IT201800003972A1 - OPTO-ELECTRONIC DEVICE INCLUDING A DIRECT POLARIZATION LED, USED AS A RADIATION DETECTOR, AND ITS USES - Google Patents

Description

OPTO-ELECTRONIC DEVICE INCLUDING A DIRECT POLARIZATION LED, USED AS A RADIATION DETECTOR, AND ITS USES

DESCRIPTION

TECHNICAL FIELD

[0001] The invention relates to improvements to opto-electronic devices using LEDs as active elements, as well as systems and appliances including such devices.

ANTERIOR ART

[0002] Light emitting diodes, also called electroluminescent diodes, or commonly "LED" (Light Emitting Diodes), are semiconductor electronic components which have undergone enormous development in recent years. These devices use p-n junctions under forward bias conditions. The transit of current through the junction causes the emission of photons due to the passage of electrons from the conduction band (with higher energy) to the valence band (with lower energy) when they recombine with the holes present in the semiconductor.

[0003] LEDs emit electromagnetic radiation from the near infrared to ultraviolet range. They have various uses, for example in lighting engineering, as lighting bodies for the production of low-consumption lamps, as optical signals in electrical and electronic devices, as emitters of remote control signals (remote controls).

[0004] In recent times it has been proposed to use LEDs as optical signal detectors, in place of the common photodiodes. When used as optical detectors, LEDs are used in reverse bias conditions. In US 2004/0056608 a device is described which uses an LED as a light detector.

WO2016 / 168398 describes methods and devices using a card for carrying out banking transactions or the like, in which the use of LEDs as photodetectors is suggested.

In general, LEDs are operated in forward polarization conditions when used as light emitters, and in reverse polarization conditions when used as photodetectors.

[0006] In devices where it is required to emit light radiation and receive light radiation, for example for the transmission of information encoded in optical signals, it is therefore necessary to have an LED under direct polarization conditions, to emit light radiation, and to a light detector, which functions as a receiver. This affects the complexity and cost of these devices.

SUMMARY OF THE INVENTION

According to one aspect, an opto-electronic device is described, comprising: at least one LED having an emission band and an absorption band; a bias circuit for the LED, adapted to bring the LED into conditions of forward bias; and a circuit for detecting a change in an electrical parameter of the LED caused by radiation received by the LED when said LED is in forward bias conditions.

[0008] In embodiments described here, the bias circuit is adapted to bring the LED into conduction and to emit an optical radiation in the emission band.

[0009] The optical emission band and the optical reception band can advantageously be at least partially overlapped. In this way it is possible with the same LED to emit an electromagnetic radiation and to detect the same electromagnetic radiation reflected or back-scattered by an object external to the LED. As will be described in greater detail below, with reference to some embodiment examples, it is thus possible to realize a plurality of innovative devices and functions, with many different functions.

[0010] According to a further aspect, an innovative use of a LED in direct polarization is described herein to receive an incident radiation on the LED and generate a signal which is a function of said incident radiation, in which the LED is preferably conducting.

[0011] According to embodiments described here, the use of an LED in direct polarization is envisaged to emit a radiation towards a target, receive backscattered or reflected radiation from said target and generate a signal based on said backscattered or reflected radiation.

[0012] According to a still further aspect, a method is described for controlling an opto-electronic device comprising at least one LED, characterized by the steps of: directly biasing said at least one LED; while said LED is directly polarized, detecting a radiation incident on said LED by detecting a variation of an electrical parameter of the directly polarized LED, caused by said electromagnetic radiation incident on the LED.

[0013] Further innovative aspects, characteristics and embodiments are defined in the attached claims and will be illustrated below with reference to the attached drawings, which show some embodiments.

[0014] In the sense used here, the term "light radiation" or "light emission" or "light pulse" is generally to be understood as referring to any electromagnetic radiation emitted by an LED. Therefore, by light radiation or optical radiation, unless otherwise specified, we mean not only radiation in the visible wavelength range, but any radiation that can be emitted by an LED, for example also infrared radiation or radiation. ultraviolet.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The invention will be better understood by following the description and the attached drawings, which illustrate an exemplary and non-limiting embodiment of the invention. More specifically, in the drawing they show:

Fig.1 is a voltage-current diagram of an LED;

Fig.2 is a diagram of an LED placed in front of a target object; Fig.3 is a diagram illustrating the normalized absorption and emission spectra of an exemplary LED;

Fig.4 shows the voltage-current diagram of a constant current controlled direct bias LED operating as a photo-detector;

Fig. 5 is a voltage-current diagram of a constant voltage controlled direct bias LED operating as a photo-detector;

Fig.6 is a circuit diagram for controlling a current driven LED;

Figs 7A and 7B circuit diagrams for controlling a voltage-driven LED;

Fig.8 is a circuit diagram with a double current driven LED;

Fig.9 is a circuit diagram with double LEDs driven in voltage;

Fig. 10 is a circuit diagram with a double current driven LED;

Figs. 10A, 10B and 10C examples of detector circuits usable in a circuit diagram with reference LEDs;

Figs.11A-11F a diagram illustrating the use of an LED for measuring distances and related measurement diagrams;

Fig.12 is a diagram of the signal obtainable with an LED according to the present description used as a button;

Fig. 13 an application of a matrix of LEDs used as buttons for the creation of a touch-screen;

Figs. 14 and 15 an application of a matrix of LEDs used as lighting and image detection systems;

Figures 16A, 16B, 16C use a LED for the detection of acoustic waves;

Figs. 17, 18, 19, 20A, 20B, 20C and 20D use of an LED for the detection of adhesive tapes or other irregularities on documents or other sheet media; Fig. 21 is an illustrative diagram of the use of two LEDs for optical transmission and reception of information;

Figs. 22 to 25 illustrative diagrams of the use of an LED as a remote temperature meter;

Fig. 26 is a diagram of the use of a LED device for controlling a tool in a numerically controlled machining center; And

Fig.26A an enlargement of a detail of Fig.26.

DETAILED DESCRIPTION OF FORMS OF CONSTRUCTION

The following detailed description of exemplary embodiments refers to the accompanying drawings. The same reference numerals in different drawings identify the same or similar elements. Furthermore, the drawings are not necessarily to scale. The detailed description that follows does not limit the invention. Rather, the scope of the invention is defined by the attached claims.

Reference in the description to "an embodiment" or "the embodiment" or "some embodiment" means that a particular feature, structure or element described in connection with an embodiment is included in at least one embodiment of the described object. Therefore the phrase "in an embodiment" or "in the embodiment" or "in some embodiment" used in the description does not necessarily refer to the same or the same embodiments. Furthermore, the particular features, structures or elements can be combined in any suitable way in one or more embodiments.

[0018] Fig. 1 shows the I-V (current-voltage) characteristic curve of a light emitting diode, hereinafter briefly referred to as LED, according to the most common nomenclature. The diagram is divided into four quadrants indicated with (I), (II), (III) and (IV).

[0019] In the diagram of Fig.1 the curve I (V) represents the characteristic curve of the LED in the absence of light radiation received by the p-n junction, while the curve I '(V) is the characteristic curve of the same semiconductor device when the p-n junction is hit by a light radiation in the absorption spectrum of the device. As a consequence of irradiation, the characteristic curve shifts downwards, as a result of the absorption of photons received by the p-n junction of the LED.

[0020] Usually, LEDs are used as light emitters and controlled in direct polarization, so that the current flowing through them generates a stream of photons. The operation in this case is in the first quadrant (I) of the I-V diagram.

[0021] In recent applications, LEDs are also used as photo-detectors.

In this case they are operated in reverse polarization and therefore work in the third quadrant (III) of the I-V diagram.

[0022] Since the uses respectively as a photo-detector and as a photo-emitter require, according to the current art embodiments, different polarization conditions, the LEDs are currently not operated simultaneously by emitters and receivers. In fact, circuit solutions are generally chosen which optimize the selected function, effectively preventing the inverse operation from being highlighted.

[0023] Vice versa, according to the embodiments described here, contrary to what happens in known devices, the LED is operated in direct polarization, in the first quadrant (I) of the current-voltage diagram, to operate both as a light emitter, both as a photo-detector. As will be clarified below with reference to a plurality of application examples, the LED can be used to capture a fraction of the radiation emitted by the LED itself, or to capture an electromagnetic radiation (in the visible or in the near IR or UV), coming from a different source than the LED. In the first case, it is necessary that the emission band of the LED and the absorption band of the LED are at least partially superimposed on at least one condition of use (voltage and / or current applied to the ends of the semiconductor).

[0024] Fig. 2 schematically shows a device 1 comprising a LED 3 which, when polarized directly, emits a light beam F1 towards a target T. The target diffuses and / or reflects (arrow F2) at least part of the light F1 emitted by the LED 3, which is collected by LED 3 causing a deviation of the characteristic curve giving rise to the I-V characteristic called I '(V) of Fig.1. This deviation of the I-V characteristic curve in the first quadrant can be detected simultaneously with the emission, thus making the LED operate at the same time as an emitter and receiver, in direct polarization.

[0025] In order for the reflected or scattered light to be picked up and detected by the LED 3, it is necessary that this has at least partially overlapping emission and absorption spectra. As an example, Fig. 3 shows the absorption Sa and emission spectra Se of an LR H9GP LED produced by OSRAM Opto Semiconductors GmbH (Germany), proposed for lighting applications. The emission spectrum Se of this LED is centered on 632 nm and is superimposed on the much wider absorption spectrum Sa. This superposition of spectra allows the use of the LED in question simultaneously as an emitter of light radiation and a receiver of the same radiation reflected or back-scattered by an object illuminated by the LED. There are numerous other LEDs which have this characteristic of at least partial superposition of the emission and absorption spectra and which can therefore be used in the applications described here, in which the radiation that the LED must detect is a part of the same radiation emitted.

[0026] The LED 3 can be generically driven in various ways, by controlling an electrical parameter, and by measuring the variation of another electrical parameter, induced by the absorbed light radiation. In general, an LED, however driven, has variations in current and / or voltage as a function of the absorbed light. In advantageous embodiments described here, the LED is driven by stabilizing the voltage to highlight the variations in the current. In other embodiments described here, the LED is driven by stabilizing the current to highlight voltage variations.

[0027] For example, with reference to Fig.4, the LED 3 can be controlled in current. In this case a constant current I0 can be applied to the ends of the LED 3. The detected parameter can consist of the voltage across the LED. In the absence of other photoelectric phenomena, and in particular in the absence of radiation incident on the p-n junction of the LED, in the wavelength range of the absorption spectrum, the voltage across the LED will assume a value V0, as shown in Fig. 4.

[0028] If, on the other hand, on the p-n junction of the LED 3 there is reflected or diffused light F2 from a target T illuminated by the LED 3, there will be an absorption of photons by the p-n junction, and therefore the generation of a weak current, inverse than that applied by the control circuit. As a result of this the characteristic curve shifts and becomes I '(V). By keeping the current I0 flowing through LED 3 constant, this causes an increase in the voltage across it which from V0 becomes V1. By applying a control circuit to the ends of LED 3, it is possible to detect the value of V1 and then determine the intensity of the light flow captured by LED 3.

[0029] Vice versa, if the LED is voltage controlled, it can for example be provided that the voltage across it is kept constant and equal to the value V0, as shown in the diagram of Fig. 5. In this case, the collected light radiation from LED 3 alters the characteristic curve and causes a reduction in the current flowing through LED 3 from value I0 to value I1, as shown in the diagram in Fig.5.

[0030] In both cases, the photoelectric phenomenon caused by the radiation received by the LED 3 causes a deviation of the I-V characteristic curve, even in the first quadrant. It is therefore possible to use the LED 3 in direct polarization as an emitter and, simultaneously, as a receiver of the light incident on it.

[0031] In Fig.6 a simple current driving circuit of the LED 3 is schematically shown. The circuit of Fig.6 is to be intended merely as an example and not a limitative one. Other solutions are possible, as known to those skilled in the art. In the driving circuit of Fig. 6, indicated as a whole with 4, the LED 3 is inserted in the feedback network of an operational amplifier 5, and is therefore connected with the anode at the output of the operational amplifier 5 and with the cathode at the The inverting input of the operational amplifier 5. A reference voltage VREF is applied to the non-inverting input of the operational amplifier 5. A resistor 7 is connected between the inverting input of the operational amplifier 5 and the ground in order to control the current on the branch of the LED 3 and keep it constant.

[0032] The constant current flowing through the LED 3 is equal to I = VREF / R. Any light radiation received by the LED 3 causes a shift in the I-V curve and therefore a variation in the voltage across the LED 3, measurable by means of a detection circuit 9. The circuit 9 can be any circuit capable of detecting the voltage across the ends. of the diode. It is also possible to directly measure the output voltage of the operational amplifier 5 as the voltage on the resistance 7 is constant.

[0033] In Fig. 7A a simple voltage driving circuit of the LED 3 is schematically shown. In the circuit of Fig.7A, indicated as a whole with 10, an operational amplifier 11 is provided, whose output is connected, through a resistive network 13 of feedback, to the inverting input. A reference voltage VREF is applied to the non-inverting input of the amplifier 11. The anode of LED 3 is connected to the inverting input of the operational amplifier 11 and the cathode is connected to ground. The circuit 10 is piloted in such a way that a constant voltage VD = VREF is present at its ends. The radiation received by the LED 3 causes a shift of the I-V curve and therefore a variation of the current through the LED 3, which can be detected by means of a voltage detection circuit 15 which detects the voltage across the resistance 13 which is directly proportional to the current flowing on the LED 3.

[0034] In both cases the signal generated by the light radiation incident on the p-n junction of the LED 3 can be amplified with suitable configurations of the signal detection circuit. For example, it is possible to filter the direct current contribution through the use of a high-pass filter upstream of the signal amplification chain.

[0035] Fig.7B shows by way of example a diagram of a driving circuit similar to that of Fig.7A, in which a signal detection circuit 15 is shown, which includes a high-pass filter 16. Using the filter high pass 16, the direct component due to the direct bias of the LED 3 is canceled. To the amplification section 18 of the circuit 15, a signal is applied which contains only the variation of the electrical parameter to be detected and not its direct component.

[0036] In some applications the voltage VREF, and therefore the current imposed on the branch of the LED 3 or the voltage imposed across it, may vary over time.

[0037] To obtain a better operation of the device, it is possible to combine LED 3 with a second reference LED driven in the same conditions as LED 3, but shielded so as not to receive the light radiation that must be picked up by LED 3. A circuit solution of this type, it allows the contribution due to its direct polarization to be subtracted from the signal detected at the ends of the LED 3, so that the amplified signal is given by the difference between the electrical parameters (current or voltage) detected at the ends of the two LEDs. Furthermore, common mode noise components are thus eliminated. In practice, using an emitter / detector LED and a reference LED it is possible to perform differential measurements.

[0038] Figures 8, 9 and 10 show, by way of fully exemplifying and non-limiting way, circuit solutions which use a reference LED, to perform differential measurements.

[0039] Fig.8 schematically shows a device 1 with an emitter / detector LED 3 and a driving circuit 20, for driving the current of the LED 3. The driving circuit 20 comprises an operational amplifier 21, at the input of which there is no inverting the reference voltage VREF is applied. LED 3 is connected with its anode to the output of the operational amplifier 21 and with its cathode to the inverting input of the operational amplifier 21. A resistor 23 connects the cathode of LED 3 to ground. So far the circuit is substantially the same as that of Fig.6. However, to perform differential measurements, the circuit 20 comprises a second LED 3A connected with the anode to the output of a second operational amplifier 21A, similar to the operational amplifier 21, and with the cathode connected to ground, by means of a resistor 23A, which can be of a value equal to the resistance 23. The same reference voltage VREF is applied to the non-inverting input of the operational amplifier 23A. LED 3A is the same as LED 3, but shielded from external light radiation. In this way the I-V curve of the LED 3A is not translated due to the effect of external radiation. A detector circuit 27 detects the voltage difference between the two LEDs 3, 3A obtaining a signal which is a function of the radiation incident on LED 3.

[0040] In some embodiments it can be envisaged to use a resistor 23A of a different value compared to the resistor 23. In fact, by suitably modifying the resistance values, the circuit can be balanced, obtaining an output voltage equal to zero in the absence of lighting . Furthermore, it is possible to compensate for the differences between the I-V characteristics which may also have nominally equal LEDs. Furthermore, by using resistors 23, 23A different from each other, it is also possible to use different LEDs 3, 3A, combined with resistors of different values to obtain the balance of the circuit.

[0041] Fig.9 shows a diagram of a device 1 with an emitter / detector LED 3 inserted in a driving circuit 30 which keeps the voltage across the LED 3 constant, to perform a current measurement. The driving circuit 30 comprises a first operational amplifier 31 to whose non-inverting input a reference voltage VREF is applied. A resistive feedback network with a resistor 33 is connected between the output and the inverting input, similarly to the configuration of Fig.7A. The anode of the LED 3 is connected to the inverting input of the operational amplifier 31, while the cathode of LED 3 is grounded. The circuit 30 also comprises a second operational amplifier 31A, similar to the operational amplifier 31, a second feedback network with a resistance 33A which can be equal to the resistance 33 and a LED 3A, equal to the LED 3, connected between the inverting input of the operational amplifier 31 and ground. The VREF voltage is applied to the non-inverting input of the operational amplifier 31A. Similarly to the LED 3A of Fig.8, the LED 3A of Fig.9 is also shielded, so as not to receive light radiation on its p-n junction. A detector circuit 35 detects a signal proportional to the current difference between the two LEDs 3, 3A. This signal is determined by the effect of light radiation that affects the p-n junction of LED 3 and the contribution of direct polarization has been eliminated from it.

A similar circuit configuration, with only one operational amplifier, is illustrated in Fig.10. In this diagram, the device 1 comprises the emitter / detector LED 3 and a current driving circuit 40, comprising an operational amplifier 41 which, similarly to the circuit 20 of Fig.8, maintains a constant current through the LED 3A.

[0043] The LED 3 is connected with its anode to the output of the operational amplifier 41, and with its cathode to ground, through an active or passive load network, represented by example by a resistor 43. A second LED 3A, equal to the LED 3 but shielded so as not to receive light radiation on its p-n junction, it is arranged in the feedback network of the operational amplifier 41, between the output and the inverting input of the latter. The cathode of the LED 3A is connected to ground via a resistive network, for example represented by a resistance 43A equal to the resistance 43. A reference voltage VREF is applied to the non-inverting terminal of the operational amplifier 41. A detector circuit is connected across the resistors 43 and 43A so as to detect, by means of a differential voltage measurement, the difference between the currents flowing through the two LEDs.

[0044] The detector circuits can be configured in any way known to those skilled in the art, for example with a differential amplifier capable of amplifying the signal differences between the outputs of the LEDs 3 and 3A, as schematically illustrated in Fig. 10A, where 46 indicates the amplification stage with the differential amplifier 46.1, the output of which is associated with an analog-digital converter 48. Differential amplifiers for instrumentation, of the type indicated with 50 and schematically represented in Fig. 10B, of which 50.1 and 50.2 indicate the two operational amplifiers. The output of the differential amplifier 50 can be acquired both in a differential manner after the first amplification stage 50, and single-ended using a further operational amplifier 52. In Fig.10C, as a further non-limiting example of detector circuits, is shown a circuit 54 using a current-to-voltage converter. The diagrams of Figs. 10A, 10B and 10C are just some of the many usable detector circuits known to those skilled in the art.

[0045] The diagrams described up to now show simplified circuit solutions of devices 1 which contain a LED 3 able to function simultaneously as an emitter and as a detector of light radiation. As mentioned initially, the signal generated by the current flow caused by the photons incident on the LED 3 can be picked up simultaneously with the emission of radiation by the directly polarized LED 3. The received light radiation can be a part of the same radiation emitted by the LED 3 and reflected or scattered by a target. Alternatively, the radiation received by the LED 3 can be a radiation coming from a different source. Non-limiting application examples of the devices described here are illustrated below. The application examples described use in some cases the radiation emitted by LED 3 and received by it following reflection or diffusion, and in others a light radiation coming from a source other than LED 3.

[0046] According to some embodiments, the device 1 with the LED 3 can be used to carry out distance measurements thus making a generic proximity sensor. The systems currently used for optical distance measurement by means of laser or LED emitters provide for the simultaneous presence of an emitter and a receiver. The distance between the measuring device and a target can in some cases be measured based on the time required by the light signal emitted by the emitter to be picked up by the detector following reflection from the object whose distance is to be measured, or based on a phase shift between the signal emitted and the signal received. Other known distance meters or proximity sensors provide for the use of an LED and a photodetector side by side. The LED emits a light radiation according to its own emission lobe and the photodetector receives, according to its reception lobe, the rear-scattered radiation from a target placed in front of the LED / photodetector pair. The non-confocality of emitter and receiver implies operating limits of the device. In any solution, however, it is necessary to have an emitter and a receiver in the device. This involves an offset between the two emitting and receiving lobes. This consequently makes the device unsuitable for measuring small distances and also affects the cost of the device.

[0047] By using an LED which functions simultaneously as a photoemitter and as a photodetector, the advantage is obtained that the emission lobe and the receiving lobe coincide and there is an overlap between the emitted and received light beam. In other words, transmitter and receiver coincide spatially as they are the same device. This ensures confocality between optical transmission and reception.

[0048] Therefore the device is able to perform measurements even of small distances, using a single semiconductor component. Fig. 11 shows the basic diagram of a device 1 containing a LED 3 polarized directly to emit a radiation beam F towards a target or sight T, and to receive and detect a radiation beam reflected or scattered from the target T towards the LED 3. The detection circuit of the light signal incident on the LED 3 detects a signal which is a function of the distance D between the LED 3 and the target T. The intensity of the signal detected by the LED 3 while it is directly polarized to illuminate the target T is a function of the distance D1 (Fig.11A), D2 (Fig.11B) or D0 (Fig.11C) between target T and device 1. In particular, Fig.11C shows a condition in which the target T is practically in contact with the emitter / receiver device. Measurement is still possible without resorting to the aid of particular optical devices, while it would not be possible with current art systems.

[0049] Fig.11D shows the trend of the luminous flux received by LED 3 (indicated with Φ in ordinates) as a function of the distance D (shown in the abscissa). The intensity of the flux is as a first approximation a function of the square of the distance (D <2>) and has its maximum value Φ0 when the distance between the LED3 and the target T is equal to D0 (contact measurement, Fig. 11C ). It is therefore possible to measure the distance D between LED 3 and target or target T based on the intensity of the light radiation emitted by LED 3 and received by it by reflection or diffusion by the target T.

[0050] Furthermore, by carrying out a measurement at a fixed distance, which for practicality can be the distance D0 at which the device 1 is in contact with the target T, it is possible to obtain information on the reflectivity of the medium of which the target T is constituted. To clarify this possibility, in Fig.11E two curves ΦA, ΦB of the flux captured by LED 3 are shown, relative to two different materials. From the diagram of Fig.11E it can be seen how the intensity of the reflected light depends not only on the distance but also on the characteristics of the sight or target T. To take into account the fact that the intensity of the reflected / diffused light also depends on the characteristics of the target T it is possible to evaluate the value Φ0A or Φ0B in contact depending on the material and normalize the result as presented in Fig.11F.

[0051] In some forms of use, the device 1 comprising at least LEDs 3 which, in direct polarization, functions simultaneously as an emitter and detector, can be used as a button. In fact, if the LED 3 is directly polarized, it emits a light radiation which can be reflected by the finger of a user who approaches the LED 3 to act on it as a proximity switch or button. The I-V curve will undergo a sudden variation over time as a result of the approaching and subsequent removal movement of the finger from the LED 3. This variation is a consequence of the fact that the finger reflects or diffuses part of the radiation emitted by the LED 3 in direct polarization, and that this radiation it is picked up by the LED 3 itself and detected by the detection circuit. Depending on whether LED 3 is driven at constant voltage or constant current, the signal generated by the user's finger will cause a change in current or voltage over time through LED 3. Fig. 12 represents the trend of an electrical quantity reported in ordinates (voltage V or current I across LED 3) as a function of time t reported in abscissa. The contact of the finger on the LED 3 as a switch causes a signal S detected by the detection circuit. This signal can be used as a command for an apparatus controlled by the switch.

[0052] This type of use can be expanded by making a matrix of LEDs 3, each equipped with its own signal detection circuit, obtaining a touch screen having functions similar to common capacitive type panels or screens. Fig. 13 schematically shows a matrix 51 formed by a plurality of LEDs 3. In this case the user uses the matrix 51 by touching or touching its surface and causing the generation of a signal S of the type illustrated in Fig. 12 by of one or the other of the LEDs 3 which form the matrix itself. Compared to current touch screens, the screen made with LED 3 can present advantages in particular conditions of use.

In some embodiments, a matrix of LEDs, for example a linear matrix of LEDs, directly biased and controlled to detect a backscattered optical signal from an object moving relative to the matrix, can serve as a command interface with more advanced functions than those of a simple button. For example, it is possible to create a curtain or linear matrix of directly polarized LEDs that are able to detect not only the approach of a hand (or other diffusing or reflecting object) to the curtain, but also its displacement in one direction or in the direction. other than the curtain. In this way it is possible to create control switches that cause different actions depending on how the user using the switch moves his hand with respect to the latter. A switch of this type can be used, for example, to raise or lower a shutter, for example, according to whether the user moves his hand in front of the curtain by moving it from top to bottom or from bottom to top. Since each LED emits optical radiation and receives backscattered radiation from the hand, the device thus made is sensitive to the direction in which the hand moves with respect to the LED curtain and is able to discern whether it moves in one or the other of two opposite lines.

[0054] Matrices of more complex shapes can allow to execute a multiplicity of commands with the same device using different hand movements (for example: up / down; left / right).

[0055] LED matrices 3 can also be used for the construction of other types of devices, for example to detect two-dimensional images of an object through the same LED matrix 3 that is used to illuminate the object. Basically, in this category of devices, a matrix of directly polarized 3 LEDs provides the illumination of the object and simultaneously receives its image, which can then be reconstructed, for example, on a display screen or stored in a file.

[0056] Figs. 14 and 15 schematically show a matrix 61 of LEDs 3 which can be placed in front of an object O with the interposition of a focusing optic 63. The light radiation emitted by each LED 3 of the matrix 61 illuminates the object O, the which reflects or diffuses the same radiation towards the LEDs 3 which capture it, generating a signal that can be detected and processed, obtaining the image of the object O. In practice, the matrix 61 represents a sensor similar to those typically used in cameras and in digital video cameras, where, however, the illumination of the object to be filmed is carried out by the same sensitive elements (LED 3) that capture the light reflected or diffused by the object. The device thus realized is advantageous in all those situations in which confocal systems are used. The area of which the image is detected coincides with the area illuminated by the matrix 61 of LED 3. The solution described here may have uses, for example, in optical microscopy, medicine and other sectors.

[0057] By using LEDs 3 that emit at different wavelengths in the same matrix 61 it is also possible to obtain multispectral images of the same object O. In Fig. 14 LEDs 3, 3X are schematically represented which emit at different wavelengths for get this function. In some embodiments it is possible to drive the LEDs 3 alternately, selectively activating one or the other group of LEDs 3, which emit at one or another wavelength. This allows the detection of spectral images at different wavelengths even in rapid succession.

[0058] Devices 1 comprising directly polarized LEDs 3 which operate simultaneously from photo-emitters from photodetectors can also be used to realize acoustic wave detection systems, useful for example for the production of acoustic microscopes, ultrasound detectors, vibration sensors and the like.

[0059] A principle diagram of the use of an LED device 1 of the type described here for the detection of acoustic waves is illustrated in Figs.16A, 16B. 1 indicates generically and by way of example a device comprising at least one LED 3 of the type described above, directly polarized and configured to operate as a photoemitter and photodetector, capable of detecting light radiation emitted by itself and reflected by a reflector 65, elastically deformable underneath the effect of a wavefront of ultrasound or other mechanical vibrations. The reflector 65 is placed in front of the device 1. The reflector 65 can be constituted by, or comprise, a sheet reflecting at least a part of the optical radiation, and of such thickness that it can be deformed to an acoustic wave that hits the surface of the foil forming the reflector 65 on the opposite face with respect to that facing the device 1 and its LED 3.

[0060] An ultrasonic transducer 67 can be positioned behind the reflector 65, i.e. on the opposite side with respect to the device 1. The ultrasonic transducer 67 can be placed in a tank 68 which contains a coupling means 69, for example a liquid. The reflector 65 can be immersed in the medium 69 or placed immediately outside it, that is, on the interface between the coupling means and the air, for example on the free surface of a liquid coupling means.

[0061] An object O to be analyzed can be placed in the coupling liquid 69, between the transducer 67 and the reflector 65. The object O can be soundproofed by the ultrasonic transducer 67. The acoustic waves passing through the object O reach the lamina forming the reflector 65 and cause a localized elastic deformation thereof. If the face of the reflector 65 is illuminated by the LED 3, this receives a light signal reflected by the reflector 65 which is modulated by the deformation of the reflector 65. Therefore, by placing the LED 3 of the device 1 in front of the ultrasonic transducer 67 it can be detected by means of the LED 3 a signal that is a function of the acoustic wave that crosses the object O under examination at the point corresponding to the volume hit by the ultrasonic waves generated by the transducer 67.

[0062] Fig. 16B shows by way of example a time diagram showing the trend of the signal detected on LED 3. Any electrical quantity (for example current or voltage) which is modulated by the light reflected by the reflector 65 can be reported on the ordinates. and which affects the p-n junction of LED 3.

[0063] By moving the object to be investigated O and the system consisting of the LED 3 and the ultrasonic transducer 67 relative to each other, it is possible to generate an image of the object O which contains information on the presence, for example, of irregularities, such as cracks or other internal defects of the object. Scanning can be performed along two axes defining a scanning plane parallel to the lamina 65.

[0064] With the structure described above it is possible to realize scanning acoustic microscopes, possibly equipped with a matrix of acoustic transducers 67 and / or a matrix of LED 3 to investigate larger portions of the object O.

[0065] While in the embodiment of Fig.16A and 16B the device 1 is configured to pick up signals obtained through acoustic waves that work in transmission, in other embodiments systems can be configured to work also in reflection of an ultrasonic wave . Fig. 16C illustrates an embodiment in which the device 1 with the LED 3 is arranged in a housing adapted to be immersed in the coupling liquid 69. The housing can integrate a lamina 65, of similar characteristics to the lamina 65 described with reference to Fig.16A, which closes the compartment in which device 1 is housed. By placing the device 1 with the lamina 65 and the acoustic transducer 67 on the same side of the object O to be investigated, it is possible to carry out an analysis of the object O in reflection rather than in transmission.

[0066] While Figs.16A, 16C show two possible applications of the device of the present description in the field of acoustic investigations, it must be understood that the device 1 can generally realize an ultrasound transducer with the consequence of being able to carry out all its possible applications. In particular, a curtain or array of devices 1 could be made to generate two-dimensional images. An ultrasonic system using an acoustic wave transducer in combination with a device 1 or a matrix of LED devices 1 which operate simultaneously in transmission and reception, detecting vibrations induced by ultrasounds on an elastically deformable reflective element, allows to carry out investigations and measurements without contact using ultrasound or vibrations that propagate through a transmission medium. While in the examples of Figures 16A and 16C the transmission medium is a liquid, the possibility of using a coupling fluid in the gaseous phase, for example for low frequency ultrasounds, or a solid is not excluded.

[0067] LED 3 controlled in direct polarization and operating simultaneously by photo-emitters and by photo-detectors according to what described here can also be used for the realization of scanners. By way of example, Fig.17 schematically illustrates a scanning system 71 which comprises a linear array of devices 1 with relative LEDs 3. The curtain can extend orthogonally to the plane of the figure and orthogonally to the scanning direction. The scanning system 71 can move relative to a sheet F according to the double arrow fF. The movement can be given to the linear LED curtain 3 by keeping the sheet F stationary on a transparent support plane, for example. In other embodiments it is possible to keep the LED curtain 3 stationary and move the sheet F with respect thereto. Regardless of how the relative movement between the LED curtain 3 and sheet F is performed, the scanning system 71 is capable of acquiring an image of the surface of the sheet F facing towards the linear LED curtain 3. At any time the LED curtain 3 illuminates a linear portion of the sheet F by effect of the light radiation emitted by the directly polarized LEDs 3. Light reflected from the surface of the sheet F is collected by the same LEDs 3 which function simultaneously as detectors and as light emitters. Through the signals generated by the fraction of light emitted by the LEDs 3, reflected by the sheet F and collected by the LEDs 3, the image of the sheet F is obtained.

[0068] A particular application of the scanning system 71 of Fig.17 can allow to detect defects or foreign bodies applied to the sheet F. For example, the scanning system 71 can be used to detect a transparent N adhesive tape applied to the sheet F. This can be particularly useful in analyzing banknotes for the purpose of identifying damaged and repaired banknotes with the application of adhesive tape, in order to remove them from circulation. WO2013 / 050931 describes a particularly efficient system for identifying pieces of adhesive tape on banknotes or other documents. With the use of LED 3 operating simultaneously as photo-emitters and photo-detectors, it is possible to create an even more efficient device.

[0069] Fig.18A shows an embodiment of a scanning system 81 with which a sheet F can be scanned, to check whether an adhesive tape N is applied to it. The scanning system 81 is based in practice on a distance measurement between the sheet F and a linear curtain or linear matrix of devices 1 equipped with LEDs 3, which develops orthogonally to the plane of the figure. The array of devices 1 can have a length equal to or greater than the width of the sheet F, i.e. its dimension in a direction orthogonal to the plane of the figure. The sheet F can move with respect to the LED curtain 3 along a direction X, parallel to the length of the sheet F. The LEDs 3 of the curtain emit a light radiation due to their direct polarization and are connected to a detector circuit, to detect the variation of an electrical quantity, for example the voltage or current across each LED 3, caused by light incident on the LEDs. The incident light is represented by a part of the same radiation emitted by the LEDs 3 and reflected or diffused by the sheet F. The variation in light radiation detected generates a signal, the trend of which is shown in the diagram of Fig.18B. The relative position between sheet F and LED curtain 3 is shown on the abscissa. As long as sheet F is not present in front of the LED curtain 3, the signal picked up by the detection circuit is low. When, in position X1, the edge of the sheet F passes in front of the LED curtain 3, part of the light emitted by the LEDs 3 is reflected by the sheet F and picked up by the LEDs 3 themselves, generating a signal. If the sheet F has, between the points X2 and X3, an adhesive tape N applied to its surface, the thickness of this adhesive tape causes the surface of the sheet F to move away from the LED curtain 3 and consequently a reduction in the signal detected by the LEDs. same, as shown in Fig. 18B. The signal increases again in position X3 and remains high until the second edge of the sheet F passes in front of the LED curtain 3 (position X4).

[0070] In the absence of adhesive tape N, the signal captured on the LED curtain 3 remains practically constant.

[0071] The scanning system 81 described with reference to Fig.18 requires that the adhesive tape N be transparent to the wavelength of the light radiation emitted by the LEDs 3 and that the sheet F be reflective at this wavelength, while any images reproduced on sheet F, for example a banknote, may be irrelevant with respect to the amount of light radiation reflected by sheet F. More generally in the case of situations in which the image represented is not irrelevant to the amount of light radiation reflected by the sheet F there is a local variation of the signal due to the presence of the adhesive tape. In fact, the acquired image depends on the image printed on the sheet. The presence of the transparent adhesive tape causes local attenuation of the signal and therefore a more gray band.

[0072] In the specific case of banknotes and systems for detecting the state of wear of banknotes, it is possible to compare the scan result with that of sample banknotes, without adhesive tape, and statistically evaluate the variations on the signal induced by the presence of the adhesive tape.

[0073] Figs. 19A and 19B show an application similar to that described with reference to Figs. 18A, 18B, in which, however, the sheet F being scanned absorbs the radiation emitted by the LED curtain 3, while any adhesive tape N is partially reflective to the wavelength used.

[0074] Linear arrays of different LEDs, for example emitting at different wavelengths, can be placed in the same device to sequentially examine the same sheet F under different conditions.

In some embodiments an LED scanning system of the type illustrated in Fig.17 can be integrated into a document control system of the type described in WO2013 / 050931. In particular, a combined solution of this type can be used to simultaneously or sequentially acquire two different images of the same object, for example a banknote whose integrity is to be verified. A first image is acquired with a matrix of emitter / receiver LEDs 3 of the type described herein; a second image is acquired with a system of emitters and receivers of the type described in WO2013 / 050931. Alternatively, the images can be acquired from the same LED matrix or curtain, which are operated selectively and alternately as described here, or as described in WO2013 / 050931.

[0076] Fig.20A illustrates an explanatory diagram similar to the diagram of Fig.8 of WO2013 / 050931, where two linear arrays of devices of the type described here are provided, and indicated with 1X and 1Y. 1X devices have 3X LEDs and 1Y devices have 3Y LEDs. The curtains extend orthogonally to the plane of the figure. A paper support, for example a banknote BA to be examined, passes along a path of advancement according to the arrow fBA in front of the 3X, 3Y LED curtains 1X and 1Y. An opaque separator septum 100 divides two zones Z1 and Z2 illuminated by the 3X and 3Y LEDs. The separator septum 100 is positioned and made in such a way that the 3Y LEDs do not receive optical radiation directly from the 3X LEDs and, conversely, the 3X LEDs do not receive direct radiation from the 3Y LEDs.

[0077] In a possible embodiment, the 3X and 3Y LEDs can be operated so that an LED curtain, for example the 3X LED curtain 1X, emits an optical radiation, which is sent to the BA banknote, on which an adhesive tape N can be applied, the presence of which must be detected by the device described here. The 3Y LEDs of the 1Y curtain are used as receivers. As described in detail in WO2013 / 050931, the adhesive tape N, when present, acts as a light guide and increases the amount of optical radiation which, emitted by the 3X LEDs, is captured by the 3Y LEDs. While for more details, please refer to the aforementioned publication, here in summary it is sufficient to observe that the presence of the adhesive tape N, transparent to the optical length used, conveys radiation along the AELCD path. This amount of radiation is missing if the adhesive tape N is missing. Therefore, the presence of the adhesive tape N can be identified by the 3Y LEDs that work in reception based on the increase in radiation received by the 3X LEDs. Obviously the system can work in reverse, with 3Y LEDs as emitters and 3X LEDs as receivers.

Alternatively, the 3X or 3Y LEDs (or both) can also be operated as described above with reference to Figs. from 17 to 19. That is, one or the other or both curtains 1X, 1Y of LED 3X, 3Y can detect the presence of the adhesive tape N based on the optical radiation emitted by the LEDs of the curtain and backscattered by the object constituted by the BA banknote and N.

[0079] The system described above can in principle be configured in various ways.

[0080] For example, the two curtains 1X, 1Y can be substantially the same and made up of LEDs that all work in the same way at a given instant. As the banknote advances in front of the 1X, 1Y optical system, the LEDs of a curtain, for example the 3X LED, are directly polarized and brought into conduction. The emitted optical radiation is partly reflected or backscattered towards the 1X curtain itself and with this a first signal is obtained as in Fig. 18 (B). At the same time, the 3Y LEDs of the 1Y curtain can be reverse biased and act as receivers to receive an optical signal emitted by the 3X LEDs and reflected or scattered by the BA banknote and N adhesive tape under the diaphragm or septum 100, as in the publication above The operation can also be reversed, to perform the same operation with the 3Y LEDs as forward bias emitters and receivers and the 3X LEDs as reverse bias receivers.

[0081] The possibility is not excluded that the LED curtain that works (temporarily) as a receiver is in direct polarization, working in the first quadrant of the I-V diagram as described above, even when it receives the optical radiation coming from the other curtain.

[0082] Since the devices described can also work directly in contact with the substrate (banknote BA and adhesive tape N, optionally) as described above, it is possible to obtain a separation of the emission and transmission lobes even without the diaphragm or septum 100.

[0083] In a further variant of embodiment, a single linear matrix or LED curtain can be used, which can be driven differently from each other, as better clarified with reference to the diagrams of Figs. 20B, 20C and 20D. Fig.20B shows a side view of the device which has a 1X curtain of 3X LEDs extending orthogonally to the plane of the figure and to the direction (arrow fBA) of advancement of the banknote BA. Figs.20C and 20D are two views according to C-C of Fig.20A in two different positions of the adhesive tape N with respect to the curtain 1X of LEDs 3X.

[0084] The 3X LEDs can be divided into two groups: the odd position LEDs, indicated by A in Figs. 20C and 20D, and the even position LEDs, indicated by B. The LEDs in position “A” can operate as those described with reference to Figs.

18-19, i.e. polarized directly and conducting, to emit light radiation and receive backscattered radiation. Instead, pairs of LEDs in position "B" can function as emitter / receiver pairs, according to the logic illustrated in WO2013 / 050931. In other embodiments, each position "B" LED can function as a receiver of radiation emitted by the adjacent position "A" LEDs. The LEDs that work in reception can be inversely polarized and do not emit radiation. The amount of optical radiation collected by the LEDs working from receivers in the condition of Fig.20D (adhesive tape N in contact with the 1X curtain of 3X LEDs) is greater than that collected in the condition of Fig.20C (LED in contact with the BA banknote), due to the light guide behavior of the adhesive tape N. This difference in signal collected by the LEDs which function as receivers provides a first information equivalent to that obtainable with the arrangement of WO2013 / 050931. The LEDs that function as receivers of the radiation emitted and backscattered by themselves provide information that is a function of the distance between the LED and the surface of the banknote, as described with reference to Fig. 18. The function of the LEDs can temporally swap roles.

[0085] While in the embodiment examples described above the LEDs are used to emit light radiation and detect a part of the same light radiation emitted and reflected or scattered by a target, in other applications the LED device 1 3 operating simultaneously as an emitter and detector it is possible to capture with the LED 3 a light radiation coming from a different source, while the LED 3 is operating as a photoemitter.

[0086] A possible application of this operating mode occurs in the sector of transmitting information encoded in a light signal between emitting and receiving LEDs. Currently, configurations are already known in which two LEDs, communicating with each other through a light transmission channel, transmit signals to each other by modulating the light emitted. In this case we speak of LED-to-LED transmission.

[0087] According to the current art, essentially two configurations are used. In the first configuration, two emitter / detector devices are used, each comprising an LED in direct polarization to emit a light signal, and a LED in reverse polarization, acting as a photodetector. In this way, each device can emit its own modulated light signal containing information, and at the same time it can receive a signal emitted by the other device.

[0088] To reduce the number of semiconductor components, in a second configuration of the current art each device comprises a single semiconductor element, i.e. a single LED, which is alternately polarized: in a direct way to emit a signal, i.e. to operate from photoemitter; and inversely to operate as a photodetector of the signal coming from the other device coupled to it via the transmission channel. In this way, a reduction in the number of components used is obtained, but a halving of the transmission speed, since it is not possible to carry out a simultaneous bidirectional transmission.

In fact, while information is being transmitted from the first device to the second, the second device must operate in detection mode, with the LED in reverse bias, and cannot transmit information.

[0089] According to configurations described here, simple systems can be used, having a single semiconductor component for each emitter / detector device, and an information transmission speed equal to that achievable with normal devices equipped with an emitter / detector pair.

[0090] In fact, as previously observed, according to what is described here, the device 1 uses the LED 3 in direct polarization, to emit light radiation, and at the same time to detect a light signal incident on the LED 3, through the variation of an electrical parameter (voltage or current) at its ends, caused by the photons incident on the p-n junction of LED 3.

[0091] Fig.21 schematically illustrates the use of two LED devices 1 3 according to the present description, used for the bidirectional transmission of information along a transmission channel. In the diagram of Fig.21A an information transmission system 91 is schematically shown, which comprises a first device 1A with a first LED 3A, a transmission channel 93 and a second device 1B with a second LED 3B.

[0092] The transmission channel 93 can be materialized by an optical fiber or by a bundle of optical fibers. Each device 1A, 1B can be configured in one of the ways described above or in other equivalent ways. What matters is that the respective LEDs 3A, 3B are driven in direct polarization and are associated with a detector circuit, which makes it possible to detect the variation of an electrical parameter, for example current or voltage, across the LEDs, determined by incident radiation. on the respective p-n junctions. Contrary to what happens in the applications described above, in the application of Fig.21 the LED 3A is able to emit its own light radiation and capture the light radiation coming, through channel 93, from LED 3B. Conversely, the LED 3B is able to emit its own light radiation and capture the light radiation coming, through the channel 93, from the LED 3A.

[0093] The LEDs 3A, 3B can be driven so as to emit a light radiation, the intensity of which is modulated to transmit information. For example, each LED 3A, 3B can be controlled to transmit information encoded in a binary code, ie consisting of sequences of "0" and "1". For this purpose it is possible to associate two voltage values to the logic values “0” and “1”, and therefore two values of light intensity emitted, if the LEDs 3A, 3B are voltage controlled. In other embodiments, the LEDs 3A, 3B can be controlled in current, and in this case the modulation of the emitted signal is obtained by modulating the bias current. The following description is by way of example based on a voltage control of the LEDs 3A, 3B.

[0094] Both LEDs 3A, 3B can transmit and receive simultaneously with different modulations.

[0095] By way of a completely non-limiting example, it can be envisaged that the logic value "0" is associated with a positive voltage value V1 and the logic value is associated with a positive voltage value V2, with V2> V1 "1". Four different conditions will then be possible:

a) LED 3A transmits a "0" symbol while LED 3B transmits a "0" symbol; in this condition at the ends of both LEDs 3A and 3B there will be a voltage V1;

b) LED 3A transmits a "1" symbol while LED 3B transmits a "0" symbol; in this condition at the ends of the LED 3A there will be a voltage V2 and at the ends of the LED 3B there will be a voltage equal to V1 + ΔV, where ΔV is the difference in voltage induced at the ends of the LED 3B induced by the light radiation emitted by the light signal coming from LED 3A;

c) LED 3A transmits a "0" symbol while LED 3B transmits a "1" symbol; in this condition there is a voltage V2 at the ends of LED 3B, while at the ends of LED 3A there is a voltage V1 + ΔV

d) LED 3A transmits a symbol "1" while LED 3B transmits a symbol "1"; in this condition at the ends of both LEDs 3A and 3B there is a voltage V2 + ΔV.

[0096] Figs. 21B, 21C and 21D summarize the four conditions (a) - (d). Fig.21B shows the voltages across the two LEDs 3A, 3B in the four conditions mentioned; Fig. 21C shows the logic signals emitted by the two LEDs 3A, 3B in the four cases (a) - (d) and Fig.21D indicates the voltage values.

[0097] The diagrams of Fig.21 show the four possible operating conditions of the pair of LEDs 3A, 3B in the case in which the detected signal is a voltage signal, but it must be understood that the same logic applies in the case in which the signal detected is a current signal.

[0098] With the configuration illustrated in Fig.21 it is therefore possible to transmit information by modulation of optical signals in a bidirectional manner, conveying information from the LED 3A to the LED 3B, which can simultaneously emit information to be conveyed to the LED 3A and detect the information from LED 3A. Similarly, LED 3A detects information from LED 3B while emitting information to the latter.

[0099] In other application forms the LED 3 of the device 1 can be used to receive an optical command signal coming from any source. In some embodiments, the control circuit of the LED 3 can be configured in such a way that a light signal captured by the LED 3 causes it to be switched on, switched off or adjusted.

[0100] In this way, for example, twilight LED lamps can be created that turn on when the ambient brightness falls below a switch-on threshold and turn off when the ambient brightness increases above a switch-off threshold. Crepuscular lamps of this type are known. However, the crepuscular lamps of current art use a separate photodetector with respect to the lighting body.

[0101] With a device 1 of the type described here, on the other hand, it is possible to eliminate the photodetector and, by simply modifying the control circuit of an LED lamp, it is possible to make it work as a twilight lamp.

[0102] In this application, the LED 3 of the device 1 is still directly biased, with a voltage that can be above or below the conduction threshold of the LED. When the lamp is off, ie it does not emit light radiation, the voltage threshold across the LED is lower than the conduction threshold. External light radiation, for example ambient light, is detected by the control circuit of LED 3. When the intensity of the ambient light radiation falls below a switch-on threshold of LED 3, the power supply circuit increases the voltage across the LED. 3 bringing it into conduction and generating light. When the ambient light radiation increases above a switch-off threshold, detectable through the effect of photons collected by the p-n junction of LED 3, the control circuit turns off LED 3 bringing the voltage across it below the conduction threshold.

[0103] The same control criterion can be used to modulate the emission of the LED 3 according to the light radiation incident on the LED 3 itself, which can be given by the sum of the ambient light (for example sunlight or other sources present in the same room) and the light emitted by the same LED 3. In this way, energy savings are obtained without the need for a photodetector.

[0104] In the embodiments described up to now the LED 3 is used in direct polarization to function simultaneously as a photoemitter and as a photodetector. This is not, however, indispensable. In fact, in other forms of use according to the present description, the LED 3 is directly polarized and used only as a photodetector, and not as a photoemitter. A possible example of use of this type is in the field of temperature measurements, by detecting radiation in the near infrared.

[0105] In these applications, single LEDs 3 can be used as detectors of information related to the temperature of an object or body. LED arrays 3 can be used to detect thermal images of an object or body.

[0106] Fig. 22 illustrates the general principle on which this further use of the LED 3 in direct polarization is based. 1 again indicates a generic device comprising a generic directly biased LED 3. As in the previously described applications, also in this case the semiconductor device 3 works in the first electrical quadrant of the I-V diagram (Fig.1).

[0107] 101 indicates a generic body or object that emits infrared IR radiation. The radiation is picked up by the p-n junction of the LED 3. The infrared radiation IR heats the p-n junction of the LED 3 by irradiation. As a consequence of this heating, the voltage across the LED 3 decreases. The control circuit of the device 1 can be configured to detect the voltage decrease and from this to go back to the temperature of the radiant body 101.

[0108] Fig. 23 shows by way of example the trend of the voltage V across the LED 3 as a function of time t when the p-n junction of the LED is hit by thermal radiation. In the interval (t0-t1) the temperature of the pn junction is constant and therefore also the voltage V across the LED 3 remains constant. At instant t1 the p-n junction of LED 3 begins to receive thermal radiation and heats up until instant t2. In the interval (t1-t2) the voltage across LED 3 decreases as a result of heating. At instant t2 the thermal radiation ceases and the p-n junction of LED 3 cools gradually returning to ambient temperature, with a consequent gradual increase in the voltage across LED 3 up to the initial value V0.

[0109] The effect of the temperature of the p-n junction on the voltage across the directly biased LED can be used to make a device capable of providing an estimate of the thermal radiation of a body, and therefore capable of estimating the temperature of a hot body which irradiates in the infrared, also using a single LED 3. Fig. 24 illustrates an implementation diagram, where 1 indicates generically the device comprising LED 3, the direct biasing circuit of LED 3 and the voltage detection circuit at the ends of the LED 3. To make the device directional, a collimator 103 or a lens can be provided which allows to select a preferential direction of reception of the thermal radiation, so as to remotely measure the temperature of a body 101 which radiates in the infrared ( IR radiation).

[0110] The phenomenon described above, through which the remote temperature of a hot body can be estimated, can also be exploited for the generation of IR images of a body or object. For this purpose it is possible to realize a matrix 105 of LEDs 3 (Fig.25), each of which is directly polarized. In front of the matrix 105 of LEDs 3 there is a collimation optic 107 which collects and focuses on the matrix 105 the IR radiation coming from a body or target 101. By means of the signals collected by the single LEDs 3 of the matrix 105 it is possible to generate a thermal image 109 of object 101.

[0111] The above description relates to some possible uses and configurations of an opto-electronic device comprising an LED or a linear or two-dimensional array of LEDs, in which each LED is directly polarized and is operated in the first electrical quadrant in the I-V plane, to detect a radiation, optical or thermal, and obtain information from this detected radiation. The detection of the incident radiation on the p-n junction can be simultaneous with the emission of optical radiation by the LED. The radiation incident on the p-n junction can be a part of the same radiation emitted by the LED or a radiation coming from a different source. In general, all the described applications are characterized by the fact that the LED is used as a radiation detector while it is directly polarized. This distinguishes the applications and uses described here with respect to what happens in the current art, where LEDs are used as detectors in reverse polarization and therefore cannot function simultaneously as light emitters and photodetectors.

[0112] While in the above description some possible devices that can be made with an LED or a matrix of LEDs have been mentioned, the new use of LEDs in direct polarization with the function of optical or infrared radiation detector allows the creation of a wide range of opto - different electronics, some of which are listed below.

[0113] A first group of opto-electronic devices comprises LED scanners, comprising a matrix of LEDs, for example a linear matrix of LEDs. The scanner can be monochrome or multi-color. In the first case it uses LEDs that all emit at the same wavelength, in the second case it uses a combination of LEDs that emit at different wavelengths, which can be arranged in the same matrix, for example a linear matrix, or in two or more linear matrices side by side. This group of devices is based on the use of the LED as an emitter of light radiation and simultaneously as a receiver of a part of the radiation it emits and reflects or diffuses from the object to be scanned.

[0114] The scanner can be used to check documents, such as bills or banknotes, possibly for the purpose of verifying their authenticity or identifying foreign material (adhesive tape) applied to the document.

[0115] A further category of opto-electronic devices that can be made with LEDs used in the manner described here includes two-dimensional LED arrays, directly polarized and used to illuminate an object and receive an image of the illuminated object. Devices of this type can be configured as microscopic image detectors, as they allow to illuminate an object placed exactly in front of and / or at a very short distance from the LED matrix, since the same emitters also act as receivers of reflected or diffused radiation. Two-dimensional matrices of this type can be used for surface checks, for example to perform surface investigations and control of defects on objects of various types, for example in metallurgy.

[0116] Two-dimensional LED arrays can be used in particular in the medical field, to make dermatoscopes. In this case, two-dimensional LED arrays can be used to illuminate a portion of the skin and receive diffused or reflected light from the same illuminated portion and obtain an image. By using LEDs that emit at different wavelengths, it is possible to obtain multispectral images. The same matrix can include a combination of several types of LEDs, to illuminate and receive images sequentially at different wavelengths and therefore perform multispectral investigations in very short times, through selective activation of different groups of emitting LEDs at different wavelengths. .

[0117] Dermatoscopes made in this way can be used, for example, for the rapid detection of ulcers or other superficial lesions of the epidermis, and also possibly for the investigation of nevi and the early detection of melanomas or other skin diseases.

[0118] LED arrays can be used to make infrared sensors capable of providing thermal images of objects at a distance, exploiting the effect of infrared radiation on the voltage and / or current through the junction of the LED. Devices made in this way may have, compared to the IR cameras of the current art, a lower cost and a higher resolution.

[0119] LEDs or LED arrays can also be used as generic proximity sensors. In this case, the LED or LEDs of the device are used in the manner described above with reference to the measurement of distances.

[0120] A further category of LED matrix devices includes panels or touch screens, that is touch or touch, as user interfaces, replacing capacitive systems. In this case, the touch device can comprise a matrix of LEDs connected to direct polarization circuits and to detectors of radiation incident on the individual LEDs. The commands are given, instead of through variations in capacity, as in traditional touch devices, by variations in brightness captured by the p-n junction of the individual LEDs forming the matrix or panel.

[0121] Single LED devices may include LED switches, where the switch is activated by the light emitted by the LED and reflected or diffused by a user's finger. In other embodiments, the LED switch can be turned on, off or adjusted by the environmental light radiation incident on the LED.

[0122] Further single LED devices can be configured as computer mice, employing an LED as a light emitter and simultaneously as a detector, avoiding the need for a dual emitter-receiver system.

[0123] Further single LED devices may comprise an LED associated with an optical fiber for making optical fiber probes. The radiation emitted by the LED is conveyed through the optical fiber to reach an investigation point inside an object or body, for example (in medical applications) inside a human or animal organ. The back-scattered or reflected radiation is conveyed by the same optical fiber to the LED, whose detection circuit provides information on the basis of the radiation collected by the same LED that emitted it.

[0124] Single LED devices may further comprise optical information transmission devices of the LED-to-LED type. Two LEDs between which information is to be exchanged are connected to each other via a transmission channel, for example an optical fiber. Each LED being directly polarized emits light radiation which can be modulated by acting on the voltage and / or current across the LED. At the same time, a detection circuit of the radiation incident on the LED and coming from the transmission channel allows to receive information transmitted by the other LED, which is received in the form of a signal generated by the photons collected by the junction of the LED.

[0125] Arrays of single or matrix LEDs can configure ultrasonic or mechanical vibration detectors, using single LEDs or LED arrays as distance meters between LEDs and a vibrating element, such as a vibrating foil, placed at a fixed distance from the LED. The vibration of the vibrating element causes a micrometric variation in the distance between the vibrating element and the LED, which can be detected by the LED. On this principle, simple devices can be made, such as vibration sensors, ultrasound sensors, acoustic sensors and microphones, but also more complex devices such as acoustic microscopes.

[0126] Single LED devices can also be used according to one or more of the descriptions made for checking the integrity of the yarn at the outlet of a package from a loom for fabric manufacturing in order to verify the absence or presence of a knot, or for the control of the thread for the manufacture of tea bags, for example.

[0127] Single or matrix LED devices can also be used according to one or more of one of the descriptions made for controlling the total or partial filling of pharmaceutical caps. The choice of the color of the LED to be used depends in various cases on the optical characteristics of the material of which the cover is made and its content.

[0128] Single or multiple LED devices can be used as crepuscular lamps, in which the light emission of the LED (s) is activated by the variation of ambient light radiation. At least one LED, directly biased, is associated with a circuit for detecting the variations of an electrical parameter induced by variations in the environmental light radiation incident on the LED. When the ambient radiation falls below a certain threshold, the LED can be brought into lighting conditions.

[0129] The proposed distance measurement system could also be effectively used on the tip of laser cutting heads for feedback control of the relative distance between the cutting head and the material to be cut. In this case, you can think of inserting a ring of LEDs around the structure of the cutting head in order to carry out the measurement on an area surrounding the laser exit hole where the fumes due to the thermal ablation of the material are no longer present. In general, the system can be considered as suitable for working in precision industrial applications as well as welding or laser marking as opposed to capacitive heads able to work effectively only on metal surfaces.

[0130] In general, therefore, a system comprising a tool, associated with a system for measuring the distance between the tool and the workpiece, is therefore also the specific object of the present description, which measuring system comprises an opto-electronic device using one or more LEDs under direct bias conditions and a circuit for detecting the variation of an electrical parameter as a function of the radiation received by the LED.

[0131] For example, the system can comprise a machine tool or a machining center, with numerical control, with at least one head carrying at least one tool, and with one or more numerically controlled axes.

[0132] Figs 26 and 26A illustrate by way of example a machining center 200, which in the specific case is a CNC machining center for laser cutting. However, it should be understood that what is described below can also be applied to different machines, which can use tools or operating heads different from a laser source. In the present context, therefore, the term "tool" must be understood as a generic component, group, organ, or unit capable of interacting with a piece to be machined. The work center comprises a base 201 and a portal structure 203, which can be movable with respect to the base 201, for example along guides 202. The portal structure can carry a slide 205, which can move along the crosspiece of the portal structure 203. The slide 205 can in turn carry an operating head 207 which comprises one or more tools. In the specific example, the tool is a tool for laser cutting which comprises a laser source 208 capable of emitting a laser beam F with which machining can be carried out on a piece P fixed on the base 201. In other embodiments, the portal structure 203 can be fixed with respect to the base and this can carry a mobile table along the direction of the guides 202, on which the workpiece P to be machined can be fixed. The manner in which the head and the operating head 207 moves with respect to the workpiece P to be machined are irrelevant for the purposes of the present description.

[0133] To accurately control the distance between the laser source 208 (or other tool) and the piece P, one or more opto-electronic devices 1 of the type described above can be associated with the tool. In Fig. 26A an annular curtain of opto-electronic devices 1 is visible, arranged around the optical axis of the laser beam F. The devices 1 can be interfaced with a control unit 210, which can comprise a PLC, a microprocessor or any other programmable control device. On the basis of the signals supplied by the devices 1, the position along the vertical direction Z of the operating head 207 carrying the tool, that is the laser source 208, can be controlled. In practice, the signal of one or more optoelectronic devices 1 is used in a ring feedback control of the distance between tool and piece P to be machined.

[0134] The principle described with reference to Figs. 26, 26A can be applied not only to laser tools, but also to mechanical machining systems for chip removal, water cutting systems, machine tools for electroerosion, systems welding machines, and also to manipulators, such as robot arms or the like, and in general to any machine that has at least one movable member, the position of which must be precisely controlled, for example, the position with respect to an object or piece to be machined or manipulate.

[0135] In some embodiments, more opto-electronic devices can be arranged as a function of proximity sensors, or distance meters, operating along different directions, for example along two or three orthogonal directions, which can be parallel to each other. numerically controlled axes.

While the invention has been described in terms of various specific embodiments, it will be clear to those skilled in the art that various changes, modifications and omissions are possible without departing from the spirit and scope of the claims. Furthermore, unless otherwise specified, the order or sequence of any process and method step described herein can be varied or rearranged according to alternative embodiments.

[0137] The methods defined in the following clauses are specifically the subject of this description and innovative aspects of the invention described here:

[0138] Clause 1:

A method for detecting a thermal image of an object, including the steps of:

receive thermal radiation from the object through a matrix of LEDs in direct polarization;

for each LED in direct polarization, generating a signal which is a function of the thermal radiation incident on said LED;

build a thermal image of the object through the signals detected by the matrix LEDs.

[0139] Clause 2:

A method of transmitting information via an optical transmission channel, comprising the steps of:

emitting a first optical signal containing a first information via a first directly polarized and conducting LED;

conveying the first optical signal along the optical transmission channel; receiving the first optical signal through a second LED in direct polarization.

[0140] Clause 3:

The method of clause 2, wherein the step of receiving the first optical signal comprises the step of detecting the variation of an electrical parameter of the second LED in direct polarization caused by the radiation coming from the first LED and incident on the second LED.

[0141] Clause 4:

The method of clause 2 or 3, further comprising the following steps: emitting a second optical signal containing a second information through the second LED directly biased and conducting;

conveying the second optical signal along the optical transmission channel; receive the second optical signal through the first LED in direct polarization.

[0142] Clause 5:

The method of clause 4, wherein the step of receiving the second optical signal comprises the step of detecting the variation of an electrical parameter of the first LED in direct polarization caused by the radiation coming from the second LED and incident on the first LED.

[0143] Clause 6:

A method of generating a command or drive signal, comprising the steps of:

conducting an LED and emitting optical radiation through it; detect the presence of an object in the vicinity of the LED as a function of radiation emitted by the LED and retro-diffused or reflected by the object, through a variation of an electrical parameter of the LED caused by said retro-diffused or reflected radiation;

generating the command or actuation signal on the basis or as a function of the detected presence of said object.

[0144] Clause 7:

The method of clause 6 applied to a LED curtain which, depending on the backscattered light from an object, for example a hand, on the individual LEDs of the curtain determines an action resulting from the movement of the object moving near the curtain.

[0145] Clause 8:

A method for measuring a distance, comprising the steps of: directly biasing an LED and generating radiation with it;

detect radiation emitted by the LED, back-scattered or reflected from a sight or target and incident on the LED, as a function of a variation of an electrical parameter of the directly polarized LED, said variation being caused by the back-scattered or reflected radiation and incident on the LED ;

determine the distance of the sight or target from the LED as a function of the back-scattered or reflected radiation incident on the LED.

[0146] Clause 9:

A method of detecting the presence of a foreign object on a substrate, comprising the following steps:

directly biasing at least one LED and generating radiation therewith; direct the radiation towards the substrate;

detecting the presence of a foreign object on the substrate as a function of a variation of a radiation emitted by the LED and back-scattered or reflected by the substrate.

[0147] Clause 10:

The method of clause 9, wherein the step of detecting the presence of said foreign object on the substrate comprises the following steps:

collecting radiation emitted by said at least one LED and backscattered or reflected by the substrate and incident on said at least one LED;

generating a signal which is a function of the radiation incident on the LED;

detect the presence of the foreign object based on the variation of said signal.

[0148] Clause 11

The method of clause 9 or 10, where the change in the signal is caused by a change in the distance of the substrate from the LED.

[0149] Clause 12:

The method of clause 9 or 10, in which the variation of the signal is caused by a variation in the intensity of the back-scattered or reflected radiation, due to a different optical property of the foreign object with respect to the substrate.

[0150] Clause 13:

The method of one or more of clauses 9 to 12, wherein the substrate is a sheet, preferably a sheet of paper, for example a banknote; and in which the foreign object is a tape adhered to the substrate, preferably an adhesive tape, for example a transparent adhesive tape.

[0151] Clause 14:

A method for detecting information related to the temperature of an object, including the steps of:

directly bias at least one LED;

place the LED in front of the object, so that the thermal radiation emitted by the object affects the LED;

determining a variation of an electrical parameter of the directly polarized LED, caused by the thermal radiation emitted by said object and incident on said LED.

[0152] Clause 15:

A method for detecting an image of an object, including the steps of: illuminating the object through a matrix of directly polarized and conducting LEDs, the LED matrix forming an image sensor;

collect radiation emitted by the LEDs and reflected or back-scattered by the object; generate, through said LEDs, signals that are a function of reflected or backscattered radiation and reconstruct an image of the object through said signals.

[0153] Clause 16:

A method of analyzing an object using ultrasound, comprising the steps of:

arrange the object to be analyzed in an ultrasound propagation medium; hit the object with an ultrasound beam propagating from an ultrasound source through the propagation medium;

causing the vibration of a vibrating plate by means of ultrasounds reflected from said object or transmitted through said object;

irradiating the vibrating foil with a radiation emitted by at least one directly polarized and conducting LED;

detecting the back-scattered or reflected radiation from the foil towards said at least one LED;

causing a variation of at least one parameter of said at least one LED in direct polarization due to the variation of the back-scattered or reflected radiation from the foil towards said at least one LED.

[0154] Clause 17:

A method of analyzing an object using ultrasound, comprising the steps of:

arrange the object to be analyzed in an ultrasound propagation medium; hit the object with an ultrasound beam propagating from an ultrasound source through the propagation medium;

causing the vibration of one or more vibrating plates by means of ultrasounds reflected by said object or transmitted through said object;

irradiating the vibrating plate (s) with a radiation emitted by a matrix of directly polarized and conducting LEDs;

detecting the back-scattered or reflected radiation from the foil (s) towards said LED matrix;

causing a variation of at least one parameter of each LED of said matrix of LEDs in direct polarization due to the variation of the backscattered or reflected radiation from the foil (s) towards the LED matrix.

Claims (25)

OPTO-ELECTRONIC DEVICE INCLUDING A DIRECT POLARIZATION LED, USED AS A RADIATION DETECTOR, AND ITS USES CLAIMS 1. An opto-electronic device, comprising: at least one LED having an emission band and an absorption band; a bias circuit for the LED, adapted to bring the LED into conditions of forward bias; a circuit for detecting a variation of an electrical parameter of the LED caused by radiation received by the LED when said LED is in conditions of forward bias. The optoelectronic device of claim 1, wherein the bias circuit is adapted to conduct the LED into conduction and emit an optical radiation in the emission band. The device according to one or more of the preceding claims, in which the optical emission band and the optical reception band are at least partially overlapped. The device of claim 1 or 2 or 3, wherein the electrical parameter is selected from the group comprising: the voltage across the LED; the current through the LED. 5. The device of one or more of the preceding claims, in which the direct biasing circuit of the LED is adapted to control an emission of the LED by controlling the current through the LED and / or the voltage across the LED. 6. The device of one or more of the preceding claims, configured to generate a reception signal as a function of radiation emitted by the LED and reflected or back-scattered towards the LED. 7. The device of claim 6, adapted to measure a distance. 8. The device of claim 6 or 7, configured as a vibration or ultrasound detector, by measuring the variation of the distance between the LED and a reflecting or diffusing element, said reflecting or diffusing element being stimulated by the vibration or by the ultrasounds to be detected . The device of claim 6, configured as a proximity switch. 10. The device of one or more of claims 1 to 5, adapted to emit a first modulated radiation, containing a first information, and to simultaneously receive a second modulated light radiation, containing a second information; and in which preferably: the biasing circuit of the LED is adapted to drive the LED to generate modulated pulses containing the first information; and the detection circuit is adapted to detect a variation in the electrical parameter of the LED caused by the second modulated radiation and to extract the second information therefrom. 11. The device of one or more of claims 1 to 6, designed to detect an image of an object by illuminating the object through radiation emitted by the LED and detecting through said LED radiation reflected or backscattered from the object. 12. The device of one or more of the preceding claims, suitable for detecting the presence of a foreign element, in particular an adhesive tape, applied to a substrate. 13. The device of claim 12, configured to detect the presence of the foreign element based on a distance measurement between the LED and the substrate. 14. The device of claim 12 or 13, configured to detect the presence of the foreign element based on a variation of radiation emitted by LEDs and backscattered by the foreign element. 15. The device of one or more of claims 1 to 5, wherein the detection circuit is adapted to detect a change in the electrical parameter caused by heating by radiation. 16. The device of one or more of the preceding claims, comprising a matrix of LEDs. 17. The device of claims 15 and 16, configured to detect a thermal image of an object that emits infrared radiation. 18. The device of one or more of claims 1 to 5, adapted to detect an external event by means of a radiation incident on the LED, different from the radiation emitted by the LED. 19. Use of an LED in direct polarization to receive an incident radiation on the LED and generate a signal which is a function of said incident radiation, in which preferably the LED is conducting. 20. Use of a forward biased LED to emit radiation towards a target, receive backscattered or reflected radiation from said target, and generate a signal based on said backscattered or reflected radiation. 21. A method for controlling an opto-electronic device comprising at least one LED, characterized by the steps of: directly bias said at least one LED; while said LED is directly polarized, detecting a radiation incident on said LED by detecting a variation of an electrical parameter of the directly polarized LED, caused by said electromagnetic radiation incident on the LED. The method of claim 21, wherein the electromagnetic radiation incident on the LED is electromagnetic radiation from a source external to the LED. The method of claim 21, wherein the electromagnetic radiation incident on the LED is radiation generated by the LED and reflected or backscattered from a target. The method of claim 23, comprising the step of measuring a distance as a function of the variation of the electromagnetic radiation incident on the LED. The method of claim 23, comprising the step of: arranging a vibrating element in front of said at least one LED; vibrating said vibrating element; irradiate the vibrating element with radiation emitted by the LED; detect the LED radiation reflected or back-scattered by the vibrating element; detecting information relating to said vibration as a function of the variation of back-scattered or reflected radiation, incident on the LED.