JPH04316087A - liquid crystal display device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device capable of displaying halftones and ensuring contrast even when viewed from an oblique angle.

0002

2. Description of the Related Art A liquid crystal display device supplies an input display signal to liquid crystal driving means. The liquid crystal driving means takes in the applied display data one line at a time and outputs it to the liquid crystal panel as liquid crystal driving power. By repeating this operation for the number of display lines, one screen is displayed.

[0003] In order to express halftones in a TFT type liquid crystal display device, the voltage applied to the liquid crystal panel must be changed, or the display on state and the display off state must be alternately taken for each frame. As a result, halftones were displayed.

However, in such conventional TFT type liquid crystal display devices, halftone display is not sufficient.

[0005] Furthermore, in order to cope with changes in contrast depending on the viewing angle (viewing angle), contrast has been adjusted by adjusting the liquid crystal drive power source.

A conventional TFT type liquid crystal display device will be explained below with reference to FIGS. 9 to 16.

FIG. 9 is a block diagram showing a conventional liquid crystal display device.

In FIG. 9, 200 to 202 are 1-bit serial display data signals; 200 is a Red signal;
01 is a Green signal, and 202 is a Blue signal.

103 to 105 are timing signals, 103 is a horizontal synchronization signal, 104 is a vertical synchronization signal, 10
5 is a dot clock synchronized with display data.

Reference numeral 110 denotes a two-level liquid crystal drive signal generating means, which generates 1-bit serial data 200 to 1 for each display color.
202 and timing signals 103 to 105 are input. The two-level liquid crystal drive signal generation means generates liquid crystal display data 113 and
It has a function of generating liquid crystal driving signals 111, 112, and 114. Here, 111 is a line start clock. 112 is a horizontal clock, and 114 is a data shift clock. It also outputs a liquid crystal drive AC clock 204 that is inverted every frame.

125 is a Y (axial direction) driving means;
26 is a Y drive signal.

203 is a power supply circuit, and 122 is a liquid crystal drive power supply. 205 is a display off-level voltage on the plus side, 206 is a display on-level voltage, 207 is an off-level voltage on the minus side, and 208 is a reference level voltage.

123 is an X (axial direction) drive means;
124 is one line data.

127 is a liquid crystal panel.

FIG. 10 shows the X driving means 123 in FIG.
FIG. 2 is a block diagram showing details of the FIG.

In FIG. 10, reference numeral 300 denotes a data shift means, which has a function of taking in one line of liquid crystal display data 113 using a data shift clock 114. 301 is shift data that is the output of the data shift means 300.

Reference numeral 302 denotes a one-line latch means, which has a function of latching the shift data 301 using the horizontal clock 110. 303 is the one line latch means 302
This is the display data that is the output of .

Reference numeral 304 denotes a two-level liquid crystal voltage selection means, which has the function of providing liquid crystal driving power as liquid crystal display data from the display data 303 and the liquid crystal driving AC clock 204.

X-D1 to X-Dm are data outputs that the two-level liquid crystal voltage selection means 304 outputs corresponding to each pixel when the number of horizontal display pixels on the liquid crystal display screen is m pixels. These data outputs X-D1 to X-Dm are input as one line data 124 to a liquid crystal panel to be described later.

FIG. 11 shows the X driving means 123 in FIG.
FIG. 4 is a timing diagram of each signal related to the operation when the Y driving means 125 drives the liquid crystal panel 127. FIG.

In FIG. 11, (a) is the horizontal clock 1
12, which is a clock generated in synchronization with each horizontal scanning period on the display screen.

(b) is a data shift clock 114, which transfers the liquid crystal display data 113 to the data shift means 30.
It is used to capture into 0.

(c) is a timing diagram showing the liquid crystal display data 113, which is synchronized with the data shift clock 114.

(d) Same as (a), the horizontal clock 11
2, but on a smaller time scale.

(e) is X-D1 of 1 line data 124
This indicates that the first line, second line, third line, etc. of ~X-Dm are synchronized with the horizontal clock 112.

(f) is a line start clock 111.

(g), (h), and (i) are Y drive signals 126 output by the Y drive means 125, respectively. That is, (g) is display line data Y-D1 that instructs display of the first line, and (h) is display line data Y-D2 that instructs display of the second line.

FIG. 12 is a diagram showing the structure of the liquid crystal panel 127.

500 is a switching element, 501 is a pixel electrode, and 502 is a liquid crystal layer. Further, 503 is a counter electrode to which a reference level voltage 208 is applied.

Reference numeral 504 is an X drive signal line to which the above-mentioned 1-line data 124 is applied. X-1, X-2, . . .
X-Dm is given.

Reference numeral 505 is a Y drive signal line to which the drive signal 126 is applied. Y, which constitutes the Y drive signal line 505
-1, Y-2, . . . are provided with display line data Y-D1 for the first line and display line data Y-D2 for the second line.

Further, 121 is a signal line to which the reference level voltage output from the power supply circuit 203 is input.

FIG. 13 shows the waveform of the liquid crystal applied voltage applied to one liquid crystal pixel in each case of display on and display off.

The liquid crystal drive AC clock 204 is inverted every frame.

The reference level 208 is as shown in (c).
Always constant.

(a) shows the display off level voltage 2 on the positive side with respect to the reference level voltage 208 among the liquid crystal applied voltages.
It is 05. On the other hand, (d) is a display off-level voltage 207 on the negative side. Note that the display off-level voltage 205 on the plus side and the display off-level voltage 207 on the minus side
Which voltage to adopt is determined in relation to the liquid crystal drive AC clock 204.

Further, the display on-level voltage 206 is (b
), it is at the same level as the reference level voltage 208.

FIG. 14 shows the arrangement of color filters on the liquid crystal panel 127 for one line. 700 is an R pixel, 701 is a G pixel, and 702 is a B pixel, and one dot 703 is composed of the three pixels, the R pixel 700, the G pixel 701, and the B pixel 702.

FIG. 15 shows the circuit configuration of the power supply circuit 203.

800 is a variable resistor that adjusts the magnitude of the liquid crystal drive voltage.

Resistors 801 and 802 are connected to the liquid crystal drive power supply 12.
This is for dividing the voltage No. 2 into a display off-level voltage 205 on the plus side. Similarly, resistors 803 and 804 are connected to the display on level voltage 206, resistors 805 and 806 are connected to the negative side display off level voltage 207, and resistors 807 and 806 are connected to the display off level voltage 207 on the negative side.
808 divides the power supply voltage into the reference level voltage 208.

Hereinafter, in order to explain the operation, FIG.
See.

In FIG. 9, the two-level liquid crystal drive signal generating means 110 receives 1-bit serial display data 200-202 for each display color and timing signals 103-1.
05, a line start clock 111, a horizontal clock 112, and a data shift clock 114, which are liquid crystal drive signals, are generated. In addition, the data shift clock 11
The liquid crystal display data 113 synchronized with 4 is generated. The liquid crystal display data 113, data shift clock 114, and horizontal clock 112 are then supplied to the X driving means 123. In addition, the horizontal clock 11 is connected to the Y driving means 125.
2 and the line start clock 111 are given.

The operations of the X drive means 123 and Y drive means 125 will be explained below using FIGS. 10 to 13.

In FIG. 10, data shift means 300
is the first horizontal clock 11 as seen in FIG.
2, one line of data is taken in during one horizontal period according to the data shift clock 114 and output as shift data 301. First shift data 3
01 is latched by the 1-line latch means 302 at the next horizontal clock 112 and becomes display data 303.

The two-level liquid crystal voltage selection means 304 selects the liquid crystal applied voltage, that is, one line data 12, based on the display data 303 and the liquid crystal drive AC clock 204.
4 (X-D1 to X-Dm) and outputs them.

That is, the X driving means 123 outputs to the liquid crystal panel 127 data one line before the line on the liquid crystal panel 127 to which the liquid crystal display data 113 currently being taken in by the data shifting means 300 corresponds.

The display operation of the liquid crystal panel is shown in FIGS. 12 and 13.
This will be explained in more detail using .

In FIG. 12, one line data 124 is transmitted to a liquid crystal pixel electrode 501 via a switching element 500.
given to. Then, the potential of the liquid crystal pixel electrode 501,
The liquid crystal layer 502 is driven by the potential difference with the reference level voltage 208 supplied to the counter electrode 503.

Furthermore, when the liquid crystal drive AC clock 204 is "high", the two-level liquid crystal voltage selection means 304 selects a positive power supply as viewed from the reference level (c) applied to the counter electrode 503 in FIG. In order to take the level, that is, the potential shown in (a), and when it is "low", the negative power supply level, that is, the potential shown in (d), the one line data 209 is the liquid crystal drive AC clock 204. Accordingly, the voltage applied to the liquid crystal is output as an alternating voltage for each frame. Note that in the display-on state, the potential is always the same as the reference level, that is, the display-on level 206.

As shown in FIG. 11, the Y driving means 125 converts the line start clock 111 into the horizontal clock 112.
By taking in the signal, the first line Y-D1 is set to "high" on the liquid crystal panel 127. Below, horizontal clock 112
Each time ``high'' is input, "high" is shifted in the order of Y-D2 on the second line, Y-D3 on the third line, and so on. As a result, the Y drive signal 12 which is the output of this Y drive means 125
6, only the switching element 500 of the line that is "high" is turned on, and one line of data 124 is displayed only on that line.

Therefore, as shown in FIG. 11, when the X driving means 123 is outputting the first line data 124, the Y driving means 125 outputs the display line data 1.
26, set Y-D1 to "high". Further, when the X driving means 123 is outputting the 1st line data 124 of the 2nd line, the Y driving means 125 outputs the display line data 124.
26, set Y-D2 to "high". Thereafter, by repeating this process, the entire screen is displayed.

[0053] The display on the TFT type liquid crystal panel 127 is a white display in which the display is on when the 1-line data 124 to each pixel is "1", and is off when it is "0". A certain black display appears.

The operation of color display will be explained using FIG. 14.

One line data 124 in FIG. 9 supplies one dot 703 by a combination of display on and display off of R pixel 700, G pixel 701, and B pixel 702 in FIG.

[0056] In the liquid crystal display, one line is 640 pixels.
In the case of dots, the number m of horizontal pixels is three times 640 dots, so m=1920, and one line data 209 in FIG. 10 becomes X-D1 to X-D1920.

[0057] Then, R constituting this one dot 703
Display on of pixel 700, G pixel 701, and B pixel 702,
Characters and figures can be displayed in eight colors by combining display off.

Next, a contrast adjustment method will be explained using FIGS. 15 and 16.

The contrast between the display on state and the display off state of the liquid crystal panel 127 changes depending on the viewing angle.

In FIG. 15, the voltage of the liquid crystal drive power source 122 can be adjusted by a variable resistor 800. In addition, a display on level voltage 206 and a display off level voltage 20
5 and 207 are set at a certain ratio by resistors 801 to 808. Therefore, when the variable resistor 800 is adjusted to change the level of the liquid crystal drive power supply 122 from (a) to (a') as shown in FIG. 16, each liquid crystal applied voltage level also maintains the above constant ratio. Be changed.

Therefore, the display on level with respect to the reference level 208 is always constant and maintains the relationship (c)-(d)=(c')-(d').

On the other hand, the display off levels 205 and 207 relative to the reference level, that is, the potentials shown in (b) and (e) change to (b') and (e'), and (b)-(d)>(b')-(d')(d)-(e)>(d')-(e').

In this way, the contrast is adjusted by changing the display off level.

[0064]

[Problems to be Solved by the Invention] In the above-mentioned prior art, the display data is a 1-bit digital signal for each display color,
“1” and “0” realize display on and display off. Therefore, as shown in FIG. 14, a liquid crystal display device in which one dot 704 of the liquid crystal panel 127 is composed of three R, G, and B pixels can only display eight colors, and each display color can display multiple bits of display data. No consideration was given to the multi-color and multi-gradation display used.

Furthermore, since the contrast adjustment was performed by adjusting only the display off level by adjusting the liquid crystal drive power supply, no consideration was given to the contrast adjustment of halftone display.

A first object of the present invention is to provide a TFT type liquid crystal display device capable of displaying multiple colors and multiple gradations.

A second object of the present invention is to provide a TFT capable of obtaining good multi-gradation display contrast for all viewing angles.
The present invention provides a type of liquid crystal display device.

[0068]

[Means for Solving the Problems] The present invention has been made to achieve the above object, and provides a liquid crystal panel configured by arranging a plurality of liquid crystal cells in a matrix, and a display data including gradation information. gradation control means for outputting the data, and liquid crystal drive signal generation means for generating a liquid crystal drive signal and a voltage switching signal based on the display data output from the gradation control means;
Generates a reference level voltage to be applied to the liquid crystal panel, a display on voltage equal to the reference level voltage, and a plurality of types of display off voltages different from the reference level voltage, and displays the display in response to the voltage switching signal. A power supply means for switching an off voltage and outputting it to the liquid crystal panel; and a power supply means for outputting display data to the liquid crystal panel according to the liquid crystal drive signal, and a display on voltage output from the power supply means and a plurality of types of the above display. There is provided a liquid crystal display device characterized in that it includes an X driving means for applying one of the off voltages to the liquid crystal cell.

In this case, it is preferable that the power supply means switches the display off voltage every frame.

Preferably, the power supply means changes the polarity of the display off voltage with respect to the reference level voltage every frame, which is the same number as the type of the display off voltage.

The power supply means described above may generate any number of display off voltages, and for example, may be of two types: a first display off voltage and a second display off voltage. In this case, the first display off voltage and the second display off voltage are alternately switched. Further, the polarity is changed every two frames.

In addition, when there are two types of display off voltages as described above, the display data outputted by the X driving means alternates between the first display off voltage and the second display off voltage. one in which the display on voltage and the first display off voltage are applied alternately, and one in which the display on voltage and the second display off voltage are alternately applied;
There may be four types, including one in which the display-on voltage is always applied.

Furthermore, the difference between the second display off voltage and the on voltage is smaller than the first display off voltage, and the power supply means turns off the second display off voltage without changing the first display off voltage. It may also be possible to change only the voltage.

To explain more specifically, there is a liquid crystal panel constructed by arranging a plurality of liquid crystal cells in a matrix, and a display on voltage and a display off voltage corresponding to one display unit of display data for this liquid crystal panel. an X driving means for outputting a voltage, and a Y driving means for selectively scanning on which line of a liquid crystal panel the display data outputted by the X driving means is to be displayed; The liquid crystal display device is characterized by a means for switching between a display on voltage and a display off voltage every one or more frames to display an intermediate tone other than the on display and the off display.

That is, in the present invention, for pixels to be displayed with high brightness, a display-on voltage is continuously applied,
A liquid crystal display can be performed by continuously applying a display-off voltage to pixels that should display low brightness, and by switching and applying a display-on voltage and a display-off voltage to pixels that should display intermediate tones. can.

Furthermore, in order to obtain many gradations, the present invention provides a second off-voltage whose brightness is slightly higher than the display off-voltage. By switching the second display-off voltage and display-on voltage, a second halftone with higher luminance than the above halftone can be obtained.

Furthermore, in order to achieve the above second objective,
In the present invention, only the second display off voltage can be adjusted.

[0078]

[Operation] The gradation control means outputs display data including gradation information to the liquid crystal drive signal generation means. Then, the liquid crystal drive signal generation means outputs a voltage switching signal to the power supply means. Further, the liquid crystal drive signal is output to the X drive means together with the display data.

Then, the power supply means switches between the first display off voltage and the second display off voltage power supply means in synchronization with the voltage switching signal. Note that in this case, the display on voltage and the reference level voltage are always output while being constant. On the other hand, the X driving means outputs display data corresponding to gradation information to the liquid crystal panel in accordance with the liquid crystal driving signal. Thereby, the first display off voltage, the second display voltage, and the display on voltage are switched in a predetermined order, for example, every frame, according to the gradation information. That is, the intermediate tone is displayed by alternately displaying display states with different brightness according to the display data.

Although only the case where there are two types of display off voltages has been described here, the same applies even when more display off voltages are set.

Next, contrast adjustment will be explained.

[0082] When a liquid crystal display device is viewed from an angle, halftone portions become difficult to see. Therefore, by changing only the second display off voltage without changing the first display off voltage, the contrast when viewed from an oblique angle can be ensured.

[0083]

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 to 8.

FIG. 1 is a block diagram showing a liquid crystal display device according to an embodiment of the present invention.

100 to 102 are 2-bit parallel liquid crystal display data for each display color;
n signal and Blue signal.

106 is a multicolor control means, which controls each display color 2.
Bit parallel LCD display data 100, 101, 10
2, each display color 1-bit serial data 107, 108
, 109.

FIG. 10 is a table explaining how the multicolor control means 106 converts the 2-bit parallel data 100-102 of each display color into 1-bit serial data 107-109.

When the 2-bit parallel data is (1, 1), it indicates that the display is on, and the 1-bit serial data is always converted to "1". 2-bit parallel data is (0,
0) indicates that the display is off, and 1-bit serial data is always converted to "0". 2-bit parallel data (
In the case of halftone display represented by 0,1), (1,0),
1-bit serial data “1”, “0” for each frame
” is switched and output. The distinction between the two intermediate tones is (0
, 1), the odd numbered frame is set to "1", and in the case of (1,0), the even numbered frame is set to "1". In other words, one 2-bit parallel data is displayed in two frames.

The two-level liquid crystal drive signal generating means 110 includes:
Line start clock 111, horizontal clock 112, liquid crystal display data 113, data latch clock 114, and multicolor liquid crystal drive AC clock 115, which are liquid crystal drive signals, are generated in the same manner as the conventional method described above. ing. However, the multicolor liquid crystal drive AC clock 115 has a period twice that of the conventional liquid crystal drive AC clock 204. In other words, the period corresponds to two frames.

Further, the two-level liquid crystal drive signal generating means 110 of this embodiment is configured to generate a voltage switching clock 116 and output it to the multicolor power supply circuit 117. This voltage switching clock 116 is a signal that is inverted every frame.

The multicolor power supply circuit 117 is connected to the liquid crystal drive power supply 1
Liquid crystal applied voltages 118 to 12 are generated from the voltage of 22. 118 is a multicolor display off-level voltage on the positive side;
119 is a display on-level voltage, and 120 is a multicolor display off-level voltage on the negative side. Further, 121 is a reference level voltage of the liquid crystal applied voltage supplied to the liquid crystal panel 127, which corresponds to the reference level voltage 208 of the prior art shown in FIG. be. Note that details will be explained later.

X driving means 123 and 1 line data 124
, the Y drive means 125, the Y drive signal 126, and the liquid crystal panel 127 are the same as those in the prior art described above.

The configuration of the multicolor power supply circuit 117 will be explained in detail.

FIG. 3 is a diagram showing its internal configuration.

122 is the same liquid crystal driving power supply as before, 120
0 to 1206 are resistors for dividing the voltage of the liquid crystal drive power source 122, and 1205 among them is a variable resistor.

The multicolor power supply circuit 117 of this embodiment differs from the conventional one in that it has two levels of display off voltage, namely:
Display off level voltage 1207 and display off level voltage 1
208. The display off-level voltage 1208 has a smaller potential difference with the reference level voltage 121 than the display off-level voltage 1207. In other words, the display using the display off-level voltage 1208 is slightly brighter than the display off-level voltage 1207. Note that the display off-level voltage 1208 is determined by the variable resistor 120.
It is adjustable by 5. The change of the display off level 1208 by the variable resistor 1205 is used to adjust the contrast, and this point will be explained later.

Reference numeral 1209 denotes voltage switching means, which switches between the dark display off-level voltage 1207 and the bright display off-level voltage 1208 according to the voltage switching signal 116 described above, and only one of them is switched to the multicolor display off-level voltage 1210. It is something to do.

The display on-level voltage 119 is at the same level as the reference level voltage 121 of the counter electrode. Note that the liquid crystal pixels to which the display on-level voltage 119 is applied are as follows:
The display becomes white.

Reference numeral 1211 is a voltage adder that adds the display on-level voltage 119 and the multicolor display off-level voltage 1210 to generate a multicolor display off-level voltage 118 on the plus side as viewed from the reference level voltage 121. Has a function.

1212 is a voltage subtracter which converts the display on-level voltage 119 to the multi-color display off-level voltage 1210.
, and generates a multicolor display off-level voltage 120 on the negative side as viewed from the reference level voltage 121.

Note that the multicolor display off-level voltage 118,
120 both change every frame depending on whether the voltage switching means 1209 outputs the display off-level voltage 1207 or the display off-level voltage 1208.

The operation of this embodiment will be explained.

The multicolor control means 106 in FIG.
The bit parallel data is converted into 1-bit serial data according to the correspondence table shown in FIG. 2, and is output to the 2-level liquid crystal drive signal generation means 110.

As shown in FIG. 2, when the 2-bit parallel data is (1, 1), the display is on, the 1-bit serial data is always converted to "1", and the 2-bit parallel data is (0, 0). ) indicates that the display is off, and 1-bit serial data is always converted to "0". In the case of halftone display represented by 2-bit parallel data (0, 1), (1, 0), 1-bit serial data is output by switching between "1" and "0" for each frame. To distinguish between two halftones, in the case of (0, 1), odd frames are marked as “1”.
, (1,0), the even frame is set to "1".

The two-level liquid crystal drive signal generating means 110 includes:
A liquid crystal drive signal is generated and output to the X drive means 123 in a manner similar to the conventional method. As described above, the multicolor liquid crystal driving AC clock 115 is a signal that is inverted every two frames at twice the period of the conventional one.

Furthermore, the two-level liquid crystal drive signal generating means 11
0 generates the voltage switching clock 116 and outputs it to the multicolor power supply circuit 117. As described above, this voltage switching clock 116 is a signal that is inverted every frame.

The reason why the period of the liquid crystal driving AC clock is doubled will be explained using FIG. 4.

In FIG. 4(A), 1100 is a liquid crystal applied voltage waveform when halftone display is performed using the conventional liquid crystal driving AC clock 204, and 1101 is a liquid crystal applied voltage waveform when the multicolor liquid crystal driving AC clock 204 of this embodiment is used. This is a voltage waveform applied to the liquid crystal when halftone display is performed using the clock 115.

The display data 113 indicates that the display is repeatedly turned on and off for each frame, and a halftone display is performed. In this case, in the conventional liquid crystal drive AC clock 204, only one polarity of voltage is applied, as shown in the liquid crystal applied voltage waveform 1100. Therefore, Fig. 4(B)
As shown in FIG. 2, in this embodiment, the multicolor liquid crystal driving AC clock 115 having a cycle twice that of the liquid crystal driving AC clock 204 is used, and the polarity is inverted as shown in the liquid crystal applied voltage waveform 1101. It has been made possible to achieve this.

Next, the operation of the multicolor power supply circuit 117 will be explained.

A dark display off-level voltage 1207 and a bright display off-level voltage 1208 are supplied from the liquid crystal drive power supply 122.
, a display on-level voltage 119, and a reference level voltage 121 of the counter electrode of the liquid crystal cell.

The voltage switching means 1209 switches the dark display off level voltage 12 according to the voltage switching clock 116.
07 and a bright display off-level voltage 1208 every frame. As a result, the level of the multicolor display off-level voltage 1210 changes every frame.

The voltage adder 1211 generates a positive multicolor display off-level voltage 118 from the multicolor display off-level voltage 1210 and the display on-level voltage 119. Further, the voltage subtracter 1212 generates a multicolor display off-level voltage 120 on the negative side.

[0114] Then, the multicolor display off-level voltage 118
, 120 to the X drive means 127.

In the X driving means 123, a liquid crystal applied voltage is selected and supplied to the liquid crystal panel 127 according to the liquid crystal display data 113 and the multicolor liquid crystal driving AC clock 115.

The operation of the X driving means will be explained in detail with reference to FIG.

FIG. 5 shows the operating waveforms of the X driving means 123 according to the liquid crystal applied voltage level generated by the multicolor power supply circuit 117 of FIG. 3, the multicolor liquid crystal drive AC clock 115, and the serial display data 113. This is what is shown.

In FIG. 5, 1300 is a voltage waveform applied to a liquid crystal pixel when display is on, 1301 is when display is off, 1302 is a dark halftone, and 1303 is a bright halftone. V0 is display on level, V1
is a bright display off level, and V2 is a dark display off level. Note that the dark display off level V2 is equal to the bright display off level V1 in the dark display off level voltage 1207 in FIG.
corresponds to the bright display off-level voltage 1208.

As described above, the period of the multicolor liquid crystal driving AC clock 115 is twice that of the conventional one, that is, two frames. Of the liquid crystal applied voltages, the multicolor display off level voltage 118 on the positive side and the multicolor display off level voltage 120 on the negative side are a dark display off level V2 and a slightly lower bright display off level V1. is switched every frame. Therefore, during one cycle of the multicolor liquid crystal drive AC clock 115, the dark display off level V2
and a bright display off level V1 are alternately switched.

The method for selecting the voltage applied to the liquid crystal is as explained using FIG. 13, and the waveforms of the voltage applied to the liquid crystal for display on, display off, dark halftone, and bright halftone are as shown by the thick lines.

The liquid crystal applied voltage 1300 when the display is on is constant at V0 in all frames, and has the same waveform as the conventional one. Therefore, in this state, the display is visually "white".

When the display is off, the voltage waveform applied to the liquid crystal is switched between V1 and V2 every frame, as shown in 1301. In V1, the display state is "black", and in V2, the display state is "gray". Therefore, by alternately displaying V1, ie, "black", and V2, ie, "gray", the intermediate tone between "black" and "gray" is visually displayed as a display off state.

[0123] Here, "white" means a display state with high brightness, and "black" means a display state with low brightness. "Gray" means a luminance between that range. Therefore, the "color" actually displayed is determined by a color filter provided corresponding to the pixel. The same applies to the following description.

[0124] When displaying dark halftones, that is, Fig. 2
If the 1-bit display data in is (1, 0),
When the multicolor display off levels 118 and 120 are the dark display off level V2, the display is turned off. When the multicolor display off levels 118 and 120 are the display off level V1, the display is turned on. Therefore, as shown in the liquid crystal applied voltage waveform 1302, the display on level V0 and the dark display off level V2 are switched every frame, and an intermediate tone between these two levels is displayed. In other words, “black”
By alternately displaying "black" and "white" every frame, an intermediate tone between "black" and "white" is displayed.

In the case of a bright intermediate tone, that is, when the 1-bit display data in FIG. Turns off. Further, at the dark display off level V2, the display is on. Therefore, as shown in the liquid crystal applied voltage waveform 1303, the display on level V0 and the bright display off level V1 are switched every frame, and an intermediate tone between these two levels is displayed. That is, by displaying "gray" and "white" alternately every frame, an intermediate tone between "gray" and "white" is displayed.

As described above, by providing two types of display off levels and switching these levels for each frame, it is possible to display four levels of gradation for one pixel.

Next, FIG. 6 shows the brightness level adjustment according to the present invention.
Explain using.

In FIG. 6, the vertical axis is luminance and the horizontal axis is voltage.
V0, V1, and V2, and the display brightness obtained at that time are shown as B0, B1, B2, and B3 in descending order of brightness. Note that the voltage in this case is the reference level 1 of the counter electrode.
This is the potential difference with 21.

The liquid crystal applied voltage levels V0 to V2 explained using FIG. 5 and each display state (display on, bright halftone, dark halftone, display off) will be applied to this V-B curve for explanation.

[0130] A dark halftone B2 can be obtained by the display on level V0 and the dark display off level V2. This bright halftone B1 corresponds to the above-mentioned halftone between "white" and "black".

[0131] A bright halftone B1 can be obtained by the display on level V0 and the bright display off level V1. This bright halftone B1 corresponds to the above-mentioned halftone between "white" and "gray".

Display off level V1 and display off level V2
As a result, B3, which is an intermediate tone, is obtained. This midtone B
3 corresponds to the above-mentioned intermediate tone between "black" and "gray". If the display-on level is always V0, B0 is displayed. This B0 corresponds to the above-mentioned "white".

[0133] As described above, B0, B
Four gradations of 1, B2, and B3 can be obtained.

The brightness of this four-gradation display changes depending on the viewing angle with respect to the liquid crystal panel 127. Therefore, a contrast adjustment method will be described next with reference to FIGS. 3, 7, and 8.

The variable resistor 1205 in FIG. 3 has a display off level voltage 1208, that is, the bright display off level V in FIG.
1.

FIG. 7 shows the operation of contrast adjustment by the variable resistor 1205 of FIG. 3.

V1 in FIG. 7(A) is the variable resistor 120 in FIG.
5 is the bright display off level before adjustment by Fig. 7 (
V1' in B) is the adjusted bright display off level.

As shown in this figure, when the bright halftone level V1 is adjusted to V1', the liquid crystal applied voltage waveform 150
0 changes like the liquid crystal applied voltage waveform 1501, and the liquid crystal applied voltage waveform changes when displaying bright halftones.

[0139] Therefore, contrast can be adjusted by adjusting only the brightness of bright intermediate tones in response to changes in contrast with respect to viewing angle. This can be expressed as V-B in Figure 8.
This will be explained using a curve.

FIG. 8 shows the change in the V-B curve depending on the viewing angle, in other words, the contrast adjustment depending on the viewing angle. In other words, the LCD panel has V-B depending on the viewing angle.
The curves are different, and the contrast is different when viewed from the front and from an angle.

This figure shows V-B curves when viewed from the front and when viewed from an angle of 10 degrees from the front.

In the figure, a curve 1601 shows the case viewed from the front, and a curve 1600 shows the case seen from an angle of 10 degrees.

[0143] When viewed from the front, the above four gradations are as follows:
They are indicated by M12, M02, M01, and M00. Note that M12 is an intermediate tone displayed by V1 and V2. The same applies to M12, M02, M01, and M00.

[0144] At these points, the brightness is sufficiently different, so that they can be sufficiently distinguished. When viewed from an oblique angle, that is, in the curve 1600, these four gradations are located at positions S12, S02, S01, and S00. Note that S12 is an intermediate tone displayed by V1 and V2. The same applies to S12, S02, S01, and S00. In this case, the curve 1600 shows a sharp drop in brightness in a region where the voltage is small, but curves horizontally from near the center, and the drop in brightness becomes gradual. Therefore, the difference in brightness between S01 and S02 existing in the gentle slope portion becomes small, making it impossible to distinguish sufficiently.

Therefore, in this embodiment, the difference in brightness is ensured by changing only V1 to V1'. In other words, by changing V1 to V1', S0
1 has changed to S01'. On the other hand, the position of S02 does not change. In other words, by moving S01' to an area where the brightness decreases rapidly, S01' and S01'
02 is ensured to enable visual angle identification. In addition, since the slope is gentle in the part where the voltage is high, by changing S12 to S1'2,
It has little effect on the contrast of the entire display screen.

As described above, when the bright display off level is changed from V1 to V1' according to the viewing angle, the brightness B1 of the bright intermediate tone is adjusted to B1'. On the other hand, the brightness B3 when the display is off does not change. Therefore, the brightness B when the display is off
It becomes possible to adjust only the brightness B1 of the bright intermediate tone to B1' without almost changing the brightness of B1, and the contrast when viewed from an oblique angle can be ensured.

In the embodiment described above, two types of display off levels are provided, but the present invention is not limited to this, and more types of display off levels may be provided. In that case, various conditions such as the timing to invert the polarity of the display off level and the timing to switch the display off level will also be changed depending on the number of types.

[0148]

[Effects of the Invention] As explained above, according to the present invention,
In a liquid crystal display device, it is possible to display halftones and to display multiple colors.

Furthermore, by adjusting only the brightness of bright halftone display, a multicolor display device that can obtain good contrast with respect to the viewing angle can be realized.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a conversion table of liquid crystal display data by the multicolor control means 106 of this embodiment.

FIG. 3 is an internal configuration diagram of a multicolor power supply circuit 117 of this embodiment.

FIG. 4 is a liquid crystal applied voltage waveform diagram showing liquid crystal alternating current.

FIG. 5 is a diagram of voltage waveforms applied to a liquid crystal for four-gradation display according to the present embodiment.

FIG. 6 is a diagram showing the luminance of four gradations according to the present example.

FIG. 7 is a waveform diagram of voltage applied to the liquid crystal during contrast adjustment according to the present embodiment.

FIG. 8 is a diagram showing luminance versus viewing angle from above during contrast adjustment according to the present embodiment.

FIG. 9 is a block diagram showing the configuration of a conventional liquid crystal display device.

FIG. 10 is a detailed block diagram of the X driving means 123.

FIG. 11 is a timing chart for driving the liquid crystal by the X driving means 123 and the Y driving means 125.

FIG. 12 is an internal structural diagram of a liquid crystal panel 127.

13 is a liquid crystal applied voltage waveform diagram showing the operation of the two-level liquid crystal voltage selection means 304. FIG.

FIG. 14 is a diagram of a pixel configuration on a liquid crystal panel 127.

FIG. 15 is an internal configuration diagram of a power supply circuit 203 of a conventional liquid crystal display device.

FIG. 16 is a diagram showing voltage levels for conventional contrast adjustment.

[Explanation of symbols]

100...Liquid crystal display Red signal (2-bit parallel) 10
1...LCD display Green signal (2-bit parallel) 10
2...Liquid crystal display Blue signal (2-bit parallel) 103
…Horizontal synchronization signal 104…Vertical synchronization signal 105…Dot clock 106…Multicolor control means 107…Liquid crystal display Red signal (1-bit serial) 10
8...LCD display Green signal (1 bit serial) 10
9...Liquid crystal display Blue signal (1 bit serial) 110
...Two-level liquid crystal drive signal generation means 111...Line start clock 112...Horizontal clock 113...Liquid crystal display data 114...Data latch clock 115...Multicolor liquid crystal drive AC clock (2 frame inversion) 116...Voltage switching clock 117... Multicolor power supply circuit 118...Display off-level voltage 119...Display on-level voltage 120...Display off-level voltage 121...Reference level voltage 122...Liquid crystal drive power supply 123...X drive means 124...1 line data 125...Y drive means 126... Display line data 127...Liquid crystal panel 204...LCD drive AC clock (1 frame inversion) 3
04...Two-level liquid crystal voltage selection means 501...Pixel electrode 502...Liquid crystal layer 503...Counter electrode 1207...Display off-level voltage 1208...Display off-level voltage 1209...Voltage switching means 1210...Display off-level voltage 1211...Voltage adder 1212... voltage subtractor

Claims (6)

[Claims] 1. A liquid crystal panel configured by arranging a plurality of liquid crystal cells in a matrix, a gradation control means for outputting display data including gradation information, and the above-mentioned display outputted by the gradation control means. a liquid crystal drive signal generating means that generates a liquid crystal drive signal and a voltage switching signal based on the data; a reference level voltage to be applied to the liquid crystal panel; a display on voltage equal to the reference level voltage; a power supply unit that generates a plurality of types of display off voltages different from the level voltage, switches the display off voltages in response to the voltage switching signal, and outputs the display off voltages to the liquid crystal panel; X driving means for outputting display data to the liquid crystal panel and applying any one of the display on voltage output from the power supply means and the plurality of types of display off voltages to the liquid crystal cell. A liquid crystal display device featuring: 2. A liquid crystal display device according to claim 1, wherein said power supply means switches said display off voltage every frame. 3. The liquid crystal display according to claim 1, wherein the power supply means changes the polarity of the display off voltage with respect to the reference level voltage every frame of the same number as the type of the display off voltage. Display device. 4. The liquid crystal display according to claim 1, wherein the power supply means generates two types of display off voltages, a first display off voltage and a second display off voltage. Display device. 5. The display data outputted by the X driving means is:
The first display off voltage and the second display off voltage are applied alternately, the display on voltage and the first display off voltage are alternately applied, and the display on voltage and the second display off voltage are applied alternately. 5. The liquid crystal display device according to claim 4, wherein there are four types: one in which the display-off voltage is applied alternately, and one in which the display-on voltage is constantly applied. 6. The second display OFF voltage has a smaller difference from the display ON voltage than the first display OFF voltage, and the power supply means operates the second display OFF voltage without changing the first display OFF voltage.
5. The liquid crystal display device according to claim 4, wherein only the display off voltage can be changed.