ELECTROLUMINESCENT CELL AND ANALOG TO DIGITAL CONVERTER

Abstract: An electroluminescent cell (20) comprises a first electrode (22), a latticed second electrode (28) and a luminiferous layer (24) and a dielectric insulating layer (26) interposed between the first and second electrodes (22, 28). The latticed electrode (28) comprises an electric conductive layer (30) with a plurality of openings (32) therein. In use an alternating electric field is applied across the first and second electrodes (22, 28). The openings (32) may be arranged in adjacent rows (35) which are electrically isolated from each other to form a plurality of separate second electrodes (28). In a particular embodiment, the electroluminescent cell (20) is used for converting an analog image of electrically conductive matter, such as an image of a human fingerprint, into a digital image and includes a sensing device such as a photodiode (34), for sensing electromagnetic radiation emitted by the luminiferous layer (24) responsive to the presence or absence of electrically conductive matter across the openings (32) and electronic circuitry for converting the electromagnetic radiation into digital information (36).

Description: ELECTROLUMINESCENT CELL AND ANALOG TO DIGITAL CONVERTER FIELD OF THE INVENTION This invention relates to an electroluminescent cell and a method and apparatus for converting an analog image, such as that of a human fingerprint, into a digital image. BACKGROUND OF THE INVENTION Luminescence is the emission of light by sources other than a hot incandescent body. When certain materials absorb energy, the incident energy causes the electrons of the atoms of the absorbing material to become excited by "jumping" from lower energy levels in the atom to higher energy levels. When the electrons fall back to their original lower energy states, the energy is released and emitted by the atoms in the form of light (photons) . In a particular form of luminescence, i.e. electroluminescence, the energy absorbing material is luminiferous and the energy is electric energy which is applied to the luminiferous material by means of an alternating electric field. SU-942-684-B (Institute of Physics of Academy of Sciences of Azerbaj n SSR) discloses an electroluminescent cell which can be used for generating an image of a relief object, such as a human fingerprint. The cell comprises a glass base, a transparent electrode, a semiconductor layer and a luminiferous layer. In use, an alternating current is applied between the transparent electrode and a relief object (human finger) which then forms the second electrode. When the finger is placed on the semiconductor layer, the valleys and ridges on the fingertip couple current to the electroluminescent cell at different magnitudes, causing the cell to generate light at different intensities corresponding with the valleys and the ridges. In this way, an image of the fingerprint is displayed through the glass base. It is an object of the present invention to provide a cell which not only displays an image of a relief object but converts the image into digital data for storage and comparison, as well as to provide an image multiplexer for use with the cell or other image recording apparatus . SUMMARY OF THE INVENTION According to the invention there is provided an electroluminescent cell, comprising a first electrode; a latticed second electrode; a luminiferous layer and a dielectric insulating layer interposed between the first and second electrodes, the first and second electrodes being for the application of an alternating electric field therebetween, wherein said latticed electrode comprises an electric conductive layer with a plurality of openings therein, and wherein the openings are arranged in adjacent rows which are electrically isolated from each other to form a plurality of separate second electrodes. The openings may be arranged in adjacent rows which are electrically isolated from each other to form a plurality of separate second electrodes. Also according to the invention there is provided an electroluminescent conversion cell for converting an analog image of electrically conductive matter into a digital image, comprising a first electrode; a latticed second electrode comprising an electric conductive layer with a plurality of openings therein and wherein the openings are arranged in adjacent rows which are electrically isolated from each other to form a plurality of separate second electrodes; a luminiferous layer and a dielectric insulating layer interposed between the first electrode and the plurality second electrodes, the first electrode and the plurality of second electrodes being for the application of an alternating electric field therebetween; and means for sensing electromagnetic radiation emitted by the luminiferous layer responsive to the presence or absence of electrically conductive or partially electrically conductive matter across said openings and converting said electromagnetic radiation into digital information. The means for sensing and converting electromagnetic radiation into digital information may comprise first conversion means for converting electromagnetic energy into electrical energy values; and second conversion means for converting said electrical energy values into binary information. The first conversion means may comprise semiconductor devices which are switchable between the rows of openings. The semiconductor devices may comprise photodiodes . The second conversion means may comprise binary value allocation means which allocates a binary number to an electric energy value if said value is below a predetermined reference value and another binary number if said value is above said reference value. The electrically conductive matter may be living organic tissue, such as a human finger. The image may be a relief image, such an image of the valleys and ridges of a human finger. The first electrode may be translucent or transparent. The electromagnetic radiation may be light. Also according to the invention there is provided an optical image multiplexer, comprising a two- dimensional array of light receiving pixel elements, the pixel elements being arranged in adjacent rows; shutter means for individually exposing the rows of pixel elements to light; and an array of photodiodes for sequentially registering light received by the exposed rows of pixel elements . The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematical illustration of an analog to digital converter cell according to one embodiment of the invention, showing both an exploded view and side view of the cell. Figure 2 is a plan view showing a portion of a lattice electrode of the cell of Figure 1. Figure 3 is a side view of the cell of Figure 1 showing a finger being applied to the cell. Figure 4 is a schematical illustration showing a digital output of the cell of Figure 1. Figure 5 is a schematical illustration of an analog to digital converter cell according to another embodiment of the invention, showing a side view of the cell . Figure 6 shows a number of successive linear snapshots of a fingerprint produced by the cell of Figure 5. Figure 7 is an illustration of a digital output of the cell of Figure 5. Figure 8 is a schematical illustration of another embodiment of an analog to digital converter cell showing both an exploded view and side view of the cell. Figure 9 is a plan view showing a portion of a lattice electrode of the cell of Figure 8. Figure 10 is a side view of the cell of Figure 8 showing a finger being applied to the cell. Figures 11 to 13 are schematical illustrations of an optical image multiplexer in different stages of operation. Figures 14 to 16 are schematical illustrations of another optical image multiplexer in different stages of operation. Figures 17 to 19 are schematical illustrations of another optical image multiplexer in different stages of operation. Figures 20 to 22 are schematical illustrations of another optical image multiplexer in different stages of operation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to Figures 1 to 3 , an electroluminescent conversion cell 20 is shown which comprises a transparent front electrode 22, a luminiferous layer 24, a dielectric insulating layer 26 and a latticed rear electrode 28. The transparent electrode 22 comprises a clear plastic support medium that has been sputtered with indium tin oxide (ITO) , which is a transparent electric conductor. The luminiferous layer 24 comprises a mixture of zinc sulphide doped with manganese suspended in a conductive liquid binder which is applied to the transparent electrode 22 by means of a conventional screen printing process. The dielectric layer 26 comprises a layer of barium titinate which is applied over the luminiferous layer 24. The latticed rear electrode 28 comprises a conductive lattice 30, having a multiplicity of small substantially circular or hexagonal algorithmically determined openings 32, as shown in more detail in Figure 2. However, it will be appreciated that any suitable shaped openings may be provided. An array of photodiodes 34 is provided below the lattice 30, a photodiode 34 being provided for and being matched with each opening 32. When a finger is placed on the latticed electrode 28 as shown in Figure 3, and an ac voltage is applied between the front electrode 22 and the latticed electrode 28 (or finger) , electric energy is absorbed by the luminiferous layer 24 below the openings 32. The amount of energy absorbed below each opening 32 will depend on whether a ridge or valley on the fingertip is present on the opening 32. Thus, if a ridge is present, a greater amount of energy is absorbed compared with when a valley is present. This results in the luminiferous layer 24 emitting light of greater or lesser intensity depending on the amount of electric energy absorbed at each opening 32, which energy is converted into a proportional electric current or voltage by the respective photodiode 34, e.g. about 5 volts or more, if a ridge is present and about 2.5 volts or less, if a valley is present. Appropriate electronic circuitry is provided which generates a value of 1 if the voltage is 5 or higher and a value of 0, if the voltage is 2.5 or less, so that a matrix 36 (Figure 4) of l's and 0's is produced which corresponds with the presence or absence of ridges on the openings 32. A digital image of the fingerprint is thus produced. Each opening 32 may represent a "pixel" in the digital image. The latticed electrode 28 can be produced by any suitable method, e.g. by screen printing a conducting layer forming the lattice 30 on a transparent nonconducting support layer or by producing a perforated metal sheet by means of etching or a laser beam or by rf sputtering. Referring to Figure 5, a conversion cell 60 according to another embodiment of the invention is shown. The cell 60 also comprises a transparent front electrode 22, a luminiferous layer 24 and a dielectric layer 26, but it has a rear latticed electrode 62 comprising a lattice of one row of openings 32, i.e. a linear array of openings 32. In use, a digital image of a fingerprint is formed by moving or pulling the finger across the electrode 62, as indicated by the arrow 64 in Figure 5. At every instant in time, a linear snapshot across the finger is taken. As the finger is progressively moved relative to the electrode 62, successive snapshots along the length of the finger are taken. Five such successive snapshots are indicated as 66,68,70,72 and 74 in Figure 6. The cell 60, therefore, operates intermittently and the time interval between successive snapshots can be set as desired. The time interval may be adjustable. Likewise, the number of successive linear snapshots can be set as desired. The number may be adjustable. Each linear snapshot is converted into a series of l's and O's as in the case of the cell 20 and a matrix 76 is produced, as shown in Figure 7. The matrix 76 has only five rows corresponding with the snapshots 68 to 74 of Figure 6. In practice, a much larger number of snapshots may be produced, depending on the accuracy required. In this way, a digital image is obtained using a single row of photodiodes 34. In a particular embodiment, the electrode 62 comprises a linear array of 128 openings 32 with a 128x1 array of photodiodes associated therewith. The cell 62 further includes associated charge amplified circuitry and pixel data-hold function that provides simultaneous- integration start and stop times for all pixels. The conversion cells 20, 60 may be used for storing and matching fingerprints, such as for law enforcement purposes or for a biometric fingerprint system that can be incorporated into smart cards, credit cards, driver's licenses, passports, keyboards, gun control, automobile ignition systems, door lock systems, access control, internet commerce validation, ATM machines and bank transactions. In particular, the cells 20, 60 may be used for fingerprint matching. A reference fingerprint may be stored in memory in the form of a look-up table or matrix, such as the matrix 36. If desired, a plurality of different reference fingerprints may be contained in memory. Fingerprints to be matched with the reference fingerprint may then be converted to digital images through the cells 20, 60 and then compared with one or more of the reference finger prints by the use of suitable algorithms. With reference to Figure 8, another analog to digital converter cell 80 is shown. The parts of the cell 80 which correspond with those of the cell 20 are given like reference numerals. As shown, the cell 80 also comprises a transparent front electrode 22, a luminiferous layer 24, a dielectric insulating layer 26, and a conductive lattice 30. In this case, the openings 32 (pixels) of the conductive lattice 30 are arranged in rows 35 which are electrically isolated from each other. Each row 35 now constitutes a separate rear electrode 28. When a finger is placed on the lattice 30, as shown in Figure 10, the rows 35 are sequentially "switched on" or operated by applying an ac voltage between the front electrode 22 and each row 35 to generate a row of l's and O's for each row 35. In this way, a digital image is obtained using a single row of photodiodes 34, since the image data from each of the rows 35 is sequentially registered by the photodiodes 34 and sequentially stored in memory. This is schematically illustrated in Figures 11 to 13. Although the pixels in the adjacent rows 35 in Figure 9 are shown staggered, Figures 11 to 13 shown an embodiment where the pixels are not staggered. In Figure 11 a first row 35 is switched on providing an input for the photodiodes 34. The photodiodes 34 register the light as indicated by the arrows 37. The light is converted into digital image data which is stored in memory. Then, as shown in Figure 12, the next row 35 is switched on or activated. The image information is again registered and stored in memory and then the next row 35 is switched on, as shown in Figure 13 and so on, until all the rows 35 have been operated. Although only a few rows 35 (and electrodes 28) are shown in the drawings, it will be appreciated that a sufficiently large number of rows 35 (electrodes 28) can be provided to produce an image. Any suitable means may be employed to form a "light pipe" 39 for conducting the light, such as a plastic material with optical transmission properties. It will be noted that a number of separate light pipes 39 are provided, depending on the number of openings 32 (pixels) in a row 35. Figures 14 to 16 illustrate the embodiment where the pixels in adjacent rows are staggered. The same principles apply as above. First the photodiodes 34 register the light of the first row, as indicated by the arrows 37 in Figure 14. Then the light of the second row (only one pixel being shown) is registered, as indicated by the arrow 37 in Figure 15. Then the light of the third row is registered, as indicated by the arrows 37 in Figure 16. In Figures 17 to 19 another optical image multiplexer 100 is shown. It comprises an array of microlenses 102 etched on a microchip surface, the lenses 102 being arranged in rows 35. Corresponding lenses 102 in the different rows 35 are interconnected by light pipes 39, as indicated. A row of photodiodes 34 is provided, one photodiode 34 being provided for registering light conducted by each light pipe 39. Each row 35 is provided with a switchable light blocking device, such as a liquid crystal display shutter 41. The shutters 41 become opaque when a voltage is applied to them and are transparent when no voltage is applied. In use, the shutters 41 are switched so that each row 35 is unblocked to receive light from an image (such as an image being photographed or recorded) . The rows 35 are unblocked in succession and the photodiodes 34 register the light as indicated by the arrows 37. The same sequential procedure is applied as in the case of Figures 11 to 13. In this way, only a single row of photodiodes 34 is required to register the image data provided by a multiplicity of rows 35. Finally, Figures 20 to 22 illustrate an embodiment where the pixels in adjacent rows 35 are staggered. Although certain preferred embodiments of the present invention have been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims.

Claims: WE CLAIM : 1. An electroluminescent cell, comprising: a first electrode; a latticed second electrode; a luminiferous layer and a dielectric insulating layer interposed between the first and second electrodes, the first and second electrodes being for the application of an alternating electric field therebetween, wherein said latticed electrode comprises an electric conductive layer with a plurality of openings therein. 2. The cell according to claim 1, wherein the openings are arranged in adjacent rows which are electrically isolated from each other to form a plurality of separate second electrodes. 3. The cell according to claim 1, further comprising conversion means for converting electromagnetic energy into electrical energy, associated with said openings. 4. The cell according to claim 3, wherein said conversion means comprises a semiconductor device associated with each of said openings. 5. The cell according to claim 4, wherein the semiconductor device comprises a separate photodiode associated with each of said openings. 6. The cell according to claim 2, further comprising conversion means for converting electromagnetic energy into electrical energy, which conversion means is switchable between said rows of openings. 7. The cell according to claim 6, wherein said conversion means comprises semiconductor devices which are switchable between said rows of openings. 8. The cell according to claim 1, wherein said openings are arranged in linear array. 9. The cell according to claim 8, wherein said openings are arranged in a plurality of adjacent parallel linear arrays . 10. The cell according to claim 2 or 9, wherein said openings are substantially circular and the openings in adjacent arrays are offset by one radius. 11. The cell according to claim 1 or 2, wherein the first electrode is transparent. 12. The cell according to claim 1 or 2 , wherein the first electrode is translucent. 13. An electroluminescent conversion cell for converting an analog image of electrically conductive matter into a digital image, comprising: a first electrode; a latticed second electrode comprising an electric conductive layer with a plurality of openings therein; a luminiferous layer and a dielectric insulating layer interposed between the first and second electrodes, the first and second electrodes being for the application of an alternating electric field therebetween; and means for sensing electromagnetic radiation emitted by the luminiferous layer responsive to the presence or absence of electrically conductive or partially electrically conductive matter across said openings and converting said electromagnetic radiation into digital information. 14. An electroluminescent conversion cell for converting an analog image of electrically conductive matter into a digital image, comprising: a first electrode; a latticed second electrode comprising an electric conductive layer with a plurality of openings therein and wherein the openings are arranged in adjacent rows which are electrically isolated from each other to form a plurality of separate second electrodes; a luminiferous layer and a dielectric insulating layer interposed between the first electrode and the plurality second electrodes, the first electrode and the plurality of second electrodes being for the application of an alternating electric field therebetween; and means for sensing electromagnetic radiation emitted by the luminiferous layer responsive to the presence or absence of electrically conductive or partially electrically conductive matter across said openings and converting said electromagnetic radiation into digital information. 15. The conversion cell according to claim 13 or 14 wherein said means for sensing and converting electromagnetic radiation into digital information comprises first conversion means for converting electromagnetic energy into electrical energy values; and second conversion means for converting said electrical energy values into binary information. 16. The conversion cell according to claim 14, wherein said first conversion means comprises a semiconductive device associated with each of said openings. 17. The conversion cell according to claim 16, wherein the semiconductor device comprises a separate photodiode associated with each of said openings. 18. The conversion cell according to claim 14, wherein said first conversion means comprises semiconductor devices which are switchable between said rows of openings . 19. The conversion cell according to claim 15, wherein the second conversion means comprises binary value allocation means which allocates a binary number to an electric energy value if said value is below a predetermined reference value and another binary number if said value is above said reference value. 20. The conversion cell according to claim 13 or 14, wherein said image is a relief image. 21. The conversion cell according to claim 13 or 14, wherein said electrically conductive matter is living organic tissue. 22. The conversion cell according to claim 21, wherein said image is a relief image of the valleys and ridges of a human finger. 23. The conversion cell according to claim 13, wherein said openings are arranged in a linear array. 24. The conversion cell according to claim 18, wherein said openings are arranged in a plurality of adjacent parallel linear arrays. 25. The conversion cell according to claim 13 or 14, wherein said digital information is in the form of a matrix of binary numbers . 26. The conversion cell according to claim 13 or 14, wherein the first electrode is transparent. 27. The conversion cell according to claim 13 or 14, wherein the first electrode is translucent. 28. The conversion cell according to claim 13 or 14, wherein the electromagnetic radiation is light. 29. An optical image multiplexer, comprising: a two-dimensional array of light receiving pixel elements, the pixel elements being arranged in adjacent rows; shutter means for individually exposing the rows of pixel elements to light; and an array of photodiodes for sequentially registering light received by the exposed rows of pixel elements. 30. The optical image multiplexer of claim 29, wherein the pixels in adjacent rows are staggered.

Inventors: DIKLICH MLADEN, DIKLICH, MLADEN
Applicants: DIKLICH MLADEN, DIKLICH, MLADEN
Application year: 2000
Main classification: H05B33
IPC codes: G06K9, H05B33