JPH0519725A - Color liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain color balance corresponding to the sensitivity of the human eye by adjusting gradation voltage supplied to picture elements of the three primary colors, i.e., red, green, and blue, relatively among the respective colors. CONSTITUTION:The mid-point voltage Vcom for a common electrode is supplied to one terminal A of a voltage-dividing resistance circuit which generates driving voltages V1-V8 for a gradational display through a level shift circuit. Further, three voltage-dividing circuits are provided so as to obtain eight independently adjustable levels for the three primary colors of red, green, and blue. Namely, the voltages supplied to the picture elements of the three primary colors are relatively adjustable among the respective colors. In this case, the relative adjustments of the voltages for the respective colors are made by a voltage generating circuit which is adjustable corresponding to each of the colors and a selector which selects and applies a voltage corresponding to a color display control signal to a drain driver.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color liquid crystal display device and, more particularly, to a technique effective for use in a color liquid crystal display device which performs multi-tone color display.

[0002]

2. Description of the Related Art A gradation voltage that determines the brightness of each color pixel of red, green and blue is supplied to a signal line (drain line) of a color liquid crystal panel through a switch element which is switch-controlled according to color data. . By setting the gradation voltage to 8 levels, 512-color multicolor display is possible. As an example of such a color liquid crystal display device,
Hitachi, Ltd. “Hitachi LCD Driver Data Book” page 650 to page 664 issued in March 1990.

[0003]

In the multi-gradation color liquid crystal display device as described above, the gradation voltage is commonly used for the pixels of each color. On the other hand, the sensitivity of the human eye is high for green and low for red and blue. Therefore, the inventor of the present application has noticed that the color balance of the combined multi-tone color display deteriorates in the color liquid crystal display device as described above. An object of the present invention is to provide a color liquid crystal display device capable of adjusting color balance. The above and other objects and novel features of the present invention are
It will be apparent from the description of this specification and the accompanying drawings.

[0004]

The outline of a typical one of the inventions disclosed in the present application will be briefly described as follows. That is, the gradation voltages supplied to the pixels of the three primary colors of red, green and blue can be relatively adjusted for each color.

[0005]

According to the above-mentioned means, since the gradation level of each color can be relatively adjusted, the color balance corresponding to the sensitivity of the human eye can be realized.

[0006]

1 is a circuit diagram of an embodiment of a gradation voltage (or drive voltage) generating circuit used in a color liquid crystal display device according to the present invention. Although not particularly limited, the grayscale voltage generating circuit of this embodiment is intended for 8-gradation display of a color liquid crystal panel. By displaying each of red, green, and blue in 8 gradations, it is possible to display 512 colors in total. Although not particularly limited, each of these circuits is composed of discrete components mounted on an appropriate mounting board.

The midpoint voltage Vcom for the common electrode is supplied to one end of a voltage dividing resistor circuit which forms drive voltages V1 to V8 for gradation display via a level shift circuit. In this embodiment, three voltage dividing resistor circuits are provided for the three primary colors of red, green and blue in order to obtain eight independently adjustable levels. In the figure, a concrete circuit of a voltage dividing circuit for forming drive voltages V1B to V8B corresponding to blue (B) and an output circuit thereof is shown as a representative. Although shown as a black box in the figure, the driving voltages V1R to V8R and V1G to V8G corresponding to the other red (R) and green (G) are also formed by the same circuit.

The level shift circuit adjusts the variable resistance element VR1 in order to perform the level shift operation corresponding to both positive and negative polarities while allowing the reference potential corresponding to the midpoint voltage Vcom to be adjusted. An NPN transistor T1 and a PNP transistor T2 whose bases are coupled to terminals are provided. The emitters of these transistors T1 and T2 are commonly used and connected to one end of the variable resistor RV1. Diodes D1 and D2 for allowing collector currents of the transistors T1 and T2 to flow are provided at collectors of the transistors T1 and T2, respectively, and the variable resistance RV1 is provided.
Is connected to the midpoint voltage Vcom side together with the other end. In this level shift circuit, a constant current corresponding to the adjustment resistance value of the variable resistor RV1 to which the constant voltage V _BE between the bases and emitters of the transistors T1 and T2 is applied is formed, and this constant current is applied to the variable resistor RV1. Adjustable level shift operation is performed by the flowing.

To the level shift circuit, one end A of a series resistance circuit for blue, which is composed of the series resistances R1 to R3 shown as a representative as described above, is connected. These series resistance circuits form the voltage dividing resistors V1B to V8B for gradation display. The divided voltage at each connection point of the series resistance circuit is not particularly limited, but operational amplifiers OP1 to OP having a voltage follower form are formed.
It is output as drive voltages V1B to V8B via a buffer amplifier (impedance conversion circuit) composed of P8.

At the other end B of the series resistance circuit composed of the series resistances R1 to R3 shown as an example above, one end of a variable resistance RV2 for adjusting the brightness of blue color is provided.
The variable resistors for red and green corresponding to the other red and green are also provided with variable resistors for brightness adjustment similar to the above. On the other end C of the variable resistor RV2, each color is shared and a voltage switching circuit as described below is provided.

The NPN transistor T3 constitutes a switch for outputting the ground potential (0V) of the circuit. PN
The P-transistor T4 constitutes a switch for outputting the doubled midpoint voltage 2Vcom. These switches are alternately turned on / off to set the variable resistor RV2.
The voltage of 0V and the voltage of 2Vcom are alternately supplied to the other end C of the. The inverter circuit IV receives the AC signal M and controls the switch of the transistor T3 via the base resistor R4. On the other hand, the AC signal M controls the switching of the NPN transistor T5 via the base resistor R6. The collector of the transistor T5 is connected to the base of the PNP transistor T4 via the base resistor R5.

The midpoint voltage Vcom is not particularly limited, but is formed by dividing 2Vcom by ½ by a resistance circuit. The ½-divided midpoint voltage Vcom is output via a buffer amplifier such as an operational amplifier having a voltage follower configuration. As a result, the drive voltage generating circuit can be operated by one power supply voltage 2Vcom.

Here, the driving voltage is V1R to V8R, V1.
G to V8G and V1B to V8B are respectively formed corresponding to the respective colors, but the following operations are common to the respective colors, so that these drive voltages V1R to V8R, V
1G to V8G and V1B to V8B will be collectively described as V1 to V8. Alternating signal M is high level (H)
At this time, the transistor T5 is turned on and a base current is supplied to the transistor T4 to turn on the transistor T4. At this time, since the output signal of the inverter circuit IV is set to the low level (“L”), the transistor T3 is turned off. Therefore, the series resistor circuit is connected to the series resistor circuit 2 through the transistor T4 which is turned on.
A double midpoint voltage of 2Vcom is supplied. Therefore, the drive voltages V1 to V8 are positive voltages based on the midpoint voltage Vcom.

When the AC signal M is at a low level (L), the transistor T5 is turned off and the base current of the transistor T4 does not flow, so the transistor T4 is turned off. At this time, since the output signal of the inverter circuit IV is set to the high level (H), the transistor T3
Is turned on. Therefore, the ground voltage GND (0V) of the circuit is supplied to the series resistance circuit via the transistor T3 which is turned on. Therefore, the driving voltages V1 to V8 are negative voltages based on the midpoint voltage Vcom. At this time, the level shift circuit has the absolute minimum positive and negative potentials with respect to the midpoint voltage Vcom. This voltage V1 is set to a visual threshold voltage of liquid crystal, for example. As a result, the reference black level is adjusted.

When the resistance value of the variable resistor RV2 is changed,
Correspondingly, the potential on the other end B side of the series resistance circuit changes, and the corresponding voltage V8 changes with the black level as a reference. That is, the brightness adjustment is performed. At this time, since the reference black level is constant by the level shift circuit, the brightness adjustment can be linearly changed until the visual characteristics of the liquid crystal are saturated. A variable resistor similar to the variable resistor RV2 has driving voltages V1R to V8.
Since it is also provided in the series resistance circuit forming R, V1G to V8G, the reference voltages V1R, VG and V1B are provided.
, Except that the gradation voltages V2R to V8R, V2G to V8G, and V2B to V8B are independently adjustable.

In the drive voltage generating method as in the above embodiment, the positive and negative voltages for AC driving of the liquid crystal are formed by the common level shift circuit and the voltage dividing circuit, and output through the common buffer amplifier. To be done. Therefore, the number of elements of the circuit can be reduced by half as compared with the conventional method of forming the positive and negative drive voltages by the series resistance circuit. Accordingly, the number of switches provided in the liquid crystal drive circuit described later can be reduced by half. Further, the output positive and negative drive voltages can be free from the influence of variations in resistance element values and changes over time, so that no DC offset voltage is generated during AC drive.

FIG. 2 is a schematic block diagram of an essential part of an embodiment of a signal line drive circuit in a color liquid crystal display device to which the present invention is applied. The signal line drive circuit shown in the figure is formed on one semiconductor substrate such as single crystal silicon, though not particularly limited, by a known semiconductor integrated circuit manufacturing technique. The signal line drive circuit of this embodiment has a function of driving m signal lines D1 to Dm of 1 to m. Although not particularly limited, the number m of the signal lines is as many as 120. Latch circuit FF
1 to FFm take in pixel data serially from the input terminal Din and output it in parallel. That is, the latch circuits FF1 to FFm constitute a shift register & latch having a serial / parallel conversion function. The respective latch circuits FF1 to FFm are
Each of them is composed of a plurality of flip-flop circuits, and performs a serial / parallel conversion operation and a holding operation of pixel data in units of a plurality of bits for gradation display.

Pixel data is composed of 3 bits in the case of 8-gradation display as described above. These pixel data are transmitted in parallel from the latch circuits FF1 to FFm to the decoders DEC1 to DECm. Decoder D
EC1 to DECm decode the pixel data of 3 bits to form a selection signal corresponding to gradation display. The selection signals formed by the decoders DEC1 to DECm are transmitted to the level shifters LS1 to LSm. The level shifters LS1 to LSm are driven by the drive voltage V formed by the drive voltage generation circuit as described above.
The control signal of the switch MOSFET for selectively outputting 1 to V8 corresponding to the gradation display is formed. That is, the latch circuits FF1 to FFn and the decoders DEC1 to DE that form the shift register & latch are provided.
Cn is not particularly limited, but is operated by receiving a power supply voltage of about 5V, and thus outputs a signal having a high level of about 5V and a low level of 0V. On the other hand, the driving voltages V1 to V8 supplied to the liquid crystal display panel are set to a relatively high level. Therefore, at the above-mentioned levels (5V, 0V), it may not be possible to turn on or off the switch MOSFETs, and thus the level shifters LS1 to LSm.
The level is converted to a level suitable for it.

The switch MOSFETs Q1 to Q3, which are shown as a representative example, constitute a drive circuit of a unit corresponding to one signal line D1, and 1 out of the drive voltages V1 to V8 formed as described above. One is selected and transmitted to the signal line D1. 8 consisting of V1 to V8 as described above
When performing gradation display consisting of 8 switches, 8 switches M
OSFETs are provided correspondingly. As in this embodiment, since the drive voltages V1 to V8 are supplied while being switched between positive and negative, this switch MOSFE is used.
T can be shared. In the liquid crystal driving method as in this embodiment, the number of switch MOSFETs can be reduced by half. It should be noted that the same switch MOSF as above is applied to the other signal lines D2 to Dm shown by way of example.
ET is provided.

The gradation voltages V1 to V8 input to the driving switch MOSFET are output through the selector SEL. The selector SEL includes the voltages V1R to V8 generated for each color by the drive voltage generating circuit as described above.
Among the R, V1G to V8G and V1B to V8B, those selected by the color selection signals SR, SG and SB are output. That is, when the color liquid crystal panel LCD has red, green, and blue filters formed in horizontal stripes for each scanning line, the color selection signals SR, SG, and SB are synchronized with the scanning line selection timing. It is formed. The color selection signals SR, SG and SB are formed by an appropriate control circuit (not shown).

In the figure, one scanning line drive circuit GDV is arranged on the left side of the liquid crystal display panel LCD.
The scanning line driving circuit GVD sequentially selects scanning lines extending in the lateral direction of the liquid crystal display panel LCD and selects TFT transistors. As a result, the signal lines D1 to D
The above driving voltages transmitted in parallel from m are written to the liquid crystal pixels corresponding to the selected scanning line. The liquid crystal pixel acts equivalently as a capacitor, and holds the written drive voltage until the next drive voltage is written.

For example, a pixel connected to the scanning line in the first row is provided with a red filter, a pixel connected to the scanning line in the second row is provided with a green filter, and a scanning line in the third row is provided. When a blue filter is provided in the pixel to be combined with the pixel and the color display panel LCD is formed by repeating the same pattern below, the scanning line in the first row is selected and writing to the pixel to be combined with the scanning line is selected. Sometimes the color selection signal SR
Is formed and the driving voltages V1R to V8R for red are transmitted to the driving switch MOSFET through the selector SEL. As a result, at the timing of selecting the scanning line in the first row, each of the signal lines D1, D2, ..., Dm has one of the eight gradation voltages V1R to V8R corresponding to the decoder output of the corresponding pixel data. One is selected and written. Similarly, at the timing of selecting the scanning line in the second row, the signal lines D1, D2, ..., Dm have the eight gradation voltages V1G to V8G corresponding to the decoder outputs of the corresponding pixel data. Any one of them is selected and written, and at the selection timing of the scanning line in the third row, eight gradation voltages V1B corresponding to the decoder output of the pixel data corresponding to the respective signal lines D1, D2 ... Dm. ~ V8B is selected and written.

FIG. 3 is a characteristic diagram for explaining the color balance adjustment according to the present invention. In the figure, the vertical axis represents luminance and the horizontal axis represents voltage. Dark indicates a black level and corresponds to the voltage V1. In this embodiment, the adjustment resistor VR1 as described above forms common black levels V1R, V1G and V1B corresponding to each color. The black level is unrelated to the sensitivity of the human eye for each color, and is thus commonly set. The black level can be adjusted to correspond to the process variation due to the threshold value of the liquid crystal.

Grayscale display is performed using a region in which the brightness of the liquid crystal changes linearly with respect to the drive voltage with reference to the black level. In this case, although not particularly limited, for blue, the drive voltage V8B when used in the saturated region of the liquid crystal is set to the maximum voltage, and the brightness at this time is adjusted so that the brightness of other colors becomes the same. To do. In order to obtain this brightness, the driving voltage V8R for red (R) and the driving voltage V8G for green (G), which has the highest sensitivity, are adjusted by the adjustment resistor VR2 and the like. Since the human eyes have almost the same sensitivity to red and blue, drive voltages V8B and V8R that are substantially the same are formed as shown by the broken line in the figure.
On the other hand, for green, which has the highest sensitivity, the same luminance can be obtained by a small drive voltage V8G, and the respective maximum voltages V8B, V8R, and V8G are divided by eight to form the above gradation voltages. It In this embodiment, since the drive voltage can be adjusted independently for each color by the drive voltage generation circuit as described above, the white balance can be adjusted according to the characteristics of the human eye by the adjustment resistor. It will be possible.

The operational effects obtained from the above embodiment are as follows. That is, (1) By making the gradation voltages supplied to the pixels of the three primary colors of colors of red, green, and blue relatively adjustable for each color, a color balance corresponding to the sensitivity of the human eye can be obtained. The effect that it can be realized is obtained. (2) In the adjustment of the relative gradation voltage of each color, the adjustable gradation voltage is formed corresponding to each color, and the corresponding gradation voltage is selected by the color display control signal. By transmitting the information to the drain driver of the liquid crystal display panel via the selector, the effect that color balance adjustment can be realized with a simple configuration can be obtained.

Although the invention made by the present inventor has been specifically described based on the embodiments, the invention of the present application is not limited to the embodiments and various modifications can be made without departing from the scope of the invention. Needless to say. For example, a gray scale voltage that maximizes the brightness can be fixedly formed by blue, which is the least sensitive, and the resistance division circuit divides the gray scale voltage into levels to generate red and green gray scale voltages. You may Alternatively, blue and red may have substantially the same gradation voltage, and only green may be level-divided and adjusted by the resistance dividing circuit. The grayscale voltage is switched between positive and negative polarities with reference to the midpoint voltage Vcom as described above, and positive and negative grayscale voltages may be formed with a resistance dividing circuit based on the midpoint voltage. Good.

When the liquid crystal display panel is provided with a color filter having a vertical stripe shape, the color is fixed for each signal line. Therefore, the switch MOSFETs forming the drain driver are divided into three groups, and the gradation voltages V1R to V8R, V1G to V8G, and V1B to V are respectively divided.
8B may be fixedly supplied. Alternatively, when the color filters are arranged in a mosaic pattern, one frame is temporally divided into three, and the gray scale voltage corresponding to each pixel is written by controlling the selector and drain driver switches as described above. Good. The gradation voltage may be a binary voltage in addition to the multi-gradation voltage such as the 8-value voltage or the 4-value voltage described above. This is because even with such a binary voltage, it is necessary to adjust the white balance due to the difference in eye sensitivity for more accurate color expression.

[0028]

The effects obtained by the typical ones of the inventions disclosed in the present application will be briefly described as follows. That is, by making the gradation voltages supplied to the pixels of the three primary colors of colors of red, green, and blue relatively adjustable for each color, it is possible to realize a color balance corresponding to the sensitivity of the human eye.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a gradation voltage (or drive voltage) generation circuit used in a color liquid crystal display device according to the present invention.

FIG. 2 is a schematic block diagram of essential parts showing an embodiment of a signal line drive circuit in a color liquid crystal display device to which the present invention is applied.

FIG. 3 is a characteristic diagram for explaining color balance adjustment according to the present invention.

[Explanation of symbols]

OP1-OP8 ... Buffer amplifier, IV ... Inverter circuit, VR1, VR2 ... Adjusting resistance, T1-T5 ... Transistor, D1, D2 ... Diode, R1-R6 ... Resistor, S
EL ... selector, Q1 to Q3 ... switch MOSFET,
FF1 to FFm ... Shift register & latch, DEC1 to
DECm ... Decoder, LS1 to LSm ... Level shifter,
LCD ... Liquid crystal display panel, PX ... Pixel, GDV ... Scan line drive circuit, G1 to G480 ... Scan line electrodes, D1 to Dn ...
Signal line electrode.

Claims (3)

[Claims] 1. A color liquid crystal display device, wherein voltages supplied to pixels of three primary colors are relatively adjustable for each color. 2. The relative voltage adjustment of each color is performed by a voltage generation circuit that is adjustable for each color and a selector that selects a corresponding voltage by a color display control signal and transmits it to a drain driver. The color liquid crystal display device according to claim 1, wherein 3. The color liquid crystal display device according to claim 1, wherein the voltage supplied to the pixels of the three primary colors of color is a gradation voltage.