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    • 专利摘要:
    The present invention relates to a capacitive sensing device comprising: at least one capacitive measuring electrode (11); a current detector (16) electrically referenced to a general mass (12); at least one alternating excitation voltage source (15) electrically connected to or coupled to a measurement input of the current detector (16) and to the at least one capacitive measuring electrode (11); guard members (14) electrically connected to or coupled to the measurement input of the current detector (16); power supply generating means capable of generating at least one secondary power source (Vf) referenced to the electrical potential of the guard elements (13), which power supply generating means are further arranged so as to present in a frequency band extending from the continuous impedance between the general mass (12) and the guard elements (14) with a reactive component of capacitive or essentially capacitive nature, or similar to an open circuit.
    公开号:FR3051896A1
    申请号:FR1654667
    申请日:2016-05-25
    公开日:2017-12-01
    发明作者:Christian Neel；Frederic Ossart；Eric Legros；Didier Roziere
    申请人:Fogale Nanotech SA；
    IPC主号:
    专利说明:

    "Capacitive sensing device with zero guard"
    Technical area
    The present invention relates to a capacitive detection device for detecting the presence or proximity of objects of interest. It also relates to an apparatus comprising such a device.
    The field of the invention is more particularly, but not exclusively, that of capacitive detection systems.
    State of the prior art
    Capacitive sensing systems are widely used to measure distances or to detect the presence or proximity of objects.
    Their general principle is to exploit and measure a coupling capacitance which is established between one or more capacitive measuring electrodes and objects that one wants to detect. The knowledge of this ability makes it possible to deduce distances between the electrodes and the objects.
    According to known techniques, the capacitive electrodes are excited at an excitation potential. When an object referenced to a general mass or earth (which is the case for almost any object) is located near an electrode, it establishes a coupling capacity between this electrode and the object. This coupling capacitance can be measured by measuring the current flowing between the electrode and the general ground at the excitation frequency. For this purpose, it is possible to use a charge amplifier connected at the input to the electrode.
    A problem that generally arises with this type of measurement is that the measurement electrodes and the electronics are also sensitive to capacitive couplings that can be established with the environment. This results in the appearance of parasitic leakage capabilities that are superimposed on the ability to measure and generates measurement errors.
    A known solution to this problem is to add a guard which prevents spurious coupling between the capacitive measuring electrodes and the environment, and thus eliminates parasitic leakage capabilities.
    This guard can be electrically referenced to the general ground potential. In this case, it does not prevent the appearance of parasitic leakage capacitance between the electrode and the guard, but it is assumed that this parasitic leakage capacity is sufficiently stable over time to be calibrated. This kind of configuration is therefore limited in terms of measurement accuracy and temporal stability. In addition, the need for periodic recalibration entails operating constraints that can be troublesome.
    Measurement configurations are also known which implement an active guard. In this case the guard is excited to an electrical potential substantially identical to the potential of the measuring electrodes. This configuration has the advantage that the capacitive couplings possibly present between the guard and the electrodes do not produce leakage currents and therefore do not generate parasitic leakage capacitors, since there is no potential difference between the guard and electrodes.
    These so-called "active guard" measurement configurations are widely used to make measurement systems with significant sensitivity and measurement range.
    These systems are in particular implemented in the form of electrode matrices making surfaces sensitive to their environment, for example to make anti-collision systems.
    For example, document WO 2004/023067 describes a proximity detector that can be used in particular as an anti-collision system for medical equipment. This document implements a capacitive measurement method which constitutes an alternative of "active guard" measurement configuration in which a part of the detection electronics is also referenced to the guard potential to completely eliminate parasitic leakage capacitances.
    These "active guard" measurement configurations have excellent measurement performances that justify the generalization of their use. However, their integration in complex electronic systems can be problematic from the point of view of the electromagnetic compatibility, because of the presence of polarized guard elements to the excitation potential.
    Also known is FR 2 337 346 which discloses a high precision capacitive measuring process which has the advantage of implementing a guard at a potential substantially equivalent to the general ground potential of the detection electronics. However, this old measurement method is limited to a differential measurement with a single electrode, and relies on a differential transformer based configuration and inductance coils that are incompatible with embodiments in integrated electronics.
    The object of the present invention is to propose a capacitive measuring device with a measurement sensitivity and an immunity to the parasitic leakage capacitances and their variations which allow the detection and measurements of distances or contact on objects of interest in a significant extent of measurement.
    The present invention also aims to provide a capacitive measuring device capable of handling a plurality or a large number of electrodes.
    The present invention also aims to provide a capacitive measuring device that generates a minimum of electromagnetic interference, so that it can be easily integrated into a complex electronic environment.
    The present invention also aims to provide a capacitive measuring device that is compatible with a realization in the form of integrated electronic components.
    Presentation of the invention
    This objective is achieved with a capacitive detection device comprising: at least one capacitive measuring electrode; a current detector electrically referenced to a general mass and sensitive to an electric current flowing on a measurement input; at least one alternating excitation voltage source electrically connected to or coupled to the measurement input of the current detector and the at least one capacitive measuring electrode; guard elements electrically connected to or coupled to the measurement input of the current detector;
    Characterized in that it further comprises power supply generating means capable of generating at least one secondary power source referenced to the electrical potential of the guard elements, which power supply generating means being further arranged so as to present in a frequency band extending from the continuous impedance between the general mass and the guard elements with a reactive component of capacitive or essentially capacitive nature, or similar to an open circuit.
    The reactive component of the impedance corresponds to its imaginary part.
    According to embodiments, the power supply generating means can: - be partially referenced to the general ground potential, or include elements referenced to the general ground potential. In this case they can in particular be arranged so as to use the energy of one or more primary power supply sources referenced to the general ground potential to generate one or more secondary power supply sources referenced to the electrical potential of the elements. of guard. - not to include elements referenced to the general mass potential. In this case they may comprise one or more secondary power sources referenced to the electrical potential of the independent guard elements, such as for example batteries, batteries or photovoltaic elements.
    According to embodiments, the impedance of the power supply generation means between the general mass and the guard elements may comprise, at least in a frequency band extending from the continuous: an imaginary part (or a reactive component) corresponding or essentially corresponding to a capacitance in series between the general mass and the guard elements; an imaginary part (or a reactive component) characterized by an absence of a significant inductive component; a value or a module which is of the same order of magnitude, or greater, than the value of the impedance of parasitic coupling capacitances between the general mass and the guard elements; a value or a module greater than 1 kOhm, or 10 kOhm, or 1 MOhm at 100 KHz, with an active component (real part) zero or non-zero;
    In a nonlimiting manner, the frequency band extending from the continuous can extend from the continuous at 200 KHz, or the continuous at 1 MHz.
    The parasitic coupling capacitances between the general mass and the guard elements can be for example of the order of 400 pF, which corresponds to a value or an impedance module of 4 kOhm to 100 kHz.
    An impedance comparable to an open circuit can be defined as an impedance whose value or modulus is very high in front of the other impedances which influence the measurement, or at least which is sufficiently high to be able to be approximated by an open circuit or an impedance infinite. This impedance can include an active component (real part) null or non-zero.
    The current detector (or detectors) may comprise any electronic circuit making it possible to measure a quantity representative of a current flowing on its measurement input, or between the measurement input and the general mass to which the current detector is referenced. Such a current detector has in particular a negligible impedance or at least very low between the measurement input and the general mass.
    The guard elements may be arranged to protect the at least one AC excitation voltage source and the at least one capacitive measuring electrode of parasitic capacitive couplings with the environment, or in other words avoid the appearance of parasitic leakage capabilities to elements referenced to the general ground potential in particular.
    The alternating excitation voltage source and the guard elements can be for example: directly connected to the measurement input of the current detector, for example by a connection track; - connected to the measurement input of the current detector (or in this case coupled) via electronic components such as capacitors and / or resistors.
    The alternating excitation voltage source and the guard elements can in particular be coupled to the measurement input of the current detector via a connection capacitance placed in series between the AC excitation voltage source. and the guard elements on the one hand and the measurement input of the current detector on the other hand. This configuration makes it possible to reduce the coupling, in the current detector, of the noise generated by the electromagnetic disturbances sensed by the guard elements.
    According to embodiments, the device according to the invention may comprise power generation means with electrical switching means.
    The electrical switching means may be in particular of one of the following types: switches, relays, switches, transistors, diodes, PN junctions.
    The device according to the invention may in particular comprise power generation means with: a first storage capacity; a second storage capacitor connected according to a terminal to the guard elements; and at least two power supply switches arranged to respectively connect the terminals of the first storage capacitor, to a primary power source referenced to the general ground potential, or to the terminals of the second storage capacitor.
    The power switches may respectively comprise electrical switching means. They can be made in particular in the form of electronic switches.
    In this embodiment, the power generation means constitute a charge pump. The second storage capacity makes it possible to produce a secondary power source referenced to the electrical potential of the guard elements. The first storage capacity makes it possible to replicate the voltage of the primary power source in a totally floating manner. The power switches are arranged to operate synchronously and periodically, so as to alternately connect the first storage capacity to the primary power source and then the second storage capacity. These power switches are further arranged so that there is never a direct electrical connection between the terminals of the primary power source and the second storage capacity.
    Thus, the impedance of the power supply generating means theoretically corresponds to an open circuit.
    In practice, the electronic switches comprise stray capacitances series, for example of the order of picofarad. It follows that the impedance of the power supply generating means is never infinite, but insofar as these parasitic capacitances are much lower than the other parasitic coupling capacitances between the general mass and the guard elements, this impedance is comparable to an open circuit.
    According to embodiments, the device according to the invention may comprise a current detector with a charge amplifier.
    According to embodiments, the device according to the invention may comprise an AC excitation voltage source with at least one of the following elements: analog electronic and / or digital excitation means referenced to the potential of the elements of keep ; an oscillator; - a digital-to-analog converter; a signal generator of pulse width modulation type; a signal generator of the type by subsampling a master signal; - an FPGA; an amplifier or an excitation follower referenced to the potential of the guard elements, and arranged to receive as input a master excitation signal referenced to the general ground potential.
    The alternating excitation voltage source can thus generate an excitation signal referenced to the potential of the guard elements. This excitation signal may comprise, for example, a sinusoidal, triangular, trapezoidal or square shaped signal.
    The downsampling of a master signal makes it possible, for example, to generate a plurality of sinusoidal excitation signals from a high frequency master sinusoidal signal by refolding the spectrum using sampling frequencies which do not satisfy the Nyquist-Shannon sampling theorem.
    The excitation signal may also comprise a pulse width modulation type (PWM) type binary signal for generating an analog signal, for example triangular or sinusoidal, by filtering.
    According to embodiments, the device according to the invention may comprise an alternating excitation voltage source with an excitation switch arranged so as to electrically connect a capacitive measuring electrode, or to a secondary power source, either to the guard elements or to the measuring input of the current detector.
    The excitation switch may be arranged to switch repetitively so as to generate on the capacitive measuring electrode an alternating excitation signal alternating between two voltage levels.
    This alternating excitation signal may comprise, for example, a periodic binary signal, a periodic binary signal according to a time sequence, or a Pulse Width Modulation (PWM) type signal making it possible to generate by filtering a analog signal, triangular or sinusoidal for example.
    According to embodiments, the device according to the invention may comprise a plurality of capacitive measuring electrodes and switches for sequentially connecting said capacitive measurement electrodes to the measurement input of the current detector, which switches are arranged according to one of the following configurations: the switches are placed between the measurement electrodes and an excitation AC voltage source connected to the measurement input of the current detector; the switches are placed between AC excitation voltage sources respectively connected to a measurement electrode and the input of the current detector; the switches are placed in alternating excitation voltage sources respectively connected to a measurement electrode or are part of said sources.
    According to embodiments, the device according to the invention may comprise a plurality of capacitive measuring electrodes and a plurality of alternating excitation voltage sources respectively connected to the capacitive measuring electrodes and to the measuring input of the detector of the capacitor. current.
    Thus, the capacitive measuring electrodes can be excited respectively by separate AC excitation voltage sources. These alternating excitation voltage sources can be connected to the same measurement input of the current detector.
    In the case where several alternating excitation voltage sources are simultaneously active, the electric current flowing on the measurement input of the current detector substantially corresponds to a sum of the currents flowing in the measurement electrodes, which currents depend respectively on the signals excitation generated by the AC excitation voltage sources.
    According to embodiments, the device according to the invention may comprise: a plurality of alternating excitation voltage sources produced in the form of distinct components; and / or at least one electronic component comprising several or all sources of AC excitation voltages. This electronic component may comprise, for example, an integrated circuit such as an FPGA.
    According to embodiments, the device according to the invention may comprise a plurality of AC excitation voltage sources arranged so as to generate excitation signals at different frequencies, and / or orthogonal to each other.
    Thus, the measurement signals from the measurement electrodes are coded differently and can be distinguished.
    When excitation signals are used at different frequencies, each current from a capacitive measuring electrode has a frequency content different from that of the other electrodes. Frequency multiplexing of the measurements resulting from the capacitive electrodes is thus performed.
    Orthogonal signals are defined as being signals whose scalar product of any two of these signals over a number of samples or a predetermined duration is zero or almost zero (with respect to the modulus of these signals, i.e. to the dot product of these signals with themselves). In addition, the conventional definition of a scalar product in a vector space with an orthonormal basis is used as the sum of the term-to-term products of the samples of the signals in the predetermined duration. The use of orthogonal excitation signals associated with a synchronous detection as explained below makes it possible to demodulate the measurements from the different capacitive electrodes independently, while minimizing the effects of crosstalk between cracks.
    It should be noted that excitation signals at different frequencies are not orthogonal to each other in the general case. However, they can be orthogonal to each other if they have frequencies that correspond to integer multiples of each other.
    According to embodiments, the device according to the invention may further comprise demodulation means with at least one of the following elements: a synchronous demodulator arranged to demodulate with a carrier signal a modulated measurement signal coming from the detector current; an amplitude detector; - a digital demodulator.
    In general, a synchronous demodulator can be modeled by (or include) a multiplier that multiplies the measurement signal from the current detector with the carrier signal and a low-pass filter.
    An amplitude detector (or asynchronous demodulator) may be modeled by (or include) a rectifying element such as a diode rectifier, switch switches or a quadratic detector, and a low-pass filter. It makes it possible to obtain the amplitude of the modulated measurement signal coming from the current detector.
    The demodulation means may also include anti-alias bandpass or low pass filters placed prior to demodulation.
    Of course, the demodulation means can be realized in digital and / or analog form. They can include an analog-to-digital converter and a microprocessor and / or an FPGA that digitally performs synchronous demodulation, amplitude detection or any other demodulation operation.
    According to embodiments, the device according to the invention may comprise a plurality of alternating excitation voltage sources connected to the measurement input of the current detector and able to generate a plurality of excitation signals, and a plurality of excitation voltage sources. synchronous demodulator apparatus arranged to demodulate a modulated measurement signal from the current detector with distinct carrier signals, which carrier signals and which alternative excitation voltages are paired so that a carrier signal selectively demodulates a signal measurement generated by a single source of AC excitation voltage.
    Carrier signals and AC excitation voltages can be matched in the frequency domain (i.e., include frequencies in common) and / or in the time domain (i.e., in phase and / or with similar shapes or temporal structures). The carrier signals and the alternating excitation voltages may in particular be substantially identical or proportional, at least for their components with at least one frequency of interest.
    According to embodiments, the device according to the invention can implement a plurality of carrier signals with different frequencies, and / or orthogonal between them.
    According to embodiments, the device according to the invention may comprise at least one alternating excitation voltage source arranged so as to generate an excitation signal of one of the following forms: sinusoidal, square, and at least one synchronous demodulator with a carrier signal of one of the following forms: sinusoidal, square.
    It may especially comprise: at least one AC excitation voltage source arranged so as to generate a square-shaped excitation signal, and at least one synchronous demodulator with a sinusoidal-shaped carrier signal with a frequency identical to the fundamental frequency of the excitation signal; at least one AC excitation voltage source arranged so as to generate a pulsed pulse width modulated square wave excitation signal (PWM) so as to correspond to a sinusoidal signal, and at least one synchronous demodulator with a carrier signal of sinusoidal shape with a frequency identical to the frequency of the sinusoidal excitation signal.
    According to embodiments, the device according to the invention may comprise signal transfer means able to generate a signal referenced to the general ground potential from a signal referenced to the electric potential of the guard elements or vice versa, which means signal transfer system comprising at least one of the following: - a follower amplifier embodied in the form of an inverting charge amplifier (for example with an input capacitance and a feedback capacitance); an electronic assembly capable of generating a compensation current between the general ground potential and the electrical potential of the guard elements of substantially identical value and of opposite polarity to a leakage current.
    The leakage current may be due in particular to the transfer of signals by the signal transfer means.
    According to embodiments, the device according to the invention may comprise: an integrated circuit integrating at least the at least one AC excitation voltage source, and at least part of the guard elements; an integrated circuit with guard elements made in the form of a guard box electrically isolated from the substrate of said integrated circuit, which guard box comprises the at least one AC excitation voltage source; an integrated circuit with a substrate referenced to the general mass, and a current detector made on said substrate.
    The device according to the invention may in particular comprise an integrated circuit with a guard box electrically insulated from the substrate by one of the following means: a succession of semiconductor material layers with P and N type dopings; at least one layer of insulating materials.
    Thus, the device according to the invention can be made in a form adapted to its integration in various devices.
    The embodiment in the form of an integrated circuit is notably made possible by the use of components that excite inductors or transformers of high inductance value.
    The embodiment in the form of an integrated circuit also makes it possible to perform the guard elements in a particularly efficient manner and optimally protect the AC excitation voltage sources or sources.
    In another aspect, there is provided an apparatus comprising a capacitive sensing device according to the invention.
    According to embodiments, the apparatus according to the invention may comprise a plurality of capacitive electrodes arranged along a surface of said apparatus. The apparatus may especially be a robot, a medical analysis or imaging apparatus or any other system with a sensitive surface. The capacitive electrodes may in particular be used to detect a presence, an approach (anticoiiision), a distance, a contact or to allow to interact with the device and / or control.
    According to embodiments, the apparatus according to the invention may comprise a plurality of capacitive electrodes superimposed or integrated in a display screen. The display screen with the capacitive electrodes can then constitute a control interface, or a human-machine interface, for example to control medical equipment, industry, etc.
    DESCRIPTION OF THE FIGURES AND EMBODIMENTS Other advantages and features of the invention will be apparent from the following detailed description of implementations and embodiments of the invention, and the following accompanying drawings: FIG. 1 illustrates a first embodiment of the device according to the invention; FIG. 2 illustrates a second embodiment of the device according to the invention; FIG. 3 illustrates a third embodiment of the device according to the invention; FIG. 4 illustrates a fourth embodiment of the device according to the invention; FIG. 5 illustrates a fifth embodiment of the device according to the invention; FIG. 6 illustrates a sixth embodiment of the device according to the invention; FIG. 7 illustrates a seventh device embodiment according to the invention; FIG. 8 illustrates an eighth embodiment of the device according to the invention; FIG. 9 illustrates a ninth device embodiment according to the invention; FIG. 10 illustrates an embodiment of the invention in the form of an integrated circuit.
    It is understood that the embodiments which will be described in the following are in no way limiting. It will be possible, in particular, to imagine variants of the invention comprising only a selection of characteristics described subsequently isolated from the other characteristics described, if this selection of characteristics is sufficient to confer a technical advantage or to differentiate the invention with respect to the state of the art. This selection comprises at least one feature preferably functional without structural details, or with only a part of the structural details if this part alone is sufficient to confer a technical advantage or to differentiate the invention from the state of the prior art.
    In particular, all the variants and all the embodiments described are combinable with each other if nothing stands in the way of this combination at the technical level.
    For the sake of clarity and brevity, the figures represent only the elements necessary for understanding the invention. In the figures, the elements common to several figures retain the same reference.
    With reference to FIG. 1, a first embodiment of a capacitive detection device according to the invention will be described.
    The object of the device is to detect and / or measure a capacitive coupling between one or more objects of interest 10 and a capacitive measuring electrode 11. In principle, it is supposed that the object or objects of interest 10 are referenced to a general mass. 12 of the electronics, which can be the earth. Depending on the applications, this or these objects of interest may be a part of the human body (a head, a hand, a finger) or any other object.
    The measurement of the capacitive coupling between the object (s) of interest 10 and the capacitive measurement electrode 11 can be used for example to obtain contact information, distance or location, or simply to detect the presence of this or these objects. The measuring electrode 11 is biased to an excitation voltage or an excitation signal E by an AC excitation voltage source 15 connected at the output to this measuring electrode 11. In the presence of an object of interest 10, a current is established in the measuring electrode 11 which depends on the capacitive coupling with this object of interest 10. This current is measured by a current detector 16 with a measurement input at which the measuring electrode 11 is connected via the alternating excitation voltage source 15. In the embodiment shown, this current detector 16 is produced by a charge amplifier 16 represented in the form of an operational amplifier with an input measurement on its (-) terminal and a capacity Cr in counter-reaction. The charge amplifier 16 is referenced to the general mass 12. It produces at its output a measurement signal in the form of a measurement voltage Vm proportional to the capacitance Cm between the measurement electrode 11 and the object of measurement. interest 10:
    Vm = - E Cm / Cr.
    In the embodiment presented, the measurement signal is then demodulated by a demodulator 17 in the form of a synchronous demodulator 17 to obtain a value representative of the capacitance Cm (and / or the distance of the object of interest 10). The synchronous demodulator is shown schematically by a multiplier or a mixer which multiplies the measurement signal Vm by a carrier signal D, and a low-pass filter.
    As will be detailed below, the carrier signal D may be substantially identical to the excitation signal E, or at least be matched to this excitation signal E so as to have common frequency and / or time characteristics.
    The device according to the invention also comprises guard elements 14 electrically connected to the measurement input of the current detector 16, or, in the embodiment presented, to the terminal (-) of the charge amplifier 16. As the terminal {+) of the charge amplifier is connected to the general ground potential 12, these guard elements are thus referenced to a guard potential 13 substantially identical to or identical to the general ground potential 12, but without being connected thereto directly.
    The guard elements 14 may comprise any material sufficiently electrically conductive. They are arranged, electrically and spatially, so as to protect at least the capacitive measuring electrode 11 and the AC excitation voltage source 15 parasitic capacitive couplings with the outside.
    In practice, these guard elements 14 may comprise, in a nonlimiting manner, a guard plane disposed near the measuring electrodes 11 in a face opposite to a measurement zone, and guard tracks arranged along the connecting tracks. to the measuring electrodes 11. They may furthermore comprise an enclosure encompassing the alternating excitation voltage source 15, made for example in the form of a box surrounding the electronic components (for an embodiment in discrete or semi-integrated form ).
    As explained above, the purpose of the guard elements 14 is to eliminate all parasitic capacitive couplings between the measuring electrode 11, the AC excitation voltage source 15 and the general mass 12. Indeed, these parasitic capacitive couplings which could appear in the absence of guard elements 14 according to the invention would generate leakage currents which would be added directly to the current to be measured at the input of the charge amplifier 16. Moreover, the parasitic capacitance which may appear between the guard elements 14 and the general mass 12 does not generate leakage current since the general ground potential 12 and the guard potential 13 are identical.
    The alternating excitation voltage source 15 is referenced to the guarding potential 13. Thus, the parasitic capacitances which can appear between the output of this alternating excitation voltage source 15 and the guard elements 14 generate leakage currents which are looped in the guard elements 14 and do not contribute to the current measured by the charge amplifier 16.
    Thus, thanks to the invention, a high-quality guard is obtained which eliminates parasitic capacitive couplings and thus enables measurements of high precision. This guard also has the advantage of being at a potential similar to the general ground potential 12, and therefore does not generate electromagnetic disturbances in its environment. Finally, it only concerns a small part of the electronics since the charge amplifier 16 and all the processing electronics are outside the zone protected by the guard elements 14.
    The device according to the invention also comprises power generation means that make it possible to generate one or more secondary power sources referenced to the guard potential 13 from primary power sources referenced to the general ground potential. .
    In the embodiments shown, these power generation means are arranged to generate a secondary power supply source Vf from a continuous primary power supply source Vg.
    This or these secondary power supply sources make it possible in particular to supply the electronic components referenced to the guard potential 13, such as the alternating excitation voltage source 15.
    As explained above, the power generation means must be arranged so as to have a very high impedance between the guard potential 13 and the general mass 12, at least in the frequency band used for the measurements (for example between 10 kHz and 200 kHz). This makes it possible to avoid leakage currents between the guard potential 13 and the general mass 12 which would be added directly to the current to be measured coming from the measuring electrode 11 at the input of the charge amplifier 16.
    In the embodiments shown, the power generation means are in the form of a charge pump. They comprise a first storage capacitor Ct, a second storage capacitor Cf connected to one terminal at the guard potential 13, and two power supply switches 18 arranged to respectively connect the terminals of the first storage capacitor Ct or to a primary power supply source Vg referenced to the general ground potential 12, ie at the terminals of the second storage capacitor Cf.
    The power switches 18 comprise electronic switches, made for example with MOS or FET switching transistors). They are operated synchronously and periodically, in two phases. Thus, they are arranged so that there is never a direct electrical connection between the terminals of the primary power supply source Vg and the second storage capacitor Cf (except via parasitic capacitors, very low and therefore very high impedance).
    In a first phase, the power supply switches 18 are actuated so as to connect the terminals of the first storage capacitor Ct respectively to the primary power supply source Vg and to the general mass 12. Thus the voltage of the source of power primary power supply Vg is replicated at the terminals of the first storage capacitor Ct.
    In a second phase, the power supply switches 18 are actuated so as to connect the terminals of the first storage capacitor Ct to the terminals of the second storage capacitor Cf, one of which is connected to the guard potential 13. From this way the voltage across the first storage capacitor Ct (corresponding to Vg) is replicated across the second storage capacitor Vf.
    Thus, at the terminals of the second storage capacitor Cf, a secondary power source Vf is referenced to the guard potential 13 which is a replica of the first power supply source vg. Switching of the power supply switches 18 are performed sufficiently frequently so that the voltage Vf across the second storage capacitor Cf does not vary too much as a function of the current consumed by the elements supplied in this manner.
    The alternating excitation voltage source 15 can be realized in any possible way.
    It may comprise, for example, an oscillator, or a digital-to-analog converter, or a signal generator implemented for example with an FPGA.
    Fig. 2 illustrates an embodiment with an excitation AC voltage source made with an excitation switch 20. This embodiment has the advantage of being simple to implement.
    The excitation switch 20 is arranged so as to electrically connect a capacitive measuring electrode 11 alternately to the secondary power supply source Vf, and to the guarding potential 13. Thus, between capacitive measuring electrode 11 and the measurement input of the current detector 16 an excitation signal E which alternates between a zero value and the secondary supply voltage Vf.
    In the embodiment shown, the excitation switch 20 is controlled by an external control signal h.
    The excitation signal E thus generated may comprise, for example, a periodic binary signal, a periodic binary signal in a time sequence, or a Pulse Width Modulation (PWM) type signal making it possible to generate filtering an analog signal, triangular or sinusoidal for example.
    Fig. 3 illustrates an embodiment that makes it possible to implement a plurality of capacitive measurement electrodes 11 to perform measurements sequentially with the same charge amplifier 16.
    In this embodiment, the device comprises a switch 30 placed between an AC excitation voltage source 15 and a plurality of measurement electrodes 11, and which makes it possible to select a particular measuring electrode 11. The switch 30 is arranged so that each measuring electrode 11 is connected to either the AC excitation voltage source 15 to enable measurement or to the guard potential 13 to contribute to the guard elements 14. This embodiment thus allows sequential measurements on the measuring electrodes 11.
    Fig. 4 illustrates an embodiment that makes it possible to implement a plurality of capacitive measurement electrodes 11 to perform measurements simultaneously with the same charge amplifier 16.
    In this embodiment, the device comprises a plurality of alternating excitation voltage sources 15 each connected to a different measuring electrode 11. The alternating excitation voltage sources 15 are all connected in parallel to the input of the charge amplifier 16. The charge amplifier 16 is connected at the output to a plurality of demodulators 17. These demodulators 17 thus receive as input a composite signal corresponding to all the measurements made on the measurement electrodes 11 connected to the input of the charge amplifier.
    In order to be able to carry out measurements simultaneously on the measurement electrodes 11, it is ensured that each demodulator 17 is able to selectively demodulate the measurement signal coming from a single measuring electrode 11.
    For this: the AC excitation voltage sources are arranged to generate different excitation signals E1, E2, ... on each of the measurement electrodes; synchronous demodulators are implemented which each use a carrier signal D1, D2,... different from and matched to a single excitation signal E1, E2,...
    In addition, certain conditions must be observed on the signals to avoid cross talk between measurement channels.
    For example, it is possible to implement carrier signals D1, D2,... Orthogonal to each other and orthogonal to the excitation signals E1, E2,... With the exception of one with which each carrier signal is matched:
    Di Dj = 0 for i Ψ j
    Di Ej = 0 for i Ψ j
    This orthogonality may for example be defined in the sense of the scalar product, which corresponds to a sum of the products of the values of the signals over a time period.
    According to a preferred embodiment, a frequency multiplexing is carried out: frequency-shifted excitation signals E1, E2 are implemented in an amount greater than the bandwidth required for the measurement; and carrier signals D1, D2,... corresponding respectively to the excitation signals E1, E2,... or at least to signals at the respective fundamental frequency of the excitation signals E1, E2, are used. ...
    An advantageous way of realizing this frequency multiplexing is to implement an integrated circuit, for example of FPGA type which realizes in the form of a single component all AC excitation voltage sources 15. This integrated circuit is of course referenced at the guard potential 13.
    A pulse width modulation (PWM) technique, well known to those skilled in the art, is used to generate sinusoidal and frequency-shifted excitation signals E1, E2,. In this case, the excitation signals correspond to digital signals oscillating between two values, but whose duty cycle is sinusoidally modulated, for example. Their frequency spectrum then comprises a line at the sinusoid frequency and high frequency energy which is naturally filtered by the limited bandwidth of the system. The advantage of such a technique is that it can be implemented with simple digital electronic means and can generate harmonic signals with very little distortion, at least in the frequency band of interest.
    The carrier signals D1, D2,... Used correspond to the generated sinusoids.
    Fig. 5 illustrates a variant of the embodiment illustrated in FIG. 4 in which AC excitation voltage sources 15 are made with excitation switches 20, as explained in connection with FIG. 2.
    As before, the alternating excitation voltage sources 15 may advantageously be embodied in the form of an integrated circuit.
    This embodiment makes it possible to implement digital-type excitation signals E 1, E 2,..., Orthogonal to one another as previously described or frequency shifted to perform simultaneous measurements on all measurement channels.
    It also makes it possible to implement the pulse width modulation (PWM) technique described with reference to FIG. 4 to generate sinusoidal frequency-shifted excitation signals E1, E2,.
    A problem common to most of the embodiments is that it is necessary to transmit signals or information between the parts of the electronics referenced to the guard potential 13 and the parts of the electronics referenced to the general ground 12, without generating significant leakage currents which, as previously explained, contribute directly to measurement errors.
    This signal transmission is in particular necessary for synchronizing the alternating excitation voltage sources 15 and the demodulators 17. The embodiments described below for the transmission of signals are therefore related to this particular problem, it being understood that they are applicable to the transmission of all types of signals.
    An ideal solution is to use a galvanically isolated coupling such as a transformer or opto-coupler (optical pair transceiver), but these two techniques are difficult to integrate into an integrated circuit.
    With reference to Figs. 6 and FIG. 7, one can also use transfer circuits with a very high input impedance.
    For example, to transmit a signal referenced to the guard potential 13 to the electronics referenced to the general earth 12, a circuit referenced to the general earth 12 with a very high input impedance can be used.
    This solution is illustrated in FIG. 6. In this embodiment, the excitation signal E coming from an AC excitation voltage source 15 (or any control signal coming from this source) is transmitted to a tracking amplifier 60 referenced to the general mass. 12, which is embodied as an inverting charge amplifier 60 with an input capacitance Ci connected to its (-) terminal and a feedback capacitance Cb. The input impedance of this circuit, such as "seen" by the signal to be transmitted, consists essentially of the input capacitance Ci. By choosing this capacitance Ci of very low value (a few femtofarads for example) it is possible to obtain a very high input impedance, or in other words corresponding to a leakage capacity value close to the already existing leakage capacity between the guard potential 12 and the general mass 13.
    By choosing a feedback capacitance Cb with a value close to the input capacitance Ci, a follower amplifier with a gain close to -1 is obtained, which outputs a signal referenced to the general mass 12 which is an image faithful of the excitation signal E referenced to the guard potential 13. In the embodiment presented, this signal is transmitted to a demodulator 17, for example to form the carrier signal D.
    In another example, to transmit a signal referenced to the general earth 12 to the electronics referenced to the guard potential, it is possible to use a circuit referenced to the guard potential 13 with a very high input impedance.
    This solution is illustrated in FIG. 7. In this embodiment, a control signal h referenced to the general earth 12 is transmitted to the AC excitation voltage source 15, which is produced with an excitation switch 20 as described in relation to FIG. . 2.
    For this, the control signal h is connected at input to a follower amplifier 70 referenced to the guard potential 13, which is embodied as an inverter charging amplifier 70 with an input capacitor Ci connected to its terminal ( -) and a feedback capacity Cb.
    As previously, the input impedance of this circuit, such as "seen" by the signal to be transmitted, consists of the input capacitance Ci. By choosing this capacitance Ci of very low value (a few femtofarads for example) can get a very high input impedance.
    By choosing a feedback capacitance Cb with a value close to the input capacitance Ci, a tracking amplifier with a gain close to -1 is obtained, which outputs a control signal referenced to the guard potentiometer 13 which is a faithful image of the control signal h referenced ia general mass 12.
    With reference to Figs. 8 and FIG. 9, another alternative for transmitting signals between the electron referenced to the guard potentiometer 13 and the general mass 12 (or vice versa) is to generate currents in opposite phase, or circulating in the opposite direction, between the guard potential 13 and general mass 12. Thus, it is possible to annihilate these leakage currents almost perfectly, at least at the working frequencies considered.
    Fig. 8 iiustre a réaisation mode that allows to transmit an excitation signal E to the electronic referenced to the potential of mass general 12.
    The excitation signal E to be transmitted is inputted to a first differential amplifier 80 referenced to the guard potentiometer 13. This first differential amplifier 80 is outputted to a second differential amplifier 81 referenced to the general mass 12. The first amplifier Differentie 80 thus provides a different signal to the second differential amplifier 81, with two currents flowing through the two inputs of the second differential amplifier 81. These two currents are in phase opposition (at least at the frequencies of the excitation signal E). Thus the residual capacitive leak created is limited by the difference of these two currents. The use of a second differential amplifier 81 with a very high input impedance and good symmetry makes it possible to very effectively limit residual capacitive leakage.
    In the presented embodiment, the signal from the second differentiated amplifier 81 is transmitted to a demodulator 17, for example to constitute the carrier signal D.
    Fig. FIG. 9 illustrates a mode of realization which makes it possible to transmit a primary signal of excitation E 'generated at the level of the electron referenced to the potential of mass of general mass 12 towards the source of tension of alternating excitation 15.
    In this embodiment, the alternating excitation voltage source 15 comprises an excitation amplifier 90 referenced to the guarding potential 13, which is embodied as a reversing charge amplifier 90 with an input capacitance Ci connected to its (-) terminal and a feedback capacitance Cb. This excitation amplifier 90 receives as input the primary excitation signal E 'referenced to the general ground potential. Its (+) terminal is connected to the guard potential 13.
    As explained above especially in connection with FIG. 7, the input impedance of this circuit, such as "seen" by the primary excitation signal E ', consists essentially of the input capacitance Ci. By choosing this input capacitance Ci of very low value (some femtofarads for example) one can obtain a very high input impedance.
    By choosing a feedback capacitance Cb with a value close to the input capacitance Ci, an excitation amplifier 90 with a gain close to -1 is obtained, which outputs an excitation signal E referenced to the potential guard 13 which is a faithful image of the primary excitation signal E 'referenced the general mass 12.
    The primary excitation signal is also transmitted at the input of a compensation follower amplifier 91 referenced to the general earth 12. This compensation follower amplifier 91 is designed as an inverter charging amplifier with an input capacitor Ci 'connected to) its (-) bound and a feedback capacity Cb'. The input capacitance Ci 'and the feedback capacitance Cb' are chosen with similar values, so that it behaves as a follower amplifier with a gain close to -1.
    Thus, at the output of the compensation follower amplifier 91, there is a signal corresponding to a replica of the primary excitation signal E 'with an inverted sign or polarity.
    This signal feeds a compensation capacitor which connects the output of the compensation follower amplifier 91 to the guard potential 13. This compensation capacitance Ce is chosen with the same value as the input capacitor Ci of the excitation amplifier. 90 reference to the guard potential 13. Ideally these two capabilities are also performed on the same substrate to have the most similar characteristics possible.
    In this way, a compensation current which is a replica of opposite sign of the current flowing in the input capacitance Ci of the amplifier is generated in the compensation capacitor Ce between the guard potential 13 and the general mass 12. excitation 90. This compensation current makes it possible to cancel or compensate the capacitive leak due to the flow of current in the input capacitance Ci of the excitation amplifier 90, between the guard potential 13 and the general mass 12 It is thus possible, for example, to use higher input capacitors Ci than for the embodiment of FIG. 7.
    It should be noted that the follower amplifiers described in the embodiments of FIGS. 6 to FIG. 9 can also be realized with conventional inverting voltage booster amplifiers with resistors instead of capacitors, or resistors in parallel with capacitors). However, the capabilities have the advantage of being easier to achieve than high value resistors in integrated electronics circuits.
    In connection with FIG. 10, we will now describe an embodiment of the device according to the invention in the form of an integrated circuit 100. This embodiment is for example particularly suitable for producing a component for controlling a large number of devices. capacitive electrodes 11. It can implement all the embodiments described above in connection with FIGS. there Fig. 9.
    This integrated circuit 100 is made for example in CMOS technology.
    It comprises a substrate 101, for example with a P-type doping. This substrate is referenced to the ground potential 12, which is the reference potential of the power supplies of the integrated circuit 100.
    The substrate 101 comprises or supports the part of the electronics referenced to the general ground potential 12, including the current detector 16 or the charge amplifier 16. It may also include the demodulator 17.
    The integrated circuit 100 also comprises a guard box 143 electrically isolated from the substrate 101 by an isolation zone 102.
    The isolation zone 102 may be made with an insulating deposit (SiO 2).
    In the embodiment shown, the isolation zone 102 is made with at least one polarized junction PN in the blocked direction. More specifically, if the substrate is of the P type, the isolation zone 102 comprises N type doping, and the guard box 143 comprises a P type doping. A DC voltage source 103 applies a DC voltage between the substrate 101 and the isolation zone 102, to maintain the corresponding PN junction in the blocked direction.
    The guard box 143 is electrically connected to the input of the current detector 16. The guard elements 14 are identified and referenced to the guard potential 13.
    The guard box 143 comprises or supports the electronic elements referenced to the guard potential 13, including the AC excitation voltage sources 15.
    This architecture has the advantage that the guard box 143 provides a very effective guard to protect the sensitive parts of the electronics. In addition, the integrated circuit 100 is generally referenced to the general mass 12, so easy to integrate into an electronic system.
    The measurement electrodes 11 may for example be made so as to constitute a sensitive surface 104. In this case, they are protected according to their rear face by a guard plane 141. This guard plane 141 is connected to the guard box 143 and therefore to the guard potential 13 of the electronics by guard elements 142 which protect the connecting tracks for example. The guard plane 141 is of course a constituent element of the guard elements 14.
    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.
    权利要求:
    Claims (20)
    [1" id="c-fr-0001]
    A capacitive sensing device comprising: - at least one capacitive measuring electrode (11); a current detector (16) electrically referenced to a general mass (12) and sensitive to an electric current flowing on a measurement input; at least one alternating excitation voltage source (15) electrically connected to or connected to the measuring input of the current detector (16) and at least one capacitive measuring electrode (11); guard elements (14) electrically connected to or coupled to the measurement input of the current detector (16); Characterized in that it further comprises power supply generation means capable of generating at least one secondary power supply source (Vf) referenced to the electric potential of the guard elements (13), which means for generating electricity. power supply being further arranged to present in a frequency band extending from the continuous an impedance between the general mass (12) and the guard elements (14) with a reactive component of capacitive or essentially capacitive nature, or comparable to an open circuit.
    [2" id="c-fr-0002]
    2. The device of claim 1, which comprises power generation means with electrical switching means (18).
    [3" id="c-fr-0003]
    3. The device of one of the preceding claims, which comprises power generation means with: a first storage capacity (Ct); a second storage capacitor (Cf) connected according to a terminal to the guard elements (14); and - at least two power supply switches (18) arranged to respectively connect the terminals of the first storage capacitor (Ct) or to a primary power source (Vg) referenced to the general ground potential (12). ), or at the terminals of the second storage capacity (Cf).
    [4" id="c-fr-0004]
    4. The device of one of the preceding claims, which comprises a current detector (16) with a charge amplifier.
    [5" id="c-fr-0005]
    5. The device according to one of the preceding claims, which comprises an alternating excitation voltage source (15) with at least one of the following elements: analog electronic and / or digital excitation means referenced to the potential guard elements (13); an oscillator; - a digital-to-analog converter; a signal generator of pulse width modulation type; a signal generator of the type by subsampling a master signal; - an FPGA; an amplifier or excitation follower (90) referenced to the potential of the guard elements (13), and arranged to receive as input a master excitation signal referenced to the general ground potential (12); an excitation switch (20) arranged to electrically connect a capacitive measuring electrode (11), either to a secondary power source (Vf), to the guard elements (14) or to the input measuring the current detector (16).
    [6" id="c-fr-0006]
    The device of one of the preceding claims, which comprises a plurality of capacitive measuring electrodes (11) and switches (20, 30) for sequentially connecting said capacitive measurement electrodes (11) to the input of measuring the current detector (16), which switches (20, 30) are arranged in one of the following configurations: - the switches (30) are placed between the measuring electrodes and an alternating excitation voltage source (15). ) connected to the measurement input of the current detector (16); the switches are placed between alternating excitation voltage sources (15) respectively connected to a measuring electrode (11) and the input of the current detector (16); the switches (20) are placed in alternating excitation voltage sources (15) respectively connected to a measurement electrode (11) or part of said sources (15).
    [7" id="c-fr-0007]
    The device of one of the preceding claims, which comprises a plurality of capacitive measuring electrodes (11) and a plurality of alternating excitation voltage sources (15) respectively connected to the capacitive measuring electrodes (11) and at the measuring input of the current detector (16).
    [8" id="c-fr-0008]
    The device of claim 7 which comprises a plurality of AC excitation voltage sources (15) arranged to generate excitation signals (E, E1, E2) at different and / or orthogonal frequencies. between them.
    [9" id="c-fr-0009]
    The device of one of the preceding claims, which further comprises demodulation means (17) with at least one of the following elements: - a synchronous demodulator arranged to demodulate with a carrier signal (D, D1, D2) a modulated measurement signal from the current detector; an amplitude detector; - a digital demodulator.
    [10" id="c-fr-0010]
    The device of claim 9, which comprises a plurality of alternating excitation voltage sources (15) connected to the measurement input of the current detector (16) and capable of generating a plurality of excitation signals ( E, El, E2), and a plurality of synchronous demodulators (17) arranged to demodulate a modulated measurement signal from the current detector (16) with separate carrier signals (D, D1, D2), which carrier signals (D, D1, D2) and which alternating excitation voltages (E, E1, E2) are paired so that a carrier signal (D, D1, D2) can selectively demodulate a measurement signal generated by a single AC excitation voltage source.
    [11" id="c-fr-0011]
    11. The device of one of claims 9 or 10, which implements a plurality of carrier signals (D, D1, D2) with different frequencies, and / or orthogonal to each other.
    [12" id="c-fr-0012]
    The device of claim 10 or 11, which comprises at least one alternating excitation voltage source (15) arranged to generate an excitation signal (E, E1, E2) of one of the following forms : sinusoidal, square, and at least one synchronous demodulator (17) with a carrier signal (D, D1, D2) of one of the following forms: sinusoidal, square.
    [13" id="c-fr-0013]
    The device of one of the preceding claims, which comprises signal transfer means (60, 70, 80, 81, 90, 91) adapted to generate a signal referenced to the general ground potential (12) from a signal referenced to the electric potential of the guard elements (13) or vice versa, which signal transfer means comprise at least one of the following elements: a follower amplifier (60, 70, 90) embodied in the form of a reverse charge amplifier; an electronic assembly (80, 81, 91) capable of generating a compensation current between the general ground potential (12) and the electrical potential of the guard elements (13) of substantially identical value and of opposite polarity to a current of leak.
    [14" id="c-fr-0014]
    The device of one of the preceding claims, which comprises an integrated circuit (100) integrating at least the at least one AC excitation voltage source (15), and at least a portion of the guard elements (14). ).
    [15" id="c-fr-0015]
    The device of claim 14 which comprises an integrated circuit (100) with guard elements (14) in the form of a guard box (143) electrically isolated from the substrate (101) of said integrated circuit (100). ), which guard box (143) comprises the at least one AC excitation voltage source (15).
    [16" id="c-fr-0016]
    The device of claim 15, which includes an integrated circuit (100) with a substrate (101) referenced to the bulk (12), and a current detector (16) provided on said substrate (101).
    [17" id="c-fr-0017]
    17. The device of one of claims 15 or 16, which comprises an integrated circuit (100) with a guard box (143) electrically isolated from the substrate (101) by one of the following means: - a succession of layers semiconductor material (102) with P and N doping; at least one layer of insulating material.
    [18" id="c-fr-0018]
    Apparatus comprising a capacitive sensing device according to one of the preceding claims.
    [0019]
    The apparatus of claim 18, which comprises a plurality of capacitive electrodes (11) disposed along a surface of said apparatus.
    [0020]
    20. The apparatus of one of claims 18 or 19, which comprises a plurality of capacitive electrodes (11) superimposed or integrated in a display screen.
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    同族专利:
    公开号 | 公开日
    WO2017202564A1|2017-11-30|
    US20190286261A1|2019-09-19|
    FR3051896B1|2018-05-25|
    EP3465236A1|2019-04-10|
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    法律状态:
    2017-05-24| PLFP| Fee payment|Year of fee payment: 2 |
    2017-12-01| PLSC| Publication of the preliminary search report|Effective date: 20171201 |
    2018-05-28| PLFP| Fee payment|Year of fee payment: 3 |
    2019-05-28| PLFP| Fee payment|Year of fee payment: 4 |
    2020-05-28| PLFP| Fee payment|Year of fee payment: 5 |
    2021-05-28| PLFP| Fee payment|Year of fee payment: 6 |
    优先权:
    申请号 | 申请日 | 专利标题
    FR1654667|2016-05-25|
    FR1654667A|FR3051896B1|2016-05-25|2016-05-25|CAPACITIVE DETECTION DEVICE WITH NULL GUARD|FR1654667A| FR3051896B1|2016-05-25|2016-05-25|CAPACITIVE DETECTION DEVICE WITH NULL GUARD|
    PCT/EP2017/059818| WO2017202564A1|2016-05-25|2017-04-25|Zero-guard capacitive detection device|
    EP17723638.7A| EP3465236A1|2016-05-25|2017-04-25|Zero-guard capacitive detection device|
    US16/301,245| US20190286261A1|2016-05-25|2017-04-25|Zero-guard capacitive detection device|
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