GB2194376A

GB2194376A - Method of and device for producing multiple colors

Info

Publication number: GB2194376A
Application number: GB08716207A
Authority: GB
Inventors: Seiichi Oseto; Yoshiyuki Kageyama; Kenji Kameyama
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 1986-07-10
Filing date: 1987-07-09
Publication date: 1988-03-02
Anticipated expiration: 2007-07-09
Also published as: GB2194376B; DE3722912C2; GB8716207D0; DE3722912A1

Description

GB2194376A 1 SPECIFICATION between the light-emitting layers being shared

as electrodes for driving the light-emitting Method of and device for producing rnul- layers on opposite sides of those electrodes, tiple colors and a driver circuit for energizing the display 70 electrodes and the scanning electrodes to

BACKGROUND OF THE INVENTION cause the light-emitting layers to sequentially

The present invention relates to a method of display respective frame pictures of the re and a device for producing a multiplicity of spective colors repeatedly in response to dis colors in multicolor display or the like. play signals corresponding to the colors of the All color display devices including conven- 75 light-emitting layers, at a repetition frequency tional cathode-ray tubes are spatial color mix- higher than a critical fusion frequency of color ing systems. One of such color mixing sys- stimulus, for thereby producing a multicol'or tems is a planar color mixing system repre- picture.

sented by cathode-ray tubes and color liquid The driver circuit may be arranged to repeat crystal displays. Another color mixing system 80 the multicolor picture at a frequency higher is a three-dimensional color mixing system as than a critical fusion frequency of brightness, disclosed in Japanese Laid-Open Patent Publi- for thereby producing a moving multicolor pic cation No. 58(1983)-30093, for example. ture.

The color mixing systems of the above Research on materials of thin-film electro- types have their own advantages and disad- 85 luminescent displays for multicolor image dis vantages, but suffer serious drawbacks as play has just entered a substantial phase in a compared with the black-and-white displays. few years. Methods of displaying images in More specifically, a planar color mixing system multiple colors using combinations of such has a resolution which is a third as high as materials are far behind those for cathode-ray the resolution of a black-and-white display. A 90 tubes and liquid crystal displays. There has planar color mixing system of the matrix elec- been proposed a method of three-dimension trode drive type such as an electro-lumines- ally producing multiple colors which are mixed cent display or a liquid crystal display requires in the transverse direction of a display panel three times as many driver circuits and active composed of stacked lightemitting layers elements as those of a black-and-while dis- 95 capable of emitting lights of mutually different play. A three-dimensional color mixing system colors with electrode layers and insulating has no resolution problem, but also requires layers interposed between the light-emitting three times as many driver circuits and active layers. This method is capable of displaying elements as those of a black-and-while dis- colored images at better resolution than two play. 100 dimensional multicolor image displays repre- The above shortcomings result from the sented by the cathode-ray tube. However, the principles of operation of the respective color driver system for driving the display panel is mixing systems, and essentially remain un- highly complex and the number of driver ICs is solved as compared with the black-and-white increased as the display panel contains many displays even if display elements are imlayers.

proved. The multicolor producing device according to the present invention comrises a multicolor SUMMARY OF THE INVENTION electroluminescent display composed of two

It is an object of the present invention to or more, e.g., three electroluminescent layers provide a method of and a device for produccapable of emitting lights of mutually different ing a multiplicity of colors with an increased colors. The electroluminescent layers are inde degree of resolution and a reduced number of pendently driven to threedimensionally pro active elements. duce multiple colors. The electrode layers dis- According to the present invention, there is posed between the electroluminescent layers provided a method of producing a multiplicity 115 are shared as electrodes for driving these of colors on a multicolor display having pixels, electroluminescent layers held in contact there comprising the step of sequentially varying the with to sequentially form frame pictures of dif colors of lights from the pixels repeatedly on ferent colors in a serial manner which are a time basis in response to display signals at mixed on a time basis to reproduce original a repetition frequency higher than a critical fu- 120 colors.

sion frequency of color stimulus for thereby As is well known, the human sense of sight enabling the sequentially varying colors to ap- is subject to a critical fusion or flicker fre pear to be mixed. - quency (CFF) of brightness and a critical fusion A device for producing a multiplicity of co- or flicker frequency (CFFF) of color stimulus.

lors includes a plurality of stacked light-emitt- 125 Generally, CCFF is a fraction of CFFF. Assum ing layers capable of emitting lights of mutu- ing that the time period of one frame formed ally different colors, a plurality of display elec- by each electroluminescent layer is indicated trodes and scanning electrodes disposed on by tF and the time period for the three elec opposite sides of each of the light-emitting troluminescent layers to serially form color-se layers, those electrodes which are interposed 130 parated pictures is indicated by AT ( = 3tF), 2 GB2194376A 2 the requirement of 1 /tF > CCFF should be light-emitting material such as Mn or a lan met in order to mix the color-separated pic- thanum-base rare earth material. The insulating tures, of red, green, and blue, for example, layer may be made of an oxide such as Y103, formed by the three electroluminescent layers Si02, A12031 or Ta205, a nitride such as SO, on a time basis to reproduce a colored picture 70 a tungsten-bronze-base ferrodielectriG sub- free of color flickering, and the requirement of stance, or a perovskite- base ferrodielectric 1 /AT-> CFF should be met in order to substance. The insulating layer may also be change the reproduced colored picture on a made of any of multilayer composite films, time basis for thereby producing a moving mixed crystals, and solid solutions of these multicolor picture free of motion flickering. 75 materials. On opposite sides of the light-emitt- -It follows from the above that 1 /AT > CFF ing layers 1 through 3, there are disposed line and 1 /tF > 3CFF should be met in order to sequential driving scanning electrodes 4 prevent color and brightness flickering in im- through 6 and display electrodes 7 through 9.

ages displayed on the electroluminescent dis- The electrodes 5 through 9 except the scann play panel composed of three electrolumines- 80 ing electrode 4 which serves as a back elec Gent layers. trode are all in the form of transparent elec- Since the repetition frequency at which the trodes made of an ITO- or ZnO- base material.

colors produced by the pixels of the multicolor The light-emitting layers 1 through 3, and the display device are sequentially varied in rescanning electrodes 4 through 6 and the dis sponse to display signals is selected to be 85 play electrodes 7 through 9 on opposite sides over the critical fusion frequency of color of the light-emitting layers jointly constitute re stimulus for color mixing, the resolution of the spective independent units which are electri display can be increased and the number of cally isolated from each other by insulating active elements used can be reduced. The ar- layers 10, 11. The insulating layer 10 isolates rangement of the display can be greatly sim- 90 the display electrode 7 and the scanning elec plified by sharing the electrodes between the trode 5 from each other to eliminate influ light-emitting layers as electrodes for driving ences of variations in the electric field distribu the light-emitting layers on opposite sides tion due to switching on and off of these thereof. electrodes, the insulating layer 10 having suffi- The above and other objects, features and 95 cient transparency to light. The insulating layer advantages of the present invention will be11 isolates the display electrode 8 and the come more apparent from the following de- scanning electrode 6 from each other and has scription- when taken in conjunction with the sufficient transparency to light.

accompanying drawings in which preferred A data signal A, a data signal S, a data embodiments of the present invention are 100 signal C, a data transfer clock signal CK, a shown by way of illustrative example. horizontal synchronizing signal HD, and a verti cal synchronizing signal VD are applied from a BRIEF DESCRIPTION OF THE DRAWINGS display control system to a control circuit 12

FIG. 1 is a block diagram of a device for in which the signals are temporarily stored.

producing a multiplicity of colors according to 105 The signals are then controlled in timing for the present invention; line sequential driving and distributed to modu- FIG. 2 is a block diagram of a conventional lator/drivers (power supply circuits) 13 device for producing a multiplicity of colors; through 18 and driver ICs (integrated circuits) FIG. 3 is a- schemalic view of a portion of 19 through 24. The modulator/drivers 13 the device of the present invention; 110 through 18 are responsive to the input signals FIG. 4 is a timing chart of operation of the from the control circuit 12 for generating device shown in FIG. 1; and power supply voltages to be applied to the FIG. 5 is a timing chart explanatory of the electrodes 4 through 9 and sending the gener- present invention. ated power supply voltages to the driver ICs 115 19 through 24. The driver ICs 19 through 24 DETAILED DESCRIPTION is in response to timing commands from the

FIG. 2 shows, in a block form, a device for control circuit 12 for applying the power sup- carrying out a conventional method of three- ply voltages from the modulator/drivers 13 dimensionally producing a multiplicity of co- through 18 to the electrodes 4 through 9. In lors. The device is an electroluminescent (EQ 120 FIG. 2, Y and X represent the scanning and display having a stack of three light-emitting display electrodes, respectively, and A, B and layers 1 through 3 for emitting different co- C represent the light- emitting layers 1 through lors. Each of the light-emitting layers 1 3, respectively.

through 3 comprises a phosphor layer with an FIG. 1 shows a device for producing a insulating layer disposed on one side thereof 125 multiplicity of colors according to an embodi or on-each of opposite sides thereof. The ment of the present invention. The device has phosphor layer may be made of a base ma- light-emitting layers 1 through 3, scanning terial such as ZnS, ZnSe, SrS, CaS, SrSe, electrodes 25 associated with the light-emitt CaSe, or any of their liquid crystals. Each of ing layer 1, scanning electrodes 26 associated the light-emitting layers contains a central 130 with the light-emitting layers 2, 3, display 3 GB2194376A 3 electrodes 27 associated with the light-emitt- signal C, a data transfer clock signal CK, a ing layers 1, 2, and display electrodes 28 as- horizontal synchronizing signal HID, and a verti sociated with the light-emitting layer 3. The cal synchronizing signal VID are applied from a electrodes 25 through 28 and the light-emitt- display control system to a control circuit 33 ing layers 1 through 3 are stacked into an 70 in the same manner as shown in FIG. 2. This electroluminescent display. The light-emitting input application is the minimum requirement layers 1 through 3 may be made of the same to be met in order to make the device of FIG.

material as that of the light-emitting layers 1 1 compatible with the conventional device.

through 3 shown in FIG. 2, and the electrodes These signals are temporarily stored in the 25 through 28 may be made of the same 75 control circuit 33, and then sequentially sup material as that of the electrodes 4 through 9 plied to modulator/drivers 34, 35 and the shown in FIG. 2. The electroluminescent dis- driver ICs 29 through 32 at the timing of FIG.

play illustrated in FIG. 1 differs primarily from 4. Since some of the electrodes sandwiched that of FIG. 2 in that those electrodes dis- by the light-emitting layers are shared by the posed between the light-emitting layers are 80 light-emitting layers, only four kinds of elec shared thereby and any insulating layers for trodes 25 through 28 are required, and hence isolating the units including the light-emitting the number of driver ICs used is reduced to layers are thereby dispensed with. 2/3 of the number of driver ICs used in the The electroluminescent display of FIG. 1 is device shown in FIG. 2.

in the form of a panel 36 as shown in FIG. 3. 85 As illustrated in FIG. 4, the scanning signals The electrodes 25 through 28 are arranged in and the display signals are applied fully in"a a matrix pattern and connected to driver ICs serial fashion from the first through third 29 through 32, respectively. The driver ICs 29 steps. This means that only one modulator/ through 32 may be disposed in vertically and driver suffices for each of the scanning and horizontally confronting relation, as illustrated 90 display electrode sets. The power supply vol in FIG. 3, or may be positioned on one side tage supplied to each of the electrode layers of the display panel 36. The driver ICs 29 is controlled by only a timing command ap through 32 may be arranged in any of various plied from the control circuit 33 to the corre ways without limitations; for example, ICs of sponding driver IC, and no problem arises one type may be put together at respective 95 from the wiring arrangement shown in FIG. 1.

odd-numbered and even-numbered addresses More specifically, the modu lator/d river 34 ap and disposed in confronting relation. plies a power supply voltage to the driver ICs FIG. 4 is a timing chart explaining a method 29, 30, and the modulator/ driver 35 applies of driving the electroluminescent display where a power supply voltage to the driver ICs 31, N scanning lines and n display lines are in- 100 32. The driver ICs 29 through 32 supply the volved. "on" and "off" in FIG. 4 indicate applied power supply voltage to the elec switching on and off, respectively, of the trodes 25 through 28 according to timing driver ICs. In a first step, the driver ICs 29, commands from the control circuit 33. This 31 are driven in a line sequential mode to manner of applying the power supply voltage enable the light-emitting layer 1 to form one 105 remains the same irrespective of whether the frame picture (picture A) which may be a red electrode ends are floated or ground when the picture, for example. Then, in a second step, driver ICs 29 through 32 are switched of f.

the driver ICs 30, 31 are driven in a line se- Therefore, the number of modulator/d rivers quential mode to enable the light-emitting layer used is reduced to 1/3 of the number of mo 2 to form one frame picture (picture B) which 110 dulator/drivers employed in the conventional may be a green picture, for example. In a final device shown in FIG. 2.

third step, the driver ICs 30, 32 are driven in As a result, the number of components of a line sequential mode to enable the light-em- the device is greatly reduced.

itting layer 3 to form one frame picture (pic- As is apparent from the timing chart of FIG.

ture Q which may be a blue picture, for 115 4, the data signal C supplied to the control example. The three color-separated pictures circuit 33 may have to be retained in a maxi thus serially formed are combined on a time mum of two frame periods. Therefore, a basis into one composite colorpicture. memory having a storage capacity which is The pictures A, B, C are sequentially dis- three times greater than that of the memory in played in repetitive cycles at a frequency 120 the device of FIG. 2 is required to store the called a frame frequency. When the frame data signal C. Use of such a larger-capacity frquency is higher than the crical fusion or memory, however, does not cause a signifi flicker frequency (CFFF) of color stimulus for cant problem. Nevertheless, by shifting peri human beings, the colors of the pictures ap- ods for sampling the data signals as shown in pear sufficiently mixed to the human eyes. If 125 FIG. 6, the data signals may be retained in the the frame frequency is higher than the range same conditions as those for FIG. 2, and no of from 40 to 50 Hz, then composite multico- increase in the storage capacity is needed. It lor pictures of good color reproducibility can has been found that by shifting the data be obtained. sampling periods, the data signals can be A data signal A, a data signal B, a data 130 sampled in a serial manner, and hence ad- 4 GB2194376A 4 dresses in the memory can be used again, so scribed with reference to an electrolumines that the storage capacity may be 1/3 of that cent display, the principles of the present in of the memory in the device shown in FIG. 2. vention are also applicable to a fluorescent As described above, where the frame fre- display tube, a plasma display, or the like.

quency at which the pictures A, B, C are se- 70 Although a certain preferred embodiment quentially repeated is higher than 40 to 50 Hz, has been shown and described, it should be the colors of the respective pictures A, B, C understood that many changes and modif ica appear to be well mixed to the human eyes. tions may be made therein without departing Conditions for preventing flickering with re- from the scope of the appended claims.

spect to brightness in displaying images will 75

Claims

be described below. CLAIMS

Assuming that the frame frequency of se- 1. A method of producing a multiplicity of quential repetition of the pictures A, B, C is colors on a multicolor display having pixels, indicated by Ff and a frequency of repeating a comprising the step of sequentially varying the multicolor picture composed of frames of pic- 80 colors of lights from the pixels repeatedly on tures A, B, C is indicated by Fm, these fre- a time basis in response to display signals at quencies are related to each other as 3Fm a repetition frequency higher than a critical fu Ff. Ff is the same as 1 /tF, and Fm = 1 /AT. It sion frequency of color stimulus for thereby was experimentally confirmed using the device enabling the sequentially varying colors to ap of the invention that Fm should be higher than 85 pear to be mixed.

Hz in order to completely eliminate flicker-
2. A device for producing a multiplicity of ing with respect to time-dependent changes in colors comprising a plurality of stacked light brightness. This result seems reasonable since emitting layers capable of emitting lights of the critical fusion or flicker frequency of mutually different colors, a plurality of display brightness in the sense of sight of human beelectrodes and scanning electrodes disposed ings ranges from 30 to 50 Hz. on opposite sides of each of said light- emitt- From the relationship between Frn and Ff, it ing layers, those electrodes which are inter- is understood that where there are three light- posed between the lightemitting layers being emitting layers, the frequency Ff should be shared as electrodes for driving the light-emitt higher than 90 Hz in order to eliminate flicker- 95 ing layers on opposite sides of those elec ing with respect to time-dependent changes in trodes, and a driver circuit for energizing said brightness. This requirement also meets the display electrodes and said scanning elec color mixing condition: Ff > 40 through 50 trodes to cause said light- emitting layers to Hz as described above. Therefore, a sufficient sequentially display respective frame pictures color mixing ef fect is obtained by selecting Ff 100 of the respective colors repeatedly in re to be over 90 Hz. Heretofore, the general sponse to display signals corresponding to the frame frequency has been in the range of from colors of the light- emitting layers, at a repeti to 60 Hz, failing to fully preventing flicker- tion frequency higher than a critical fusion fre ing in displaying images including moving im- quency of color stimulus.

ages. With Ff > 90 according to the present 105
3. A device for producing a multiplicity of invention, flickering can be prevented irrespec- colors comprising a plurality of stacked light tive of whether displayed images are still or emitting layers capable of emitting lights of moving. mutually different colors, a plurality of display The frame frequency Over 90 Hz is a high electrodes and scanning electrodes disposed frequency which would make it difficult for im- 110 on opposite sides of each of said light-emitt ages to be displayed in good response. How- ing layers, those electrodes which are inter ever, the thin-film electroluminescent display posed between the light- emitting layers being including phosphorous layers suffers no signif shared as electrodes for driving the light-emitt icant problem as to display response, No ing layers on opposite sides of those elec problem would also be experienced even by 115 trodes, and a driver circuit for energizing said adding a brightness modulation circuit of the display electrodes and said scanning elec amplitude, pulse duration, frequency, or phase trodes to cause said lightemitting layers to modulation type to the display driver system. sequentially display respective frame pictures It is necessary to add a reverse voltage ap- of the respective colors repeatedly in re- plication mode for reproducing images while 120 sponse to display signals corresponding to the eliminating a remaining electric field in a lightcolors of the light- emitting layers, at a repeti emitting layer. This can be effected by apply- tion frequency higher than a critical fusion fre ing a reverse voltage pulse to all pixels imme- quency of color stimulus, for thereby produc diately before or after each frame, or applying ing a multicolor picture, and for repeating the a reverse voltage pulse to the pixels each time 125 multicolor picture at a frequency higher than a a scanning line is selected, or reversing a critical fusion frequency of brightness, for light-emitting voltage pulse in each frame. Any thereby producing a moving multicolor picture.

of these processes is applicable to the pre-
4. A device according to claim 3, wherein sent invention. said frequency at which the multicolor picture While the present invention has been de- 130 is repeated is higher than 30 Hz.

GB2194376A 5 -
5. A method of producing a multiplicity of colors on a multicolor display substantially as hereinbefore described with reference to Claim 1
6. A device for producing a multiplicity of colors substantially as hereinbefore described with reference to Figure 1 and Figures 3 to 5 of the accompanying drawings.

Published 1988 at The Patent Office, State House, 66/71 High Holborn, London WC 1 R 4TP. Further copies may be obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD.

Printed by Burgess & Son (Abingdon) Ltd. Con. 1/87.