EP2987056A2

EP2987056A2 - Method of multi-zone capacitive sensing, device and apparatus implementing the method

Info

Publication number: EP2987056A2
Application number: EP14724650.8A
Authority: EP
Inventors: Didier Roziere; Eric Legros
Original assignee: Fogale Nanotech SA
Current assignee: Quickstep Technologies LLC
Priority date: 2013-04-15
Filing date: 2014-04-09
Publication date: 2016-02-24
Also published as: CN105452998A; WO2014170180A2; CN105452998B; US10592046B2; KR20150143543A; JP6284623B2; WO2014170180A3; KR101911135B1; JP2016515744A; US20160034102A1; FR3004551A1

Abstract

The present invention concerns a method of capacitive sensing, implementing a plurality of electrodes (5, 7) capable of enabling the detection of objects (1) in the vicinity of same by capacitive coupling, and comprising a step of simultaneously polarising at least one portion of said electrodes (5, 7) with different excitation potentials, said excitation potentials being generated relative to a reference potential such that the scalar product over a predefined period of at least two of these excitation potentials is zero or much lower than the scalar product of one and/or the other of these excitation potentials with same over said predefined period. The invention also concerns a device and an apparatus implementing the method.

Description

"Multizone capacitive detection method, device and apparatus implementing the method"

Technical area

The present invention relates to a multi-zone capacitive sensing method and device. The field of the invention is more particularly but in a nonlimiting manner that of capacitive detection systems and tactile and non-contact human-machine interfaces.

State of the art

Many communication and work devices use tactile or non-contact measurement interfaces as a human-machine interface for entering commands. These interfaces can in particular take the form of pads or touch screens. They are found for example in mobile phones, smartphones, touch screen computers, tablets, pads, PCs, mice, touch panels and giant screens.

These interfaces frequently use capacitive technologies. The measuring 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 the object to be detected in order to carry out a command.

It is possible to make transparent electrodes, which can superimpose an interface on a display screen, for example smartphone.

Most of these interfaces are tactile, that is, they can detect the contact of one or more object (s) of interest or control (such as fingers or a stylus) with the surface of the interface.

More and more gestural or non-contact interfaces are being developed which are able to detect control objects at a greater distance from the interface, without contact with the surface.

The development of contactless interfaces requires the implementation of capacitive measurement techniques of very high sensitivity and offering high immunity to environmental disturbances. Indeed, the capacitance which is created between capacitive electrodes of the interface and control objects is inversely proportional to the distance that separates them.

For example, document FR 2 756 048 by Rozière discloses a capacitive measurement method which makes it possible to measure the capacitance and the distance between a plurality of independent electrodes and an object in the vicinity.

This technique makes it possible to obtain capacitance measurements between the electrodes and the objects with a high resolution and sensitivity, making it possible to detect for example a finger several centimeters or even ten centimeters apart. The detection can be done in the space in three dimensions but also on a surface, called measuring surface.

In general, the control object can be considered to be at a reference electrical potential such as an electrical ground or earth.

In most capacitive sensing techniques, the electrodes are biased to an excitation voltage. Capacitive coupling is thus measured between these polarized electrodes and the object at the reference potential.

In the case of a portable device such as a smartphone or tablet, the electrical circuit comprises a reference potential or an internal mass that is floating relative to the earth, since it is powered by a battery. However, by the interplay of capacitive couplings with its environment (particularly when held in a user's hand), this internal reference potential is brought back to earth or at least to the potential of the user's body. Thus, when another hand approaches the measurement electrodes, it is "seen" as being substantially at the internal reference potential or the device's ground potential.

There is interest in developing portable devices, such as smartphones or tablets, that have sensitive surfaces with measuring electrodes in places other than the display screen. Such devices may for example be equipped with electrodes on the face opposite the screen and / or on the sides, in order to detect additional information on their environment, the manner in which they are held, etc.

The problem which arises in this case is that, because of the floating nature of the on-board electronics with respect to earth, if measurement electrodes biased to an excitation voltage are in electrical contact or strongly coupled (capacitively) with for example the hand of the user holding the device, the entire body of the user is "seen" by the electronics as being substantially at this excitation potential. And in this case the control object which is for example its second hand is also "seen" as being substantially at the excitation potential of the electrodes. The capacitive coupling is then zero or very weak and the object is not detected or only at a short distance.

Capacitive sensing techniques are also used to equip systems such as robots or mobile medical imaging devices (scanners, ...) to make them sensitive to their environment. The principle is the same: the capacitive coupling is measured between polarized capacitive electrodes at an excitation voltage and supposed environmental objects at an electrical reference potential, ground or earth.

When two objects equipped with capacitive electrodes are moving relative to one another, they may not detect each other because if the measuring electrodes are at the same potential there is no capacitive coupling between they. It is also the principle of the guard which is used in most capacitive detection systems: the electrodes are protected from undesired influences of the environment (parasitic capacitances) by disposing conductive surfaces with the same potential of excitement nearby.

An object of the present invention is to propose a capacitive detection method and a device that make it possible to solve these disadvantages of the prior art.

Another object of the present invention is to propose a capacitive detection method and a device which makes it possible to equip electrically floating apparatus with respect to a general mass or earth capacitive detection electrodes able to detect the approach of objects of interest so that the measurements are not or hardly affected by strong electrical couplings of certain electrodes with the mass or the earth.

Another object of the present invention is to propose a capacitive detection method and a device that makes it possible to equip portable devices such as smartphones or capacitive detection electrode tablets on a plurality of faces so that the measurements are not not or little affected by strong electrical couplings of some electrodes with mass or earth.

Another object of the present invention is to propose a capacitive detection method and a device which makes it possible to equip a plurality of capacitive detection electrode devices so that these devices are also able to detect each other mutually.

Presentation of the invention

This objective is achieved with a capacitive detection method, implementing a plurality of electrodes able to allow the detection of objects in their vicinity by capacitive coupling, characterized in that it comprises a step of polarization simultaneously of at least a portion of said electrodes with different excitation potentials, which excitation potentials are generated with respect to a reference potential such that the dot product has a predetermined duration of at least two of these excitation potentials either zero or much less than the dot product of one and / or the other of these excitation potential with itself over said predetermined duration.

The excitation potentials may correspond, for example, to time values of electrical excitation signals referenced to the reference potential, or else to differences in electrical voltage with respect to the reference potential.

Of course, it may be implemented in the context of the invention any number of different excitation potentials. It can be implemented in particular two excitation potentials, or a number greater than two excitation potentials.

According to embodiments, the excitation potentials generated may comprise:

at least one excitation potential that varies over time;

periodic excitation potentials of different frequencies;

at least one excitation potential whose frequency content is dispersed over a spectral band;

two periodic excitation potentials of the same frequency in quadrature phase;

at least one excitation potential whose scalar product with a perturbation signal is minimized; at least one excitation potential substantially equal to the reference potential.

The method according to the invention may further comprise a step of measuring the capacitive coupling of an electrode, comprising:

an acquisition of measurements representative of the electrical charge of the electrode, and

a demodulation of said representative measurements of the charge by using the excitation potential of said electrode.

According to another aspect, there is provided a capacitive detection device, comprising a plurality of electrodes adapted to allow the detection of objects in their vicinity by capacitive coupling, and further comprising excitation means able to polarize simultaneously. at least a portion of said electrodes with different excitation potentials, which excitation potentials are generated with respect to a reference potential such that the dot product has a predetermined duration of at least two of these excitation potentials either zero or much less than the dot product of one and / or the other of these excitation potential with itself over said predetermined time.

The device according to the invention may furthermore comprise:

measurement means referenced to the same excitation potential as the electrodes to which they are connected.

- Demodulation means connected to the measuring means, and able to produce a representative measurement of the capacitive coupling referenced to the reference potential.

According to embodiments, the device according to the invention may further comprise means for polarizing at least one electrode:

- at several different excitation potentials, and / or

at least one excitation potential or the reference potential.

In another aspect, there is provided an apparatus comprising a capacitive detection device, and implementing the method according to the invention.

According to embodiments, the apparatus according to the invention can comprise, according to a first face, a display screen and first substantially transparent electrodes polarized at a first potential. excitation, and in a second face opposite to the first face of the second electrodes biased to a second excitation potential.

The device can be in particular one of the following types: smartphone, tablet.

According to embodiments, the apparatus according to the invention may comprise a plurality of modules able to move relative to each other, each module comprising polarized electrodes at a different excitation potential from the other modules.

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 first mode of implementation of the invention,

FIG. 2 illustrates a second embodiment of the invention, - FIG. 3 illustrates an electronic block diagram for implementing the invention

FIG. 4 illustrates a timing diagram of the acquisition of measurements.

Of course, the modes of implementation of the invention presented as well as the distributions and arrangements of the electrodes described in these embodiments are in no way limiting. They are simply presented as representative examples.

Firstly, with reference to FIG. 1, a first embodiment of the invention.

This mode corresponds for example to the implementation of the invention in an electronic device 2 or a device 2 such as a telephone, a smartphone, a tablet PC, which comprises for example several screens, or a screen and sensitive areas such as buttons, ....

In the example illustrated in FIG. 1, the apparatus 2 which is shown in section is representative of a smartphone or a tablet PC. It comprises a first face with a display screen 4 equipped with first transparent capacitive electrodes 5 distributed (for example in a matrix arrangement) on its surface. These first electrodes 5 and their associated electronics make it possible to detect the position, the distance 3 and / or the contact of a control object 1 on the display screen 4. The control object 1 can be for example a finger of the user. Positions and distances detected are then trad uites in terms of commands by the control software of the human-machine interface of the apparatus 2.

Typically, the apparatus comprises a first guiding surface 6 located behind the first electrodes 5 of the screen, between these electrodes 5 and the other elements of the apparatus 2. This first guard 6 is biased to the same potential The first electrodes 5 are energized electrically so as to avoid parasitic capacitive coupling between the first electrodes 5 and the internal elements of the apparatus 2, such as the electronics 12.

The electrical excitation potential is defined with respect to a reference potential 13 which corresponds to the general mass of the electron 12 of the apparatus 2. It should be noted that in the case of a device When the portable battery is powered, in the absence of a galvanic connection or significant coupling with the earth, this reference potential 13 is floating relative to the earth.

The apparatus 2 also comprises second electrodes 7 distributed

(For example according to a matrix deposition) on a second surface 14 opposite the surface surporting the screen 4. These second electrodes 7 may be transparent electrodes superimposed on a second display screen, or electrodes simply equipping the housing of the device 2.

These second electrodes 7 and their associated electronics make it possible to detect the position, the distance 3 and / or the contact of objects in their environment.

The apparatus 2 further comprises a second conductive guard surface 8 located behind the second electrodes 7 of the screen, between these electrodes 7 and the other elements of the apparatus 2. This second guard 8 is polarized at the same electrical potential of the excitation that the second electrodes 7, so as to avoid spurious capacitive coupling between the second electrodes 7 and internal elements of the device 2, such as the electronic 12.

The apparatus 2 may further comprise third electrodes 10, 11 on the side faces.

When the screen 4 is used (for example), the second face 14 and the side faces are privileged places to hold the device 2 in the hand, or place it on the palm of the hand, or to put it on a table or on the floor. The devices of the prior art which comprise only first electrodes 5 are designed so that when they are held or placed, the general mass of the electronics 12 is coupled (by electrical contact or by capacitive coupling) to the body of the electronics. the user and / or the support. Under these conditions it is possible to ensure that the reference potential 13 corresponds substantially to the potential of the body of the user and / or the earth. A finger or a conductive object held by the user then constitutes a control object 1 substantially at the reference potential 13 and can therefore be detected under the best conditions by the first electrodes 5.

When a device 2 as illustrated in FIG. 1 is placed on a support 9 such as a hand or a table on the side for example of the second electrodes 7, it establishes a strong capacitive coupling between the support 9 and these electrodes 7. It follows that, compared to internal reference potential 13 of the apparatus 2, the support 9 appears as polarized at the excitation potential of the second electrodes 7. According to the same reasoning as above, the control object 1 is "seen" with respect to the reference potential internal 13 of the device 2 as being biased substantially at the same potential as the support 9, that is to say the excitation potential of the second electrodes 7. And if the excitation potential is identical for all electrodes as in the devices of the prior art, the control object 1 no longer generates capacitive coupling with the electrodes and can therefore no longer be detected (or at least only with very degraded performances).

The solution implemented by the invention, which is detailed below, comprises the generation of different and substantially orthogonal excitation potentials in the mathematical sense for the first electrodes 5 and the second electrodes 7.

Regarding the third electrodes 10, 11 on the side faces, different options are possible, especially when the device 2 is a smartphone or tablet. According to a section or a sectional view:

the apparatus 2 may comprise third electrodes 10, 11 distinct respectively to the first and second faces 4, 14, as illustrated in FIG. 1. In this case one of the third electrodes 10 may be at the excitation potential of the first electrodes 5, and one of the third electrodes 11 may be at the excitation potential of the second electrodes 7; the apparatus 2 may comprise only a third electrode 10 or 11 which covers at least a part of the lateral face. In this case, this third electrode may be at the excitation potential of the first electrodes 5 or at the excitation potential of the second electrodes 7. It may optionally be switched from one excitation potential to the other depending on information. from the measurements of the first and / or second electrodes. The third electrode 10 or 11 may also be at a different excitation potential from that of the first and second electrodes.

Along the lateral faces, the third electrodes may constitute a ring surrounding the apparatus 2, or comprise a plurality of electrodes distributed on these lateral faces.

We will now describe, with reference to FIG. 2, a second embodiment of the invention.

This mode corresponds for example to the implementation of the invention in modules 21, 22 movable relative to each other and with respect to their environment. This type of configuration can be found for example in robotics or in medical imaging devices with moving parts, such as scanners.

For example, in medical imaging robotics, it may be necessary to implement several modules 21, 22 or more robots 21, 22 that operate near the same patient. Each module 21, 22 has at least one capacitive detection zone 23, 24 with electrodes 5, 7 to avoid collisions and / or to make its movement without collision independent. It is also necessary that the capacitive detection zone 23 of a module 21 can recognize the detection zone 24 of another module 22 as a target object to avoid any risk of collision between these modules.

However, again, if the capacitive electrodes of the respective detection zones 23, 24 of the modules 21, 22 are subjected to the same excitation potential as in the systems of the prior art, there is no capacitive coupling between they can not detect each other.

The solution implemented by the invention, which is detailed below, comprises the generation of different excitation potentials and substantially orthogonal to the mathematical sense for the electrodes of the detection zones of the different modules 21, 22. The measurements of the various modules 21, 22 are managed by the same capacitive measuring device 25.

Of course, the modules 21, 22 of FIG. 2 may also be provided with a plurality of detection zones or multi-face electrodes as shown in FIG. 1. In this case the detection zones can be managed as explained below so as not to disturb each other between zones of the same module and / or different modules.

With reference to FIG. 3, we will now describe a circuit diagram of electronic assembly 12 for the implementation of the invention.

The diagram presented is based on the teaching of the document FR 2756048 which can be referred to for the details of implementation.

The diagram presented comprises a plurality of measurement channels in parallel. Fig. 3 shows an example with two measurement channels.

Each measurement channel allows the control and acquisition of measurements on one or a plurality of electrodes, as well as the generation of a distinct excitation potential for these electrodes.

Of course, the scheme of FIG. 3 can be generalized so as to:

- implement any number of parallel measurement channels;

implementing any number of distinct excitation potentials for different measurement paths;

- Implement measurement channels in parallel with the same excitation potential, so as to allow the acquisition of several measurements simultaneously on polarized electrodes at the same excitation potential.

The diagram for the first measurement channel will now be described in detail, with the numerical references corresponding to the second measurement channel in brackets.

The detection electronics 12 comprises a so-called "floating" portion 32 (33), referenced to the excitation potential 42 (43), and which comprises the first measurement stages as close as possible to the electrodes. The excitation potential 42 (43) is generated by a time-varying voltage source (31) referenced to the reference potential 13 of the electronics 12. The floating electronics 32 (33) essentially comprises a charge amplifier 34 (35) referenced to the excitation potential 42 (43). This charge amplifier 34 (35) is input connected to a measurement electrode (7). It makes it possible to generate a voltage proportional to the charge accumulated in the electrode 5 (7), which depends on the coupling capacitance generated by the objects 1 (9) in the vicinity of the electrode 5 (7).

The floating electronics 32 (33) also includes a multiplexer 44 (45) or a scanner which allows sequential "interrogation" of a plurality of electrodes 5 (7) with a single measurement channel. This multiplexer 44 (45) is designed in such a way as to connect the electrodes 5 (7):

at the input of the charge amplifier 34 (35) to acquire measurements,

or to the reference potential 42 (43), in which case the corresponding electrodes behave like guard electrodes 6 (8), which makes it possible to avoid the appearance of parasitic capacitances with active electrodes connected to the input of the charge amplifier 34 (35).

The output signal of the charge amplifier 34 (35) is referenced to the excitation potential 42 (43). It is converted by a differential amplifier 36 (37) into a signal referenced to the reference potential 13. Of course, the differential amplifier 36 (37) can be replaced by any other component for transferring a signal between electronic stages with different reference potentials.

The measurement signal is then demodulated by a demodulator 38 (39) to produce a measurement 40 (41) representative of the distance or coupling of the electrodes 5 (7) with the object (s) 1 (9). In practice, the demodulator 38 (39) is digital.

This detection principle allows measurements with very high sensitivity and very high precision because all the electronic elements close to the electrodes 5 (7) are referenced and / or polarized at the excitation potential 42 (43). Because of the structure of the charge amplifier 34 (35), the electrodes 5 (7) are also biased at the excitation potential 42 (43). So it can not appear parasitic abilities. In addition, biasing elements at the excitation potential 42 (43), including guard electrodes 6 (8), may be added in the vicinity of the measuring electrodes 5 (7) or their connection tracks to avoid appearance of parasitic capacitances with nearby elements subject to another potential.

The electronics of FIG. 3 can be implemented in the device of FIG. 1 such that, for example,

all the electrodes of a face 4, 14 are controlled by the same electronic measuring channel. Thus according to the configurations shown, the first measurement channel controls all the first electrodes 5 of the first face 6, and the second measurement channel controls all the second electrodes 7 of the second face 14;

the electrodes of a face 4, 14 are divided into zones and controlled respectively by several electronic measurement channels. This may improve the accuracy and independence of measurements in different areas;

the lateral electrodes 10, 11 are respectively controlled by a first and a second measurement channel;

the lateral electrodes 10, 11 are optionally connected to a first measurement channel or to a second measurement channel by switching means. The switching can be performed according to information from other electrodes;

the lateral electrodes 10, 11 are controlled by a third electronic measurement channel;

Similarly, the electronics of FIG. 3 can be implemented in the device of FIG. 2 of the kind q ue, for example, all the electrodes of a module 21, 22 are controlled pa r a same electronic measurement channel. Thus, according to the configurations shown, the first measurement channel controls all the first electrodes 5 of the first module 21, and the second measurement channel controls all the second electrodes 7 of the second module 22.

As explained above, an object of the invention is to provide a method that allows the management of a multiplicity of detection zones, some of which may be in strong coupling with the user or the target.

According to a first variant embodiment of the invention, the set of electrodes of one or more detection zones is switched to the reference potential 13 when measurements with electrodes of another zone are acquired. detection. Thus, it is possible to avoid that The detection zones are mutually interfering, either by coupling irect as in the case of FIG. 2, or by coupling with a control object as in the case of FIG. 1.

More specifically, referring to the scheme of FIG. 2, this can be done advantageously by switching to the reference potential 13 u n excitation potential 43 for example. In practice, this can be done in particular by transforming the voltage source 31 into a short circuit, which amounts to extinguishing it or generating zero voltage. Thus, all the elements referenced to this excitation potential 43 are brought back to the reference potential 13, including the guard elements 8.

This first variant of the invention can be implemented in the embodiment of FIG. 1 in the following way:

the excitation potential 43 of the second electrodes 7 is switched to the reference potential 13, so that the second electrodes 7 of the second face 14 are placed at this reference potential 13;

measurements are made with the first electrodes 5. Thus, even if the second electrodes 7 are in strong coupling with the hand of the user 9 which holds the telephone by its second face 14 (for example), it is possible to detect a finger 1 with the first electrodes 5 in the best conditions; the user is "seen" by these electrodes as being at the reference potential 13;

then, in the same manner, the excitation potential 42 of the first electrodes 5 is switched to the reference potential 13 so as to set the first electrodes 5 of the first face 4 to this reference potential 13, or measurements with the second electrodes 7.

Thus, the device can be held and used on both sides, possibly in the same way.

The first variant of the invention can also be implemented in the embodiment of FIG. 2 as follows:

the excitation potential 43 of the second electrodes is switched to the reference potential 13, so that the second electrodes 7 of the second module 22 are put at this reference potential 13;

measurements are made with the first electrodes 5 of the first module 21. Thus, these first electrodes 5 are sensitive of the same so as to the presence of the second module 22, including according to the detection zone 24, that the rest of the environment;

then, in the same way, the excitation potential 42 of the first electrodes 5 is switched to the reference potential 13 in such a way as to set the first electrodes 5 of the first module 21 at this reference potential 13, and then measurements are taken with the second electrodes 7 of the second module 22.

Of course, all the time division multiplexing and scanning strategies of the different detection zones can be implemented within the scope of the invention.

This first variant of the invention, however, has the drawback that the electrodes of the different detection zones must be activated and interrogated sequentially.

We will now present a second variant, corresponding to a preferred implementation mode of the invention, which makes it possible to perform measurements simultaneously in several detection zones while minimizing the risk of interference between these zones.

With reference to FIG. 4, V _el (1) is the (digital) coupling signal obtained at the output 40 of the demodulator 38 of the first channel of the detection electronics, and which provides a measurement representative of the capacitive coupling or the distance between a first measuring electrode 5 and an object of interest 1.

More generally, V _ei (1) is the coupling signal coming from the channel i (i = 1, 2, ...) of the detection electronics.

The coupling signal v _ei (1) is updated with a time period greater than or equal to the accumulation time τ _ε of the measurements in the demodulator 38, as will be seen below. It can correspond for example:

- to a series of measurements acquired with the same first electrode 5, OR

successive measurements acquired with different first polarized electrodes 5 at the same reference potential 42, and switched by the multiplexer 44. U _sl (t) is the analog load measurement signal, referenced to the reference potential 13, which appears at the output of the differential amplifier 36.

More generally, called U _si (t) the load measuring signal of the channel i (i = l, 2, ...) of the detection electronics.

This U load measuring signal _si (t) is the product of the electric charge Q _ei (t) accumulated in the measuring electrode (either the electrode 5 for channel i = 1) with a gain G _ei of 'charge amplification, ie,

U _S i (t) = G Q _ei _ei (t) (Eq. 1) or, in digital form sampled with a time period T _S,

U _if {k) = G _ei Q _ei {k), (Eq.2)

The load measuring signal is demodulated in the demodulator 38 (for channel 1) to obtain the coupling signal V _ei (1). This demodulation is a synchronous amplitude demodulation (baseband transposition and low-pass filtering) in which the excitation signal of the channel concerned is used as local oscillator 30, 31. It is done numerically. It comprises a term-to-term multiplication of the load measurement signal U _if (k) with the excitation signal of the corresponding channel i and a summation of the terms of the product over a storage time duration τ _ε , that is,

V _ei (= Σ £ ô ¹ y «(fc) ½ (fc) (Eq - 3)

With k = 0 ... N _s - 1 and N _s = τ _ε / τ _Σ .

The excitation signal can be written in the general form of a product of an amplitude term and a basic function bi (k which defines its temporal form, ie:

V _i (k) = \ V _i \ b _i (k). (Eq.4)

As explained above, the presence of polarized elements at potentials different from the reference potential 13 may disturb the measurements. These disturbances can be modeled by equivalent capacitances, essentially in parallel, connecting a measurement electrode to the different sources of disturbance voltage.

For example, in the case of FIG. 3, taking into account a source of additional electrical disturbance V _p , the load measured on a first electrode 5 polarized at a first excitation potential V _t (t) in the presence of an object of interest 1 can be expressed as follows:

Q _e iit) = CV ^ t) + C ₁₂ V ₂ {t) + C _{lp p} (t). (Eq.5)

The capacitance C _lt is the capacity to be measured between the electrode 5 and the object of interest 1 assumed at the reference potential 13. The capacitance C ₁₂ is a parasitic capacitance due for example to a partial coupling between the object of interest 1 and second electrodes 7 (and guard electrodes 8) biased to the second excitation potential v ₂ (t). Similarly, the capacitance c _lp is a parasitic capacitance due to couplings with the source of additional electrical perturbation.

The source of additional electrical disturbance V _p may be due for example to a connection of a portable device to a charger.

It can also be a voltage source present at the object of interest 1, for example:

- due to a disturbance related to its operation;

- Voluntarily generated for its operation, in the case for example where the object of interest 1 is an active stylet polarized to its own excitation potential. This exciting potential of the stylus can then be chosen to contribute to measuring or improving the measurement with at least one of the measuring channels, or with several measurement channels sequentially. In this case, it may for example be synchronous with the excitation potential of the electrodes of at least one measurement channel.

The measured load can be rewritten in a factored numerical form, either

Q _el k) = C _el [a _lt V ^ k) + a ₁₂ V ₂ k) + a _lp V _p k)]. (Eq.6)

By combining the Eq. 6 and Eq. 3, the expression of the coupling signal is obtained:

V _el (= G _e i Qi . (Eq.7)

This expression can be rewritten as:

V _ei (= G _ei C _ei {a _il Σ _k V _i (fc) V ₁ (fc)

+ a ₁₂ ΣMk) V ₂ {k)

+ a _ip ΣMk) V _p (k)}. (Eq 8)

Introducing the Eq. 4 in the Eq. 8, the expression of the coupling signal is finally obtained:

+ a ₁₂ \ V _t \ \ ν ₂ \ ΣΜ b ₂ {k)

+ a _ip ΣMk) V _p (k)}. (Eq.9)

This expression can be generalized for any number of ½ excitation potential in the form:

V _ei (= G _ei C _ei {a _u \ V _i \ ² Σ _k b _i ² {k)

+ Σ _{j ≠} i (cx _ij \ V _i \ \ Σ _k b _i (k) b _j (k))

+ aipΣ _k Vi ( _. k) V _p ( _. k)}. (Eq.10)

The first term of the general expression of the coupling signal V _ei (Q, which depends only on the excitation potential i, corresponds to the value that it is desired to measure.

Other terms, which depend on other excitation potentials; or additional perturbation signals are parasitic terms whose influence must be minimized.

To simplify the notations, we can define the scalar product on the vector space of dimension N _s of the basic functions b _t such that:

b _i - b _j = Σ ^N _k L ₀ ¹ b _i (k) b _j (k). (Eq.11)

The standard of a function b _t is then:

It can thus be seen that, in order to minimize the influence of the disturbances in the general expression of the coupling signal V _ei, it is necessary to choose excitation signals ½ such that the scalar product of two different basic functions b _ir b _j (for example corresponding to different measurement channels) is negligible or at least much lower than the standard of the basic function b _t of the excitation signal ½ of the electrode in question:

W (Eq 13)

Of course, if you want to simultaneously perform measurements with polarized electrodes to the excitation potential _jr v must also satisfy symmetric condition

The same reasoning can be applied to a perturbation signal V _p insofar as this signal can be sufficiently known (either theoretically or thanks to measurements). Its influence on the measurements can be minimized if it is possible to choose an excitation signal ½ such that its scalar product with the perturbation signal V _p is negligible or at least much lower than the excitation signal standard

All the basic functions which make it possible to satisfy or at least to approximate these criteria can be used in the context of the invention.

In order to ensure a good independence of the signal detected by each measurement channel i with respect to the other terms, it is possible to choose basic functions so as to obtain for example a ratio in decibels

of the order of -20 d B or less, or of the order of -30 d B, or -40 d B, or less. Thus, the disturbance on the amplitude of the coupling signal due to parasitic sources will not exceed this decibel value.

Basic functions can be discrete functions that can take two values, such as + 1 and - 1.

Basic functions can also be discrete functions that can take a more complete discrete set of values such as:

+ 1; 1 / root (2); 0; - 1 / root (2); - 1.

This makes it possible to better control the energy spectrum generated towards the high frequencies, by choosing adjacent values for successive indices k. It also allows to generate functions that approach pure sinusoids.

Here, as non-limiting examples, are criteria that can be used to generate basic functions:

the basic functions can be chosen so as to generate a periodic square signal pattern, or close to a sinusoid. Each basic function can then be essentially represented by a frequency f 1;

- We can then choose to distance the frequencies from each other, or to choose them appropriately to obtain the orthogonality between different basic functions bi;

- to generate two potential excitation, can generate signals with frequencies f _lf f ₂ the same, but with a 90 degree phase shift. We then have signals in quadrature phase.

the basic functions can be chosen in such a way as to minimize energy peaks, or to smooth the spectrum. We can have a strategy of frequency dispersion, which can minimize the energy radiated at certain frequencies by the device;

the basic functions b _t may be chosen so as to minimize the energy at low frequencies where the noise in 1 / f penalizes the system, and / or to avoid the energy at high frequencies for reasons of electromagnetic compatibility or of consumption ;

for each of the above strategies, the choice may be further oriented to minimize the scalar product term with a parasitic disturbance V _p undergone, so as to minimize its influence.

At the implementation level in a device,

the basic functions b _t can be pre-calculated and recorded in the device that has them in real time without additional calculation;

- several sets of functions may be available in advance. The choice between these bases can then be performed according to criteria such as minimizing the effects of disturbance signals V _p ;

- It is possible to switch between the different sets of basic functions between successive acquisitions of the coupling signal v _ei (l), therefore between periods τ _ε if necessary. In the diagram of FIG. 2, this amounts to changing the signal forms generated by the excitation sources 30, 31 over time, or switching different excitation sources 30, 31. The entire device can thus be dynamically reconfigured according to its environment.

It should be noted that the variant embodiment in which electrodes are biased at the reference potential 13 is in accordance with the polarization potential generation criterion which minimizes the scalar product of the crossed terms. Indeed, if b _t is the basic function of the polarization potential of the electrodes used for the measurement and bj the basic function of the electrodes at the reference potential, we have bj = 0, b _t - bj = 0 and therefore \ bi \ »Bi ^■ bj according to Eq. 13.

Of course, in this case, simultaneous measurements are not made with the electrodes polarized at the reference potential 13, and therefore it is not necessary to satisfy the symmetrical condition of the Eq. 14.

As an example of application, the invention can be implemented under the following conditions: τ _Σ = 5 ps

τ _ε = 8 ms

N _s = 1600

In addition, the following families of excitation potentials can be generated, with k = 0 ... N _s - 1:

- with two different and orthogonal frequencies:

b ^ k) = +1; +1; -1; -1; +1; +1; -1; -1; ... repeated 199 times;

b ₂ (k) = +1; +1; +1; +1; -1; -1; -1; -1; ... repeated 199 times.

- with two identical frequencies and quadrature signals:

b ^ k) = +1; +1; -1; -1; +1; +1; -1; -1; ... repeated 199 times; b ₂ (k) = -1; +1; +1; -1; -1; +1; +1; -1; ... repeated 199 times.

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

1. Capacitive detection method, implementing a plurality of electrodes (5, 7) adapted to allow the detection of objects (1, 21, 22) in their vicinity by capacitive coupling, characterized in that it comprises a a step of simultaneously polarizing at least a portion of said electrodes (5, 7) with different excitation potentials (42, 43), which excitation potentials (42, 43) are generated with respect to a potential of reference (13) such that the scalar product over a predetermined duration of at least two of these excitation potentials (42, 43) is zero or much less than the dot product of one and / or the other of these excitation potential (42, 43) with itself over said predetermined time.

The method of claim 1, wherein the generated excitation potentials (42, 43) comprise at least one time-varying excitation potential.

The method of one of the preceding claims, wherein the generated excitation potentials (42, 43) comprise periodic excitation potentials of different frequencies.

4. The method of one of the preceding claims, wherein the generated excitation potentials (42, 43) comprise at least one excitation potential whose frequency content is dispersed over a spectral band.

5. The method of one of the preceding claims, wherein the generated excitation potentials (42, 43) comprise two periodic excitation potentials of the same frequency in quadrature phase.

The method of one of the preceding claims, wherein the generated excitation potentials (42, 43) comprise at least one excitation potential whose scalar product with a disturbance signal is minimized.

The method of one of the preceding claims, wherein the generated excitation potentials (42, 43) comprise at least one excitation potential substantially equal to the reference potential.

The method of any of the preceding claims, which further comprises a step of measuring the capacitive coupling of an electrode (5, 7), comprising:

demodulating said representative measurements of the charge by using the excitation potential (42, 43) of said electrode (5, 7).

9. Capacitive detection device, comprising a plurality of electrodes (5, 7) capable of enabling the detection of objects (1, 21, 22) in their vicinity by capacitive coupling, characterized in that it further comprises excitation means (30, 31) capable of simultaneously biasing at least a portion of said electrodes (5, 7) with different excitation potentials (42, 43), which excitation potentials (42, 43) being generated with respect to a reference potential (13) so that the dot product over a predetermined time of at least two of these excitation potentials (42, 43) is zero or much less than the dot product of the one and / or the other of these excitation potential (42, 43) with itself over said predetermined time.

The device of claim 9, which further comprises measuring means (34, 35, 36, 37) referenced to the same excitation potential (42, 43) as the electrodes (5, 7) to which they are connected. .

The device of claim 10, which further comprises demodulation means (38, 39) connected to the measuring means (34, 35, 36,

37), and able to produce a representative measurement of the capacitive coupling referenced to the reference potential (13).

The device of one of claims 9 to 11, which further comprises means for biasing at least one electrode: at several different excitation potentials (42, 43), and / or

at least one excitation potential (42, 43) or the reference potential (13).

13. Apparatus comprising a capacitive sensing device according to one of claims 9 to 12, and implementing the method according to any one of claims 1 to 8.

14. The apparatus of claim 13, which comprises in a first face (4) a display screen and first electrodes (5) substantially transparent polarized at a first excitation potential (42), and in a second face (14) opposite the first face of the second electrodes (7) polarized at a second excitation potential (43).

15. The apparatus of claim 14, which is of one of the following types: smartphone, tablet.

16. The apparatus of claim 13, which comprises a plurality of modules (21, 22) able to move relative to each other, each module comprising electrodes (5, 7) polarized at a potential of excitation (42, 43) different from the other modules (21, 22).