CA1117618A - Capacitive touch-pad devices with dynamic bias - Google Patents
Capacitive touch-pad devices with dynamic biasInfo
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- CA1117618A CA1117618A CA000311805A CA311805A CA1117618A CA 1117618 A CA1117618 A CA 1117618A CA 000311805 A CA000311805 A CA 000311805A CA 311805 A CA311805 A CA 311805A CA 1117618 A CA1117618 A CA 1117618A
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- 239000003989 dielectric material Substances 0.000 claims description 10
- 239000000758 substrate Substances 0.000 claims description 8
- 239000010409 thin film Substances 0.000 claims description 5
- 239000007787 solid Substances 0.000 claims description 3
- 230000003071 parasitic effect Effects 0.000 abstract 1
- 239000003990 capacitor Substances 0.000 description 4
- 238000000034 method Methods 0.000 description 4
- 230000008859 change Effects 0.000 description 2
- 229920000136 polysorbate Polymers 0.000 description 2
- QHGVXILFMXYDRS-UHFFFAOYSA-N pyraclofos Chemical compound C1=C(OP(=O)(OCC)SCCC)C=NN1C1=CC=C(Cl)C=C1 QHGVXILFMXYDRS-UHFFFAOYSA-N 0.000 description 2
- 206010001497 Agitation Diseases 0.000 description 1
- 230000004913 activation Effects 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000005284 excitation Effects 0.000 description 1
- 238000009413 insulation Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
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Abstract
ABSTRACT OF THE DISCLOSURE
A dynamic biasing capacitance is formed between a trans-mitting electrode and a receiving electrode of a capacitive touch-pad device to couple a portion of the scan voltage signal into the sense node of a voltage comparator circuit, coupled to the receiving electrode, to offset the comparator circuit threshold voltage. The dynamic biasing capacitance may be formed by overlapping portion of the electrode, with a dielectric layer positioned therebetween, or by the parasitic capacitance between sligned and surfaces of the two electrodes, with the magnitude of the dynamic biasing capacitance being adjusted by variation of interelectrode geometries.
A dynamic biasing capacitance is formed between a trans-mitting electrode and a receiving electrode of a capacitive touch-pad device to couple a portion of the scan voltage signal into the sense node of a voltage comparator circuit, coupled to the receiving electrode, to offset the comparator circuit threshold voltage. The dynamic biasing capacitance may be formed by overlapping portion of the electrode, with a dielectric layer positioned therebetween, or by the parasitic capacitance between sligned and surfaces of the two electrodes, with the magnitude of the dynamic biasing capacitance being adjusted by variation of interelectrode geometries.
Description
RD-94S~
The present invention rela-tes to capac;-tive touch-pad devices and, more particularly, to means for adjus-ting the ou-tpu-t of a capacitive touch-pad device -to match the threshold voltage of a comparator circuit used to sense the touch and no-touch conditions.
; Known capacitive touch-pad devices have a pair of spatially-separated electrodes, commonly referred to as the transmitting elec-trode and -the receiving electrode, fabrica-ted upon a first surface of a dielectric layer, with a touch electrode fabricated upon the re-maining surface of the dielectric layer and having an area enclosing the boundaries of the transmitting and receiving electrodes fab-ricated upon the opposite substrate surface. A source of a scanning voltage, comrnonly a voltage pulse, is coupled to the transmitting electrode and an input of a voltage comparator means is typically connected to the receiving electrode. A pair of series-connected capacitances (between the transmitting electrode and the touch electrode and between -the touch electrode and the receiving electrode) allow a certain pro-portion of the scan voltage to reach the voltage comparator input, when an object is not contacting or placed adjacent to -the touch electrode; a differen-t proportion of the scan voltage appears at the voltage comparator input when a relatively low impedance is placed between the touch electrode and a circuit ground. The comparator is configures to sense the change in signal amplitude at its input in the touch and in the no-touch conditions and to change the magnitude of its output accordingly.
The voltage compara-tor generally has a minimum threshold voltage which is typically greater in absolute value than the output signal from a capacitance touch-pad device which is ac-tivated by a relatively low scanning voltage,up to a magni-tude of about 30 volts peak. Thus, the use of low scanning voltages, e.g. 30 vol-ts peak or less, are not practical as -the comparator imput signal, is either the touch or no-touch condition is less than the minimum -threshold voltage ~D-945~
and the comparator remains in a single state in either condition.
It has been suggested to use direct current biasing tech-niques at the voltage comparator input to achieve an offset against the minimum threshold voltage and thereby reduce the threshold vol~
tage to a value sufficiently small, to allow low amplitude scan vol-tages are usable. However, in the scanning mode, wherein exci-tation signals are applied to thetransmit-ting electrode as a pulse occurring only at certain predetermined times, the voltage comparator input is typically reset to a fixed voltage level (to prevent false activation of the comparator output by noise and other extraneous signals occur-ring between scan pulses) and is released from the fixed voltage level immediately prior to the leading edge of the scan voltage pulse, whereby any D.C. bias introduced a-t the voltage comparator input would be rendered unusable by the comparator input reset circuit.
A dynamic biasing scheme which introduces a signal, offsetting the minimum threshold voltage, at the start of the scan voltage pulse will not be offset by the reset-ting of -the comparator input and allows reduction in magnitude of the relatively high amplitude scan voltages presently utilized, thus reducing the cos-t of the electronics associated with the capacitive touch-pad device.
In accordance with the invention, a capacitive touch-pad device having dynamic biasing means comprises a dielectric substrate having a touch electrode fabricated on a first surface and having spatially-separated transmit-ting and receiving electrodes fabricated upon the remaining surface and positioned opposite the touch electrode and within the boundaries of the latter; a portion of one of the receiving and transmitting elec-trodes is geometrically configured to provide a predetermined value of capacitance between the transmitting and receiving electrodes to facilitate coupling of a proportional amount of the scan voltage pulse direc-tly to the co~lparator input is offset the -threshold vol-tage thereof.
In one preferred e-mbodiment, the dynamic biasing capacitance G~
RV-9~,55 is of multilayer configura-tion and is formed by overlapping a portion of one of the receiving and transmitting electrodes over the other of the receiving and transmitting electrodes over the other of the elec-trodes with a layer of dielectric therebetween.
In another preferred embodimen-t, at least one portion of ; one of the receiving and transmitting electrodes is configured to have an edge therof extending at lesser or greater length adjacent to at least one edge of the remaining one of the electrodes to provide greater or lesser capacitance, with an air dielectric in the space therebetween;
dielectric materia] having a dielectric constant differing from the dielectric constant of air, may be utilized to achieve a desired value of dynamic biasing capacitance.
Accordingly, it is one object of the present invention -to - provide a capacitive touch-pad device having dynamic biasing means for substantially reducing the threshold voltage of a comparator coupled to the device.
~- It is another object of the present invention to provide a capacitive touch-pad device with a dynamic biasing means to facilitate scanning of the device with rela-tively low voltage signals.
These and other objects of -the present invention will become apparent upon consideration of the following detailed description taken in conjunction with the drawings.
Figure 1 is a schematic diagram illustrating the principles of operation of the present invention;
Figures 2a and 2b are a plan view and a sectional view, respectively, of one preferred embodiment of the nove] capacitive touch-pad device with dynamic biasing means of the present invention; and Figures 3a and 3b are a plan view and a sectional view, respectively, of another preferred embodiment of the present invention.
Referring initially -to Figures 1, 2a and 2b, a first preferred embodiment of a capaci-tive touch-pad device 10 comprises a substrate 11 of a dielectric material having a conductive touch electrode 12 fabrica-ted upon a first surface lla -thereof. A pair Or electrodes 14 and 15, commonly referred to as a transmit-ting electrode and a receiving electrode, respectively, are fabricated upon the remaining, or inwardly-facing, surface llb of the substrate. Electrodes 14 and 15 are con-figured and positioned to be substan-tially within the boundaries defined by touch electrode 12 upon the opposi-te surface of -the dielectric substrate. A layer of 16 of dielectric material is fabricated over one of the transmitting and receiving electrodes, e.g. transmi-t-ting electrode 14, to provide an insulative supporting surface for an extension 15a of the remaining electrode, whereby a capacitance of magnitude C is formed between electrode extension 15a and the underlying portion of the remaining electrode 14. Capacitance C is generally of lesser magnitude than either of the capacitance Ca formed between transmitting electode 14 and the underlying touch electrode 12, and the capacitance Cb formed be-tween touch electrode 12 and the overlying receiving electrode 15. By fabricating the multilayered combination of electrodes 14 and 15, a dielectric layer 16 and electrode extension 15a by thin film techniques, the magnitude of overlap between electrode 14 and extension 15a is rela-tively easily changed to facilitate adjustment of the value of capacitance C.
Use of thin film fabrication techniques is particularly ad-vantageous in tha-t a palr of lead means 16 and 17, each coupled to one of electrodes 14 and 15, respectively, can be integrally fabricated wi-th the planar electrodes prior to enclosing at least one of the electrodes, e.g. electrode 14, in dielectric layer 16.
In operation, a scan voltage source 19, producing a voltage pulse of amplitude Vs at predetermined periodic intervals, is coupled between transmitting electrode 14 and a circuit ground 20. A vol-tage comparator 21 has a first inpu-t 21a coupled -to receiving elec-trode 15 and has a second imput 21b coupled to circuit ground. Prior to receiving scan voltage pulse, a switch S (coupled be-tween comparator imput leads 21a and 21b) is closed to prevent noise and o-ther ex-traneous signals from ~ RD-9455 triggering the comparator and enabling the ou-tpu-t 21c -thereof. A-t the time tha-t transmit-ting electrode 14 receives the scan vo~tage pulse, switch S is opened and a minimal threshold voltage of magnitude Vth appears between comparator imput terminals 21a and 21b. If a relatively high impedance Z exists between touch electrode 12 and circuit ground 20, a portion of the scan voltage Vs is coupled to the comparator inpu-t via the series capacitance arrangement of capacitors Ca and Cb, while an additional por-tion of the scan voltage pulse is coupled by dynamic biasing capacitance C between source 10 and com-parator input 21a. As previously stated herein, -the value of dynamic biasing capacitance C is adjusted -to supply a portion of the scan voltage pulse to the comparator imput to reduce -the threshold voltage substantially to zero, whereby the comparator now senses only the absolute value of the signal coupled to its imput via the touch pad capacitors Ca and Cb; a high value of impedance Z allows a rela-t;vely large touch-pad voltage to appear at the comparator and mainta;n comparator output 21c in the disabled condition. If a relatively low magni-tude of impedance Z occurs between -touch plate 12 and ground, the signal coupled to the comparator input via series capa-citors Ca and Cb is drastically reduced, whereby only the dynamie biasing capacitor C couples a signal to the comparator input of sufficient magnitude -to overeome the threshold voltage. This rela-tively low voltage at the comparator input is sensed to enable com~
parator outp~;t 21c even when relatively low amplitude scan voltages are utilized.
Referring now to Figures 3a and 3b, another preferred em-bodiment 10' of a capacitive touch-pad device with dynamic biasing means is shown. Touch electrode 12, having been fabricated upon -the outwardly-facing surface lla of the dielectric substrate 11, provides the boundaries within which a transmitting electrode 23 and a receiving electrode 24 are fabricated in planar manner, preferably by use of thin film -techniques. One of electrodes 23 and 24 is of smaller area, ~D-9455 e.g. electrode 24, than the o-ther, whereby the large electrode may be fabricated with at least one, and preferably a pair, of electrode extensions 23a and 23b extending adjacent to the boundaries of the smal-ler electrode. A channel 25 is formed between the adjacent edges of the two electrodes to provide insulation therebetween. Thus, the dynamic biasing capacitance C is formed as a fringing capacitance between the edges of thetwo, relatively closely spaced electrodes. Channel 25 may be filled with air or may be filled with a solid dielectric mat-erial having a dielectric cons-tant differing from that of air, to increase or reduce the capac;tance per unit length of the confronting edges.
As previously explained hereinabove, electrode leads, such as a receiving electrode lead means 27 and a transmitting electrode lead means 28, may be fabricated integral with, and at -the same time as, the pair of electrodes and the electrode extensions. This planar electrode-extension-lead approach is less costly to fabricate than the multi-layer embodiment of Figures 2a and 2b and also provides a certain de-gree of electrical shielding for electrode 240 It should be unders-tood that, in either preferred embodi-ment, the transmitting and receiving electrodes may be interchanged,although electrode 24, being shielded by electrode extensions 23a and 23b, is best connected as the recei-ving electrode in many applications.
While several preferred embodiments of the present invention have been described, many variations and modifications will now become apparent to -those skilled in the art. I-t is my intent, therefore,to be limited solely be the scope of the appending claims.
The present invention rela-tes to capac;-tive touch-pad devices and, more particularly, to means for adjus-ting the ou-tpu-t of a capacitive touch-pad device -to match the threshold voltage of a comparator circuit used to sense the touch and no-touch conditions.
; Known capacitive touch-pad devices have a pair of spatially-separated electrodes, commonly referred to as the transmitting elec-trode and -the receiving electrode, fabrica-ted upon a first surface of a dielectric layer, with a touch electrode fabricated upon the re-maining surface of the dielectric layer and having an area enclosing the boundaries of the transmitting and receiving electrodes fab-ricated upon the opposite substrate surface. A source of a scanning voltage, comrnonly a voltage pulse, is coupled to the transmitting electrode and an input of a voltage comparator means is typically connected to the receiving electrode. A pair of series-connected capacitances (between the transmitting electrode and the touch electrode and between -the touch electrode and the receiving electrode) allow a certain pro-portion of the scan voltage to reach the voltage comparator input, when an object is not contacting or placed adjacent to -the touch electrode; a differen-t proportion of the scan voltage appears at the voltage comparator input when a relatively low impedance is placed between the touch electrode and a circuit ground. The comparator is configures to sense the change in signal amplitude at its input in the touch and in the no-touch conditions and to change the magnitude of its output accordingly.
The voltage compara-tor generally has a minimum threshold voltage which is typically greater in absolute value than the output signal from a capacitance touch-pad device which is ac-tivated by a relatively low scanning voltage,up to a magni-tude of about 30 volts peak. Thus, the use of low scanning voltages, e.g. 30 vol-ts peak or less, are not practical as -the comparator imput signal, is either the touch or no-touch condition is less than the minimum -threshold voltage ~D-945~
and the comparator remains in a single state in either condition.
It has been suggested to use direct current biasing tech-niques at the voltage comparator input to achieve an offset against the minimum threshold voltage and thereby reduce the threshold vol~
tage to a value sufficiently small, to allow low amplitude scan vol-tages are usable. However, in the scanning mode, wherein exci-tation signals are applied to thetransmit-ting electrode as a pulse occurring only at certain predetermined times, the voltage comparator input is typically reset to a fixed voltage level (to prevent false activation of the comparator output by noise and other extraneous signals occur-ring between scan pulses) and is released from the fixed voltage level immediately prior to the leading edge of the scan voltage pulse, whereby any D.C. bias introduced a-t the voltage comparator input would be rendered unusable by the comparator input reset circuit.
A dynamic biasing scheme which introduces a signal, offsetting the minimum threshold voltage, at the start of the scan voltage pulse will not be offset by the reset-ting of -the comparator input and allows reduction in magnitude of the relatively high amplitude scan voltages presently utilized, thus reducing the cos-t of the electronics associated with the capacitive touch-pad device.
In accordance with the invention, a capacitive touch-pad device having dynamic biasing means comprises a dielectric substrate having a touch electrode fabricated on a first surface and having spatially-separated transmit-ting and receiving electrodes fabricated upon the remaining surface and positioned opposite the touch electrode and within the boundaries of the latter; a portion of one of the receiving and transmitting elec-trodes is geometrically configured to provide a predetermined value of capacitance between the transmitting and receiving electrodes to facilitate coupling of a proportional amount of the scan voltage pulse direc-tly to the co~lparator input is offset the -threshold vol-tage thereof.
In one preferred e-mbodiment, the dynamic biasing capacitance G~
RV-9~,55 is of multilayer configura-tion and is formed by overlapping a portion of one of the receiving and transmitting electrodes over the other of the receiving and transmitting electrodes over the other of the elec-trodes with a layer of dielectric therebetween.
In another preferred embodimen-t, at least one portion of ; one of the receiving and transmitting electrodes is configured to have an edge therof extending at lesser or greater length adjacent to at least one edge of the remaining one of the electrodes to provide greater or lesser capacitance, with an air dielectric in the space therebetween;
dielectric materia] having a dielectric constant differing from the dielectric constant of air, may be utilized to achieve a desired value of dynamic biasing capacitance.
Accordingly, it is one object of the present invention -to - provide a capacitive touch-pad device having dynamic biasing means for substantially reducing the threshold voltage of a comparator coupled to the device.
~- It is another object of the present invention to provide a capacitive touch-pad device with a dynamic biasing means to facilitate scanning of the device with rela-tively low voltage signals.
These and other objects of -the present invention will become apparent upon consideration of the following detailed description taken in conjunction with the drawings.
Figure 1 is a schematic diagram illustrating the principles of operation of the present invention;
Figures 2a and 2b are a plan view and a sectional view, respectively, of one preferred embodiment of the nove] capacitive touch-pad device with dynamic biasing means of the present invention; and Figures 3a and 3b are a plan view and a sectional view, respectively, of another preferred embodiment of the present invention.
Referring initially -to Figures 1, 2a and 2b, a first preferred embodiment of a capaci-tive touch-pad device 10 comprises a substrate 11 of a dielectric material having a conductive touch electrode 12 fabrica-ted upon a first surface lla -thereof. A pair Or electrodes 14 and 15, commonly referred to as a transmit-ting electrode and a receiving electrode, respectively, are fabricated upon the remaining, or inwardly-facing, surface llb of the substrate. Electrodes 14 and 15 are con-figured and positioned to be substan-tially within the boundaries defined by touch electrode 12 upon the opposi-te surface of -the dielectric substrate. A layer of 16 of dielectric material is fabricated over one of the transmitting and receiving electrodes, e.g. transmi-t-ting electrode 14, to provide an insulative supporting surface for an extension 15a of the remaining electrode, whereby a capacitance of magnitude C is formed between electrode extension 15a and the underlying portion of the remaining electrode 14. Capacitance C is generally of lesser magnitude than either of the capacitance Ca formed between transmitting electode 14 and the underlying touch electrode 12, and the capacitance Cb formed be-tween touch electrode 12 and the overlying receiving electrode 15. By fabricating the multilayered combination of electrodes 14 and 15, a dielectric layer 16 and electrode extension 15a by thin film techniques, the magnitude of overlap between electrode 14 and extension 15a is rela-tively easily changed to facilitate adjustment of the value of capacitance C.
Use of thin film fabrication techniques is particularly ad-vantageous in tha-t a palr of lead means 16 and 17, each coupled to one of electrodes 14 and 15, respectively, can be integrally fabricated wi-th the planar electrodes prior to enclosing at least one of the electrodes, e.g. electrode 14, in dielectric layer 16.
In operation, a scan voltage source 19, producing a voltage pulse of amplitude Vs at predetermined periodic intervals, is coupled between transmitting electrode 14 and a circuit ground 20. A vol-tage comparator 21 has a first inpu-t 21a coupled -to receiving elec-trode 15 and has a second imput 21b coupled to circuit ground. Prior to receiving scan voltage pulse, a switch S (coupled be-tween comparator imput leads 21a and 21b) is closed to prevent noise and o-ther ex-traneous signals from ~ RD-9455 triggering the comparator and enabling the ou-tpu-t 21c -thereof. A-t the time tha-t transmit-ting electrode 14 receives the scan vo~tage pulse, switch S is opened and a minimal threshold voltage of magnitude Vth appears between comparator imput terminals 21a and 21b. If a relatively high impedance Z exists between touch electrode 12 and circuit ground 20, a portion of the scan voltage Vs is coupled to the comparator inpu-t via the series capacitance arrangement of capacitors Ca and Cb, while an additional por-tion of the scan voltage pulse is coupled by dynamic biasing capacitance C between source 10 and com-parator input 21a. As previously stated herein, -the value of dynamic biasing capacitance C is adjusted -to supply a portion of the scan voltage pulse to the comparator imput to reduce -the threshold voltage substantially to zero, whereby the comparator now senses only the absolute value of the signal coupled to its imput via the touch pad capacitors Ca and Cb; a high value of impedance Z allows a rela-t;vely large touch-pad voltage to appear at the comparator and mainta;n comparator output 21c in the disabled condition. If a relatively low magni-tude of impedance Z occurs between -touch plate 12 and ground, the signal coupled to the comparator input via series capa-citors Ca and Cb is drastically reduced, whereby only the dynamie biasing capacitor C couples a signal to the comparator input of sufficient magnitude -to overeome the threshold voltage. This rela-tively low voltage at the comparator input is sensed to enable com~
parator outp~;t 21c even when relatively low amplitude scan voltages are utilized.
Referring now to Figures 3a and 3b, another preferred em-bodiment 10' of a capacitive touch-pad device with dynamic biasing means is shown. Touch electrode 12, having been fabricated upon -the outwardly-facing surface lla of the dielectric substrate 11, provides the boundaries within which a transmitting electrode 23 and a receiving electrode 24 are fabricated in planar manner, preferably by use of thin film -techniques. One of electrodes 23 and 24 is of smaller area, ~D-9455 e.g. electrode 24, than the o-ther, whereby the large electrode may be fabricated with at least one, and preferably a pair, of electrode extensions 23a and 23b extending adjacent to the boundaries of the smal-ler electrode. A channel 25 is formed between the adjacent edges of the two electrodes to provide insulation therebetween. Thus, the dynamic biasing capacitance C is formed as a fringing capacitance between the edges of thetwo, relatively closely spaced electrodes. Channel 25 may be filled with air or may be filled with a solid dielectric mat-erial having a dielectric cons-tant differing from that of air, to increase or reduce the capac;tance per unit length of the confronting edges.
As previously explained hereinabove, electrode leads, such as a receiving electrode lead means 27 and a transmitting electrode lead means 28, may be fabricated integral with, and at -the same time as, the pair of electrodes and the electrode extensions. This planar electrode-extension-lead approach is less costly to fabricate than the multi-layer embodiment of Figures 2a and 2b and also provides a certain de-gree of electrical shielding for electrode 240 It should be unders-tood that, in either preferred embodi-ment, the transmitting and receiving electrodes may be interchanged,although electrode 24, being shielded by electrode extensions 23a and 23b, is best connected as the recei-ving electrode in many applications.
While several preferred embodiments of the present invention have been described, many variations and modifications will now become apparent to -those skilled in the art. I-t is my intent, therefore,to be limited solely be the scope of the appending claims.
Claims (11)
1. A capacitive touch pad device comprising:
a substrate of dielectric material having first and second opposed surfaces;
a single conductive touch electrode responsive to human communication fabricated upon said first surface over a preselected continuous area;
a pair of spatially separated electrodes fabricated upon said second surface substantially within an area overlying and bounded by the area of said touch electrode;
at least one of said pair of electrodes having at least one extension therefrom extending parallel to and spaced from at least one surface of the remaining one of said pair of electrodes; and dielectric material filling the volume defined between said electrode extension and the confronting portion of said remaining electrode to provide a first electrical capacitance therebetween of essentially constant value;
the dielectric material of said substrate separating said conductive touch electrode and each of said spatially separated electrodes providing second and third electrical capacitances respectively therebetween of essentially constant value.
a substrate of dielectric material having first and second opposed surfaces;
a single conductive touch electrode responsive to human communication fabricated upon said first surface over a preselected continuous area;
a pair of spatially separated electrodes fabricated upon said second surface substantially within an area overlying and bounded by the area of said touch electrode;
at least one of said pair of electrodes having at least one extension therefrom extending parallel to and spaced from at least one surface of the remaining one of said pair of electrodes; and dielectric material filling the volume defined between said electrode extension and the confronting portion of said remaining electrode to provide a first electrical capacitance therebetween of essentially constant value;
the dielectric material of said substrate separating said conductive touch electrode and each of said spatially separated electrodes providing second and third electrical capacitances respectively therebetween of essentially constant value.
2. A device as set forth in claim 1, wherein the dielectric material between said electrode extension and said remaining electrode is air.
3. A device as set forth in claim 1, wherein the dielectric material between said electrode extension and said remaining electrode has a dielectric constant differing from the dielectric constant of air.
4. A device as set forth in claim 1, wherein said pair of electrodes are planar arranged, said electrode extension being positioned above the plane of said electrodes and extending over a predetermined area of said remaining electrode; the volume between confronting surfaces of said electrode extension and said remaining electrode being filled with a solid dielectric material.
5. A device as set forth in claim 4, wherein said remaining electrode is completely enclosed by solid dielectric material.
6. A device as set forth in claim 5, wherein said pair of electrodes and said electrode extension are thin film members.
7. A device as set forth in claim 1, wherein said pair of electrodes are coplanar, each of said extension elec-trodes lying in the same plane thereof and having an edge extending adjacent to at least one edge of said remaining electrode.
8. A device as set forth in claim 1, further compris-ing lead means coupled to each of said pair of electrodes.
9. A device as set forth in claim 8, wherein said lead means are thin film members integrally fabricated as part of the associated one of said pair of electrodes.
10. A device as set forth in claim 1, in combination with: first means coupled to only one of said pair of electrodes for generating a signal; second means coupled to the remaining one of said electrodes for comparing, against a reference signal amplitude, the amplitude of the signal at said remaining electrode produced responsive to the signal from said first means, said second means having a threshold signal amplitude;
and the magnitude of said capacitance between said pair of electrodes being adjusted to supply said second means with a portion of the signal from said first means selected to offset said threshold signal amplitude.
and the magnitude of said capacitance between said pair of electrodes being adjusted to supply said second means with a portion of the signal from said first means selected to offset said threshold signal amplitude.
11. A combination as set forth in claim 10, wherein the signal from said first means is periodically applied to said device; and wherein an input of said second means is substantially short-circuited at all time intervals when said first means signal is not present at said device.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000311805A CA1117618A (en) | 1978-09-21 | 1978-09-21 | Capacitive touch-pad devices with dynamic bias |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000311805A CA1117618A (en) | 1978-09-21 | 1978-09-21 | Capacitive touch-pad devices with dynamic bias |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1117618A true CA1117618A (en) | 1982-02-02 |
Family
ID=4112417
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000311805A Expired CA1117618A (en) | 1978-09-21 | 1978-09-21 | Capacitive touch-pad devices with dynamic bias |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1117618A (en) |
-
1978
- 1978-09-21 CA CA000311805A patent/CA1117618A/en not_active Expired
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