GB2156133A

GB2156133A - Reproducing graphical presentations on a display screen

Info

Publication number: GB2156133A
Application number: GB08505291A
Authority: GB
Inventors: Carlos Garcia-Victoria; Bernhard Heine
Original assignee: International Standard Electric Corp
Current assignee: International Standard Electric Corp
Priority date: 1984-03-15
Filing date: 1985-03-01
Publication date: 1985-10-02
Also published as: GB2156133B; GB8505291D0; DE3409531A1

Abstract

A display screen consists of a matrix display device (2) including, transparent row- and column leads (6, 4). Between the glass plates (3, 12) there is disposed an electro-optical layer 8. A detector field (11) consists of radiation-sensitive circuit elements, such as photodiodes. Individually controllable via row- and column leads (13, 17). The input is effected by a light pen. The light pen is designed as an optical radiator whose beam (23), when the light pen is led over the surface of the display device (2, passes through the latter and impinges upon the radiation-sensitive circuit elements (surface areas 19) of the detector field (11). Via a control circuit, the radiation-sensitive circuit elements are associated with individual image points of the display device (2), which are activated whenever the associated circuit element surface area (19) is hit by the beam (23). <IMAGE>

Description

SPECIFICATION Arrangement for reproducing graphical presentations on a display screen This invention relates to an arrangement for reproducing graphic presentations on a viewing screen, of the kind in which the input of the graphical presentation is effected with the aid of a light pen which is led over the surface of the screen An arrangement of this kind is known from the technical journal "Computer Personlich", No.4 of February 8, 1984, pup. 134 to 137.

This arrangement employs a cathode-ray tube.

By a serial readout from a display storage, the unblanked cathode-ray beam is led in a rowand image-point-wise manner over the display screen. The light pen is provided at its point end with a photo-transistor. Whenever the light pen is placed into position, and the photo-transistor is hit by a beam, a connected control circuit recognises the position of the light pen from the associated addressing of the beam, thus further causing the beam to be blanked in this image point.

This arrangement places high technical requirements on the signal transmission between the light pen and the control circuit.

The cathode-ray tube does not make for equipment of a size which would be easy to handle. The display screen, for the input of graphical presentations, cannot be brought into a position permitting easy writing. For correcting a presentation, the entire screen picture has to be inverted.

It is an object of the invention to provide an arrangement for reproducing graphical presentations, which does not require a cathode-ray tube and in which the screen picture, for being corrected, does not have to be inverted.

According to the invention in its broadest aspect, an arrangement for reproducing graphical presentations on a viewing screen of the kind referred to is characterised in that the pen emits optical rays, that the viewing screen is a display device whose front and rear sides are transparent and which, between the transparent first row- and column leads has a layer which is capable of being electrically influenced, which is transparent in the noninfluenced state and, in the influenced state, forms image points, that on the rear side of the display device there is provided a detector field of circuit elements which are sensitive to optical radiation, and which are disposed in the raster pattern of the intersecting row- and column leads of the display device, that the circuit elements which are sensitive to optical radiation, are connected to secondary rowand column leads, and that a control circuit is provided which successively interrogates the circuit elements which are sensitive to optical radiation, in a row- and column-wise manner and, when influenced by the rays of the pen, causes the display device to be controlled in such a way that the image points associated with the controlled circuit elements become visible.

The advantages achievable by the invention reside above all in that the display screen is of a flat design and can be used in a position permitting easy writing, that the light pen only serves as an optical radiator, and that corrections can be carried out directly.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows, on a considerably enlarged scale and in a schematical representation, the cross-sectional view of an arrangement according to the invention consisting of a reproduction device comprising a display device and a field of photodiodes, Figure 2 is a top view of the display device according to Fig. 1, Figure 3 is a view of the field of photodiodes according to Fig. 1, and Figure 4 shows a control circuit for the reproduction device according to Fig. 1.

The input and reproduction device 1 shown in Figs. 1, 2 and 3 consists of a display device 2 on the rear side of which is disposed a detector field 11 although in Fig. 1, for the sake of clarity, the two parts 2 and 11 are shown to be at a distance from each other, the detector field 11 in actual practice embodiment, is applied to the rear side of the display device 2 and connected thereto.

Fig. 2 shows part of the display device 2 in a top view, and Fig. 3 is the top view of the corresponding section of the detector field 11.

Fig. 1 shows, on a considerably enlarged scale and in a schematical representation, part of a reproduction device 1 for graphical presentations, in a cross-sectional view (section taken on lines la-la of Fig. 2 and Ib-Ib of Fig. 3).

The display device 2 consists of two transparent glass plates 3 and 5 which are spaced apart from each other and which, on their insides, are provided with strip-shaped column and row leads 4 and 6 respectively, extending vertically in relation to one another, so that an X-Y matrix results. The leads are likewise transparent. A layer which is capable of being electrically influenced is disposed between the glass plates 3 and 5. In the embodiment, this layer consists of liquid crystals 8. The layer, may however, also consist of an electroluminescent substance. In either case, the layer is transparent when in the electrically neutral state. By applying a voltage to two leads 4 and 6 intersecting each other, the liquid crystal layer within the area of intersection of the leads 4 and 6 becomes milky white. When employing an electroluminescent substance, light is emitted.This kind of display, unlike the liquid-crystal display, is independent of the ambient light. The range of intersection of the leads 4 and 6 represents one image point 9 of the display, as can be recognised from Fig. 2. Between the intersecting leads 4 and 6 there are fields 7 within the area of which the liquid crystal layer or the electroluminescent layer remains electrically uninfluenced.

The detector field 11 consists of a matrix of radiation-sensitive circuit elements. The number and the divisional spacing are the same as with the image points 9 of the display device 2. The radiation-sensitive circuit elements are photodiodes.

Figs. 1 and 3 show the constructional features of the detector field 11. On a baseplate 12 of insulating material, the column leads 13 are deposited at a defined divisional spacing. On this there is placed a layer of silicon 14 with a diffusion layer 15. Above this layer there is positioned an insulating layer 16 which, at the defined divisional spacing, comprises recesses for the annular electrodes 1 7a (Fig. 3) each of which enclose a radiationsensitive surface area 19. These annular electrodes 1 7a are connected to one another in a row-wise manner by strip lines 17. For the purpose of increasing the contrast of the display, the surface of the detector field 11 has a dull black finish. In order to avoid disturbing influences caused by ambient light, the surfaces 19 are only sensitive to infrared light.

As can be recognised from Figs. 1 to 3, the radiation-sensitive surface areas 19 of the detector field 11 are congruent with the image points 9 of the display device 2. Accordingly, the radiation-sensitive surface areas 19 are disposed directly below the image points 9. Between the image points 9 and the radiation-sensitive surface areas 19 there exists a firm circuitwise assignment, that is the respective image point 9 is associated with the radiation-sensitive area 19 of a photodiode positioned therebelow.

The input of the graph to be presented, is effected with the aid of an optical radiator positioned inside a light pen 22 (schematically shown in Fig. 4 only), which is placed on to the glass plate 3 of the display device 2. This radiator is a light-emitting diode radiating within the infrared region. Through a lens, the beam is bundled. In order to avoid an unintended input during initial placing of the light pen 22 on to the glass plate 3, the point end of the light pen 22 is manually held in a disconnected position by a weak axial spring.

The connection of the light-emitting diode with an external or internal voltage source is effected when the point end of the light pen, owing to the pressure exerted when "writing", assumed a rearward stop position by moving back a few millimeters against the spring.

If, as is shown in Fig. 1, the light pen 22 is moved over the surface of the glass plate 3, the beam 23 of the light pen 22 passes freely through the display device 2 and meets upon the surface of the detector field 11. This surface, with the exception of the radiationsensitive surface areas 19, is insulated by the layer 16. When the beam 23 as shown in Fig.

1, in the course of the light pen movement, impinges upon one of the radiation-sensitive surface areas 19, for example, upon the surface area 19', then the photodiode matrix is rendered conductive at this particular point.

Via the association column and row leads 13' and 17', the X-Y coordinate values of the marked diode are ascertained by a control circuit as shown in Fig. 4, in a way to be described in greater detail hereinafter. By an evaluating device it is effected that a voltage is applied to the corresponding column and row leads 4 and 6 of the display device 2.

The electric field which is being built up within the range of intersection (image point 9') of the two leads 4' and 6', causes in a manner known per se, the molecules 8a of the liquid-crystal layer to rotate transversely in relation to the direction of the electric field, and cause the image point 9' to appear milky white. Owing to the blackening of the surface area of the detector field 11, the image point 9' or the graphic presentation consisting of a plurality of image points 9, is well distinguishable against the dark background. The same also applies when using an electroluminescent substance as the layer which is capable of being electrically influenced.

A graph must be correctable, that is, individual parts of the recording must be capable of being erased. For this purpose a switch (not shown) is provided within the area of the reproduction device 1. This switch permits the control circuit to be switched over in such a way that those image point markings are erased whose associated diodes in the detector field are activated during the time of the switch actuation by the beam 23. The diodes are controlled through the marked image points 9, because the liquid crystals 8, also in the state of being electrically influenced, still permit the passage of infrared light.

Fig. 4 shows a control circuit for operating the reproduction device 1 as described hereinbefore. The display device 2 and the detector field 11 are schematically shown in a perspective representation. The light pen 22 connected to a power supply unit 21, is placed into position at one point of the display device 2. Its beam 23 meets the radiation sensitive surface area 19' of a diode in the detector field 11.

The row and the column leads 17 and 13 of the detector field 11 are marked at the connecting points by the references Xt to Xn and Y, to Yn respectively. The X leads are connected to a row selector 31, and the Y leads are connected to a column selector 32.

The two selectors 31 and 32 are connected to a driver stage 33 with a coder 33a, which, in turn, is in connection with an evaluating device 37. Between the column selector 32 and the coder 33a there exists a return channel for the result of the detector-field interrogation.

The row and column leads 6 and 4 of the display device 2 are indicated at the connecting points by the references X11 to Xln and Yt, to Yln respectively.

The X'-leads are connected to a row selector 34, and the Y'-leads are connected to a column selector 35. Both selectors 34 and 35 are connected to a driver stage 36 with a decoder 36a which, in turn, is connected to the evaluating device 37 and is in connection with an image point memory contained therein.

By the driver stage 33, both the row selector 31 and the column selector 32 are stepped on at different frequencies in such a way that the photodiodes of the detector field 11 are interrogated in a row-wise manner in series via the X-Y cordinates by the application of a voltage. The cyclical interrogation is effected, for example, at a 50 kHz frequency, in order thus to obtain an unobjectionable solution also in cases where the light pen 22 is moved quickly.

If, for example, at the time position of a scanning, the photodiode at the coordinate system point X4/V4 as shown in Fig. 4, is illuminated by the beam and is thus rendered conductive, this is recognised by the column selector 32 which, via the return channel, causes the coder 33a, from the coordinate values as available in the driver stage 33, to submit to the photodiode as an address, a stored information via the evaluating device 37, to the image-point memory.

While the input into the image-point memory is effected at the interrogation frequency of the diode matrix, the readout is effected at a substantially lower frequency. This frequency is determined by the decay time of the layer capable of being electrically influenced, and by the inertia of the human eye, and is in the order of 50 Hz. Via the evaluating device 37, there is effected the readout of the individual image-point information in synchronism with the clock control of the driver stage 36.

The clock steps on the row selector 34 and the column selector 32 in such a way at a different frequency, that the individual image points 9 are offered to the display device 2 in rows in series via their associated X'-Y' coordinates for the purpose of control. This selection control, however, is only carried out when the decoder 36a provides a positive image-point information. Only in that case does the driver stage 36 cause a voltage to be applied tothe X' and Y' leads as selected by the row and column selectors 34 and 35 respectively. In the example given, these are the leads X'4 and V'4, in whose intersection area the layer which is capable of being electrically influenced is subjected to a structural change, as described hereinbefore, and acted upon by the electric field, so that the image point 9' becomes visible.When the light pen 22 is moved, a quantity of positive image-point information is intermediately stored in the image-point memory, causing the corresponding image points 9 to become visible and to reproduce the course of the light-pen movement.

Liquid crystals and luminescent substances are known, which, in the electrically influenced state, do not permit the passage of infrared light. If these are used as a display layer, the detector field 11 will have to be staggered with respect to the matrix of the image points 9 of the display device 2 by half a divisional spacing in both coordinate directions X and Y. In that cae, the radiationsensitive surface areas 19 come to lie below the fields 7 of the display device 2. As already mentioned hereinbefore, the layer which is capable of being electrically influenced, is not changed within the area of the fields 7, that is, the fields 7 always remain transparent. Via the control circuit, the respective image point 9 is associated, for example, with the radiation-sensitive surface area 19 which is positioned below the field 7 on the left below the corresponding image point 9. Owing to the alignment of the radiation-sensitive surface areas to the always transparent fields 7, it becomes possible for the marked image points 9 to be erased.This offset, for example at a resolution of nine image points per square millimeter, has not proved to have any disadvantages, because the optical beam 23, in contrast to the simplified representation shown in Fig. 1, has a diameter corresponding to at least two image points 9.

Claims

1. An arrangement for reproducing graphical presentations on a viewing screen of the kind in which the input of the graphical presentation is effected with the aid of a light pen which is led over the surface of fthe screen, characterised in that the pen emits optical rays, that the viewing screen is a display device (2) whose front and rear sides are transparent and which, between the transparent first row- and column leads (6, 4) has a layer which is capable of being electrically influenced, which is transparent in the noninfluenced state and, in the influenced state, forms image points (9), that on the rear side of the display device (2) there is provided a detector field (11) of circuit elements which are sensitive to optical radiation, and which are disposed in the raster pattern of the intersecting row- and column leads (4, 6) of the display device (2), that the circuit elements which are sensitive to optical radiation, are connected to secondary row- and column leads (17, 13), and that a control circuit is provided which successively interrogates the circuit elements which are sensitive to optical radiation, in a row- and collumn-wise manner and, when influenced by the rays of the pen (22), causes the display device (2) to be controlled in such a way that the image points (9) associated with the controlled circuit elements, become visible.

2. An arrangement as claimed in claim 1, characterised in that the matrix of the detector field (11) is disposed congruently with the matrix of the display device (2).

3. An arrangement as claimed in claim 1, characterised in that the matrix of the detector field (11) is staggered with respect to the matrix of the display device (2) by half the divisional spacing in both coordinate directions (X, Y).

4. An arrangement as claimed in claim 1, characterised in that the layer which is capable of being electrically influenced, consists of liquid crystals (8).

5. An arrangement as claimed in claim 1, characterised in that the layer which is capable of being electrically influenced, is an electroluminescent substance.

6. An arrangement as claimed in claim 1, characterised in that the radiation-sensitive circuit elements are only sensitive to infrared light, and that the light pen (22) has a source of infrared light.

7. An arrangement as claimed in claim 6, characterised in that the light source is a lightemitting diode.

8. An arrangement as claimed in claim 6, characterised in that the point end of the light pen (22) is capable of being axially displaced by the pressure of writing into a stop position in opposition to the force of a weak spring, in which position the light source is connected to a power supply.

9. An arrangement as claimed in claim 8, characterised in that the light pen (22) is connected via a line to an external power supply (21).

10. An arrangement as claimed in claim 8, characterised in that the power supply unit is accommodated inside the light pen (22).

11. An arrangement as claimed in claim 1, characterised in that the surface of the detector field (11) has a dull-black finish.

12. An arrangement as claimed in claim 1, characterised in that a control circuit is provided which interrogates the radiation-sensitive circuit elements of the detector field (11) one at a time in a cyclical succession, which contains an image point memory serving as an intermediate memory for storing the values obtained from the detector field interrogation, and which, in accordance with the intermediately stored values, controls the display device (2) in the same cylical succession.

13. An arrangement as claimed in claim 12, characterised in that the frequency of the cylical interrogation of the detector field (11) is higher than the frequency of the cyclical control of the display device (2).

14. An arrangement for reproducing graphical presentations on a viewing screen substantially as described with reference to the accompanying drawings.