended capacitance path.
. In accordance with the invention, a capacitive touch-pad ~... 10 20 essentially overcoming the above problems of parasitic ,, :
:~. capacitance, while maintaining the required total thickness T
of a dielectric material, comprises a first dielectric substrate 21 of a relatively small thickness Tl, upon a front, or outwardly-facing, surface 21a of which is abricated touch electrode 12.
The spatially separated transmitting and receiving electrodes , , ~: 14 and 15, respectively, are abricated upon the remaining J or inwardly-facing, surface 21b of first dielectric layer 21 and may ~ be formed, in one preferred embodiment,by thin film fabrication .. techniques It should be understood that touch electrode 12 ma~ also be fabricated by thin film techniques. The electrodes and leads may also be fabricated as thick films, if desired, ln a particular applicatlon.
Lead means 23 and 24 each respectively associated with re~pective transmitting and receiving electrodes 14 and lS, are advantageously fabricated by thin film techniques, at th~
same time as the transmitting and receiving electrodes are the~selves fabricated, whereby the members forming lead mean~
23 and 24 are integrally joined to their respective electrodes.
A second layer 26 of dielectric material is fabricated to a thickness T~, which may be equal to, or diferent from, the ~ t~Z~ ~D~9454 thickness Tl of first layer 21, Layer 26 ls laminal:ed agalnst the inwardly-faring surface 21b of the fir.st dielPc~ric layer, and the transmltting and recelvi~g elec~rc)des abricated khereon~
Thus, the total thickness (T2+Tl) of the dielectric insul~tion of our novel laminated touch-pad i5 easily established to be equal to the total dielectric insulation thickness T of the prior art touch pad 10, yet the total separation distance Tl between each of transm~tting and receiving electrodes L4 and 15, respectively, and overlying touch electrode 12 is substantially reduced over the prior art embodi.ment, whereby the value of each series capacitance (between transmitting electrode 14 and touch electrode 12 and between touch electrode 12 cmd receiving electrode 15) i~ substantlally increased and i~ relatively g-Leater than the parasltic capacity between transmitting and receiving electrodes of a single touch-pad or the parasitic capacitance between electrodes of adjacent touch-pads in high denslty arrays. The relatlvely greater magnitude o signal current enabled between transmltting and receiving electrodes via the series path (through the touch-plate), as opposed to ~0 thb parasitic path, snables touch--pad arrays o~ greater den~lty than hitherto posslble, Use of spaclng simllar to the array spacing ach~eved in prlor art dispLays allows relatlvely lower amplitudes of the waveform driving the ~ransmlttlng ~lectrode to be used, due to the increased magnitude of the desired signal coupled be~ween electrodes 14 and 15, via Ca, Cb and the to~ch plate electrode. Thus, lower imple~.entation CGS~ of associated driving and sensing circuitry is facllikated by reducing dri~lng ~ignal magnitude and the difficul~y of sensing alse signals.
While the present ln~ention has been described wlth reference to one preferred embodlment thereof, many ~Tariations ', ~-, -6-~ ~ ~ 1f~q1 RD-9454 ~.
and modifications will now become apparent to tho~e skilled in the art. It is our intent, therefore, to be limited solely by the ecope of the appending clai=~.
:' :
,; ~
:
, .
';' :
~ ~7~
,:~
.~ . .
Touch-pads capable of changing capacitance, when ap-proached or contacted, are well known. Capacitive touch-pads are often used in high voltage environments where relatively thick dielectrics are required for safety purposes; the value of a parasitic capacity between a pair of spaced transmitting and receiving electrodes r fabricated upon a first surface of -' a relatively thick dielectric substrate, often approaches the capacitance value between each of the electrodes and a touch-pad electrode fabricated upon the remaining surface of the substrate, whereby erroneous signals are frequently generated.
The problem is compounded when arrays of discrete touch-pad devices are utilized; the separation distance between each device -in the array and all other adjacent devices must be relatively greater to prevent additional parasitic capacitance, and the - associated signal leakage attributable thereto, from totally masking the desired change in signal when the touch electrode is approached and/or contacted. A capacitive touch-pad having a relatively large ratio of desired coupling capacity to parasitic ~.~.6~;~7 capacity, yet r~taining a relatively thick dielectric for safety reasons in high voltage environments, i5 desirable.
Brief Descri tion o~_the Invention A laminated capacitive touch-pad, i.n accordance wi~h the invention, has a first, relatively thin clielec~ric layer having a conductive touch electrode fabricated upon an exterior surface thereof and has a transmitting electrode and a receiving elec-trode fabricated, within the outline of the touch pad, upon the remaining substrate surface. A second layer o~ dielectric material, of relatively greater thickness with respect to the thickness of the first layer, is laminated against the surface of the first layer bearing the spatially ~eparated transmitting and receiving elec~rodes to achieve a total dielectric thickness as required for safety reasons, while having a dielectric thickness between the touch electrode and the transmitting and receiving electrodes o relatively small dimension to cause the touch-pad capacity to be relatively greater than the parasitic capacity between transmitting and receiving ele~trodes, thereby preventlng erroneous signal generation, even when a pl~rality of the laminated capacitive touch~pads are arrayed wi~h relatively small separation dlstances therebetween.
In a preferred embodiment of the invention, the electrodes are fabricated by thin film deposition techniques; the receiving and ~ransmitting electrode leads are of the thin film type and are integrally fabricated with the electrodes. Thlck film leads and electrodes may also be utilized.
Accordingly, it is one object of the present invention to provide a novel capacitive touch-pad having a relatively large dielectric thickne9s whlle minimizing parasitic capacitance e~ects.
It is another ob~ect of the present invention to provide ,.
_, R~-945~
a novel capacitive ~ouch pad havlng lamina~ed dielectric lsyers, It is a further object of the preseant inventlon to prQ-~ide a laminated capacitive touch-pad having ~hin ilm electrodes.
~hese and other objects of the present invention will become apparent upon consideration of the following detailed description and accompanying drawings.
Figures la and lb are respectively plan and sect:ional views of a prior art capacltive touch pad; and Figures 2a and 2b are respectively plan and sectional views of a laminated capacitive touch-pad in accordance with the prirlciple~ o the present invention.
etaile~ Descripti n o~ ~he Present Invention ; 15 Referring ini.tially to Figures la and lb, a prior art capaci~ive touch-pad 10 comprises a dielectric substra~e 11, upon a fron~, or outwardly-facing, ~urface lla on which is fabricated a touch electrode 12 of conductive or semiconductive material and having a preselected boundary, hereln illustrated as'being of rectangular shape, A pair of electrodes 14 and 15, commonly referred to as a transmitting electrode and a r~ceiving electrode, respectively, are :~abricated of a conduct-. ive or semiconductive material upon the remaining, inwardly-facing surface llb of ~he substrate, Both transmi~ing and receiving electrodes 14 and lS are typically o substantially smaller area than, and are positloned substantially within the boundaries of, the area of touch electrode 12, The closest points between transmitting and recaiving electrode~ 14 and lS are se~ara~ied by a preselected di~tance ~, while each of lelectrode~
14 and 15 are 3eparated from ~ouch electrode 12 by a preselccted .D-~54 , dielectric thicknes~ T, derived in accordance with the insula-tion characteristics to be achieved, Each of transmi~ting and receiving electrodes 14 and 15 has an associated conductive lead wire 16 and 17, respectlvely, coupleld to a polnt thereon for connection of the touch-pad to known circu'~try (not shown for purposes of simplicity) configured to drive the transmitting electrode with a pPriodically varying waveform an~ to recognize :~ a change in the peak amplitude of that waveform at the receiving :~ electrode a~ the effective serie~ coupling impedance between transmitting and receiving electro~es varies when touch elec- ;;
trode 12 is approached and/or contacted.
In situations where relatively large values of dielectric thickness T are required, to pro~ect personnel contacting touch electrode 12 from high voltages present in apparatus adjacent substrate rear surface llb, the relative magn-Ltude of a para-sitic capacity Cp (between the facing surfaces of the trans-mitting and receiving electrodes 14 and 15 separated by the relatively small distance D), approaches the magnitude of the :~ desired 6eries capacity C (C=CaCb/(Ca+Cb) between electrodes 14 a~d 15 via touch electrode 12, Similarly, when arrays of a plurality of such touch-pads are posltioned with relatlvely close spacing, the ~ransmitting electrode of one touch-pad is positioned relatively close to the receiving electrode of an :~
adjacent touch-pad, whereby the magnitude of the pad-to-pad parasitic capacities approach the magnitude of electrod~
capacity through the substrate. These and other parasitic ~.apacities cause relatively large coupling between transmitting and receiving electrodes leading to the generation of erroneous signals which are not always easily lden~ifled or rejected, The coupl~ng problem is even more severe where the value o the 7~Y
, touch-pad capacitor C is small due to increasingly greater dLelectric thickness T, In many circum~tances, dielectric thickness and the distance separating individual touch-pad~ of an array are configured, in high density arra~s, such that device and parasitic capa.citances are su~stantially equal and allow a signal, introduced into the transmittlng electrode 14, to have substantial equal coupling to r~ceiving electrode 15 through either the parasitic or the intended capacitance path.
. In accordance with the invention, a capacitive touch-pad ~... 10 20 essentially overcoming the above problems of parasitic ,, :
:~. capacitance, while maintaining the required total thickness T
of a dielectric material, comprises a first dielectric substrate 21 of a relatively small thickness Tl, upon a front, or outwardly-facing, surface 21a of which is abricated touch electrode 12.
The spatially separated transmitting and receiving electrodes , , ~: 14 and 15, respectively, are abricated upon the remaining J or inwardly-facing, surface 21b of first dielectric layer 21 and may ~ be formed, in one preferred embodiment,by thin film fabrication .. techniques It should be understood that touch electrode 12 ma~ also be fabricated by thin film techniques. The electrodes and leads may also be fabricated as thick films, if desired, ln a particular applicatlon.
Lead means 23 and 24 each respectively associated with re~pective transmitting and receiving electrodes 14 and lS, are advantageously fabricated by thin film techniques, at th~
same time as the transmitting and receiving electrodes are the~selves fabricated, whereby the members forming lead mean~
23 and 24 are integrally joined to their respective electrodes.
A second layer 26 of dielectric material is fabricated to a thickness T~, which may be equal to, or diferent from, the ~ t~Z~ ~D~9454 thickness Tl of first layer 21, Layer 26 ls laminal:ed agalnst the inwardly-faring surface 21b of the fir.st dielPc~ric layer, and the transmltting and recelvi~g elec~rc)des abricated khereon~
Thus, the total thickness (T2+Tl) of the dielectric insul~tion of our novel laminated touch-pad i5 easily established to be equal to the total dielectric insulation thickness T of the prior art touch pad 10, yet the total separation distance Tl between each of transm~tting and receiving electrodes L4 and 15, respectively, and overlying touch electrode 12 is substantially reduced over the prior art embodi.ment, whereby the value of each series capacitance (between transmitting electrode 14 and touch electrode 12 and between touch electrode 12 cmd receiving electrode 15) i~ substantlally increased and i~ relatively g-Leater than the parasltic capacity between transmitting and receiving electrodes of a single touch-pad or the parasitic capacitance between electrodes of adjacent touch-pads in high denslty arrays. The relatlvely greater magnitude o signal current enabled between transmltting and receiving electrodes via the series path (through the touch-plate), as opposed to ~0 thb parasitic path, snables touch--pad arrays o~ greater den~lty than hitherto posslble, Use of spaclng simllar to the array spacing ach~eved in prlor art dispLays allows relatlvely lower amplitudes of the waveform driving the ~ransmlttlng ~lectrode to be used, due to the increased magnitude of the desired signal coupled be~ween electrodes 14 and 15, via Ca, Cb and the to~ch plate electrode. Thus, lower imple~.entation CGS~ of associated driving and sensing circuitry is facllikated by reducing dri~lng ~ignal magnitude and the difficul~y of sensing alse signals.
While the present ln~ention has been described wlth reference to one preferred embodlment thereof, many ~Tariations ', ~-, -6-~ ~ ~ 1f~q1 RD-9454 ~.
and modifications will now become apparent to tho~e skilled in the art. It is our intent, therefore, to be limited solely by the ecope of the appending clai=~.
:' :
,; ~
:
, .
';' :
~ ~7~
,:~
.~ . .
Claims (9)
1. A capacitive touch-pad comprising a first layer of dielectric material having first and second surfaces, said first surface being outwardly facing and exposed to an external environment;
a first electrode fabricated upon said first surface to be exposed to said external environment and responsive to contact with a human body member;
a pair of spatially separated second and third electrodes fabricated upon said second surface substantially within the boundaries of said first electrode; and a second layer of rigid dielectric material laminated to said second surface in abutment with said second and third electrodes;
said first layer having a thickness predeterminately selected to cause an electrical capacitance between each of said second and third electrodes and said first electrode to be greater than the parasitic capacitance between said first and second electrodes.
a first electrode fabricated upon said first surface to be exposed to said external environment and responsive to contact with a human body member;
a pair of spatially separated second and third electrodes fabricated upon said second surface substantially within the boundaries of said first electrode; and a second layer of rigid dielectric material laminated to said second surface in abutment with said second and third electrodes;
said first layer having a thickness predeterminately selected to cause an electrical capacitance between each of said second and third electrodes and said first electrode to be greater than the parasitic capacitance between said first and second electrodes.
2. A touch-pad as set forth in claim 1, wherein said second layer has a thickness chosen to cause the total thickness between furthest opposed surfaces of said first and second layers to equal a selected total thickness.
3. A touch-pad as set forth in claim 2, wherein the thicknesses of said first and second layers are substantially equal.
4. A touch-pad as set forth in claim 2, wherein the thickness of said first layer is substantially less than the thickness of said second layer.
5. A touch-pad as set forth in claim 1 wherein said second and third electrodes are each members of one of the group consisting of a conductive material film and a semiconductive material film.
6. A touch-pad as set forth in claim 5, further comprising lead means coupled to each of said second and third electrodes.
7. A touch-pad as set forth in claim 6, wherein each of said lead means is a film member fabricated upon said second surface and having an end thereof in electrical contact with associated one of said third and second electrodes.
8. A touch-pad as set forth in claim 7, wherein said second and third electrodes and the associated lead means are fabricated to the same thickness upon said second surface.
9. A touch-pad as set forth in claim 5, wherein said first electrode is a film member fabricated upon said first surface.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA311,806A CA1110727A (en) | 1978-09-21 | 1978-09-21 | Laminated capacitive touch-pad |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA311,806A CA1110727A (en) | 1978-09-21 | 1978-09-21 | Laminated capacitive touch-pad |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1110727A true CA1110727A (en) | 1981-10-13 |
Family
ID=4112418
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA311,806A Expired CA1110727A (en) | 1978-09-21 | 1978-09-21 | Laminated capacitive touch-pad |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1110727A (en) |
-
1978
- 1978-09-21 CA CA311,806A patent/CA1110727A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |