Multiple-tone display system

Abstract
A dot matrix display system for multiple-tone displays, including a display device in which pixels are arrayed in a matrix shape, an LC (liquid-crystal) drive signal generator which converts color display data into LC display data, an 8-level data driver which selects one of 8-level voltages in accordance with the LC display data and then delivers the selected voltage, and an 8-level voltage generator by which the 8-level applied LC voltages to be applied to the pixels are produced so as to substantially make uniform color differences between the respectively adjacent tones of the multiple-tone displays. Owing to the substantially uniform color differences between the respectively adjacent tones, multiple-tone displays which are uniformly seen by the human eye can be obtained.
Description




BACKGROUND OF THE INVENTION




1. Field of the Invention




The present invention relates to a display system of the dot matrix type, and a display method therefor. More particularly, it relates to a method of driving a display system for presenting multicolor/multiple-tone (or polytonal) displays, and a system therefor.




2. Description of the Related Art




An LC (liquid-crystal) display system in the prior art displays an image in such a way that interface signals received as external inputs are converted into drive signals for driving the LC display system, the drive signals are delivered to LC drive means, and the LC drive means accepts for 8-level display data among the delivered drive signals every horizontal line of a frame and then applies the accepted data to an LC panel as 8-level LC drive voltages conforming to the display data. With this mode, 8 tones or gradations are displayed by the 8-level voltages divided uniformly or equally, as stated in “Lecturing thesis C-480”, the Spring National Meeting of the Institute of Electronics, Information and Communication Engineers of Japan, 1991.





FIG. 5

of the accompanying drawings illustrates the circuit arrangement of an 8-level uniform applied LC voltage generator (a generator by which the 8-level uniform voltages to be applied to the: LC panel are produced) in the prior art. Numeral


27


indicates an LC driving supply voltage, which is divided into the 8-level voltages by resistors


28


-


36


. Operational amplifiers


37


-


44


are respectively connected to the nodes of the adjacent resistors


28


-


36


. Herein, the 8-level uniform voltages


22


to be applied to the LC panel (8-level voltages V


1


-V


8


) are produced by equalizing all the resistances of the resistors


29


-


35


. The values of the voltages V


1


-V


8


on this occasion are listed in Table 1 below. As can be understood from this table, all the voltage differences between the respectively adjacent levels are 0.7 [V].















TABLE 1











TONE




VOLTAGE VALUE [V]













#1




6.50







#2




5.80







#3




5.10







#4




4.40







#5




3.70







#6




3.70







#7




2.30







#8




1.60
















FIG. 8

is a diagram showing an example of the relationship between the applied voltage to the LC panel and the display intensity or brightness of this LC panel in the prior art. The levels of the display intensity correspond respectively to the 8-level applied LC voltages V


1


-V


8


obtained by uniformly dividing the supply voltage


27


. In the illustrated graph, the display intensity levels are plotted on a logarithmic scale.




In this manner, the 8-level applied LC voltages are based on the uniform voltage division in the prior-art example. The uniform LC voltages incur the problem that the displayed tones are not always seen uniformly or in a well-balanced manner by the human eye.




SUMMARY OF THE INVENTION




An object of the present invention is to provide a method of and a system for presenting multiple-tone displays in which tones or gradations are made visible to the human eye uniformly or in a well-balanced manner in consideration of the optical characteristics of the displays.




In the present invention, the object is accomplished by contriving 8-level applied LC voltage generation means so as to make uniform or equalize the color differences between the respectively adjacent tones of a tonal display operation.




In one aspect of performance of the present invention, a multiple-tone display system wherein multiple-tone representations are presented on a display device which has a large number of pixels arrayed in a dot matrix shape comprises a data converter for receiving multiple-tone display information which contains a plurality of bits per pixel, and then sequentially converting the multiple-tone display information into display data which correspond to one horizontal line of the display device; a drive voltage generator for generating a plurality of drive voltage levels which substantially make uniform color differences between respectively adjacent ones of a plurality of tones that can be displayed by the multiple-tone display information containing the plurality of bits per pixel; a data driver connected to the drive voltage generator and data converter, for selecting one of the plurality of drive voltage levels from the drive voltage generator for every pixel on one line of the display device and then applying the selected drive voltage level to the display device in accordance with the display data delivered from the data converter; and a scan driver for selecting one of the horizontal lines of the display device which is to be successively displayed, in synchronism with the operations of the data converter and data driver.




According to the above construction of the present invention, the multiple-tone or polytonal representations which can be seen uniformly or in a well-balanced manner by the human eye can be realized by making uniform or equalizing the color differences between the respectively adjacent tones in a tonal display operation. Such a function and effect will be clarified from the following detailed description of embodiments read with reference to the accompanying drawings.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a block diagram of an embodiment of an 8-tone display system which adopts the present invention;





FIG. 1A

depicts a type of switching element which can be utilized in a display device within a display system in accordance with the present invention;





FIG. 2

is a block diagram of an embodiment of a 16-tone display system which adopts the present invention;





FIG. 3

is a timing chart for explaining the operation of an LC (liquid-crystal) drive signal generator depicted in

FIG. 1

;





FIG. 4

is a diagram showing the pixel configuration of an LC panel depicted in

FIG. 1

;





FIG. 5

is a circuit diagram showing the internal arrangement of an 8-level uniform applied LC voltage generator in the prior art;





FIG. 6

is a block diagram of an 8-level data driver depicted in

FIG. 1

;





FIG. 7

is a circuit diagram showing the internal arrangement of an 8-level voltage selector depicted in

FIG. 6

;





FIG. 8

is a graph showing an example of the relationship between the applied voltage of an LC panel and the display intensity thereof in the prior art;





FIG. 9

is a circuit diagram showing the internal arrangement of an 8-level applied LC voltage generator depicted in

FIG. 1

;





FIG. 10

is a graph showing an example of the setting of 8-level applied LC voltages;





FIG. 11

is a graph showing the characteristics of 8-tone display intensity levels which are attained by the voltage setting illustrated in

FIG. 10

;





FIG. 12

is a graph showing the coordinates of a white display and a black display within the CIELUV uniform color space;





FIG. 13

is a graph showing display intensity levels in the case of setting applied voltages so as to make uniform color differences.





FIG. 14

is a graph showing the characteristics of the 8-tone display intensity levels which are attained by the voltage setting illustrated in

FIG. 13

; and





FIG. 15

is a graph showing the display intensity characteristics of a 16-tone display operation according to the present invention.











DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS




First, an embodiment of the present invention will be described with reference to

FIG. 1

,

FIGS. 3 and 4

,

FIGS. 6 and 7

,

FIGS. 9

thru


14


, and Table 2.





FIG. 1

is a block diagram of The embodiment of a multiple-tone display system to which the present invention is applied. Referring to the figure, numeral


1


indicates “red” input display data, numeral


2


“green” input display data, numeral


3


“blue” input display data, and numeral


4


a clock signal. A set of input display data


1


-


3


correspond to one pixel, and is fed set by set in synchronism with the clock signal


4


. Each of the red input display data


1


, green input display data


2


and blue input display data


3


is composed of 3 bits, and which represents any of 8 tones. Here, the word “pixel” is intended to mean one lighting element for red, green or blue, and 3 pixels constitute one dot in the case of a color display system. The details of such pixels will be explained later. Further, numeral


5


indicates a horizontal clock signal, and numeral


6


a head signal. The display data corresponding to one horizontal line are fed in one cycle of the horizontal clock signal


5


(one horizontal period). Besides, the head signal


6


indicates the head line of the display data, and the display data corresponding to one frame are fed in one cycle of the head signal


6


. The multiple-tone display system in this embodiment comprises an LC (liquid-crystal) drive signal generator


7


, which produces LC display data


8


, a data clock signal


9


, an LC horizontal clock signal


10


and an LC head signal


11


. The LC drive signal generator


7


rearranges the input display data


1


-


3


into the order of R (red) pixels, G (green) pixels and B (blue) pixels for the purpose of presenting LC displays, whereupon it delivers the display data for 8 pixels in parallel. In this regard, each display data for one pixel is composed of 3 bits representing any of the 8 tones as stated before. Besides, the LC drive signal generator


7


receives the clock signal


4


, horizontal clock signal


5


and head signal


6


so as to produce the data clock signal


9


, LC horizontal clock signal


10


and LC head signal


11


, respectively.




An 8-level applied LC voltage generator


12


produces 8-level voltages


13


which are to be applied to an LC panel


20


. As will be explained later, the 8-level applied LC voltages


13


are obtained by dividing an LC driving supply voltage (


27


in

FIG. 9

) nonuniformly. An 8-level data driver


14


, a typical example of which is a product “HD66310” manufactured by Hitachi, Ltd., accepts the LC display data


8


for one horizontal line in accordance with the data clock signal


9


. Thereafter, it shifts the accepted data to its output stage in synchronism with the LC horizontal clock signal


10


. In accordance with the shifted data, one level is selected for each of the output data lines of the 8-level data driver


14


from among the 8-level applied LC voltages


13


, whereby LC horizontal data


15


are output. Accordingly, the 8-level data driver


14


delivers as the output LC horizontal data


15


the LC display data


8


of a horizontal line which is one line precedent to the line, accepted by the data clock pulse


9


. The LC display data


8


are data which are conformed to the input specifications of the 8-level data driver


14


.




The inputs of the aforementioned product “HD66310” are such that the data for one pixel is composed of 3 bits, and that 4 pixels are received in parallel. In the ensuing description of the illustrated example, the inputs of the 8-level data driver


14


shall be so assumed that the data for one pixel is composed of 3 bits and that the 8 pixels (24 bits) are received in parallel. Shown at numeral


16


is a scan driver, which delivers its output to any of the first scan line


17


, the second scan line


18


, . . . through the nth scan line


19


. That is, the scan driver


16


produces its output voltage for selecting that one of the scan lines


17


-


19


which corresponds to the horizontal line for displaying the LC horizontal data


15


delivered from the 8-level data driver


14


. The LC panel


20


has a resolution of m horizontal dots (3·m pixels) and n vertical lines, and presents the 8-tone displays in accordance with the voltages of the LC horizontal data


15


.





FIG. 3

is a timing chart of the various signals concerning the operation in which the LC drive signal generator


7


produces the LC display data


8


from the input display data


1


-


3


in the embodiment of FIG.


1


. Symbol (a) in

FIG. 3

denotes the “red” input display data


1


, symbol (b) the “green” input display data


2


, and symbol (c) the “blue” input display data


3


. The data


1


-


3


are signals which are simultaneously fed pixel by pixel, and which for one pixel is 3-bit data representative of any one of 8 tones. Symbols (d)-(f) denote those parallel signals for 8 pixels into which the input display data


1


-


3


fed pixel by pixel as shown at (a)-(c) have been respectively converted. Symbol (g) denotes the LC display data


8


. The data


8


are those parallel data for 8 pixels into which all of the red, green and blue data have been rearranged in conformity with the pixel array of the LC panel


20


.





FIG. 4

illustrates the pixel configuration of the color LC panel


20


. The 3 pixels of a “red” pixel


23


, a “green” pixel


24


and a “blue” pixel


25


constitute one dot


26


. The LC display data


8


are generated in conformity with the depicted pixel array.





FIG. 9

illustrates an example of the internal circuit arrangement of the 8-level applied LC voltage generator


12


shown in FIG.


1


. Numeral


27


indicates an LC driving supply voltage. The voltage,generator


12


includes resistors


68


-


83


, and operational amplifiers


84


-


91


. Pairs of resistors


68


and


69


,


70


and


711


,


72


and


73


,


74


and


75


,


76


and


77


,


78


and


79


,


80


and


81


, and


82


and


83


divide the LC driving supply voltage


27


so as to deliver the 8-level applied LC voltages


13


(V


8


-V


1


) through the corresponding operational amplifiers


91


-


84


, respectively. In this embodiment, the voltages


13


to be applied to the LC panel


20


are set at a relationship of V


1


>V


2


> . . . >V


7


>V


8


. It is also assumed that the tone or gradation #


1


(black display: lowest intensity or brightness level) of each pixel is attained by the voltage V


1


, that the tone #


8


(white display: highest intensity level) thereof is attained by the voltage V


8


, and that the tones #


2


-#


7


(halftones: intermediate intensity levels) thereof are respectively attained by the other voltages V


2


-V


7


.





FIG. 6

is a block diagram showing the details of the 8-level data driver


14


. Numeral


45


indicates a data shifter, and numeral


46


shifted data. The data shifter


45


accepts the LC display data


8


for one line within one horizontal period, and delivers them as the shifted data


46


in accordance with the data clock signal


9


. Besides, numeral


47


indicates a one-line latch, and numeral


48


display data. The one-line latch


47


latches the shifted data


46


corresponding to one line, and delivers them as the display data


48


in synchronism with the LC horizontal clock


10


. An 8-level voltage selector


49


selects one of the 8-level applied LC voltages


13


for each of the output lines thereof in accordance with the display data


48


, and delivers the selected voltage levels as the LC horizontal data


15


(X-D


1


to X-D


3


m) to the output lines. The symbols X-D


1


to X-D


3


m signify that the horizontal lines of the LC horizontal data


15


are in the number of (3×m) because the LC panel


20


has the resolution of the m horizontal dots each of which is composed of 3 pixels.





FIG. 7

is a circuit diagram showing the internal arrangement of the 8-level voltage selector


49


of the 8-level data driver


14


. The voltage selector


49


includes a 3-to-8 decoder


50


, decoder output lines


51


-


58


and switching elements


59


-


66


. Numeral


67


indicates an LC horizontal data line, which is one of the output lines for the LC horizontal data (X-D


1


to X-D


3


m). The 3-to-8 decoder


50


brings one of the decoder output lines


51


-


58


to “1” in accordance with the display data


48


each being composed of 3 bits per pixel, thereby turning “on” one of the switching elements


59


-


66


. Thus, one level of the 8-level applied LC voltages


13


is selected and is delivered to the LC horizontal data line


67


.




Now, the operation of this embodiment will be described.




Referring to

FIG. 1

, the LC drive signal generator


7


produces the LC display data


8


synchronous with the data clock signal


9


for the LC displays from the “red” input display data


1


, “green” input display data


2


, “blue” input display data


3


and clock signal


4


. Also, it produces the data clock signal


9


, LC horizontal clock signal


10


and LC head signal


11


which are LC driving signals, from the horizontal clock signal


5


and head signal


6


.




The 8-level applied LC voltage generator


12


produces the applied LC voltages


13


(the voltages to be applied to the LC panel


20


) of 8 levels whose voltage differences are set as desired as will be detailed later.




The 8-level data driver


14


produces the LC horizontal data


15


from the LC display data


8


, data clock signal


9


, LC horizontal clock signal


10


and 8-level nonuniform applied LC voltages 13. The scan driver


16


accepts the “1” level of the LC head signal


11


in accordance with the LC horizontal clock signal


10


, and supplies the first scan line


17


with the selecting voltage (the output voltage of the scan driver


16


for selecting the horizontal line of the LC panel


20


). Thereafter, the selecting voltage of the scan driver


16


is successively shifted to the second scan line


18


, and on and on to the nth scan line


19


in accordance with the LC horizontal clock signal


10


. Thus, one frame of the LC panel


20


is scanned. On this occasion, the voltages of the LC horizontal data lines


15


are fed from the 8-leel data driver


14


to the LC panel


20


, while the selecting voltage is delivered from the scan driver


16


on the scan line


17


,


18


, . . .


19


, causing the panel switching elements, such as switching element


20




a


in

FIG. 1A

, to present a conforming display. Incidentally, the color display operation is effected with 8


3


(512) colors on the basis of the combination of the 8 tones of the respective primary colors (red, green and blue).




A method of setting the 8-level applied LC voltages


13


adjusted to the visual characteristics of the human eye will be explained in detail.




The display intensity or brightness in the case of setting the voltages V


1


-V


8


nonuniformnly is illustrated in FIG.


10


. The display intensity characteristics of the 8 tones in this case become as shown in FIG.


11


. Herein, the tones or gradations #


1


-#


8


are set so as to make uniform the levels of the display intensity on a logarithmic scale.





FIG. 12

illustrates the CIELUV uniform color space stipulated by the CIE (Commission International de 1 'Eclairage). The distance between coordinate points within this space expresses that difference of colors which is visible to the human eye. Marks*are affixed to the coordinate values of the coordinate point


92


of the black display based on the level V


1


among the 8-level applied LC voltages 13 and the coordinate point


93


of the white display based on the level V


8


. These marks*indicate that psychological factors are considered in addition to coordinates (Y, u′, v′) obtained by an optical measurement. Shown at numeral


94


is the locus of coordinates obtained by changing the 8-level applied LC voltages 13 from the level V


1


to the level V


8


for each of the R, G and B pixels. Incidentally, the coordinates are obtained irrespective of the properties (LC material, color filter characteristics, etc.) of the LC panel


20


by conducting the optical measurement after the voltage setting. The method of optical measurement in this embodiment will be stated below.




An optical measuring apparatus employed in this embodiment is a product “1980B” fabricated by PHOTO RESEARCH INC. The coordinate (Y) expressive of the intensity and the coordinates (u′, v′) expressive of the colors can be obtained by measuring light on the front surface of the LC panel


20


in SPECTRARADIOMETER MODE among the measurement modes of the apparatus “1980B”. The range of the measurement is within a circle having a diameter of about 5 mm at the central part of the LC panel


20


. The same voltage is applied to all of the R, G and B pixels on each occasion. The coordinates (Y, u′, v′) obtained by the optical measurement for any desired voltage setting are computed in accordance with Equations (1), whereby they can be reduced to the coordinates within the CIELUV uniform color space:















L
*

=


116



(

Y
Y0

)


1
/
3



-

16






(


where






Y
Y0


>
0.008856

)




,








u
*

=

13



L
*



(


u


-

u0



)




,






v
*

=

13



L
*



(


v


-

v0



)








}




(
1
)













The distances between the coordinates contained in the CIELUV uniform color space are called “color differences” which are the differences of the colors seen by the human eye. Incidentally, coordinate values (Y


0


, u


0


′, v


0


′) express the intensity and color coordinates of a known reference color (for example, the white of a fluorescent lamp). By way of example, the color difference (dE*) between the black display


92


based on the 8-level applied LC voltage V


1


and the white display


93


based on the voltage V


8


as shown in

FIG. 12

is computed by Eq. (2):










dE
*

=




(


L8
*

-

L1
*


)

2

+


(


u8
*

-

u1
*


)

2

+


(


v8
*

-

v1
*


)

2







(
2
)













Herein, the exemplified distance is a distance in a straight line and is different from a distance extending along the locus


94


depicted in FIG.


12


. Accordingly, the distance of the locus


94


can be found in such a way that, while the applied voltage is changed little by little between the levels V


1


and V


8


, the color differences involved between the respective voltages are computed, and the computed color differences are added up. Incidentally, the above equations (1) and (2) are respectively contained on page 143 and page 149 in “Mitsuo Ikeda: Shikisai-k{overscore (o)}gaku no Kiso (Fundamentals of Color Engineering)” (issued by Asakura Book Store in 1980).




In this embodiment, while the applied voltage is changed little by little (for example, every 0.1 or 0.2 V between the levels V


1


and V


8


, the color differences involved between the respective voltages are calculated, and the calculated color differences are added up, thereby finding the distances involved between the respectively adjacent applied voltages and the distance along the locus


94


. According to the present invention, in order to make uniform or equalize the color differences among the 8 tones or gradations of the display operation, the distance of the locus


94


is divided by (the number of tones−1), namely, by 7 in the case of the 8-tone display operation. Subsequently, a set of applied voltages (voltages to be applied to the LC panel


20


) are evaluated in order that the color differences between the respectively adjacent tones may substantially agree with a value obtained by the division.




After setting the applied voltages, the optical measurement is conducted for the individual tonal displays, and the color differences between the respectively adjacent tones are computed using Eq. (2). Herein, in a case where the computed color differences are different from the requested ones, the steps of the voltage setting, optical measurement and color difference computation are performed again. Such processing is iterated until the requested color differences are obtained. Results thus obtained are listed in Table 2 below.














TABLE 2









Tone




Voltage value [V]




Color difference











#1




6.50







#2




4.96




15.2






#3




4.92




15.4






#4




3.83




15.4






#5




3.43




15.4






#6




3.00




15.4






#7




2.51




15.3






#8




1.77




15.3














In this table, the value of each “color difference” represents the color difference with respect to the tone of the adjoining upper row. For example, the value of the color difference of the row of the tone #


3


represents the color difference with respect to the tone #


2


. Here, the color differences are substantially uniform and are 15.3 on average.




The display intensity or brightness levels of the LC panel


20


attained; by setting the 8-level applied LC voltages


13


as listed in Table 2 become as shown in

FIG. 13

, while the display intensity characteristics of the 8 tones become as shown in FIG.


14


.




Meanwhile, an embodiment in the case of increasing the number of tones from 8 to 16 in accordance with an FRC (frame rate control)mode will be described with reference to

FIG. 2

,

FIG. 15

, and Tables 3 and 4.




The “FRC mode” is a method wherein the displays of two tones for a certain pixel are changed-over alternately in successive frames (each frame corresponding to one frame scan period), thereby attaining a tone intermediate between the two tones.





FIG. 2

is a block diagram of the embodiment of an LC (liquid-crystal) multiple-tone display system which employs the FRC mode. Referring to the figure, numeral


95


indicates “red” input display data, numeral


96


“green” input display data, numeral


97


“blue” input display data, and numeral


4


a clock signal. In this embodiment, each of the input display data


95


-


97


is assumed to be 4-bit data which is fed in synchronism with the clock signal


4


. Shown at numeral


98


is a tone controlling LC drive signal generator, which delivers LC display data


8


, a data clock signal


9


, an LC horizontal clock signal


10


and an LC head signal


11


. More specifically, the tone controlling LC drive signal generator


98


converts the input display data


95


-


97


each being composed of 4 bits, into the LC display data


8


composed of 3 bits. Also, it produces the data clock signal


9


, LC horizontal clock signal


10


and LC head signal


11


in the same manner as in the foregoing embodiment. An 8-level applied LC voltage generator


12


produces 8-level applied LC voltages (voltages to be applied to an LC panel


20


)


13


for the FRC mode. A method of converting the 4-bit input display data


95


-


97


into the 3-bit LC display data


8


, and a method of setting the 8-level applied LC voltages


13


will be detailed later. An 8-level data driver


14


, a scan driver


16


and the LC panel


20


are similar to the corresponding devices in the case of the 8-tone display operation, respectively.





FIG. 15

is a graph showing the display intensity or brightness characteristics of 16-tone displays which are presented in each of colors R (red), G (green) and B (blue) by this embodiment.




In order to explain the details of the operation of this embodiment,

FIGS. 2 and 15

will be referred to again.




In the construction of

FIG. 2

, the LC drive signal generator


98


produces the LC display data


8


of 3 bits synchronous with the data clock


9


for the LC display operation, on the basis of the “red” input display data


95


, “green” input display data


96


and “blue” input display data


97


which are respectively fed in serial 4-bit units and in synchronism with the clock signal


4


. An example of the conversion of the 4-bit data into the 3-bit data is indicated in Table 3 below.




That is, Table 3 exemplifies the data of 16-tone displays and the values of attained color differences in this embodiment.
















TABLE 3









Tone




4-bit data




3-bit data




Voltage value [V]




Color diff.



























 #1




0000




000




6.50







 #2




0001




000-001




6.50-4.57




4.695






 #3




0010




001




4.57




5.751






 #4




0011




001-010




4.57-4.02




6.242






 #5




0100




010




4.02




6.943






 #6




0101




010-011




4.02-3.72




6.212






 #7




0110




011




3.72




6.714






 #8




0111




011-100




3.72-3.37




7.240






 #9




1000




100




3.37




7.435






#10




1001




100-101




3.37-3.12




8.192






#11




1010




101




3.12




8.059






#12




1011




101-110




3.12-2.77




7.573






#13




1100




110




2.77




7.585






#14




1101




101-111




3.12-1.77




5.689






#15




1110




110-111




2.77-1.77




7.072






#16




1111




111




1.77




10.707














Each of the tones which indicates two sorts of 3-bit data, is subjected to the FRC mode. The tone controlling LC display data generator


98


changes-over the two sorts of data alternately in the successive frames.




Besides, the LC drive signal generator


98


produces the data clock signal


9


, LC horizontal clock signal


10


and LC head signal


11


which are LC driving signals, from a horizontal clock signal S and a head signal


6


in the same manner as in the foregoing case of the 8-tone display operation.




The 8-level applied LC voltage generator


12


produces the 8-level applied LC voltages 13 (voltages to be applied to the LC panel


20


) the differences of which are set as desired. The voltages are set so that the LC panel


20


may exhibit intensity or brightness characteristics similar to those in the case of the 8-tone display operation. The values of the voltages and the color differences between the respectively adjacent tones or gradations on that occasion are listed in Table 3. As seen from the table, the color differences have errors of ±50[%] or so with respect to their average value of 7.1, but the errors pose no problem in vision. The 16-tone display intensity characteristics shown in

FIG. 15

are similar to the 8-tone display intensity characteristics shown in FIG.


14


. Incidentally, the large errors of the color differences in this embodiment are ascribable to the fact that, with the FRC operation, when the voltage value of any tone not based on the FRD (for example, the tone #


3


) is changed, also the voltage values of the FRC-based tones adjoining the tone (the tones #


2


and #


4


) change, so the color differences are difficult to make uniform.




The 8-level data driver


14


produces LC horizontal data


15


from the L.C display data


8


, data clock signal


9


, LC horizontal data


10


and 8-level nonuniform applied LC voltages


13


in the same manner as in the foregoing embodiment shown in FIG.


1


. The scan driver


16


accepts the “1” level of the LC head signal


11


in accordance with the LC horizontal clock signal


10


, and supplies the first scan line


17


with a selecting voltage. Thereafter, the selecting voltage of the scan driver


16


is successively shifted to the second scan line


18


, and on and on to the nth scan line


19


in accordance with the LC horizontal clock signal


10


. Thus, one frame of the LC panel


20


is scanned. On this occasion, the voltages on the LC horizontal data lines


15


are fed from the 8-level data driver


14


to the LC panel


20


, while the selecting voltage is delivered for the scan driver


16


on the scan lines


17


,


18


, . . .


19


, causing the panel switching elements, such as switching element


20




a


in

FIG. 1A

, to present a conforming display.




Moreover, 16 tones or gradations which are seen uniformly or in a well-blanced manner in each of the colors of “red”, “green” and “blue” by the human eye can be attained by modifying the embodiment of

FIG. 2

as follows: Three 8-level applied LC voltage generators


12


are disposed for the colors of, respectively, red, green and blue independently of one another. Also, the tone controlling LC drive signal generator


98


converts the 4-bit data into the 3-bit data for the colors of red, green and blue independently of one another.




Table 4 indicates another example of the combination between a voltage setting and the FRC mode for presenting 16-tone displays which have the intensity or brightness characteristics as shown in FIG.


15


. Even when the combination is changed, the 16-tone displays uniformly visible to the human eye can be obtained by conforming the intensity characteristics to those shown in FIG.


15


.















TABLE 4











Tone




Voltage value [V]













 #1




7.00







 #2




7.00-4.60







 #3




7.00-4.00







 #4




4.60







 #5




4.60-4.00







 #6




4.00







 #7




4.00-3.62







 #8




3.62







 #9




3.62-3.21







#10




3.21







#11




2.99







#12




2.99-2.59







#13




2.59







#14




3.21-0.01







#15




2.99-0.01







#16




0.01















Even in a case where the number of tones or gradations has been further increased, tonal displays seen to be uniform by the human eye can be presented by conforming intensity or brightness characteristics to a curve as shown in FIG.


15


.




According to the present invention, the color differences between the respectively adjacent tones of a tonal display operation are made uniform, whereby multiple-tone displays uniformly visible to the human eye can be obtained.



Claims
  • 1. A liquid crystal display device, for providing multiple-tone representations, said liquid crystal display device comprising:a data driver for receiving display data and providing a drive voltage corresponding with the display data; a scan driver for providing a selecting voltage; and a liquid crystal panel having a plurality of pixels arranged in a matrix, said liquid crystal panel coupled to said data driver and to said scan driver to provide the drive voltage from said data driver to a pixel of said liquid crystal panel selected in accordance with the selecting voltage, wherein the selected pixel of said liquid crystal panel displays a tone corresponding to the drive voltage, and wherein the intensities or brightnesses of all the intermediate tones between the maximum tone corresponding to the maximum drive voltage and the tone one tone higher than the minimum tone corresponding to the minimum drive voltage are at least as great as the intensity or brightness on a straight line linking the intensity or brightness of the maximum tone and the intensity or brightness of the minimum tone when the intensities or brightnesses as a function of the tones are plotted on a graph having the tones along the graph abscissa and the intensity or brightness on a logarithmic scale along the graph ordinate.
  • 2. A liquid crystal display device as claimed in claim 1, further comprising a drive signal generator for producing a data clock signal for driving said data driver and a horizontal clock signal for driving said scan driver.
  • 3. A liquid crystal display device as claimed in claim 1, further comprising:data driver lines coupling said data driver and said liquid crystal panel; and scan driver lines coupling said scan driver and said liquid crystal panel.
  • 4. A liquid crystal display device as claimed in claim 1, wherein a line linking the intensities or brightnesses of the intermediate tones has a convex shape with respect to the straight line.
  • 5. A liquid crystal display device as claimed in claim 1, wherein the display data is N-bit digital display data representing 2N tones.
  • 6. A liquid crystal display device as claimed in claim 1, wherein the plurality of pixels include red (R) pixels, green (G) pixels and blue (B) pixels.
  • 7. A liquid crystal display device as claimed in claim 6, wherein the display data is N-bit digital display data representing 2N tones.
  • 8. A liquid crystal display device as claimed in claim 7, wherein the drive voltage for each of the R, G, and B pixels is the same when the N-bit digital display data representing the R, G, and B pixels are the same.
  • 9. A liquid crystal display device as claimed in claim 1, further comprising a drive voltage generator for generating drive voltage levels corresponding to tones which the display data can represent, wherein the data driver selects one of the generated drive voltage levels in accordance with the display data and provides the selected drive voltage level.
  • 10. A liquid crystal display device as claimed in claim 1, further comprising a drive signal generator for deserializing the display data and outputting the deserialized display data to the data driver.
  • 11. A liquid crystal display device as claimed in claim 1, wherein the pixels display black for the maximum tone and white for the minimum tone.
  • 12. A liquid crystal display device as claimed in claim 1, wherein the number of tones is eight.
  • 13. A liquid crystal display device for providing multiple-tone representations, said liquid crystal display device comprising:a data driver for receiving display data, and providing a drive voltage corresponding with the display data; a scan driver for providing a selecting voltage; and a liquid crystal panel having a plurality of pixels arranged in a matrix, said liquid crystal panel coupled to said data driver and to said scan driver to provide the drive voltage from said data driver to a pixel of said liquid crystal panel selected in accordance with the selecting voltage, wherein the selected pixel of said liquid crystal panel displays a tone corresponding to the drive voltage, and wherein the intensities or brightnesses of all the intermediate tones between the maximum intensity or brightness and the intensity or brightness one intensity or brightness higher than the minimum intensity or brightness which the liquid crystal panel is capable of showing are greater than the intensity or brightness on a straight line linking the maximum intensity or brightness and the minimum intensity or brightness when the intensities or brightnesses as a function of the tones are plotted on a graph having the tones along the graph abscissa and the intensities or brightnesses on a logarithmic scale along the graph ordinate.
  • 14. A liquid crystal display device as claimed in claim 13, further comprising a drive signal generator for producing a data clock signal for driving said data driver and a horizontal clock signal for driving said scan driver.
  • 15. A liquid crystal display device as claimed in claim 13, further comprising:data driver lines coupling said data drive and said liquid crystal panel; and scan driver lines coupling said scan driver and said liquid crystal panel.
  • 16. A liquid crystal display device as claimed in claim 13, wherein a line linking the intensities or brightness of the intermediate tones has a convex shape with respect to the straight line.
  • 17. A liquid crystal display device as claimed in claim 13, wherein the display data is N-bit digital display data representing 2N tones.
  • 18. A liquid crystal display device as claimed in claim 13, wherein the plurality of pixels include red (R) pixels, green (G) pixels and blue (B) pixels.
  • 19. A liquid crystal display device as claimed in claim 18, wherein the display data is N-bit digital display data representing 2N tones.
  • 20. A liquid crystal display device as claimed in claim 19, wherein the drive voltage for each of the R, G, and B pixels is the same when the N-bit digital display data representing the R, G, and B pixels are the same.
  • 21. A liquid crystal display device as claimed in claim 13, further comprising a drive voltage generator for generating drive voltage levels corresponding to tones which the display data can represent, wherein the data driver selects one of the generated drive voltage levels in accordance with the display data and provides the selected drive voltage level.
  • 22. A liquid crystal display device as claimed in claim 13, further comprising a drive signal generator for deserializing the display data and outputting the deserialized display data to the data driver.
  • 23. A liquid crystal display device as claimed in claim 13, wherein the pixels display black for the maximum tone and white for the minimum tone.
  • 24. A liquid crystal display device as claimed in claims 13, wherein the number of tones is eight.
  • 25. A liquid crystal display device for providing multiple-tone representations, said liquid crystal display device comprising:a data driver for receiving display data and providing drive voltages corresponding with the display data; a scan driver for providing a selecting voltage; and a liquid crystal panel having a plurality of pixels arranged in a matrix, said liquid crystal panel coupled to said data driver and to said scan driver to provide the drive voltages to a line of pixels of said liquid crystal panel selected in accordance with the selecting voltage, wherein the selected line of pixels of said liquid crystal panel displays tones corresponding to the drive voltages, and wherein the intensities or brightnesses of all the intermediate tones between the maximum tone corresponding to the maximum drive voltage and the tone one tone higher than the minimum tone corresponding to the minimum drive voltage form a line above a straight line linking the intensity or brightness of the maximum tone and the intensity or brightness of the minimum tone on a graph having the tones along the graph abscissa and the intensities or brightnesses on a logarithmic scale along the graph ordinate.
  • 26. A liquid crystal display device as claimed in claim 25, further comprising a generator for producing a data clock signal for driving said data driver and a clock signal for driving said scan driver.
  • 27. A liquid crystal display device as claimed in claim 25, further comprising:data driver lines coupling said data drive and said liquid crystal panel; and scan driver lines coupling said scan driver and said liquid crystal panel.
  • 28. A liquid crystal display device as claimed in claim 25, wherein a line linking the intensities or brightnesses of the intermediate tones has a convex shape with respect to the straight line.
  • 29. A liquid crystal display device as claimed in claim 25, wherein the display data is N-bit digital display data representing 2N tones.
  • 30. A liquid crystal display device as claimed in claim 25, wherein the plurality of pixels include red (R) pixels, green (G) pixels and blue (B) pixels.
  • 31. A liquid crystal display device as claimed in claim 30, wherein the display data is N-bit digital display data representing 2N tones.
  • 32. A liquid crystal display device as claimed in claim 31, wherein the drive voltage for each of the R, G, and B pixels is the same when the N-bit digital display data representing the R, G, and B pixels are the same.
  • 33. A liquid crystal display device as claimed in claim 25, further comprising a drive voltage generator for generating drive voltage levels corresponding to tones which the display data can represent, wherein the data driver selects one of the generated drive voltage levels in accordance with the display data and provides the selected drive voltage level.
  • 34. A liquid crystal display device as claimed in claim 25, further comprising a drive signal generator for deserializing the display data and outputting the deserialized display data to the data driver.
  • 35. A liquid crystal display device as claimed in claim 25, wherein the pixel display black for the maximum tone and white for the minimum tone.
  • 36. A liquid crystal display device as claimed in claim 25, wherein the number of tones is eight.
  • 37. A liquid crystal display device for providing multiple-tone representations, said liquid crystal display device comprising:a data driver for receiving display data, and providing a drive voltage corresponding with the display data; a scan driver for providing a selecting voltage; and a liquid crystal panel having a plurality of pixels arranged in a matrix, said liquid crystal panel coupled to said data driver and to said scan driver to provide the drive voltage to a pixel of said liquid crystal panel selected in accordance with the selecting voltage, wherein the selected pixel of said liquid crystal panel displays a tone corresponding to the drive voltage, and wherein all the intensities or brightnesses between the maximum intensity or brightness and the intensity or brightness one intensity or brightness higher than the minimum intensity or brightness which the liquid crystal panel is capable of showing are greater than the intensity or brightness on a straight line linking the maximum intensity or brightness and the minimum intensity or brightness when the intensities or brightnesses as a function of the tones are plotted on a graph having the tones along the graph abscissa and the intensities or brightnesses on a logarithmic scale along the graph ordinate.
  • 38. A liquid crystal display device as claimed in claim 37, further comprising a drive signal generator for producing a data clock signal for driving said data driver and a horizontal clock signal for driving said scan driver.
  • 39. A liquid crystal display device as claimed in claim 37, further comprising:data driver lines coupling said data drive and said liquid crystal panel; and scan driver lines coupling said scan driver and said liquid crystal panel.
  • 40. A liquid crystal display device as claimed in claim 37, wherein a line linking the intensities or brightnesses of the intermediate tones has a convex shape with respect to the straight line.
  • 41. A liquid crystal display device as claimed in claim 37, wherein the display data is N-bit digital display data representing 2N tones.
  • 42. A liquid crystal display device as claimed in claim 37, wherein the plurality of pixels include red (R) pixels, green (G) pixels and blue (B) pixels.
  • 43. A liquid crystal display device as claimed in claim 42, wherein the display data is N-bit digital display data representing 2N tones.
  • 44. A liquid crystal display device as claimed in claim 43, wherein the drive voltage for each of the R, G, and B pixels is the same when the N-bit digital display data representing the R, G, and B pixels are the same.
  • 45. A liquid crystal display device as claimed in claim 37, further comprising a drive voltage generator for generating drive voltage levels corresponding to tones which the display data can represent, wherein the data driver selects one of the generated drive voltage levels in accordance with the display data and provides the selected drive voltage level.
  • 46. A liquid crystal display device as claimed in claim 37, further comprising a drive signal generator for deserializing the display data and outputting the deserialized display data to the data driver.
  • 47. A liquid crystal display device as claimed in claim 37, wherein the pixels display black for the maximum tone and white for the minimum tone.
  • 48. A liquid crystal display device as claimed in claim 37, wherein the number of tones is eight.
  • 49. A liquid crystal display device, for providing multiple-tone representations, said liquid crystal display device comprising:a data driver for receiving display data and providing a drive voltage corresponding with the display data; a scan driver for providing a selecting voltage; and a liquid crystal panel having a plurality of pixels arranged in a matrix, said liquid crystal panel coupled to said data driver and to said scan driver to provide the drive voltage from said data driver to a pixel of said liquid crystal panel selected in accordance with the selecting voltage, wherein the selected pixel of said liquid crystal panel displays a tone corresponding to the drive voltage, and wherein the intensities or brightnesses of all the intermediate tones between the maximum tone corresponding to the maximum drive voltage and the minimum tone corresponding to the minimum drive voltage are at least as great as the intensity or brightness on a straight line linking the intensity or brightness of the maximum tone and the intensity or brightness of a tone one tone higher than the minimum tone when the intensities or brightnesses as a function of the tones are plotted on a graph having the tones along the graph abscissa and the intensities or brightness on a logarithmic scale along the graph ordinate.
  • 50. A liquid crystal display device as claimed in claim 49, further comprising a drive signal generator for producing a data clock signal for driving said data driver and a horizontal clock signal for driving said scan driver.
  • 51. A liquid crystal display device as claimed in claim 49, further comprising:data driver lines coupling said data driver and said liquid crystal panel; and scan driver lines coupling said scan driver and said liquid crystal panel.
  • 52. A liquid crystal display device as claimed in claim 49, wherein a line linking the intensities or brightnesses of the intermediate tones has a convex shape with respect to the straight line.
  • 53. A liquid crystal display device as claimed in claim 49, wherein the display data is N-bit digital display data representing 2N tones.
  • 54. A liquid crystal display device as claimed in claim 49, wherein the plurality of pixels include red (R) pixels, green (G) pixels and blue (B) pixels.
  • 55. A liquid crystal display device as claimed in claim 54, wherein the display data is N-bit digital display data representing 2N tones.
  • 56. A liquid crystal display device as claimed in claim 55, wherein the drive voltage for each of the R, G, and B pixels is the same when the N-bit digital display data representing the R, G, and B pixels are the same.
  • 57. A liquid crystal display device as claimed in claim 49, further comprising a drive voltage generator for generating drive voltage levels corresponding to tones which the display data can represent, wherein the data driver selects one of the generated drive voltage levels in accordance with the display data and provides the selected drive voltage level.
  • 58. A liquid crystal display device as claimed in claim 49, further comprising a drive signal generator for deserializing the display data and outputting the deserialized display data to the data driver.
  • 59. A liquid crystal display device as claimed in claim 49, wherein the pixels display black for the maximum tone and white for the minimum tone.
  • 60. A liquid crystal display device as claimed in claim 49, wherein the number of tones is eight.
  • 61. A liquid crystal display device for providing multiple-tone representations, said liquid crystal display device comprising:a data driver for receiving display data, and providing a drive voltage corresponding with the display data; a scan driver for providing a selecting voltage; and a liquid crystal panel having a plurality of pixels arranged in a matrix, said liquid crystal panel coupled to said data driver and to said scan driver to provide the drive voltage from said data driver to a pixel of said liquid crystal panel selected in accordance with the selecting voltage, wherein the selected pixel of said liquid crystal panel displays a tone corresponding to the drive voltage, and wherein the intensities or brightnesses of all the intermediate tones between the maximum intensity or brightness and the minimum intensity or brightness which the liquid crystal panel is capable of showing are greater than the intensity or brightness on a straight line linking the maximum intensity or brightness and the intensity or brightness one intensity or brightness higher than the minimum intensity or brightness when the intensities or brightnesses as a function of the tones are plotted on a graph having the tones along the graph abscissa and the intensities or brightnesses on a logarithmic scale along the graph ordinate.
  • 62. A liquid crystal display device as claimed in claim 61, further comprising a drive signal generator for producing a data clock signal for driving said data driver and a horizontal clock signal for driving said scan driver.
  • 63. A liquid crystal display device as claimed in claim 61, further comprising:data driver lines coupling said data drive and said liquid crystal panel; and scan driver lines coupling said scan driver and said liquid crystal panel.
  • 64. A liquid crystal display device as claimed in claim 61, wherein a line linking the intensities or brightnesses of the intermediate tones has a convex shape with respect to the straight line.
  • 65. A liquid crystal display device as claimed in claim 61, wherein the display data is N-bit digital display data representing 2N tones.
  • 66. A liquid crystal display device as claimed in claim 61, wherein the plurality of pixels include red (R) pixels, green (G) pixels and blue (B) pixels.
  • 67. A liquid crystal display device as claimed in claim 66, wherein the display data is N-bit digital display data representing 2N tones.
  • 68. A liquid crystal display device as claimed in claim 67, wherein the drive voltage for each of the R, G, and B pixels is the same when the N-bit digital display data representing the R, G, and B pixels are the same.
  • 69. A liquid crystal display device as claimed in claim 61, further comprising a drive voltage generator for generating drive voltage levels corresponding to tones which the display data can represent, wherein the data driver selects one of the generated drive voltage levels in accordance with the display data and provides the selected drive voltage level.
  • 70. A liquid crystal display device as claimed in claim 61, further comprising a drive signal generator for deserializing the display data and outputting the deserialized display data to the data driver.
  • 71. A liquid crystal display device as claimed in claim 61, wherein the pixels display black for the maximum tone and white for the minimum tone.
  • 72. A liquid crystal display device as claimed in claim 61, wherein the number of tones is eight.
  • 73. A liquid crystal display device for providing multiple-tone representations, said liquid crystal display device comprising:a data driver for receiving display data and providing drive voltages corresponding with the display data; a scan driver for providing a selecting voltage; and a liquid crystal panel having a plurality of pixels arranged in a matrix, said liquid crystal panel coupled to said data driver and to said scan driver to provide the drive voltages to a line of pixels of said liquid crystal panel selected in accordance with the selecting voltage, wherein the selected line of pixels of said liquid crystal panel displays tones corresponding to the drive voltages, and wherein the intensities or brightness of all the intermediate tones between the maximum tone corresponding to the maximum drive voltage and the minimum tone corresponding to the minimum drive voltage form a line above a straight line linking the intensity or brightness of the maximum tone and the intensity or brightness of a tone one tone higher than the minimum tone on a graph having the tones along the graph abscissa and the intensities or brightnesses on a logarithmic scale along the graph ordinate.
  • 74. A liquid crystal display device as claimed in claim 73, further comprising a drive signal generator for producing a data clock signal for driving said data driver and a horizontal clock signal for driving said scan driver.
  • 75. A liquid crystal display device as claimed in claim 73, further comprising:data driver lines coupling said data drive and said liquid crystal panel; and scan driver lines coupling said scan driver and said liquid crystal panel.
  • 76. A liquid crystal display device as claimed in claim 73, wherein a line linking the intensities or brightnesses of the intermediate tones has a convex shape with respect to the straight line.
  • 77. A liquid crystal display device as claimed in claim 73, wherein the display data is N-bit digital display data representing 2N tones.
  • 78. A liquid crystal display device as claimed in claim 73, wherein the plurality of pixels include red (R) pixels, green (G) pixels and blue (B) pixels.
  • 79. A liquid crystal display device as claimed in claim 78, wherein the display data is N-bit digital display data representing 2N tones.
  • 80. A liquid crystal display device as claimed in claim 79, wherein the drive voltage for each of the R, G, and B pixels is the same when the N-bit digital display data representing the R, G, and B pixels are the same.
  • 81. A liquid crystal display device as claimed in claim 73, further comprising a drive voltage generator for generating drive voltage levels corresponding to tones which the display data can represent, wherein the data driver selects one of the generated drive voltage levels in accordance with the display data and provides the selected drive voltage level.
  • 82. A liquid crystal display device as claimed in claim 73, further comprising a drive signal generator for deserializing the display data and outputting the deserialized display data to the data driver.
  • 83. A liquid crystal display device as claimed in claim 73, wherein the pixels display black for the maximum tone and white for the minimum tone.
  • 84. A liquid crystal display device as claimed in claim 73, wherein the number of tones is eight.
  • 85. A liquid crystal display device for providing multiple-tone representations, said liquid crystal display device comprising:a data driver for receiving display data, and providing a drive voltage corresponding with the display data; a scan driver for providing a selecting voltage; and a liquid crystal panel having a plurality of pixels arranged in a matrix, said liquid crystal panel coupled to said data driver and to said scan driver to provide the drive voltage to a pixel of said liquid crystal panel selected in accordance with the selecting voltage, wherein the selected pixel of said liquid crystal panel displays a tone corresponding to the drive voltage, and wherein all the intensities or brightnesses between the maximum intensity or brightness and the minimum intensity or brightness which the liquid crystal panel is capable of showing are greater than the intensities or brightnesses on a straight line linking the maximum intensity or brightness and the intensity or brightness one intensity or brightness higher than the minimum intensity or brightness when the intensities or brightnesses as a function of the tones are plotted on a graph having the tones along the graph abscissa and the intensities or brightnesses on a logarithmic scale along the graph ordinate.
  • 86. A liquid crystal display device as claimed in claim 85, further comprising a drive signal generator for producing a data clock signal for driving said data driver and a horizontal clock signal for driving said scan driver.
  • 87. A liquid crystal display device as claimed in claim 85, further comprising:data driver lines coupling said data drive and said liquid crystal panel; and scan driver lines coupling said scan driver and said liquid crystal panel.
  • 88. A liquid crystal display device as claimed in claim 85, wherein a line linking the intensities or brightnesses of the intermediate tones has a convex shape with respect to the straight line.
  • 89. A liquid crystal display device as claimed in claim 85, wherein the display data is N-bit digital display data representing 2N tones.
  • 90. A liquid crystal display device as claimed in claim 85, wherein the plurality of pixels included (R) pixels, green (G) pixels and blue (B) pixels.
  • 91. A liquid crystal display device as claimed in claim 90, wherein the display data is N-bit digital display data representing 2N tones.
  • 92. A liquid crystal display device as claimed in claim 91, wherein the drive voltage for each of the R, G, and B pixels is the same when the N-bit digital display data representing the R, G, and B pixels are the same.
  • 93. A liquid crystal display device as claimed in claim 85, further comprising a drive voltage generator for generating drive voltage levels corresponding to tones which the display data can represent, wherein the data driver selects one of the generated drive voltage levels in accordance with the display data and provides the selected drive voltage level.
  • 94. A liquid crystal display device as claimed in claim 85, further comprising a drive signal generator for deserializing the display data and outputting the deserialized display data to the data driver.
  • 95. A liquid crystal display device as claimed in claim 85, wherein the pixels display black for the maximum tone and white for the minimum tone.
  • 96. A liquid crystal display device as claimed in claim 85, wherein the number of tones is eight.
Priority Claims (1)
Number Date Country Kind
4-39203 Feb 1992 JP
Parent Case Info

This application is a continuation of application Ser. No. 09/773,728 filed Feb. 2, 2001 now U.S. Pat. No. 6,320,564, which is a continuation of application Ser. No. 09/459,341 filed Dec. 13, 1999, now U.S. Pat. No. 6,191,766, which is a continuation of application Ser. No. 09/080,234 filed May 18, 1998, now U.S. Pat. No. 6,100,864, which is a continuation of application Ser. No. 08/813,387 filed Mar. 7, 1997, now U.S. Pat. No. 5,786,798, which is a continuation application of Ser. No. 08/486,291 filed Jun. 7, 1995, now U.S. Pat. No. 5,610,626, which in turn was a division of application Ser. No. 08/018,494 filed Feb. 17, 1993, now U.S. Pat. No. 5,495,287.

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Continuations (5)
Number Date Country
Parent 09/773728 Feb 2001 US
Child 09/972924 US
Parent 09/459341 Dec 1999 US
Child 09/773728 US
Parent 09/080234 May 1998 US
Child 09/459341 US
Parent 08/813387 Mar 1997 US
Child 09/080234 US
Parent 08/486291 Jun 1995 US
Child 08/813387 US