US20080018611A1

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Publication number: US20080018611A1
Application number: US11/679,535
Authority: US
Inventors: Bogdan Serban; Philippe Boyer; Aloyse Schoos
Original assignee: IEE International Electronics and Engineering SA
Current assignee: IEE International Electronics and Engineering SA
Priority date: 2006-07-18
Filing date: 2007-02-27
Publication date: 2008-01-24
Also published as: EP2041641A2; US20080018608A1; EP2041641B8; WO2008009687A2; WO2008009687A3; EP2041641B1; US8063886B2

Abstract

An input device comprises a capacitive proximity and pressure sensor, which includes a first carrier layer, a second carrier layer and a spacer arranged between the first and second carrier layers, the first carrier layer having a first capacitor electrode applied thereon, the second carrier layer having a second capacitor electrode applied thereon, the first and second capacitor electrodes being arranged opposite one another with respect to the spacer in such a way that, in response to a compressive force acting on the pressure sensor, the first and second capacitor electrodes are brought closer together. The input device further comprises a control circuit configured so as to operate in at least two modes of operation, including a first and a second mode of operation. The control circuit determines, while in the first mode of operation, a quantity indicative of a capacitance between the first capacitor electrode and ground and, while in the second mode of operation, a quantity indicative of a capacitance between the first capacitor electrode and the second capacitor electrode.

Description

TECHNICAL FIELD

This invention relates to input devices and more particularly to data input devices including a film-based pressure sensor for human-appliance interaction.

BACKGROUND ART

Input devices are commonly used in conjunction with electronic appliances to feed the latter with various kinds of inputs, including e.g. control data influencing directly or indirectly the behavior of the appliance, input that is processed by the appliance and/or input that is simply stored.

It is known to construct input devices based upon film-type pressure sensors, whose resistance varies with pressure. Such film-type pressure sensor comprises two carrier films, which are arranged at a certain distance from one another by means of a spacer. The spacer is provided with at least one opening that defines an active zone of the sensor, in which the two carrier films face one another. Inside this active zone, at least two electrodes are arranged on the carrier films, in such a way that electrical contact is established between the electrodes when the two carrier films are pressed together under the action of a compressive force acting on the sensor in the active zone. The pressure acting on the sensor is detected and/or determined as a function of the resistance between the electrodes.

Depending on the application of such a pressure sensor, a layer of semiconducting material may be disposed between the electrodes, so that the sensor shows a gradual pressure sensitive behavior, that is to say its resistance varies gradually or even continuously as a function of the force applied. The layer of semiconducting material may comprise a material whose internal electrical resistance varies as a function of compression or of deformation of the layer or a material whose surface structure confers to the layer a surface resistance that is reduced following an increase in the number of points of contact with a conducting surface of an electrode, against which the layer of semiconducting material is pressed under the action of the compressive force.

WO 2004/049364 relates to a data input device comprising several keys arranged in at least two rows. A unidirectional position detector of film-type construction is associated with each row of keys. Each unidirectional position sensor enables the detection of the actuated key along the direction of the unidirectional position detector. The unidirectional position sensors are interconnected in such a way that a control circuit can detect in which row a key has been actuated.

A different kind of sensors is based upon capacitive sensing. U.S. Pat. No. 3,896,425 discloses an electrical proximity detector that senses the changes in the contents of a defined sensitive volume. The detector comprises an antenna that is driven by an oscillator and that emits an electric field into the sensitive volume. A person or an object intruding into the sensitive volume causes a change of the electric field of the antenna, which is detected by the detector. To shape the electric field of the antenna the detector comprises a first shield, driven by the oscillator with a signal of same amplitude and phase as the signal of the antenna, and a second, grounded shield.

Other sensors based on electric field or “capacitive” sensing have been proposed by J. Smith et al. in “Electric Field Sensing for Graphical Interfaces”, IEEE Computer Graphics and Applications, Issue May/June 1998, 54-60, as a human-computer interface. The interfaces are based upon an array of electrodes to detect the gestures of a user.

The above-mentioned documents are herewith included herein by reference.

SUMMARY OF THE INVENTION

The invention provides an improved input device.

According to a second aspect of the invention, the input device comprises a capacitive proximity and pressure sensor, which includes a first carrier layer, a second carrier layer and a spacer arranged between the first and second carrier layers. The first carrier layer has a plurality of first capacitor electrodes applied thereon and the second carrier layer has a plurality of second capacitor electrodes applied thereon, each one of the plurality of first capacitor electrodes being arranged opposite a respective one of the plurality of second capacitor electrodes with respect to the spacer in such a way that, in response to a compressive force acting on the pressure sensor, respectively opposite ones of the first and second capacitor electrodes are brought closer together. The input device according to the second aspect further comprises a control circuit configured so as to operate in at least two modes of operation, including a first and a second mode of operation. The control circuit determines, while in the first (proximity-sensing) mode of operation, a quantity indicative of a capacitance between individual ones (single ones or groups) of the plurality of first capacitor electrodes and ground and, while in the second (pressure-sensing) mode of operation, a quantity indicative of a capacitance between individual ones of the plurality of first capacitor electrodes and the respectively opposite ones of the plurality of second capacitor electrodes.

According to a fourth aspect of the invention, the input device comprises a capacitive proximity and pressure sensor, which includes a first carrier layer, a second carrier layer and a spacer arranged between the first and second carrier layers for keeping the first and second carrier layers apart from one another. The first carrier layer has a plurality of first capacitor electrodes applied thereon, the second carrier layer has a second capacitor electrode applied thereon, the plurality of first capacitor electrodes being arranged opposite the second capacitor electrode with respect to the spacer in such a way that, in response to a compressive force acting locally on the pressure sensor, individual ones of the first capacitor electrodes are brought closer to the second capacitor electrode at the location where the compressive force acts on the pressure sensor. The input device according to the fourth aspect comprises a control circuit, which determines, while in a first mode of operation, a quantity indicative of capacitance between individual ones of the first capacitor electrodes and ground and, while in a second mode of operation, a quantity indicative of a capacitance between the second capacitor electrode and individual ones of the first capacitor electrodes.

For the purposes of the present, the terms “first mode of operation” and “second mode of operation” are primarily used for distinguishing the modes of operation; these terms therefore should not be understood as indicating an order of the modes of operation in time. The control circuit may operate in the first mode of operation before and/or after operating in the second mode of operation. The control circuit may cyclically switch between the modes of operation, e.g. several times per second. Preferably, however, the control circuit remains in the proximity-sensing mode (first mode) until the proximity of a body having an electric-field-changing property is detected. Alternatively, the control circuit could remain in the pressure-sensing mode (second mode) until a force or pressure exceeding a predefined threshold has been detected.

For the purposes of the present, a “quantity indicative of a capacitance” can be any physical quantity that is linked to the capacitance by the laws of physics, such as, for instance, amplitude and/or phase of a current, amplitude and/or phase of a voltage, charge, impedance, etc.

According to a preferred embodiment of the input devices as recited hereinabove, the spacer is electrically insulating and compressible. According to this embodiment, opposite ones of the first and second capacitor electrodes are brought closer together when the spacer is compressed in response to a compressive force acting on the pressure sensor.

According to another preferred embodiment of the input device as recited hereinabove, the spacer has one or more openings therein, with respect to which the first capacitor electrode or electrodes are arranged opposite the second capacitor electrode or electrodes. The first capacitive electrode(s) and/or the second capacitor electrode(s) have an insulating layer or insulating pattern arranged thereon in such a way as to prevent a short circuit between the first capacitive electrode(s) and the second capacitor electrode(s). The insulating layer or pattern could be separate from the spacer or part of it (in the latter case the opening would rather be considered as a recess than as a through-hole). The spacer may be compressible or incompressible. In the latter case, the first and second capacitor electrodes are brought closer together when one or both of the carrier layers bend into the opening(s) of the spacer under the action of the compressive force.

If the spacer has a plurality of openings therein, if the first carrier layer has a plurality of first capacitor electrodes applied thereon and if the second carrier layer has a plurality of second capacitor electrodes applied thereon, each one of the plurality of first capacitor electrodes is preferably arranged opposite a respective one of the plurality of second capacitor electrodes with respect to a respective one of the plurality of openings. In this case, when a compressive force acts on the pressure sensor, respectively opposite ones of the first and second capacitor electrodes are brought closer together.

Those skilled will appreciate that various options exist for determining a quantity indicative of capacitance between the first capacitor electrode(s) and ground. For instance, the control circuit could determine, while in the first mode of operation,

(a) an amount of electric charge accumulated on (individual ones of) the first capacitor electrode(s) in response to applying a defined voltage to this (these) first capacitor electrode(s); or
(b) an amplitude and/or a phase of a loading current flowing in (individual ones of) the first capacitor electrode(s) in response to applying an oscillating voltage to this (these) first capacitor electrode(s); or
(c) an in-phase component and/or a 90°-phase-offset component of a loading current flowing in (individual ones of) the first capacitor electrode(s) in response to applying an oscillating voltage to this (these) first capacitor electrode(s); or
(d) a charge time and/or a discharge time of (individual ones of) the first capacitor electrode(s).

(a) an amount of electric charge accumulated on (individual ones of) the first capacitor electrode(s) and/or (on individual ones of) the second capacitor electrode(s) in response to an applying a defined voltage to the respectively opposite capacitor electrode(s);
(b) an amount of electric charge accumulated on (individual ones of) the first capacitor electrode(s) and/or (on individual ones of) the second capacitor electrode(s) in response to an applying a defined voltage to this (these) capacitor electrode(s);
(c) an amplitude and/or a phase of a loading current flowing (in individual ones of) the first capacitor electrode(s) in response to applying an oscillating voltage to this (these) first capacitor electrode(s);
(d) an amplitude and/or a phase of a loading current flowing (in individual ones of) the second capacitor electrode(s) in response to applying an oscillating voltage to this (these) second capacitor electrode(s);
(e) an amplitude and/or a phase of a loading current flowing (in individual ones of) the first capacitor electrode(s) in response to applying an oscillating voltage to the respectively opposite one(s) (of the) second capacitor electrode(s);
(f) an amplitude and/or a phase of a loading current flowing (in individual ones of) the second capacitor electrode(s) in response to applying an oscillating voltage to the respectively opposite one(s) (of the) first capacitor electrode(s);
(g) an in-phase component and/or a 90°-phase-offset component of a loading current flowing (in individual ones of) the first capacitor electrode(s) in response to applying an oscillating voltage to this (these) first capacitor electrode(s);
(h) an in-phase component and/or a 90°-phase-offset component of a loading current flowing (in individual ones of) the second capacitor electrode(s) in response to applying an oscillating voltage to this (these) second capacitor electrode(s);
(i) an in-phase component and/or a 90°-phase-offset component of a coupling current flowing (in individual ones of) the first capacitor electrode(s) in response to applying an oscillating voltage to the respectively opposite one(s) (of the) second capacitor electrode(s);
(j) an in-phase component and/or a 90°-phase-offset component of a coupling current flowing (in individual ones of) the second capacitor electrode(s) in response to applying an oscillating voltage to the respectively opposite one(s) (of the) first capacitor electrode(s);
(k) a charge and/or a discharge time of the first and/or the second capacitor electrode.

While in the first mode of operation, the control circuit preferably applies a first voltage to the first electrode(s) and a second voltage to the second electrode(s), the first and second voltages having same amplitude and phase. As will be appreciated, this substantially cancels the electric field between the first and second capacitor electrodes so that the first capacitor electrode(s) becomes (become) substantially insensitive in direction of the second capacitor electrode(s).

According to a preferred embodiment of the input device, the first carrier layer, the spacer and the second carrier layer are laminated together.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details and advantages of the present invention will be apparent from the following detailed description of several not limiting embodiments with reference to the attached drawings, wherein:

FIG. 1 is a schematic cross sectional view of capacitive pressure and proximity sensor according to a first embodiment;

FIG. 2 is a schematic cross sectional view of an input device according to a second embodiment;

FIG. 3 is an illustration of different examples of electrically insulating patterns;

FIGS. 4aand4bare cross sectional views of a touchpad having keypad functionality;

FIGS. 5aand5bare cross sectional views of an alternative touchpad having keypad functionality;

FIGS. 6aand6bare cross sectional views of yet another example of a touchpad having keypad functionality;

FIGS. 7a-7care illustrations of a touchpad with keypad functionality, in which the keys are arranged along a straight line;

FIGS. 8a-8eare illustrations of an input device implemented as a linear slider;

FIGS. 9a-9dare illustrations of an input device implemented as a circular slider;

FIGS. 10a-10dare illustrations of variants of an alternative embodiment of a touchpad;

FIGS. 11a-11bare cross-sectional schematic views of yet another example of an input device.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows adata input device10, comprising a capacitive proximity andpressure sensor12 of film-type construction. The capacitive proximity andpressure sensor12 comprises first and second carrier layers in the form of the first andsecond carrier films16,18, made of substantially flexible, electrically insulating material, such as e.g. PET, PEN, PI or the like. Aspacer20 is sandwiched between the first andsecond carrier films16,18 so as to keep them apart from one another. Thespacer20 is also be made of a substantially flexible, electrically insulating material, e.g. a double-sided adhesive. Thespacer20 is provided with anopening14 therein, which delimits an active zone of thepressure sensor10. In theactive zone14, the first carrier foil16 carries afirst capacitor electrode22 on the side directed towards thesecond carrier film18, while thesecond carrier foil18 carries asecond capacitor electrode24 on the side directed towards the first carrier film16. The first and

second capacitor electrodes

22,24 are formed from conductive material (e.g. silver ink) applied directly on the first andsecond carrier films16,18, respectively. The second capacitor electrode has formed thereon alayer26 of electrically insulating material (dielectric, e.g. PET, PEN, PI, etc.).

The right-hand side ofFIG. 1 shows acontrol circuit28 connected to the first and

second capacitor electrodes

22,24 by

leads

30,32. Thecontrol circuit28 comprises a microprocessor, an application-specific integrated circuit (ASIC) or a programmable chip, configured so as to operate in at least a first and a second mode of operation. The control circuit determines, while in the first mode of operation, a quantity indicative of a capacitance between the first capacitor electrode and ground and, while in the second mode of operation, a quantity indicative of a capacitance between the first capacitor electrode and the second capacitor electrode.

The first mode of operation is associated to sensing the proximity of an object to be sensed, e.g. of a user'sfinger34. In the first mode of operation the control circuit keeps the first and second electrodes essentially at the same electric potential so that the electric field substantially cancels between the first and second electrodes. Thesecond electrode24 thus acts as a driven shield for thefirst electrode22 and the sensitivity of the latter is directed away from thesecond electrode24. If an oscillating voltage is applied to the first capacitor electrode an oscillating electric field to ground is built up. The object to be sensed modifies the capacitance between the first capacitor electrode and ground, which is sensed by thecontrol circuit28. It should be noted that in the first mode of operation detecting the proximity of the object to be does not require the object touching or being in contact with the proximity andpressure sensor12.

The second mode of operation is associated with sensing pressure exerted on the sensor by some kind of actuator, such as e.g. the user's finger or stylus. In the second mode of operation, the control circuit essentially determines the capacitance of the capacitor formed by the first and the

second capacitor electrodes

22,24. It is well known that the capacitance of a capacitor depends upon the distance between its electrodes. In the illustrated case, the distance between the first and second capacitor electrodes decreases with increasing pressure exerted upon the pressure sensor by the user. As a consequence, the capacitance between the capacitor electrodes increases, which is detected by thecontrol circuit28.

FIG. 2 shows a variant of the proximity and pressure sensor ofFIG. 1. The construction is the same, except that thefirst capacitor electrode22, like thesecond capacitor electrode24, has formed thereon alayer26 of electrically insulating material. Those skilled will appreciate that patterning one of the electrically insulatinglayers26 allows tailoring the response of the proximity and pressure sensor in the second mode of operation. As long as the electrically insulating layers are spaced from one another (i.e. for low pressures exerted by the user) the pattern has no significant influence on sensor response. However, as the pressure increases the electrically insulating layers come into contact and a contact surface forms. A patterned insulating layer results in that the minimum distance between the first and second electrodes is varying on the contact surface. Accordingly, the capacitance increase is different from the case where the insulating layers are uniform. Examples of patterned insulating layers are shown inFIG. 3.

InFIGS. 4a-4b, elements similar to elements ofFIG. 1 have been attributed the same reference numeral as the corresponding element ofFIGS. 1 and 2, preceded by a prefix according to the number of the drawing.

FIGS. 4aand4bshow a cross section of atouchpad412 having keypad functionality. Thetouchpad412 comprises a laminated structure of afirst carrier film416, asecond carrier film418 and aspacer420, sandwiched between the first and second carrier films so as to keep them spaced apart. Thespacer420 has a matrix-like arrangement ofopenings414 therein, which define keys of thetouchpad412. To each key is associated a pair of afirst capacitor electrode422 and asecond capacitor electrode424 arranged on the first and

second carrier films

416,418, respectively. Eachfirst capacitor electrode422 is arranged opposite its second-capacitor-electrode counterpart424, with respect to the associatedopening414 of thespacer420. Thetouchpad412 further comprises a control circuit (not shown, for the sake of clarity of the drawings), which determines, in a first mode of operation, a quantity indicative of capacitance between individual ones of thefirst capacitor electrodes422 and ground and, in a second mode of operation, a quantity indicative of a capacitance between individual ones of thefirst capacitor electrodes422 and the associated ones of thesecond capacitor electrodes424.

InFIG. 4a, a user'sfinger434 lightly touches thefirst carrier film416. The force exerted is not sufficient to cause significant bending of thefirst carrier film416 in the region of a key. The position of the user'sfinger434 is detected by determining, for each one of thefirst capacitor electrodes422, the quantity indicative of capacitive coupling between thiselectrode422 and ground. The position may e.g. be computed as the centroid of the positions of thefirst capacitor electrodes422, weighed with the corresponding quantity indicative of capacitance. The first mode of operation is suitable, for instance, when the user controls a cursor (e.g. on the display of an appliance) with thetouchpad412.

InFIG. 4b, the user presses down thefirst carrier film416, so that it bends into anopening414 of thespacer420 and the distance between the corresponding first and

second capacitor electrodes

422,424 decreases. This causes the capacitance between these capacitor electrodes to go up, which can be detected in the second mode of operation of thetouchpad412. The second mode of operation is, therefore, associated to actuation of a key of thetouchpad412, e.g. by a user'sfinger434 or a stylus.

In operation, the first and second modes of operation are carried out in alternance, i.e. thetouchpad412 is switched, more or less periodically, from the first mode of operation to the second mode and inversely. It should be noted that, in the second mode of operation, the touchpad does not need to determine the quantity indicative of capacitance for each key. Indeed, it is considered advantageous if the latter is determined only with respect to that key or those keys in the neighborhood of which the position of the user'sfinger434 has been detected when thetouchpad412 operated in the first mode of operation.

FIGS. 5aand5bshow a cross section of analternative touchpad512 having keypad functionality. Thetouchpad512 comprises afirst carrier film516, asecond carrier film518 and a spacer521, sandwiched between the first and

second carrier films

516,518 so as to keep them spaced apart. The spacer521 is made of an electrically insulating, compressible foam material, e.g. polyurethane foam or the like. The first and second carried

films

516,518 have

capacitor electrodes

522,524 applied on the surfaces that face the spacer521. Eachfirst capacitor electrode522 is arranged on the first carrier film opposite asecond capacitor electrode524 on the second carrier film, with respect to the spacer521. Each pair of opposite first and second capacitor electrodes defines a key of thetouchpad512. The latter further comprises a control circuit (not shown), which determines, in a first mode of operation, a quantity indicative of capacitance between individual ones of thefirst capacitor electrodes522 and ground and, in a second mode of operation, a quantity indicative of a capacitance between individual ones of thefirst capacitor electrodes522 and the associated ones of thesecond capacitor electrodes524.

InFIG. 5a, a user'sfinger534 lightly touches thefirst carrier film516. The force exerted is not sufficient to cause significant bending of thefirst carrier film516 in the region of a key. The position of the user'sfinger534 is detected by determining, for each one of thefirst capacitor electrodes522, the quantity indicative of capacitive coupling between thiselectrode522 and ground. As in the previous example, the position may e.g. be computed as the centroid of the positions of thefirst capacitor electrodes522, weighed with the corresponding quantity indicative of capacitance. The first mode of operation is suitable, for instance, when the user controls a cursor (e.g. on the display of an appliance) with thetouchpad512.

InFIG. 5b, the user presses on thefirst carrier film516, so that the underlying spacer521 is compressed, whereby the distance between a pair of first and

second capacitor electrodes

522,524 decreases. This causes the capacitance between these capacitor electrodes to go up, which can be detected in the second mode of operation of thetouchpad512. The second mode of operation is, therefore, associated to actuation of a key of thetouchpad512, e.g. by a user'sfinger534 or a stylus.

Operation of thetouchpad512 is similar to the previous example: the first and second modes of operation are carried out in alternance, i.e. thetouchpad512 is switched, more or less periodically, from the first mode of operation to the second mode and inversely. In the second mode of operation, it is considered advantageous if the quantity indicative of capacitance between a first and a

second capacitor electrode

522,524 is determined only with respect to that key or those keys in the neighborhood of which the position of the user'sfinger534 has been detected when thetouchpad512 operated in the first mode of operation.

FIGS. 6aand6billustrate that it is also possible to combine the embodiments of the preceding examples within a single touchpad. Thetouchpad612 comprises a first carrier film616, asecond carrier film618 and afirst spacer620, sandwiched between the first andsecond carrier films616,618 so as to keep them spaced apart. Thespacer620 has a matrix-like arrangement ofopenings614 therein, which define keys of thetouchpad612. To each key is associated a pair of afirst capacitor electrode622 and asecond capacitor electrode624 arranged on the first andsecond carrier films616,618, respectively. Eachfirst capacitor electrode622 is arranged opposite its second-capacitor-electrode counterpart624, with respect to the associatedopening614 of thespacer620. Some of the openings (middle keys inFIGS. 6aand6b) inspacer620 are filled with electrically insulating,compressible foam material621, e.g. polyurethane foam or the like. Thespacer620 is made, in this example, from a flexible material, which has substantially lower compressibility than thefoam material621. The haptic properties of keys withfoam material621 differ from those without the foam material. Similarly, their capacitance as a function of pressure behaves differently. Nevertheless, operation oftouchpad621 is analogous to operation of

touchpads

412 and512.

FIGS. 7a-7cshow atouchpad712 with keypad functionality, in which the keys are arranged along a straight line (a curve would also be feasible).FIG. 7ashows the layout of the keys,FIGS. 7band7cshow cross-sectional views of thetouchpad712. Thetouchpad712 comprises a laminated structure of afirst carrier film716, asecond carrier film718 and aspacer720, sandwiched between the first and second carrier films so as to keep them spaced apart. Thespacer720 hasopenings714 therein, which are arranged along a line and which define the keys of thetouchpad712. To each key is associated afirst capacitor electrode722 arranged on thefirst carrier film716. A commonsecond capacitor electrode724 extends over all the keys of thetouchpad712. Thetouchpad712 further comprises a control circuit (not shown), which determines, in a first mode of operation, a quantity indicative of capacitance between individual ones of thefirst capacitor electrodes722 and ground and, in a second mode of operation, a quantity indicative of a capacitance between individual ones of thefirst capacitor electrodes722 and the commonsecond capacitor electrode724.

InFIG. 7b, a user'sfinger734 lightly touches thefirst carrier film716. The force exerted is not sufficient to cause significant bending of thefirst carrier film716 in the region of a key. The position of the user'sfinger734 is detected by determining, for each one of thefirst capacitor electrodes722, the quantity indicative of capacitive coupling between thiselectrode722 and ground. The position may e.g. be computed as the centroid of the positions of thefirst capacitor electrodes722, weighed with the corresponding quantity indicative of capacitance. The first mode of operation is suitable, for instance, when the user controls a cursor (e.g. on the display of an appliance) with thetouchpad712.

InFIG. 7c, the user presses down thefirst carrier film716, so that it bends into anopening714 of thespacer720 and the distance between the correspondingfirst electrode722 and thesecond capacitor electrode724 decreases. This causes the capacitance between these capacitor electrodes to go up, which can be detected in the second mode of operation of thetouchpad712. The second mode of operation is, therefore, associated to actuation of a key of thetouchpad712, e.g. by a user'sfinger734 or a stylus.

In operation, the first and second modes of operation are carried out in alternance, i.e. thetouchpad712 is switched, more or less periodically, from the first mode of operation to the second mode and inversely. It should be noted that, in the second mode of operation, the touchpad does not need to determine the quantity indicative of capacitance for each key. Indeed, it is considered advantageous if the latter is determined only with respect to that key or those keys in the neighborhood of which the position of the user'sfinger734 has been detected when thetouchpad712 operated in the first mode of operation.

FIGS. 8a-8cshow possible layouts of aslider812,FIGS. 8dand8eshow cross-sectional views thereof. Theslider812 comprises a laminated structure of afirst carrier film816, asecond carrier film818 and aspacer820, sandwiched between the first and second carrier films so as to keep them spaced apart. Thespacer820 has anopening814 therein, which extends, in this case, along a straight line (a curvilinear course is possible, seeFIGS. 9a-9d). Theopening814 defines the active zone of theslider812. Thefirst carrier film816 has first capacitor electrodes arranged thereon in the active zone, the second carrier film has a commonsecond capacitor electrode824 applied thereon in the active zone. Thefirst capacitor electrodes822 are arranged in facing relationship to thesecond capacitor electrode824. The second capacitor electrode has athin dielectric layer826 arranged thereon, which prevents short-circuits between thefirst capacitor electrodes822 and thesecond capacitor electrode824, if they are brought closer to one another by a compressive force acting on theslider812.

InFIG. 8d, a user'sfinger834 lightly touches thefirst carrier film816. The force exerted is not sufficient to cause significant bending of thefirst carrier film816 in the region of the active zone. InFIG. 8e, however, the user presses down thefirst carrier film816, so that it locally bends into theopening814 of thespacer820 and the distance between thefirst electrodes822 and thesecond capacitor electrode824 decreases at the point where the force is applied.

In the sliders ofFIGS. 8aand8b, thefirst capacitor electrodes822 are separately connected to a control circuit (not shown). Accordingly, these sliders are able to detect the position of the user's finger834 (in the first and the second mode of operation). In the first mode of operation, the control circuit determines, for each one of thefirst capacitor electrodes822, the quantity indicative of capacitive coupling between thiselectrode822 and ground. The said position may e.g. be computed as the centroid of the positions of thefirst capacitor electrodes822, weighed with the corresponding quantity indicative of capacitance. In the second mode of operation, a quantity indicative of a capacitance between single ones of thefirst capacitor electrodes822 and the commonsecond capacitor electrode824 can be detected. As can be seen, operation of theslider812 as shown inFIGS. 8aand8bis similar to operation of thekeypad712.

Given the reduced number of external connectors, the slider ofFIG. 8cis particularly interesting if the absolute position needs not to be known, e.g. for navigating though list-based menus (scrolling through a list of items displayed and selecting an item to enter a sub-menu or start a certain function). The action of selecting an item from the list can e.g. take place when the user presses on the slider with a force that causes the quantity indicative of capacitance between the first and second capacitor electrodes to exceed the predetermined threshold.

FIGS. 9a-9dshowcircular sliders912. The sliders ofFIGS. 9aand9bare configured for detecting position (sliders with keypad functionality); those ofFIGS. 9cand9dare analogous to the linear slider ofFIG. 8c.

FIGS. 10a-10cshow schematic top views,FIG. 10da schematic cross-sectional view of variants of an alternative embodiment of atouchpad1012. Thetouchpad1012 has a plurality of firstelongated capacitor electrodes1022 applied on thefirst carrier film1016 and a plurality of secondelongated capacitor electrodes1024 applied on thesecond carrier films1018. Thefirst capacitor electrodes1022 are arranged opposite the second capacitor electrodes with respect to anopening1014 inspacer1020, which is sandwiched between the

carrier films

1016,1018. Thefirst capacitor electrodes1022 extend crosswise to thesecond capacitor electrodes1024. In the shown embodiment, the angle between any one of the first capacitor electrodes and any one of the second capacitor electrodes is 90°; it should, however, be noted that this angle could also be different from 90°, e.g. between 30° and 90°. Thesecond capacitor electrodes1024 are covered with a thin dielectric layer, which prevent a short-circuit when the first and

second capacitor electrodes

1022,1024 are brought closer together at the location where a compressive force acts on thetouchpad1012. Thetouchpad1012 is connected to control circuit (not shown), which determines, while in the first mode of operation, a quantity indicative of capacitance between individual ones of thefirst capacitor electrodes1022 and ground and, while in the second mode of operation, a quantity indicative of a capacitance between individual ones of thefirst capacitor electrodes1022 and individual ones of thesecond capacitor electrodes1024.

In the touchpads ofFIGS. 10aand10b, the

capacitor electrodes

1022 and1024 are separately connected to a control circuit (not shown). Accordingly, these touchpads are able to detect the position of the user's finger1034 (with respect to one dimension in the first mode of operation and with respect to two dimensions in the second mode of operation). In the first mode of operation, the control circuit determines, for each one of thefirst capacitor electrodes1022, the quantity indicative of capacitive coupling between thiselectrode1022 and ground. The position may e.g. be computed as the centroid of the positions of thefirst capacitor electrodes1022, weighed with the corresponding quantity indicative of capacitance. It should be noted that in first mode of operation, the position of the user'sfinger1034 is detected in the direction perpendicular to the direction along which the first capacitor electrodes extend. In the second mode of operation, the control circuit determines, for each one of thefirst capacitor electrodes1022, the quantity indicative of capacitance between thiselectrode1022 and each one of thesecond capacitor electrodes1024. The position of the user's finger (the point of application of the force) is obtained from those first and second electrodes, which show maximum capacitive coupling.

InFIG. 10c, the first and the

second capacitor electrodes

FIGS. 11aand11bshow yet another alternative embodiment of an input device including a proximity and pressure sensor1112. The capacitive proximity and pressure sensor1112 comprises a first carrier layer in the form of a substantiallyrigid cover1116 and a second carrier layer in the form of asubstrate1118. Therigid cover1116 includes a plurality of component layers, such as a protective hard plastic1116a, a double-sided adhesive1116band a flexible thermoplastic film1116c. Apivot1123 is sandwiched between the first and second carrier layers1116,1118. The capacitive proximity and pressure sensor1112 comprises electrode pairs diametrically opposed with respect to thepivot1123. Each electrode pair comprises afirst capacitor electrode1122 arranged on the first carrier layer1116 (on the side directed towards the second carrier layer1118) and asecond capacitor electrode1124 on the second carrier layer1118 (on the side directed towards the first carrier layer1116). The first and

second capacitor electrodes

1122,1124 are formed from conductive material (e.g. silver ink) applied directly on the first and second carrier layers, respectively. Aspacer1121 made of electrically insulating foam material is arranged between the first and second capacitor electrodes of a pair.

The first and

second capacitor electrodes

1122,1124 are connected to a control circuit (not shown). The control circuit determines, while in the first mode of operation, a quantity indicative of a capacitance between the first capacitor electrodes and ground and, while in the second mode of operation, a quantity indicative of a capacitance between the first capacitor electrode and the second capacitor electrode of each pair.

The first mode of operation is associated to sensing the proximity of an object to be sensed, e.g. of a user'sfinger1134. In the first mode of operation the control circuit keeps the first and second electrodes essentially at the same electric potential so that the electric field substantially cancels between the first and second electrodes. Thesecond electrodes1124 thus act as driven shields for the respectivefirst electrodes1122 and the sensitivity of the latter is directed away from the respectivesecond electrode1124. If an oscillating voltage is applied to the first capacitor electrode, an oscillating electric field to ground is built up. The object to be sensed modifies the capacitance between the first capacitor electrode and ground, which is sensed by the control circuit1128.

The second mode of operation is associated with sensing pressure exerted on the sensor by some kind of actuator, such as e.g. the user'sfinger1134 or stylus. In the second mode of operation, the control circuit essentially determines the capacitance of the capacitor formed by the first and the

second capacitor electrodes

1122,1124. In the embodiment ofFIGS. 11aand11b, pressure exerted on the proximity and pressure sensor1112 by the user causes the first carrier layer to tilt, whereby the first and second capacitor electrodes of a first pair get closer together (right-hand side inFIG. 11b) and those of a second pair are moved away from one another (left-hand side inFIG. 11b). When the user stops pressing on the sensor, thefoam spacers1121 bring the first carrier layer back into the neutral position.