WO1989009960A1

WO1989009960A1 - Display and writing device

Info

Publication number: WO1989009960A1
Application number: PCT/FR1989/000129
Authority: WO
Inventors: Marc Arques
Original assignee: Thomson-Csf
Priority date: 1988-04-11
Filing date: 1989-03-21
Publication date: 1989-10-19
Also published as: FR2629939B1; FR2629939A1; JPH02504192A; EP0378593A1

Abstract

A display device (1) of compact design makes it possible to display an image and to write with an optical pencil (15), simultaneously or not. The display device (1) comprises an image generator (7, 20) and an optical pencil (15) used to indicate a point on a writing surface (5). The display device (1) also comprises a matrix (2) of light-sensitive surface of said matrix forming the writing surface (5). The optical pencil emits a light beam. The light-sensitive matrix (2) is arranged in front of the image generator (7, 20) so that an image produced by the latter can be seen through the light-sensitive matrix (2).

Description

VISUALIZATION AND WRITING DEVICE.

The invention relates to a display and writing device of the type making it possible, in particular, simultaneously or not, on the one hand to observe an image, and on the other hand, to write or draw or carry markers on a surface 'writing with an optical pencil; that is to say a device combining the functions of "image display" and "graphics tablet".

Such devices are known in which, on the one hand: - the image display function is provided by an image generator comprising a cathode ray tube; the image is formed in the cathode ray tube on a screen constituted by a front face or slab of the cathode ray tube, under the effect of a scanning of one or more electron beams; - on the other hand, the "graphic tablet" function is ensured using an optical pencil, and a writing surface which corresponds to the screen on which the image is formed, more precisely to a outer face and therefore opposite to that qtii is swept by the electron beam (s). An operator holding the optical pencil can designate with the aid of the latter, a point on the writing surface or a succession of points whose coordinates are memorized and can be reproduced by the image generator, possibly overprinted with a another picture. The optical pencil is sensitive to the light emitted by the screen or writing surface, and the location of a point on this writing surface designated by the optical pencil is obtained generally by locating the instant at which the optical pencil captures the light relative to the time during which a complete scanning of the screen or writing surface takes place.

The combination of the two functions "image display" and "graphics tablet" by the same device of the type described above offers many advantages. However, one of the drawbacks of this type of device lies in the fact that it has a relatively large size, particularly in depth, that is to say in a direction perpendicular to the surface "of the screen; this mainly because of scanning by * or electron beams which requires a significant distance between the screen and the electron sources or electron guns. So that, for a given maximum deflection angle of the electron beams (for scanning), it is necessary to increase this depth when we want to increase the dimensions of the image surface and therefore of the writing surface. It follows that such a device, because of its size, but also its cost, lends itself poorly to be used in the context of office automation, and in large quantities. The present invention relates to an apparatus which combines the functions of image display and graphics tablet, without having the above-mentioned drawbacks. To this end, the device of the invention uses, on the one hand, a functioning writing surface. in a completely different manner from that described above, and uses on the other hand, an image generator of a different type from that mentioned above.

The image generator capable of being used in the apparatus of the invention can be a display device of the type constituted for example by a panel of light-emitting diodes, arranged in line and in column according to a matrix arrangement, the functioning is in itself known; the matrix array of light emitting diodes is controlled, in a conventional manner, to produce the desired image. But the display device may also be of the plasma type, that is to say operating in a conventional manner according to a matrix arrangement of electrodes. The display device can also be a display device of the liquid crystal type, which also uses in known manner an array of electrodes. Also, these different display devices or image generators can fall into the same category which can be called a matrix type display device or a matrix type image generator; and all these

10 display devices of the matrix type have the advantage in particular of being of the surface type, and of having a small thickness.

According to the invention, a display and writing device, comprising, an image generator, a pencil

^ optical, a writing surface, is characterized in that it comprises a matrix of photosensitive elements, one photosensitive face of which constitutes the writing surface, and in that the optical pencil emits light radiation, the photosensitive matrix being placed in front of the image generator so that an image produced by the image generator is seen through the photosensitive matrix.

The invention will be better understood and other effects and advantages which it provides will appear on reading the description which follows, given by way of nonlimiting example, and 5 in the appended figures, among which:

- Figure 1 shows schematically and partially a display and writing device according to the invention, and illustrates how it provides at least the two functions "image display" and "graphics tablet"; 0 - Figure 2 schematically shows a second version of the device of the invention, particularly with regard to the position of a light source used to provide a third function "document reader";

- Figure 3 shows the electrical diagram of a -5 photosensitive matrix shown in Figures 1 and 2; - Figures 4a to 4c show explanatory signals for the operation of the photosensitive matrix shown in Figure 3, in the context of a "document reader"function; - Figures 5a to 51 show explanatory signals for the operation of the photosensitive matrix shown in Figure 3, in the context of the "graphics tablet"function;

- Figures 6a and 6b are side sections in two orthogonal directions, showing schematically by way of non-limiting example, an embodiment of the photosensitive matrix shown in Figure 3;

- Figure 7 schematically illustrates, in a perspective view, a second embodiment of the photosensitive matrix.

Figure 1 shows partially, schematically, a display and writing device 1 according to the invention.

According to a characteristic of the invention, the display device 1 comprises a photosensitive matrix

2 of the photosensitive solid state detector type; the photosensitive matrix 2 is represented by a substrate 3 carrying a plurality of photosensitive points PI, P2,. . . , Pn each comprising at least one photosensitive element, as is further explained in a continuation of the description relating to FIG. 3.

In contrast to the substrate 3, the end of the photosensitive points PI to Pn is contained substantially in the same plane symbolized in FIG. 1 by a line in dotted lines marked 5, this plane representing a photosensitive surface 5 which extends in a plane perpendicular to that of the figure. The photosensitive surface 5 is divided into a plurality of n elementary surfaces Sel to Sen equal, each containing a photosensitive point PI to Pn. It should be noted that in the representation of Figure 1, the proportions between the different dimensions are not respected, for better clarity of the figure: thus for example, one side of an elementary surface Salt to Sen can have a length 11 of the order of 200 micrometers, while the height h of a photosensitive point PI to Pn, above the substrate 3, is of the order of only a few micrometers; the substrate 3 may itself have a thickness E of the order of 2 to 3 millimeters for example, especially if this substrate is made of glass in order to be transparent, as is necessary for the operation of the device.

Indeed, under the substrate 3, that is to say opposite to the photosensitive points PI to Pn, is arranged a surface image generator 7, of matrix type, the surface of which extends in a perpendicular plane to that of the figure. The image generator 7 can be constituted for example as it was previously mentioned, by a panel of light-emitting diodes (not shown) arranged in line and in column according to a matrix arrangement, the operation of which is known in itself: the matrix array of light emitting diodes is controlled, in a conventional manner, to light only some of the light emitting diodes and produce the desired image. The light (represented by arrows) which contains the image is emitted in the direction of the photosensitive matrix 2 which is partially crossed by this light, so that the image is visible through the photosensitive matrix 2.

To this end, the photosensitive points PI to Pn have surface areas Sal to San of surface ^• sufficiently weak to allow the light emitted by the display device or image generator 7 to pass in sufficient quantity for the image projected under these conditions is visible through the photosensitive surface 5 under correct conditions (the active surfaces Sal to San are situated in a plane perpendicular to that of the figure and symbolized on the latter by the length 12 on their side, these active surfaces corresponding in a way to the section of the photosensitive elements that comprise the photosensitive points PI to Pn). Tests have shown that the image which is thus projected through the photosensitive surface 5, is visible under correct conditions when the active surface

Sal to San photosensitive points PI to Pn is equal to or less than substantially 50% of an elementary area Salt to Sen.

The photosensitive surface 5 constitutes the photosensitive face of the photosensitive matrix 2, and so that the photosensitive points PI to Pn are not illuminated by the light coming from the image generator 7, an opaque screen 12 is disposed between the substrate 3 and each photosensitive points PI to Pn. The display device 1 further comprises an optical pencil 15. According to a characteristic of the invention, the optical pencil 15 emits light radiation in the form of a light brush 16, light to which the points are sensitive. photosensitive PI to Pn on the side of the photosensitive surface 5; so that the photosensitive surface 5 represents a writing surface 5.

The optical pencil 15 being a light emitter, it is possible for an operator (not shown) holding the optical pencil 15 by hand, to illuminate the photosensitive surface 5 or writing surface using an optical pencil , and thus to designate a given zone (formed of one or more elementary surfaces Salt to Sen contiguous) at a given time. The operator can thus successively designate different zones on the writing surface 5, to constitute, for example, fixed references distant from each other; the operator can also illuminate the photosensitive surface or writing surface 5 so as to describe thereon any curve of pace. The illumination of an elementary surface Sel to Sen is detected by the photosensitive point PI to Pn contained in this elementary surface, and which delivers a signal which allows to locate it; the location of a succession of adjacent photosensitive points PI to Pn makes it possible to reconstruct a curve drawn on the photosensitive surface 5 or writing surface using the optical pencil 15. It should be noted that the image generator 7 can be constituted by a display device of a different type, for example a display device of the plasma type, in itself conventional.

It is also possible to use a display device of the conventional liquid crystal type, which is represented by a rectangle in dotted lines 20. In this case, the image generator or display device 7 can be replaced by a light source, that is to say constitute a light device 7. It can in fact be considered that a display device of the plasma type or of the type comprising a matrix of light-emitting diodes constitutes a light device, which can provide either a light source function or an image display function. In fact, in the light source operation of a light device 7 formed by light-emitting diodes for example, all the light-emitting diodes are actuated and supply light; for operation as an image display, the matrix array of light-emitting diodes is controlled to produce the desired image (of course the use of the optical pencil 15 is possible during the viewing of the image); and for operation as a graphics tablet only, all the light-emitting diodes are off and the light device 7 produces no light, thus allowing the free use of the optical pencil 15.

Consequently, the use of a light device

7 consisting of a display device of the plasma type, for example, or of the light-emitting diode panel type, performs the function of displaying images, while allowing operation as a graphic tablet, and also allows using the photosensitive matrix 2, to obtain a third function with the viewing and writing device 1, which consists in reading a document 10. In this third function, the light device 7 constitutes a source of light: the light emitted by. this light source illuminates a face 11 to be analyzed of the document 10, which is pressed against the photosensitive surface or writing surface 5. In fact, in the nonlimiting example represented in FIG. 1, the document 10 is pressed against a transparent screen 9 made of glass or plastic for example, which mainly fulfills a mechanical protection function with respect to the photosensitive surface or writing surface 5. The light coming from the light device 7 is reflected by the face 11 to be analyzed , and illuminates the photosensitive points PI to Pn of the matrix 2.

It should be noted that in the case where the image generator is constituted by the liquid crystal display device 20, the light device 7 can in this case constitute only a light source, the liquid crystal display device 20 being disposed between the light device 7 and the photosensitive matrix 2. Of course in this case, the light device 7 can be designed in a much simpler manner, and contain for example fluorescent tubes (not shown), and include a surface 8 constituted by a perfectly diffusing partition, in itself conventional, so as to emit a flow of light in a relatively homogeneous manner over the entire surface 8.

The liquid crystal display device 20 usually comprises two partitions or substrates 21, 22 carrying electrodes (not shown); between these substrates 21, 22 is arranged a volume 23 filled with the liquid crystal. In order to simplify the production of the display device 1, the substrate 3 belonging to the photosensitive matrix 2 can also constitute the partition or substrate 21 of the liquid crystal display device 20. FIG. 2 shows another version of the invention in which the document to be analyzed, identified 10a, is of a transparent or semi-transparent type, such as for example a graphic radio film. In this case, the document 10a is placed on the protective screen 9, that is to say above the photosensitive surface or writing surface 5. The reading of the document 10a is obtained using a light source 25, of surface type which is placed above the document 10a, the latter being thus disposed between the photosensitive surface 5 and this

10; second light source 25; the photosensitive points PI to Pn each capture the light coming, appreciably from the opposite face of the document 10a, the luminous image of this document being this time formed by transmission of the light and not by reflection as in the case of the example previous. In

15 this configuration, it is not mandatory to have the light device 7, as a light source, except of course if the display device or image generator is constituted by the liquid crystal display device 20 .

However the light device 7 as a source

20 of light can be kept. Indeed, the second light source 25 can be moved away from the analyzed document 10a, so as to allow access to the optical pencil 15 (not shown in FIG. 2). It should be noted that in the latter case, in particular if the document 10a is an X-ray film, the

__ optical pencil 15 can be used, for example, to carry markers superimposed on the image itself, and for this purpose the light device 7 as a light source, can be useful for illuminating the image carried by document 10a, while having a minimal influence on the photosensitive points PI to Pn.

₃₀ Figure 3 shows partially the electrical diagram of the photosensitive device 1 according to the invention, and particularly illustrates, by way of nonlimiting example, the photosensitive matrix 2 and the manner in which the photosensitive pixels are formed with it; the structure presented

_ _ photosensitive dots so particularly interesting in this that it allows the operation of the matrix 2 both in the "document reading" function and in the "graphics tablet" function.

The matrix comprises a plurality of photosensitive points PI, P2,. . . , P9 which are arranged in rows and columns and which each consist of a first and a second element respectively Da, Db connected in series with each other, and at least one of which is a photosensitive element. In the nonlimiting example described and shown in FIG. 3, the first and second elements Da, Db each consist of a diode, the two diodes Da, Db being connected in series with each other and mounted at the head spade, that is to say with opposite directions of conduction with respect to each other; such an assembly of photosensitive dots being described in a French patent application No. 8G 14058 filed on October 9, 1986 in the name of THOMSON-CSF. This patent application relates to a photosensitive device in the solid state, having a photosensitive matrix, the photosensitive dots of which are constituted in the same manner as mentioned above and this patent application describes. in detail the operation of such photosensitive dots, and further describes a reading method and a method of manufacturing a matrix comprising such photosensitive dots; also, this French patent application n ° 86 14058 must be considered as being part of the present description.

In the nonlimiting example described, the number of photosensitive points PI to P9 is limited to 9 according to a 3 × 3 matrix assembly to simplify FIG. 3, but in the spirit of the invention this matrix assembly can have a much greater capacity. larger, by several million points for example.

The matrix 2 comprises in-line conductors LI to L3 and in column conductors FI to F3, the number of each type of these conductors being limited to 3, taking into account the example of FIG. 3 where only 9 photosensitive points PI to P9 are represented.

In practice, and in a conventional manner in itself, but not necessarily, the photosensitive points PI to P9 are each formed at the intersection of a line conductor LI to L3 and a column conductor FI to F3 . Each photosensitive point PI to P9 has a first end 10 connected to a row conductor LI to L3, and has a second end 11 connected to a column conductor FI to F3. For each photosensitive point PI to P9, the meeting point between the first diode Da and the second diode Db constitutes an area A where charges generated by at least one of the two diodes Da, Db can be stored; the amount of charge being proportional to the illumination of the photosensitive point, ^• that is to say to the illumination of photosensitive elements or that comprises the photosensitive point.

Indeed, the two diodes Da, Db can be photosensitive elements, but according to a characteristic of the invention, it is sufficient that only one of these two diodes Da, Db is photosensitive to allow the two operating modes provided for the photosensitive matrix 2, namely: operation in "graphics tablet" mode and operation in "document reader" mode. As it clearly appears from the operation explained in the following description, the diode Da or Db which is necessarily photosensitive, is the one which, during illumination of the photosensitive points PI to P9, is the only one which is reverse biased in the tablet function graphic.

In the nonlimiting example of the description, for each photosensitive point PI to P9, the first and second diodes Da, Db are photodiodes, and they are mounted so that their anodes respectively 10 and 11 are connected respectively to a line LI to L3 and a column FI to F3. But in the spirit of the invention, the photodiodes or diodes Da, Db could be mounted in opposite directions of conduction to those shown in FIG. 3. It should also be noted that by the term diode is meant not only a semiconductor diode, but also possibly a transistor or phototransistor of a NIPIN or PINIP type for example, as soon as the base of this transistor is floating, that is to say not connected.

It should also be noted, as it clearly appears both from the operation described in the French patent application No. 86 14058 cited above, and from the explanations which follow in the present description, that of the two diodes Da, Db which is necessarily photosensitive, is always reverse polarized, so that it is always capable of generating photocharges if it is illuminated. Consequently, the function of such a photosensitive element can be ensured by a photosensitive element other than a photodiode, and this photosensitive element can be constituted for example by a photoresistor.

On the other hand, assuming (as shown in FIG. 3) that the first and second elements Da, Db of each photosensitive point PI to P9 are constituted by diodes Da, Db of which the second diode Db is that which is necessarily photosensitive, it is noted that the function provided by the first diode Da is that of a switch or switch which, when the first diode Da is forward biased, is "on" (that is to say that it has a low resistance), and which, when the first diode Da is reverse biased is "open" (that is to say that it has a very high resistance).

The operation of the matrix 2, within the framework of the "document reading" function, corresponds to the operation described in the French patent application No. 86 14058 previously mentioned, and requires in particular that, for each photosensitive point PI to P9, during the illumination of the latter by the light coming from document 10, 10a to be read, the two diodes Da, Db are reverse biased; this being obtained by bringing the column conductors FI to F3 to a given potential or reference voltage VR, and on the other hand, by applying successively to each of the line conductors LI to L3 a voltage pulse with respect to the reference voltage column VR ; this pulse is a positive pulse, taking into account the direction of mounting of the diodes Da, Db in the nonlimiting example shown in FIG. 3.

We indicate below, by way of nonlimiting example, a possible assembly (other arrangements are ^• possible to obtain the desired operation).

Each column conductor FI to F3 is connected to the negative input "-" of an amplifier GF1 to GF3 mounted as an integrator; an integration capacitor CF1 to CF3 being mounted between the negative input "-" of the amplifier GF1 to GF3, and the output OF1 to OF3 of this amplifier. The second positive input "+" of each amplifier GF1 to GF3 is connected to the reference potential VR previously mentioned which may be ground for example as shown in FIG. 3. Each integrating amplifier GF1 to GF3 further includes a switch IF1 to IF3 called reset switch, mounted in parallel with the integration capacitor CFl to CF3; the reset switches IF1 to IF3 consist of MOS transistors controlled by reset signals V. RESET. The reset switch IF1 to IF3 of a given integrating amplifier GF1 to GF3 is maintained

"closed", that is to say "on" so as to short-circuit the integration capacitor CF1 to CF3, except during the reading sequence of the photosensitive point PI to P9 which is connected to this amplifier. The outputs OF1 to OF3 of the amplifiers GF1 to GF3 are connected to an analog data acquisition register 32 called column acquisition register, constituted for example by a shift register with parallel input EF1 to EF3 and serial output SF1, of the CCD type ( Charge Coupled Device) for example. The connection diagram of the column conductors FI to F3 which has just been described is a conventional diagram, which constitutes a reading device and which makes it possible to acquire the charges which - circulate on these conductors

5 columns when reading photosensitive points PI to P9.

On the other hand, at the level of the line connections LI to L3, a slightly greater complexity than in the prior art allows the same structure of the photosensitive points PI to P9 to be used for the two types of operation (document reader and

10 graphics tablet).

In the nonlimiting example of the description, the line conductors LI to L3 must be connected not only to an addressing device (comprising in particular a line register 46 and a pulse generator 42) making it possible to apply a

1 ^ positive pulse successively to each of the line conductors LI to L3 for the operation in document reader, but also the line conductors LI to L3 must be connected to means which make it possible, for each photosensitive point PI to P9, to polarize the one of the two diodes Da, Db live and

20 polarize the other in reverse (for operation in graphics tablet mode), and to means which make it possible, on the other hand, to recognize to which line conductor LI to L3 is connected a photosensitive point PI to P9 which is illuminated by the optical pencil 15; the column conductor FI to F3 to which the

25 photosensitive point thus lit being recognized using the integrating amplifiers GF1 to GF3.

Each of the line conductors LI to L3 is connected to the negative input "-" of an integrating amplifier GL1 to GL3, of the same type as the integrating amplifiers connected to the

30 columns FI to F3, that is to say that the potential to which each line conductor LI to L3 is carried corresponds to the potential of the second input or positive input "+" of the amplifier GL1 to GL3. For each amplifier GL1 to GL3, an integration capacitor CL1 to CL3 is mounted between the negative input "-" and

"The OL1 to OL3 output of this amplifier. In parallel on each of the integration capacitors CL1 to CL3 is mounted a reset switch IL1 to IL3; these switches being constituted for example by MOS transistors controlled by second reset signals V2. RESET. These second reset signals V2. RESET are intended to short-circuit the integration capacitors CLl to CL3 and CFl to CF3 during a given phase of operation in "graphics tablet" mode, and they are also applied to the integration capacitors mounted on the amplifiers GF1 to GF3 of the column conductors FI to F3; to this end, the switches IF1 to IF3 mounted on the amplifiers GF1 to GF3 are controlled by the first reset signals V. RESET, or by the second reset signals V2. RESET, via "OR" circuits 37. The outputs OL1 to OL3 of the amplifiers GL1 to GL3 are connected to inputs ELI to EL3 of a second acquisition register 33 called the line acquisition register, constituted for example by a shift register of the type with parallel input and serial SOL output. In the nonlimiting example described, the column and line acquisition registers 32, 33 respectively comprise a control input 34, 35 to which loading control signals SCI, SC2 are applied respectively, when it is desired to load into these registers 32 , 33 the signals which are applied to their inputs EF1 to EF3 and ELI to EL3. The information contained in the acquisition registers 32, 33 is transferred to main memories (not shown), in themselves conventional, and this information is then processed in a conventional manner so as to reconstruct an image formed on the sensitive surface 5 of matrix 2, either in document reader mode (only for column 32 acquisition register in this case), or in graphics tablet mode. The output of the signals contained in the acquisition registers 32, 33 is operated under the control of pulses or transfer signals ST applied to a transfer control input 38, 39 that comprise respectively the column 32 acquisition register and the row 33 acquisition register; these transfer pulses ST being delivered by the same transfer pulse generator 40, so as to determine a known phase relationship in the output of the signals from the two acquisition registers 32, 33, with a view to designating between which line conductor LI to L3 and which column conductor FI to F3 was connected a photosensitive point PI to P9 lit at a given time by the optical pencil 15 (shown in Figure 1). The potential of a line LI to L3 corresponding to the potential which is applied to the positive input "+" of the amplifier GLl to GL3 to which this line conductor is connected, the positive input "+" of each of the amplifiers GLl GL3 can be connected either to a line pulse generator 42 which delivers SL pulses of positive voltage with respect to ground, or connected to a DC voltage source 45 which delivers a positive voltage with respect to ground, c that is to say, with respect to the potential of the columns FI to F3. To this end, each positive input "+" of the amplifiers GL1 to G13 is connected on the one hand to the line pulse generator 42 via a line pulse interrupter IL1 to IL3, and connected on the other hand to the DC voltage source 45 via another switch IV1 to IV3; at the level of an amplifier GL1 to GL3, only one or the other of these switches being made "on" at the same instant.

The switches IL1 to IL3 are constituted by MOS transistors, and are controlled respectively by an output Ul, U2, U3 of a line shift register 46, so as to successively connect the line conductors LI, L2, L3 to the generator. line pulses 42, this succession taking place under the control of line shift signals SDL which are applied to an offset control input 47 of the shift register 46.

The other switches IV1 to IV3 also connected to the positive inputs "+" of the amplifiers GL1 to GL3 are also MOS transistors, and are controlled simultaneously by a DC voltage signal VSG which is established at the same time as the "graphics tablet" function is established.

In this configuration, when the "document reader" function is in progress, a voltage pulse SL delivered by the line pulse generator 42 is applied to the positive input of the amplifier GL1, and this pulse positive is found on the negative "-" input of this amplifier, that is to say on the line conductor LI, so that the pulse SL is applied to all the photosensitive points PI to P3 connected to this line conductor. As explained in more detail in FIG. 4 relating to the operation in document reader mode, the result of the application of this line pulse SL is an injection of charges on each of the column conductors FI to F3, these charges each corresponding to the charges stored in zones A of photosensitive points PI to P3. The signals constituted by these charges are present at the output of the amplifiers GFl to GF3 in the form of voltage, and these signals are injected into the column acquisition register 32. The integration capacitors CFl to CF3 mounted on the amplifiers GFl to GF3 are then short-circuited, and the line pulse generator 42 is connected to a line conductor along L2 to which is also applied a line pulse SL which leads to injecting on each of the column conductors FI to

F3 a charge signal corresponding to the charges accumulated at point A of the photosensitive points P4 to P6. The column acquisition register 32 having been emptied beforehand and the charges it contained transferred to a main memory as previously mentioned, the column acquisition register 32 can be loaded again by the charges contained in point A of the photosensitive points P4, P5, P6, as in the previous example; and the same cycle is reconstituted for the third conductor line L3 and so on until all the photosensitive points of all the lines of the matrix; the signals corresponding to the entire image of the document to be read being delivered at the output SF1 of the column acquisition register 32, they can be stored in a main memory. For operation in graphic tablet mode, all the switches IL1 to IL3 connected to the positive "+" inputs of the line amplifiers GL1 to GL3 are in the open state, and. the DC voltage switches IV1 to IV3 are all in the closed state, that is to say that all the positive inputs "+" of line amplifiers GL1 to GL3 are connected to the positive polarity V + of the DC voltage delivered by the DC voltage source 45. Under these conditions, all the first diodes Da are forward biased, that is to say that the same voltage is found at the various points A as the voltage delivered by the DC voltage source 45 , at the threshold near the diode Da. On the other hand, the second diode Db of each photosensitive point PI to P9 remains reverse biased and, if it is lit, it generates charges which circulate on the row conductor and on the column conductor between which the photosensitive point PI to P9 is connected located in the elementary surface Salt to Sen lit by the optical pencil 15.

For example, if the optical pencil illuminates the elementary surface Se6, that is to say the photosensitive point P6, the zone A of the latter is at a positive potential close to that delivered by the DC voltage source 45. Consequently , the second photosensitive diode Db is reverse biased and delivers charges and a current represented by an arrow 50 flows on the line L2 and the column F3 crossing the photosensitive point P6, that is to say passing through the diodes Da, Db of the latter. This results in a voltage variation at the output OF3 of the third column amplifier GF3 (voltage reduction) and, simultaneously, a voltage variation at the output OL2 of the second line amplifier GL2 (voltage increase); these voltage variations constituting signals which make it possible to distinguish the second line conductor L2 and the third column conductor F3 of the other row conductors and of the other column conductors, and consequently of determining that the elementary surface Se6 has been designated or illuminated by the optical pencil 15. Supposing that the light brush 16 supplied by the optical pencil 15 ( represented in FIG. 1) simultaneously illuminates several contiguous elementary surfaces, there will be simultaneously signals delivered by contiguous line conductors and by contiguous column conductors, so that it is possible to determine a central illuminated zone.

In the case where it is a curve which is described on the photosensitive surface 5, there are successively several photosensitive points PI to P9 which are lit, but for each of them, it is only between the conductor line LI to L3 and the column conductor FI to F3 between which the photosensitive point is connected that there is simultaneity in the signals delivered; this simultaneity must be respected or identified, during the acquisition and transfer of these signals, to the main memories of a central processing unit (not shown). Also the values contained in output OLl to

OL3 of all the line amplifiers GL1 to GL3 on the one hand, and on the other hand, the values present at output OF1 to OF3 of all the column amplifiers GFl to GF3 are loaded simultaneously into the line acquisition register 33 for the amplifiers line GL1 to GL3, and in the acquisition register column 32 for the column amplifiers GFl to GF3. This charging operation having been carried out, all the integration capacitors CLl to CL3 and CFl to CF3 are discharged

I 'that is to say short-circuited by the reset switches which are themselves controlled by the second reset signals V2. RESET. All the line and column amplifiers GL1 to GL3 and GFl to GF3 are then ready again to integrate the current which may be injected into the line conductor LI to L3 where the column conductor FI to F3 to which these amplifiers are connected; we recall that the current which has a given instant circulates at the same time on a line conductor LI to L3 and a column conductor FI to F3 corresponds to the photocharge generated by the second diode Db of the photosensitive point PI to P9 which is lit at this given instant and which is located at the intersection of this row conductor and this column conductor, and in a way the recognition of the row conductor LI to L3 gives the coordinate "Y" and the recognition of the column conductor gives the coordinate "X".

During the time when the line and lOZ-column amplifiers GL1 to GL3 and GFl to GF3 are able to integrate the current which is injected into them, the data or signals contained in the acquisition registers 32, 33 can be transferred to main memories : this is accomplished by simultaneously applying to the two acquisition registers 32, 33 the same 5 ST transfer control pulses delivered by the transfer signal generator 40. These ST transfer signals are delivered at a frequency for example of 1 MHz : under these conditions, assuming that the matrix 2 is a matrix of for example 4 million photosensitive points formed using 0 using 2,000 row conductors and 2,000 column conductors, the simultaneous transfer of the 2,000 data stored in the register line 33 and 2000 data stored in the column 32 acquisition register, is performed in a time of 2 milliseconds. If the sides of an elementary surface Sel to 5 Se9 have the same length 11 of the order of 100 micrometers for example, and if on the other hand the speed of movement of a light brush on the photosensitive surface 5 is of l '' order of 3 to 4 cm per second, the time which elapses between the start of the illumination of an element surface Sel at Se9 and the moment when this elementary surface has been fully illuminated is much greater than the time of transfer of the above-mentioned data, so that the acquisition of the data relating to a complete image of the photosensitive surface 5 can be carried out for the time necessary to pass through an elementary surface 5. In the nonlimiting example shown in FIG. 3, the active surfaces Sal to Sa9 of the photosensitive points PI to P9 are much smaller than the elementary surfaces Sel to Se9.

By the term largely lower we mean to define that these active surfaces Sal to Sa9 are smaller than the elementary surfaces Sel to Se9 not only to avoid short-circuits between adjacent photosensitive points as is the case in practice, but sufficiently to project an image under satisfactory conditions, as explained with reference to the figure

1; the active surface Sal to Sa9 of a photosensitive point pi to p9 corresponding to the section of the photosensitive element which the latter comprises, that is to say generally to the crossing surface between the line conductors L1 to L3 and the column conductors F1 to F3 and which is given by the width of these conductors.

FIGS. 4a to 4c illustrate the operation of the photosensitive matrix 2 in the document reader mode which has been explained with reference to FIG. 3. FIG. 4a shows the application to the first line conductor L1 of a line pulse SL, delivered by the line pulse generator 42, so as to particularly illustrate the operation of the second photosensitive point P2; - Figure 4b shows the potential variations

VA in zone A of the second photosensitive point P2, located at the intersection of the line conductor L1 and the column conductor F2;

- Figure 4c illustrates the correlation in time between the charges Q delivered by the photosensitive point P2 and the application of the line pulses SL. It should be noted that, in FIG. 4c, only the charges generated by illumination are represented, and the charges which can circulate on the column conductors F1 to F3 are not represented consequently only voltage variations applied to photosensitive points.

In FIG. 4a, at a time t0, a line pulse SL begins which reaches an amplitude VO, this amplitude VO is kept until an instant t3. FIG. 4b shows that with the start of the pulse SL, the voltage Va in the zone A increases, from the instant tO, to reach a value substantially equal to the value VO at an instant t2 which precedes the instant t3 . FIG. 4c shows that a quantity of charge Q circulates on lO ^' i column F2, charge which is generated by the second photosensitive point P2 at an instant tl comprised between instant tO and instant t2; this instant tl corresponding to the moment when the first diode Da goes into direct polarization. At time t3, the pulse SL applied to the line conductor L1 (FIG. 4a)

15 goes from the value VO to zero so that the two diodes Da and

Db are reverse biased and behave like capacitors; it is noted that the voltage Va at point A (FIG. 4b) has passed to a value VI substantially equal to half of VO, which confirms that the two diodes Da and Db are polarized at

20 reverse. Also from the instant t3, charges can be stored in the zone A, generated by the illumination of the photosensitive point P2. The accumulation of charges leads to a decrease in the voltage VA in zone A (as shown in FIG. 4b). At time t4, a second line pulse SL,

25 applied to the first line conductor Ll, generates a variation of the voltage VA (FIG. 4b): the voltage VA increases to reach at a time t5 a value Vd at which the first diode Da passes directly back from where it results the injection a second charge Q on the second column F2; this cycle

30 being repeated in the same way as long as the reading of a document. A similar operation is obtained for all the photosensitive points PI to P9 of the photosensitive matrix 2, by applying the line pulses SL to each of the line conductors L1 to L3, successively, this during the "time Tl included between two SL line signal pulses applied to the same line conductor.

FIGS. 5a to 51 illustrate the operation of the photosensitive matrix 2 in the case of operation as a graphics tablet.

Assuming that from a time t0 only a photosensitive point is illuminated, the second photosensitive point P2 for example, this illumination is illustrated in FIG. 5a by a slot which begins at time tO. FIGS. 5b and 5f show respectively that at time t0 the circulation of a current I begins on the first row conductor L1 and on the second column conductor F2; FIGS. 5c, 5d, 5e, 5g, show that no current flows on the other row conductors and column conductors when only the second photosensitive point P2 is lit. Figure 5h illustrates a variation in output voltage V. OLl generated at the output of the first line amplifier GLl by the integration of the current IL1; and FIG. 5i shows a variation in output voltage V. OF2 generated at the output of the second column amplifier GF2 by the column current IF2.

FIG. 5j shows that at an instant t2 the loading control signal SC is applied to the acquisition registers 32, 33, in order to load therein the signals which correspond to the output voltages of the amplifiers GL1 to GL3 and GFl to GF3. Since only the second photosensitive point P2 is lit, only the output voltages V are modified. OLl and V. OF2 (Figures 5h and 5i) which correspond respectively to the first row amplifier GL1 and to the second column amplifier GF2; the signals thus loaded being the voltage levels VS1, VS2 which, at time t2, comprise the output voltages V. OLl and V. OF2 (Figures 5h and 5i).

FIG. 5k illustrates the application of the second reset signal V2. RESET, at an instant t3 following the end of the loading command signal SC; the second signal from reset- to zero V2. RESET is used to short-circuit all the integration capacitors CLl to CL3 and CFl to CF3, so as to prepare all the line and column integrating amplifiers GLl to GL3 and GFl to GF3 to integrate a possible current on a line or a column, in a subsequent cycle. The following cycle begins at an instant t4, corresponding to the end of the signal V2.RAZ, from which the operations described above are repeated. We see that in this operation the integrating amplifiers GL1 to GL3, each connected to an online conductor L1! to ^; Eî, and the column amplifiers GFl to GF3 each connected to a column conductor Fl to F3, fulfill a function of current detector.

Assuming that the operation in graphic tablet mode began before the first instant t0, the operating cycle which has just been explained has therefore already taken place, that is to say that the data have already been transferred to the registers 32, 33. The data or signals contained in the acquisition registers 32, 33 are transferred to the main memories during a transfer time T2 comprised between the end of a loading command signal SC and the start of the next load control signal SC, as shown in FIG. 5j. This transfer of the data contained in the acquisition registers 32, 33 is effected by applying, during the transfer times T2, the transfer pulses ST (shown in FIG. 51) simultaneously to the two acquisition registers 32, 33.

Figures 6a and 6b are side sections in two orthogonal directions, which show, by way of nonlimiting example and schematically, a first embodiment of a photosensitive matrix 2 according to the invention.

The photosensitive matrix 2 is formed on a transparent substrate 3, for example made of glass or else made of quartz. On the substrate 3 is deposited a layer 61 of an electrically conductive material, opaque to light, in chromium or molybdenum for example. This conductive layer 61 is etched so as to constitute the column conductors F1 to F3. It should be noted that the column conductors being opaque, they can constitute the screens 12 shown in FIG. 1, and which are arranged between the substrate and the photosensitive points PI to Pn. The conductive layer 61 is covered, after etching, by a stack 60 of several semiconductor layers 62, 63, 64, 65, 66 intended to constitute the first and second diodes Da and Db arranged one above the other; these two diodes Da, Db being in the nonlimiting example both described as photodiodes: there is first above the conductive layer 61, a layer 62 of hydrogenated amorphous silicon, doped with a P-type impurity; then above the layer 62 of P doped silicon there is a layer 63 of intrinsic hydrogenated amorphous silicon; then above the layer 63 of intrinsic amorphous silicon, there is a layer of hydrogenated amorphous silicon 64 doped with an N-type impurity, phosphorus for example. The semiconductor layers are thus deposited from which the second diodes Db are made; the third semiconductor layer 64 formed of hydrogenated amorphous silicon doped with an N-type impurity being common also to the first diodes Da. Next, above this third semiconductor layer 64 of N-doped silicon, there is a layer 65 of intrinsic hydrogenated amorphous silicon, then finally a layer 66 of hydrogenated amorphous silicon doped with a P-type impurity, for example boron, is deposited. .

The five semiconductor layers 62, 63, 64, 65, 66 are then etched in an island pattern. Above the last layer 66 of P-doped amorphous silicon, a layer 67 of an electrically insulating and transparent material, for example made of silicon nitride, is deposited. Conventionally, openings are made in this last insulating layer 67, above the first diodes Da, so as to bring the latter into contact with a layer 70 of material electrically conductive and transparent, made of indium tin oxide (ITO) for example, this conductive layer 70 being etched to constitute the conductors in line L1 to L3.

It can also be deposited, above the layer 70, after the latter has been etched to form the in-line conductors L1 to L3, a transparent insulating layer 71 made of silicon nitride for example, the role of which is to produce a mechanical protection, and which thus optionally makes it possible to replace the protective glass or transparent screen 9 placed above the photosensitive surface 5 (shown in FIG. 1).

It is also possible to use the substrate 3 of the photosensitive matrix 2 to produce one of the partitions, the first partition 21 for example, of the liquid crystal display device 20 shown in FIG. 1. It Sufficient for this purpose to deposit an electrically conductive layer 73 and transparent, made of indium tin oxide (ITO) for example, on a face 72 of the substrate 3 which is opposite to the diodes Da, Db; this transparent conductive layer constituting for example the solid surface electrode that conventionally comprises a liquid crystal display device.

Figure 7 is a perspective view which schematically and partially shows the photosensitive matrix 2 in another embodiment. This new embodiment has the advantage, compared to the embodiment shown in FIGS. 6a, 6b, of requiring less masking and engraving operations.

In the nonlimiting example shown in FIG. 7, the electrically conductive layer 61 has been deposited on the substrate 3 and then etched so as to constitute the column conductors F1, F2. Next on the column conductors are deposited the 5 semiconductor layers 61 to 65 which form a stack 60 intended to constitute the superimposed diodes Da and Db. Then, above the stack 60 of semiconductor layers, the layer is deposited directly electrically. upper conductor 70, transparent, intended to be etched to form the line conductors L1 to L3. The upper electrically conductive layer 70 and the stack 60 of semiconductor layers are then simultaneously etched, so that the stack 60, after etching, forms strips 60a located under the line conductors L1, L2 and consequently having the same shape and the same surface as these conductors L1, L2. In this embodiment where the stack 60 of semiconductor layers is not etched in the form of islands but etched in the same way as the line conductors L1, L2, the photosensitive points PI, P2, P4, P5 which are thus produced are located at the intersection of the line conductors L1, L2 and the column conductors Fl, F2. The active surface Sal, Sa2, Sa4, Sa5 (represented by a hatched surface in FIG. 7) of the photosensitive points PI, P2, P4, P5, consists solely of the intersection surface of the line conductors and the column conductors Ll, L2, Fl, F2. That is to say that the superimposed diodes Da and Db are formed only between the "crossing points of the row and column conductors, in particular because it is only in the volume located under the active surfaces Sal, Sa2 , Sa4, Sa5 that a sufficient electric field has been established. Consequently, the resistance presented by zones Z situated between two adjacent photosensitive points and located under the same line conductor (the photosensitive points PI and P2 for example), is large and these photosensitive points are not short-circuited, of course this technique is made possible by the fact that the active surfaces Sal to Sa9 have a surface "considerably less" than the surface of an elementary surface Salt to Se9.

Claims

. 1. Display and writing device comprising an image generator (7, 20), an optical pencil (15), a writing surface (5), characterized in that it comprises a matrix (2 ) of photosensitive points (PI to P9) and in that the optical pencil (15) emits a radiation of light (16), the writing surface (5) being constituted by a photosensitive surface (5) of the matrix (2 ) photosensitive, the matrix (2) being placed in front of the image generator (7, 20) so that the image produced by the image generator (7, 20) is visible through the photosensitive matrix (2).

2. Display device according to claim 1, characterized in that the image generator (7, 20) is of the matrix type.

3. Display device according to one of the preceding claims, characterized in that the photosensitive surface (5) is divided into a plurality of elementary surfaces (Sel to Se9) each comprising a photosensitive point (PI to P9), each photosensitive point comprising an active surface (Sal to Sa9) much lower than an elementary surface Sel to Se9.

4. Display device according to one of the preceding claims, characterized in that it further comprises at least one light source (7, 25) intended to illuminate a document (10, 10a) located above the matrix (2) photosensitive, with a view to further using the photosensitive matrix (2) to read the document (10, 10a).

5. Display device according to claim 4, characterized in that the light source (25) is located opposite the photosensitive matrix (2) relative to the document (10a) to be read.

6. Display device according to claim 4, characterized in that the light source (7) is located opposite the photosensitive matrix (2) relative to the image generator (20).

7. Display device according to claim 4, characterized in that the light source (7) is constituted by an image generator.

8. Display device according to one of the preceding claims, the photosensitive surface (5) being divided into elementary surfaces (Sel to Se9) each comprising a photosensitive point (PI to P9), the matrix (2) £L comprising a network of line conductors (Ll to L3) and a network of column conductors (Fl to F3), each photosensitive point (PI to P9) being connected between a line conductor (Ll to L3) and a column conductor (Fl to F3) , characterized in that the writing display device (1) further comprises means (Da, Db, GLl, GFl, 45, 32, 33) for distinguishing the conductor (Ll to L3) and the column conductor ( Fl to F3) between which is connected a photosensitive point (PI to P9) located in an elementary surface Sel to Se9 illuminated by the optical pencil (15).

9 - Display device according to claim 8, characterized in that it further comprises an addressing device (46, 42) and a reading device (32) allowing the matrix (2) to be used in a mode of functioning as a document reader.

10. Display device according to one of the preceding claims, characterized in that each photosensitive point (PI to P9) comprises a first and a second elements (Da, Db) connected in series, a first element (Da) constituting a means switching and the second element (Db) being a photosensitive element.

11. Display device according to claim

10, characterized in that the first element (Da) is a diode.

12. Display device according to claim

11, characterized in that the diode (Da) forming the first element is a photosensitive element.

13. Display device according to one of claims 10 to 12, characterized in that the second element (Db) is a diode.

14. Display device according to one of claims 10 to 12, characterized in that the second element

(Db) is a photoresistor.

15. Display device according to one of claims 11 to 14, characterized in that it comprises means (45, IV1 to IV3) for direct biasing the diode (Da) forming the first element.

16. Display device according to one of the preceding claims, characterized in that each photosensitive point (PI to P9) comprises two diodes (Da, Db) connected in series with opposite directions of conduction, at least one of the diodes (Db ) being photosensitive.

17. Display device according to claim 16, characterized in that it comprises means (45, IV1 to IV3) for polarizing the two diodes (Da, Db) so that a first diode (Da) is direct biased and that the second diode (Db) is reverse biased, at least the second diode (Db) being photosensitive.

18. Display device according to one of the preceding claims, characterized in that a screen (12) opaque to light is interposed between the photosensitive points (PI to P9) and the image generator (7, 20).

19. Display device according to one of the preceding claims, characterized in that the photosensitive matrix (2) comprises a substrate (3) carrying a stack (60) of semiconductor layers (62, 63, 64, 65, 66 ) arranged between column conductors (Fl to F3) and line conductors (Ll to L3) so as to form a structure of which one face opposite the substrate (3) constitutes the photosensitive surface (5), and in that an insulating and transparent layer (71) is deposited on the photosensitive surface (5).

20. Display device according to one of the preceding claims, characterized in that the photosensitive matrix (2) comprises a substrate (3) carrying a stack (60) of se i-conductive layers (62, 63, 64, 65, 66) arranged between column conductors (Fl to F3) and line conductors (Ll to L3), the stack (60) of semiconductor layers being etched so as to constitute strips (60a) each located under each line conductor (Ll to L3) and obtained by simultaneous etching of the line conductors

10. (Ll to L3) and the stack (60) of semiconductor layers.

21. Display device according to one of the preceding claims, the image generator (20) being constituted by a liquid crystal display device (20), the photosensitive matrix (2) comprising a substrate (3)

15 transparent, is characterized in that the substrate (3) further constitutes a partition (21) of the display device (20).