EP2997455A1

EP2997455A1 - Capacitive control interface device and method adapted for the implementation of highly resistive measurement electrodes

Info

Publication number: EP2997455A1
Application number: EP14721224.5A
Authority: EP
Inventors: Didier Roziere
Original assignee: Fogale Nanotech SA
Current assignee: Quickstep Technologies LLC
Priority date: 2013-05-17
Filing date: 2014-04-09
Publication date: 2016-03-23
Also published as: WO2014183932A1; CN105531656A; FR3005763A1; US20160188038A1; CN105531656B; US9983746B2; FR3005763B1

Abstract

The present invention relates to an interface device for controlling actions of at least one object of interest, comprising (i) a detection surface (4) provided with a plurality of capacitive‑measurement electrodes (5), (ii) electronic and processing means comprising excitation means able to polarize said measurement electrodes (5) to an alternating electrical excitation potential, and measurement means able to measure a capacitive coupling between at least one measurement electrode (5) and at least one object of interest, (iii) guard elements (6) made of an electrically conducting material which are polarized to an alternating electrical guard potential substantially identical to said electrical excitation potential, (iv) electrical linking tracks (7) disposed at least in part on said detection surface (4), in which device the excitation means are arranged in such a way as to generate an electrical excitation potential with an excitation frequency low enough for the measurement electrodes (5) coupled capacitively to at least one object of interest and their linking track (7) to have an electrical impedance at said excitation frequency whose resistive part is much lower than the modulus of the reactive part. The invention also relates to an apparatus and a method implemented in this device or this apparatus.

Description

"Device and method of capacitive control interface adapted to the implementation of highly resistive measurement electrodes"

Technical area

The present invention relates to a capacitive control interface device adapted to the implementation of measurement electrodes with highly resistive connection tracks. It also relates to an apparatus with a control interface comprising such a device, and a method implemented in this device or this apparatus.

The field of the invention is more particularly but not limited to that of touch and / or gesture control interfaces, in particular for smartphones, tablets or touch screens.

State of the art

Touch and / or gesture control interfaces (that is to say, able to determine the presence of control objects in their contactless neighborhood) are frequently used in particular in smartphones, tablets and touch screens. They are then transparent and superimposed on the display screen.

Many of these interfaces use capacitive technologies.

The touch surface is equipped with conductive electrodes connected to electronic means which make it possible to measure the variation of the capacitances appearing between electrodes and objects to be detected (such as fingers) in order to carry out a command.

Capacitive techniques commonly implemented in touch interfaces most often use two layers of conductive electrodes in the form of rows and columns. Electronics measure the coupling capabilities that exist between these lines and columns. When a finger is very close to the active surface, the coupling capabilities near the finger are modified and the electronics can thus locate the position in 2D (XY), in the plane of the active surface.

These techniques are often called "mutual capacitance". They make it possible to detect the presence and the position of the finger through a dielectric of small thickness. They have the advantage of allowing a very good resolution in the localization in the plane (XY) of the surface sensitive one or more fingers. They also allow, with appropriate processing software, to manage a large number of fingers if the surface of the interface is large enough.

Techniques are also known that make it possible to measure the absolute capacitance that appears between electrodes and an object to be detected. These techniques are also called "self capacitance".

The electrodes can also be in the form of lines and columns as the techniques of the "mutual capacitance" type.

There are also so-called matrix electrode structures with individual electrodes, often of rectangular shape, distributed over the entire tactile surface.

For example, FR2949007 from Rozière discloses a capacitive proximity sensor comprising a plurality of independent electrodes, which makes it possible to measure the capacitance and the distance between the electrodes and one or more objects in the vicinity.

The implemented technology uses a guard to eliminate any stray capacitance. All the electrodes are at the same potential and there is thus no coupling capacity between the electrodes likely to degrade the measurement of the capacitance.

This technology is well suited to the realization of capacitive control interfaces in the form of pads or small transparent tactile and gestural (3D) panels, such as laptop touchpad or screens for smartphones.

These techniques generally use an excitation signal (on the transmitting lines or columns for the "mutual capacitance" type techniques and on all the electrodes for the "self capacitance" type techniques) whose frequency is relatively high.

Indeed the measurement of the ability to detect is generally performed with a voltage capacitance converter using charge transfer circuits with capacitive switching or charge amplifiers. The analog measurement signal thus obtained, which is at the frequency of the excitation signal, is then demodulated and digitally processed.

The demodulation and digital processing solutions used in these systems generally require processing a large number of periods the analog measurement signal to obtain a measure of usable capacity. In practice, at least ten periods of the excitation signal are used to obtain a capacity measurement.

The use of a high frequency also makes it possible to process a large number of electrodes or measurement points sequentially.

For example, to obtain a measurement rate of 100 frames per second over the entire interface which comprises 100 electrodes (or in other words to measure 100 times per second 100 electrodes), using a dozen periods of the signal to obtain each capacitance measurement, an excitation frequency of at least 100 KHz is required.

Another advantage of using a frequency of the order of 100 KHz is that it makes it possible to work in a frequency window relatively remote from the most common electromagnetic disturbances, including in particular the 50-60 Hz of the sector and the frequencies of the order of magnitude. 1 M Hz and beyond digital and radio circuits.

Finally, the capacitive impedances (1 / coC) obtained at these frequencies are relatively low and therefore easier to process.

So, in practice, the excitation frequencies commonly used are between 50 KHz and 500 KHz.

A constraint of transparent matrix electrode structures is that they require the presence on the touch surface of connecting tracks that connect each individual electrode to the electronics. Indeed, the technologies used to make transparent capacitive slabs do not allow the use of multilayer solutions with metallized holes as for printed circuits, where the connecting tracks can be buried under the electrodes.

The connecting tracks and the transparent electrodes are generally made with ΙΊΤΟ (indium-tin oxide). This material is relatively resistive (100 to 200 ohm / square), and it is necessary to make wide tracks to limit the total electrical resistance of these tracks. This constraint is well known to manufacturers of transparent touch panels. It is easily compatible with electrode solutions in the form of lines and columns. Indeed, these lines and these columns are generally a width of several millimeters, which allows to obtain a total resistance less than about 10 kohm for slabs up to 10 inches (250 mm) diagonally.

The presence of bonding paths on the surface which supports a matrix structure of transparent electrodes used to make measurements in "self capacitance" mode has the disadvantage of greatly degrading the quality of the detection, in particular of several fingers. Indeed, these tracks create parasitic electrodes insofar as they are sensitive to the presence of an object in the same way as the electrodes to which they are connected. And this effect is all the more important as the connection tracks are wide.

One possible solution is to greatly reduce the width of these tracks in order to make their surface as negligible as possible relative to the individual electrodes. But in this case their resistance increases sharply, which requires to limit the length to maintain a total resistance compatible with the known detection electronics. Thus, in practice, this technique is limited to transparent panels with a maximum size of the order of 4 inches (100 mm).

An object of the present invention is to provide a capacitive control interface device and method which is less sensitive than the devices and methods of the prior art to the resistivity of elements such as electrodes, link tracks and the guard elements, and which is able to perform precise measurements even with highly resistive elements.

Another object of the present invention is to provide a device and a method of capacitive control interface that allow the implementation of matrix structures of transparent electrodes on large panels.

Another object of the present invention is to provide a device and a capacitive control interface method that allow the implementation of matrix structures of transparent electrodes with connection tracks on the same layer as the transparent electrodes, and arranged so that the detection of control objects is not disturbed by the presence of these link tracks.

Presentation of the invention This objective is achieved with an interface device for controlling actions of at least one object of interest that is capacitively detectable in a measurement zone, comprising:

a detection surface provided with a plurality of capacitive measuring electrodes,

electronic and processing means, comprising excitation means capable of biasing said measuring electrodes to an alternating electric excitation potential, and measuring means able to measure a capacitive coupling between said measurement electrodes and at least one object of interest,

guard elements made of electrically conductive material disposed in proximity to said measuring electrodes at least in their opposite face to the measurement zone and biased to an alternating electrical reserve potential substantially identical to said electric excitation potential,

electrical connection tracks arranged at least in part on said detection surface between measuring electrodes and arranged in such a way as to connect said measurement electrodes to said electronic and processing means,

characterized in that the excitation means are arranged so as to generate an electric excitation potential with a sufficiently low excitation frequency for measuring electrodes capacitively coupled to at least one object of interest and their tracking track. link have an electrical impedance at said excitation frequency whose resistive portion is much lower than the module of the reactive part.

This electrical impedance is the complex impedance Z of an electrode and its associated track such as "seen" for example by the electronic and processing means. It comprises a resistive part R which is essentially due to the electrical resistance of the elements such as the connecting track and the electrode. It also comprises a reactive portion l / jcoC _T which depends on the excitation frequency f (co = 2nf) and the equivalent capacitance C _T. This equivalent capacitance C _T represents the capacitive couplings between the electrode and its connecting track, and, on the one hand, the object of interest (capacitance of interest C _x ), and on the other hand, the environment and the guard (parasitic capacitance C _P) . j is the imaginary unit. It should be noted that the parasitic capacitance C _P due to the coupling of the measuring electrode with the guard elements located in the vicinity is necessarily of a relatively large value, and therefore not negligible.

Advantageously, according to the invention, the excitation frequency f is chosen such that the resistive portion R of the complex impedance Z is much smaller than the 1 / coC _T module of the reactive part.

This excitation frequency f may in particular be chosen such that:

the resistive part R does not introduce significant measurement error, in the context of the measurement, when it is not taken into account in the calculation of the equivalent capacitance C _T from the impedance Z complex;

the resistive portion R is negligible, in the context of the measurement, with respect to the l / coC _T module of the reactive part;

the resistive portion R is less than 1/2, respectively 1/5 or 1/10 of the value of the l / coC _T module of the reactive part.

The range of equivalent capacities C _T to be taken into account for the evaluation of the preceding criteria may correspond in particular to:

at capacities less than or equal to the maximum possible coupling capacity between a predetermined control object such as a finger or a stylet and a measuring electrode;

to the range of capacitances that can be generated by the capacitive coupling between a measurement electrode and a predetermined control object (such as a finger or a stylet) which evolves in a predetermined measurement zone (for example between 0 and 10 cm from the electrode, or 0 and 5 cm from the electrode, or 0 and 2 cm from the electrode);

at capacities less than or equal to the coupling capacitance between a measuring electrode and the guard.

According to embodiments, the excitation frequency can be chosen so as to be:

- equal to or less than 20 KHz;

- equal to or less than 10 KHz;

- equal to or less than 4 KHz;

- equal to or less than 3.5 KHz;

- between 4 and 10 KHz;

- between 3 and 20 KHz. The excitation frequency may in particular be less than or equal to at least one of the following values: 20 Khz, 4 Khz.

According to embodiments, the device according to the invention can comprise:

switching means capable of selectively connecting the measuring electrodes to the measuring means;

measurement electrodes and substantially transparent connection tracks;

- measuring electrodes and ITO connection tracks;

connecting tracks disposed on the detection surface in such a way as to electrically connect the measurement electrodes to connection means disposed at the periphery of said detection surface;

measuring electrodes distributed on the detection surface in a matrix arrangement, and connecting tracks arranged in such a way as to individually connect each measurement electrode to the connection means;

connecting tracks whose part on the detection surface has a width that is sufficiently narrow so that the surface of said connection tracks on said detection surface is negligible in front of the surface of the measurement electrodes;

connecting tracks whose part on the detection surface has a width of less than 100 μm.

According to embodiments, the device according to the invention may comprise measuring electrodes distributed in a row and column arrangement. These electrodes can be made in two superimposed layers of material, or consist of patches made in a layer of material and interconnected by bridge connections so as to form lines and columns.

Advantageously, the device according to the invention allows the realization of panels or measuring surfaces, in particular transparent, in a simple and inexpensive way, and which allow precise measurements. Indeed :

the electrodes and the connecting tracks can be deposited on the same surface in a single layer of conductive material (for example ITO), which makes it possible to minimize the production costs; the connection tracks can be made with a width that is sufficiently narrow so that they do not influence the detection of an object of interest significantly. This influence is geometric in nature: it depends on the width of the connecting track on the detection surface, which determines the surface of the track and therefore the coupling capacity that can appear between an object of interest and this connection track . As this capacitive coupling is assigned to the electrode to which the track is connected, it introduces an error in the location in the plane of the control surface of the object of interest. And therefore this geometric error can be minimized with the device according to the invention;

- Narrow link tracks are highly resistive, but as explained above, the device according to the invention is able to perform accurate capacity measurements including under these conditions.

It should be noted moreover that the device according to the invention can be designed so as to optimize overall measurement characteristics:

the track width on the measurement surface can be chosen such that the location errors due to the capacitive couplings between the object of interest and the connection tracks are negligible or at least acceptable;

the excitation frequency f can then be chosen as explained above as a function of the value of the resistive portion R which is determined by the selected track widths and their resistivity.

According to embodiments, the device according to the invention may comprise measurement means at least partly referenced to the electrical excitation potential.

In another aspect, there is provided a method for controlling actions of at least one object of interest that is capacitively detectable in a measurement zone, implementing:

electronic and processing means comprising excitation means and measuring means,

guard elements made of electrically conductive material disposed in proximity to said measuring electrodes at least along their face opposite to the measurement zone, and electrical connection tracks arranged at least in part on said detection surface between measuring electrodes and arranged in such a way as to connect said measurement electrodes to said electronic and processing means,

which method comprises steps:

biasing said measurement electrodes to an alternating excitation electric potential,

polarization of the guard elements to an alternating electrical reserve potential substantially identical to said electrical excitation potential; measurement of a capacitive coupling between at least one measuring electrode and at least one object of interest;

which method further comprises a step of generating an electric excitation potential with a sufficiently low excitation frequency so that measuring electrodes capacitively coupled to at least one object of interest and their connecting track have an electrical impedance at said excitation frequency whose resistive portion is much smaller than the modulus of the reactive part.

Capacitive coupling measurement can include steps:

- acquisition of a measurement signal at the frequency of the electric excitation potential representative of the electric charge of at least one measuring electrode,

digitizing said measurement signal, and

- analysis of its temporal form to determine its amplitude.

In yet another aspect, there is provided an apparatus comprising an interface device according to the invention.

This apparatus may comprise a display screen and a detection surface provided with a plurality of transparent capacitive measuring electrodes superimposed on said display screen.

According to embodiments, this device can be of one of the following types: smartphone, tablet, touch screen.

Description of the Figures and Embodiments

Other advantages and particularities of the invention will appear on reading the detailed description of implementations and non-limiting embodiments, and the following appended drawings: FIG. 1 illustrates a transverse view of a measurement interface implemented in an interface device according to the invention,

FIG. 2 illustrates a front view of a measurement interface implemented in an interface device according to the invention,

FIG. 3 shows a block diagram of a capacitive detection electronics implemented in an interface device according to the invention,

FIG. 4 shows an electronic diagram equivalent to that of FIG. 3 which takes into account the resistivity of the connecting tracks and the resulting leakage capacities,

FIG. 5 shows an electronic diagram equivalent to that of FIG. 3 which takes into account the resistivity of the connecting tracks and the guard elements, and the resulting leakage capacities.

A nonlimiting example of an embodiment of a control interface according to the invention will be described.

Such a control interface is particularly suitable for producing tactile and contactless control interfaces, or human-machine interfaces, for systems or devices such as mobile phones (smartphones), tablets, computers or computers. control slabs.

With reference to FIG. 1 and in FIG. 2, the control interface 2 comprises a detection surface 4 provided with capacitive measuring electrodes 5.

These measurement electrodes 5 are distributed for example in a matrix arrangement on the detection surface 4, as shown in FIG. 2.

The measuring electrodes 5 are made of a substantially transparent conductive material, such as, for example, ΙΊΤΟ (indium tin oxide) deposited on a dielectric material (glass or polymer). They can be superimposed on a display screen, for example TFT (thin film transistor) or OLED (organic light-emitting diodes) type.

The measurement electrodes 5 can detect the presence and / or the distance of at least one object of interest 1, which is also a control object 1, in a measurement zone. Preferably, the measurement electrodes 5 and their associated electronics are configured so as to allow the simultaneous detection of several objects 1. The position of the object 1 or objects 1 in the plane of the detection surface 4 is determined from the position (on this detection surface 4) of the measurement electrodes 5 which detect the objects 1.

The distance 3, or at least one piece of information representative of the distance 3, between the objects 1 and the detection surface is determined from measurements of the capacitive coupling between the electrodes 5 and the objects 1.

One or more guard electrodes 6 are positioned according to the rear face of the measurement electrodes 5, relative to the detection zone of the objects 1. They are also made of a substantially transparent conductive material, such as, for example, ΙΊΤΟ (oxide of indium-tin), and are separated from the measuring electrodes 5 by a layer of dielectric material.

With reference to FIG. 3, the measuring electrodes 5 are connected to capacitive measurement electronic means 17.

Advantageously, this connection is made in particular by substantially transparent connection tracks 7 which are arranged on the detection surface 4 between the electrodes 5. These connecting tracks 7 are made of the same material as the electrodes 5, for example ΙΊΤΟ (indium tin oxide). The connecting tracks 7 and the electrodes 5 can be deposited simultaneously, in one or the same layers.

The connecting tracks 7 are connected to connection means 8 located at the periphery of the detection zone 4, outside the transparent useful zone. These connection means 8 are in turn connected to the capacitive measurement electronic means 17.

The capacitive measurement electronic means 17, in the embodiment of FIG. 3, are in the form of a floating bridge capacitive measuring system as described for example in the document FR 2 949 007 Rozière.

The detection circuit comprises a so-called floating portion 16 whose reference potential 11, called guarding potential 11, oscillates with respect to the ground 13 of the overall system, or to the ground. The potential difference between the guard potential 11 and the ground 13 is generated by an excitation source, or an oscillator 14.

The guard electrodes 6 are connected to the guard potential 11. The floating part 16 comprises the sensitive part of the capacitive detection, in particular a charge amplifier. It can of course include other means of processing and conditioning the signal, including digital or microprocessor-based, also referenced to the potential of guard 11.

The electrical supply of the floating part 16 is provided by floating supply transfer means 15, comprising, for example, DC / DC converters.

This capacitive measuring system makes it possible to measure capacitance information between at least one measuring electrode 5 and a control object 1.

The control object 1 must be connected to a potential d ifferent of the guarding potential 11, such as, for example, the ground potential 13. This is the case when the control object 1 is a finger of a user whose body defines a mass, or an object (such as a stylus) manipulated by that user.

The device according to the invention may furthermore include analog switches or switches 10, controlled by electronic control means. These switches 10 make it possible to selectively select measurement electrodes 5 and connect them to the capacitive detection electronics 17 to measure the coupling capacitance with the object 1. The switches 10 are configured in such a way that a measuring electrode 5 is connected either to the capacitive detection electronics 17 or to the guard potential 11.

The switches 10 thus make it possible to selectively interrogate all the measurement electrodes 5 to obtain an image of capacitive coupling between one or more control objects 1 and the measurement electrodes 5.

Different configurations are possible within the scope of the invention:

the capacitive detection electronics 17 may comprise as many parallel detection channels, each with its charge amplifier, as there are measuring electrodes 5 to be interrogated. In this case, the device does not necessarily include switches 10;

the capacitive detection electronics 17 may comprise a plurality of detection channels in parallel with each of its charge amplifiers, and the switches may be configured in such a way that each channel of detection can sequentially interrogate a plurality of measuring electrodes 5;

the capacitive detection electronics 17 may comprise only one detection channel, and switches 10 configured so as to be able to interrogate sequentially all the measurement electrodes 5. This is the configuration illustrated in FIG. 3;

Preferably, the sensitive part of the detection is protected by a guard shield 12 connected to the guard potential 11.

The active measuring electrodes 5, ie those which are connected (directly or by a switch 10) to the capacitive detection electronics 17 to carry out measurements, are at the holding potential 11. These measuring electrodes 5 active are surrounded by guard planes formed by guard electrodes 6 connected to the guard potential 11, and optionally by inactive measuring electrodes 5, that is to say connected by a switch 10 to the guard potential 11 .

This avoids the appearance of parasitic capacitances between these active measuring electrodes 5 and their environment, so that only their capacitive coupling with the object of interest 1 is measured with maximum sensitivity.

The floating electronics 16 is connected at the output to the electronics of the system 18 referenced to ground by electrical connections compatible with the difference of reference potentials. These links may comprise, for example, differential amplifiers or optocouplers.

With reference to FIG. 4, the charge amplifier 16 as implemented in the diagram of FIG. 3 makes it possible to convert the capacitance C _x created between an electrode 5 and the control object 1 into voltage.

An advantage of this technique is that when the resistance R of the connecting track 6 is negligible, the measurement of the capacitance C _x is very little dependent on the value of the frequency f of the excitation signal generated by the excitation source. 14. Indeed, in this case the signal V _s at the output of the charge amplifier is:

V _s = V (Cx / C _B ). (Eq. 1)

V is the amplitude of the excitation signal generated by the excitation source

14, and C _B is the feedback capacitance of the charge amplifier 16. When the resistor R is no longer negligible, the signal V _s at the output of the charge amplifier then becomes:

V _s = V (C _x / C _B ) (1 / (1 + j R (C _x + C _P ) co)). (Eq 2)

C _P is the parasitic capacitance created between the guard 11 and the measuring electrode 5 with the connecting track 7, co = 2nf and j is the imaginary unit.

The resistance R of the connecting tracks 7 is therefore troublesome according to several aspects:

it causes a sensitivity to the parasitic capacitances C _P between the electrode 5 and the guard 11, due to the voltage drop in the resistive link track 7. The guard becomes imperfect;

these parasitic capacitances C _P are unknown and contribute directly to the measurement error of the capacitance of interest C _x . Indeed the measured capacitance is the equivalent capacitance C _T which is affected by the parasitic capacitances C _P (C _T "C _x + C _P );

the contribution of this error is all the more important as the excitation frequency f is high.

This explains why the matrix configuration of measuring electrodes 5 as shown in FIG. 2 is not currently used despite its simplicity for making transparent panels of large size with a high number of electrodes.

Indeed, as previously explained, for the presence of the connection tracks 7 between the measurement electrodes 5 does not interfere with the detection and location of the object of interest 1, it is necessary to reduce their width, for example to less than 100 pm. The resistances of these connection tracks 7 can then easily exceed 100 KOhm when they are made of ITO.

Under these conditions, to obtain a signal V _s at the output of the charge amplifier that is directly representative of C _x , the following condition must be fulfilled:

R ^■ (C _x + C _P ) ^■ ω << 1. (Eq.3)

Advantageously, this condition can be satisfied by choosing an excitation frequency f such that:

f "1 / (2 n R (C _x + C _P )) (Eq.4) In practice, values of equivalent capacity C _T = C _x + C _P of the order of 40 pF are reached. Under these conditions, the excitation frequency f must be less than about 20 KHz.

In pulsed mode, that is to say for example using for example a square excitation signal, we obtain the same order of magnitude of frequency f.

Under these conditions, by way of non-limiting example, it is possible to choose an excitation frequency f less than 10 KHz for the left-hand term of the Eq. 3 has an impact on the capacity measurement C _x less than 10%.

One can also choose for example an excitation frequency f of the order of 3.5 KHz for the left-hand term of the Eq. 3 has an impact on the measurement of capacitance C _x even lower (of the order of 1%).

In practice, the measurement signal V _s is a signal modulated at the excitation frequency f, and it is its modulation amplitude at this excitation frequency f which is representative of the capacitance measurement.

The measurement signal V _s can be demodulated by a synchronous demodulator at the electronics of the system 18 referenced to ground. This procedure, however, has the disadvantage of requiring a large number of periods of the excitation signal to obtain a measurement value.

According to a preferred embodiment, the device according to the invention comprises sampling and digitizing means which make it possible to directly digitize the measurement signal V _s , for example at the electronics of the system 18 referenced to ground. This digitization is all the easier as the excitation frequency f is low. The amplitude of modulation at the excitation frequency f is then directly deduced from an analysis of the temporal shape of one or a few periods of this measurement signal V _s .

Thus, a panel comprising a few hundred measuring electrodes 5 can be "read" several times per second, even with an excitation frequency of less than 10 KHz.

Fig. 5 shows an equivalent diagram of the complete structure of a control interface 2 in the form of a transparent panel 2 superimposed on a display screen.

The guard plane 6, in ITO, has a much lower electrical resistance r than that of the connecting tracks 7 but which is nevertheless significant. Indeed, this electrical resistance r can be of the order of a few tens to a few hundred ohm depending on the nature of ΙΊΤΟ deposited and the size of the screen.

There is then a capacitive coupling C between the guard plane 6 and the part of the device present below (LCD screen, pad chassis ....). As illustrated in FIG. 5, this capacitor C with the guard resistor r creates a capacitive leak "seen" by the electronics despite the presence of the guard plane 6. Indeed, the potential of the guard 6 present under the electrodes 5 drops slightly because of couple (r, C).

This phenomenon can generate a capacitive offset of several tens of femtofarads.

Advantageously, the invention and in particular the implementation of a low excitation frequency also makes it possible to make this capacitive leak negligible.

Of course, the invention is not limited to the examples that have just been described and many adjustments can be made to these examples without departing from the scope of the invention.

Claims

An interface device for controlling actions of at least one object of interest (1) capacitively detectable in a measurement zone, comprising:

a detection surface (4) provided with a plurality of capacitive measuring electrodes (5),

electronic and processing means (17, 18), comprising excitation means (14) capable of biasing said measurement electrodes (5) to an alternating excitation electric potential, and measuring means (16) capable of measuring a capacitive coupling between said measuring electrodes (5) and at least one object of interest (1),

guard elements (6) made of electrically conductive material disposed in proximity to said measurement electrodes (5) at least along their face opposite to the measurement zone, and biased to an alternately identical electric guard potential electrical excitation potential,

electrical connection tracks (7) arranged at least in part on said detection surface (4) between measuring electrodes (5) and arranged in such a way as to connect said measuring electrodes (5) to said electronic and processing means (17, 18),

characterized in that the excitation means (14) are arranged in such a way as to generate an excitation electric potential with a sufficiently low excitation frequency for measuring electrodes (5) capacitively coupled to at least one object. interest (1) and their connecting track (7) have an electrical impedance at said excitation frequency whose resistive portion is much smaller than the module of the reactive part.

The device of claim 1, wherein the excitation frequency is less than or equal to at least one of the following values:

20 Khz, 4 Khz.

3. The device of one of claims 1 or 2, which further comprises switching means (10) capable of selectively connecting the measuring electrodes (5) to the measuring means (16).

4. The device of one of the preceding claims, which comprises measuring electrodes (5) and connecting tracks (7) substantially transparent.

5. The device of claim 4, which comprises measurement electrodes (5) and connection tracks (7) made of ITO.

The device of one of the preceding claims, which comprises connecting tracks (7) arranged on the detection surface (4) so as to electrically connect the measuring electrodes (5) to connection means (8). ) disposed on the periphery of said detection surface (4).

The device of claim 6, which comprises measuring electrodes (5) distributed on the detection surface (4) in a matrix arrangement, and connecting tracks (7) arranged so as to individually connect each measuring (5) to the connection means (8).

8. The device of one of the preceding claims, which comprises connecting tracks (7) whose portion on the detection surface (4) has a width sufficiently narrow for the surface of said connecting tracks (7) on said detection surface (4) is negligible in front of the surface of the measuring electrodes (5).

9. The device of one of the preceding claims, which comprises connecting tracks (7) whose portion on the detection surface (4) has a width less than 100 pm.

10. The device of one of the preceding claims, which comprises measuring means (17) at least partly referenced to the electrical excitation potential.

11. A method for controlling actions of at least one object of interest (1) capacitively detectable in a measurement zone, implementing:

electronic and processing means (17, 18) comprising excitation means (14) and measuring means (16),

guard elements (6) made of electrically conductive material disposed in proximity to said measuring electrodes (5) at least along their face opposite to the measurement zone, and

which method comprises steps:

biasing said measuring electrodes (5) to an alternating excitation electric potential,

biasing the guard elements (6) to an alternating electrical reserve potential substantially identical to said electrical excitation potential; measuring a capacitive coupling between at least one measuring electrode (5) and at least one measuring object; interest (1),

characterized in that it further comprises a step of generating an excitation electric potential with a sufficiently low excitation frequency for measuring electrodes (5) capacitively coupled to at least one object of interest (1). ) and their connecting track (7) have an electrical impedance at said excitation frequency whose resistive portion is much smaller than the modulus of the reactive part.

The method of claim 11, wherein the capacitive coupling measurement comprises steps:

- acquisition of a measurement signal at the frequency of the electric excitation potential representative of the electric charge of at least one measuring electrode (5),

digitizing said measurement signal, and

- analysis of its temporal form to determine its amplitude.

Apparatus comprising an interface device according to one of claims 1 to 10.

Apparatus according to claim 13, comprising a display screen and a detection surface (4) provided with a plurality of transparent capacitive measuring electrodes (5) superimposed on said display screen.

15. Apparatus according to one of claims 13 or 14, of one of the following types: smartphone, tablet, touch screen.