JPH08110767A - Liquid crystal display device - Google Patents

Abstract

PURPOSE: To adjust the root-mean-square values applied to respective picture elements so that the optimum picture quality is simply obtained according to the desire of a user under any conditions by changing the bias value and amplitude of the image signal input or the selection level and nonselection level of a gate line or both of them. CONSTITUTION: A bias voltage changing circuit is constituted of a transistor 81 and a variable resistor 80. The transistor 81 plays the same role as a diode clamping a synchronization signal section Sy. When the variable resistor 80 is changed, the clamp level Vl , is changed, and the input bias level to an amplifier transistor 84 is changed. The bias voltage is changed, and the intensity of a display device can be adjusted. A resistor 88 and a variable resistor 89 constitute an amplitude value changing circuit. When the emitter resistance of the amplifier transistor 84 is changed, the variable resistor 89 changes the output amplitude to a transistor 93 inverting and amplifying the image signal. The contrast can be adjusted, thereby.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called active matrix panel driving method for driving a liquid crystal using active elements.

Conventionally, a liquid crystal has been used as a display body mainly for a timepiece calculator, but in the future, there is an increasing demand for large-capacity display of a terminal for a computer, a pocket TV and the like. However, the drive duty is 1 in the conventional voltage averaging method.
The limit is / 30 to 1/50, and it is difficult to increase the capacity to about 1/500. Therefore, a thin film transistor (TF
T) and other transistors, metal-insulator-metal (MIM)
It has been proposed to improve the drive duty by performing writing-holding for each pixel by using an active element (MIM is not strictly active but is defined as such in the present invention) such as an element.

FIG. 1 shows cells arranged in a matrix of (n.times.m) cells. An active matrix in which each pixel is selected by n data lines and m gate lines to perform write and hold operation. It is Bunnell.

FIG. 2 shows the structure and driving method of an active matrix using TFTs for a specific data line Di. There are m cells vertically arranged from Pi1 to Pim. The transistor is turned on by the gate line, the display content is written to the pixel from the data line, and then the transistor is turned to 0FF until the next selection is made. Hold the data. An equivalent liquid crystal resistance RL and capacitance CL are connected to the transistor. This data line sequentially selects the image signals V and S from the shift register 1,
The capacitance Csi is sample-held via the transistor 2. This is so-called dot sequential driving.

FIG. 3 shows an equivalent circuit of one pixel cell, and a transistor can be expressed by a variable channel resistance RTR and overlapping capacitors COVS and COVD. When RTR is ON, 10 ⁶ Ω or less OFF
It is set as high as 10 ⁹ Ω or more.

FIG. 4 shows an example of operation waveforms in this dot sequential drive. Two 1 frame to drive the liquid crystal AC
Divide into fields and write a positive voltage in the odd field and a negative voltage in the odd field. The potential VD of the data line is ± VDH when the liquid crystal is lit, ± VDL is provided when the liquid crystal is not lit, a voltage within this range is applied for gradation, and the gate voltage VG is sequentially selected from top to bottom as shown in the figure. . For example, 20 scan lines
Considering the display of a television screen using about 0 lines, the selection time Ts of one scanning line is 6 Oμsec, and the field cycle is 16 msec.
Becomes Therefore, each pixel is written in 60 μsec,
Holds the contents written for 6 msec. Therefore, each Y line (corresponding to the scanning line) is sequentially written by the gate signals VG1 to VGm, and each pixel potential Vc1 to Vcm is held as shown in (c).

Further, in one scanning line period, as shown in FIG. 5, the image signal V and S inputs are sampled and held sequentially from VD1 to VDn by the sample and hold clock SH, and this data is predetermined while the gate signal VGj is open. Written on the line.

With such a dot-sequential method, data is written to each pixel so as to form a predetermined image while scanning each pixel. However, the input image signal is unstable, and the power supply voltage used varies. Alternatively, an appropriate effective value in a liquid crystal pixel may change due to various factors such as the characteristics of the liquid crystal and the characteristics of the transistor.

Therefore, an object of the present invention is to provide a method capable of appropriately and easily performing an effective value of a liquid crystal display in each pixel so that an appropriate display operation can be always performed against various changes in conditions. To provide.

There are roughly two means for adjusting the pixel effective value in the present invention. One is to make the bias level and the amplitude of the image signal in the data line variable,
The other is to make the selection potential of the selection signal on the gate line and the bias level variable.

First, the former method will be described. FIG. 6 shows the contrast power of the liquid crystal display, the horizontal axis is the back effective value, and the vertical axis is the contrast. When displaying an image, a bias voltage VB having a central effective value is determined, and an image signal is formed around this bias voltage VB, thereby displaying an image.

FIG. 7 shows image signals V and S used in the present invention. As shown in FIG. 4, data inversion is performed for each field of the I signal that has passed through the video IF of the television receiving circuit. The center of the figure shows the switching of fields. In this waveform, the center of the image signal swing is the bias voltage VB.
And the amplitude at that time is Aν. Although VB and Aν may be better shifted by field depending on the transistor characteristics, a better image quality may be obtained in some cases, but they are made the same for the sake of simplicity. Considering this bias voltage VB as the bias point in the contrast curve shown in FIG. 6, in this case, if VB is increased, the screen becomes darker, and if it is decreased, the screen becomes brighter, that is, the brightness can be adjusted. Further, when the amplitude Aν is set to be large, the black level and the white level are clearly differentiated, and when the amplitude is set to be small, the whole is grayed, that is, the contrast can be adjusted.

FIG. 8 shows a concrete example of this system. Video I
The output V of F and the signal of IF are unipolar signals, and the transistor 81 plays the same role as a diode that clamps the synchronization signal section Sy. When the volume 80 is changed, the clamp level VL shown in (b) changes, so that the input bias level to the amplitude transistor 84 becomes variable. Further, the volume 89 makes the output amplitude to the transistor 93 variable by making the emitter resistance of the transistor 89 variable. Transistor 93, resistor 9
A signal whose polarity is inverted by 1 and 92 is formed, a signal obtained by inverting the transmission gate for each field by the frame signal Sf is selected, and further image signals V and S are formed through the buffer 96. Therefore, the volume 80 serves as a direct adjusting means for varying the bias voltage VB and the volume 89 for varying the amplitude Aν.

Another variable system of the present invention will be described. FIG. 9 shows a characteristic example of a typical thin film transistor (TFT). The horizontal axis represents the gate voltage, and the vertical axis represents the drain / current when the source / drain voltage is constant. See also FIG.
Is a gate signal for selecting one scanning line, and assuming that the center value between fields of the image signal is the GND potential,
Assuming that a potential of Vν when selected and a potential of VH when not selected are applied to this potential, the ON current ION at the time of selection changes depending on the value of Vω. This is the same as the change of RTR in FIG. If Vω becomes small and RTR becomes large, the data on the data line cannot be sufficiently written in the pixel within the predetermined period TS, and the effective value of the pixel is lowered. This relationship is shown in FIG. Write voltage V on the horizontal axis
ω, the vertical axis is the ratio of how much the potential of the data line is written in the pixel through the transistor. By varying Vω from this curve, the effective value of the pixel can be varied even if the image signal is constant.

Further, the gate bias voltage VH in the non-selected state can make the transistor resistance RTR in the non-selected state variable in FIG. If a large value is applied to the VH (-) side, the resistance value when not selected will decrease. As a result, the signal of the data line is slightly written in the pixel even when it is not selected. As a result, Figure 4 (c)
The discharge characteristics of the signal of each pixel shown by are gradual, and the effective pixel value is increased.

FIG. 12 shows a concrete example of this relationship. The effective value becomes substantially minimum when VH is set to a potential at which the current of the transistor becomes minimum.

FIG. 13 shows an implementation example of this system, in which the power supply voltages VDD and VSS of the gate driver 103 directly determine the selection level and non-selection level of the selection signal of the gate output. The power supply circuit 100 inputs the VCC input to VDD
Convert to VSS potential. The volume 101 makes VSS, that is, the non-selection level VH, and the volume 102 makes VDD, that is, the selection level Vω.

In the method of changing the bias voltage VB and the amplitude Aν of the image signal sent to the data line in the present invention, the brightness and the contrast can be changed independently.
This is effective when the contrast curve of the liquid crystal is not smooth or when the video IF signal is unstable and easily changed.

On the other hand, the method of varying the selection level Vω and the non-selection level VH of the gate signal has the convenience of simultaneously changing the brightness and the contrast, and is easy to use under a relatively fixed contrast curve. Especially, Vω is useful for raising the black level, VH is useful for raising the white level,
By using each nonlinearity, both can be used at the same time, and stable image quality can be obtained by properly using both. Further, depending on the contrast curve, even if the image signal and the level of the gate line are mixed and used, it is naturally possible to perform better adjustment.

As described above, the present invention optimizes the effective value given to each pixel by varying the bias value and amplitude of the image signal input, the selection level and non-selection level of the gate line, or both in combination. The image quality can be easily adjusted under any condition, and the system of the present invention can always realize good TV display.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of a liquid crystal display body using an active matrix substrate.

FIG. 2 is a circuit diagram thereof.

FIG. 3 is an equivalent circuit diagram of a cell.

FIG. 4 is a drive waveform diagram of the circuit of FIG.

5 is a drive waveform diagram of the circuit of FIG.

FIG. 6 is a diagram showing a contrast curve of a liquid crystal display element.

FIG. 7 shows the variable portion VB of the image input signal according to the present invention. Av
FIG.

FIG. 8 is a diagram showing a specific circuit example thereof.

FIG. 9 is a base transistor characteristic diagram.

FIG. 10 is a waveform diagram showing a variable part of the level of the gate signal according to the present invention.

FIG. 11 is a graph showing a variable effect.

FIG. 12 is a graph showing a variable effect.

FIG. 13 is a diagram showing each of the examples.

[Explanation of symbols]

 1. . . Data side shift register 2. . . Sample hold transistor

[Procedure amendment]

[Submission date] November 22, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction content]

[Document name] Statement

Title of the invention Liquid crystal display device

[Claims]

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device.
It is related to the drive of .

[0002]

2. Description of the Related Art Conventionally, a liquid crystal has been used as a display body mainly for a timepiece calculator, but in the future, there is an increasing demand for large-capacity display for a computer terminal, a pocket TV and the like. However, in the conventional voltage averaging method, the drive duty is limited to 1/30 to 1/50, and it is difficult to increase the capacity to about 1/500. Therefore, a transistor such as a thin film transistor (TFT), a metal-insulator-metal (M
It has been proposed to improve the drive duty by performing writing / holding for each pixel using an active (IM) element or the like (MIM is not strictly active, but defined in the present invention) element. There is.

FIG. 1 shows cells arranged in a matrix of (n × m) cells, in which each pixel is selected by n data lines and m gate lines to perform write / hold operations. It is an active matrix panel.

FIG . 2 shows the structure and driving method of an active matrix using TFTs for a specific data line Di. There are m cells vertically arranged from Pi1 to Pim. The transistor is turned on by the gate line, the display content is written to the pixel from the data line, then the transistor is turned to 0FF, and the data is written until the next selection. Hold the data. An equivalent liquid crystal resistance RL and capacitance CL are connected to the transistor. This data line is selected by sequentially selecting the image signal VS from the shift register 1,
This is so-called dot-sequential driving in which the capacitor Csi is sample-held via the transistor 2.

FIG. 3 shows an equivalent circuit of one pixel cell, and a transistor can be expressed by a variable channel resistance RTR and overlapping capacitors COVS and COVD. RTR is less than 10 ⁶ Ω when ON ,
Set to 10 ⁹ Ω or more when OFF.

[0006] Figure 4 is an example of an operation waveform in this respect sequential drive. One frame is divided into two fields to drive the liquid crystal in alternating current, and the positive voltage is even in the odd field.
Write a negative voltage in the field . Data line potential VD
Gives ± VDH when the liquid crystal is lit and ± VDL when it is not lit, and applies a voltage within this range for gradation . Also, the gate voltage VG
Select from top to bottom as shown in the figure. For example, considering the display of a television screen using about 200 scanning lines, the selection time Ts for one scanning line is 6 Oμsec and the field period is 16 msec. Therefore, each pixel is written in 60 μsec and holds the written contents for 16 msec. Therefore, each Y line (corresponding to the scanning line) is sequentially written by the gate signals VG1 to VGm, and each pixel potential Vc1 to Vcm is held as shown in FIG.

Further , in one scanning line period, as shown in FIG. 5, the image signal VS input is sequentially sampled and held from VD1 to VDn by the sample and hold clock SH, and this data is kept predetermined while the gate signal VGj is selected. Written on the line.

With such a dot-sequential method, data is written to each pixel so as to form a predetermined image while scanning each pixel. However, the input image signal is unstable, the power supply voltage used varies, various characteristics such as liquid crystal characteristics and transistor characteristics may cause
It is possible that the appropriate effective value in the liquid crystal pixel will vary.

[0009]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to determine the effective value of the liquid crystal display in each pixel so that the optimum display operation can be always performed against various changes in conditions.
An object of the present invention is to provide a display device that can be appropriately and easily changed as needed .

[0010]

There are roughly two means for adjusting the pixel effective value in the present invention. One is a method for changing the bias level and the amplitude of the image signal in the data line , and the other is the method. Is a method of varying the selection potential and the bias level of the selection signal in the gate line .
In particular, in the liquid crystal display device of the present invention, the liquid crystal is between the pair of substrates.
Encapsulated, in matrix form on one of the substrates
Arranged pixel electrodes, thin film connected to the pixel electrodes
Transistor, predetermined on the source electrode of the thin film transistor
Do not supply a data signal whose phase is inverted at time intervals of
Data line, gate to the gate electrode of the thin film transistor
For a liquid crystal display device having a gate line for supplying a signal.
The voltage level when the gate signal is not selected is
With respect to the center value of the inversion of the phase of the data signal,
The voltage that reduces the source-drain current of a film transistor.
Set to a voltage with a specified bias voltage applied in the pressure direction.
It is characterized by becoming.

[0011]

EXAMPLE First, the bias level and amplitude of an image signal are determined.
The method of changing will be described. FIG. 6 shows the contrast power of the liquid crystal display, the horizontal axis shows the effective value, and the vertical axis shows the contrast . When performing the display image, it defines the bias voltage VB of the central effective value, to form an image signal around the value of this an image is displayed.

FIG. 7 shows the image signal V.V. used in the present invention. S. As shown in FIG. 4 (a) , the image signal that has passed through the video IF of the television receiver circuit is changed every one field (an odd number of frames).
Data inversion is performed every field (even field).
FIG. 7 is inverted between the odd field and the even field.
The image signal is shown. In this waveform, the reference for inversion
Image signal of positive polarity and negative image
Signal and the reference voltage and image signal for inversion.
The difference between the center voltage of the amplitude of No. a bias voltage VB, the amplitude of the image signal at that time and A _V. By shifting the VB and A _V is less for each field in accordance with the transistor characteristics, even when the better image quality can be obtained, and once the same for the sake of thinking. This bias voltage VB
Considering as the bias point of the contrast curve shown in FIG. 6, the screen can be darkened by increasing VB and brightened by decreasing VB . That is, the brightness can be adjusted. Further, when the amplitude A _V is increased, the black level and the white level are clearly differentiated, and conversely, when the amplitude A _V is decreased, the whole is grayed . That is, the contrast can be adjusted.

FIG. 8 shows a concrete example of this system. Video I
The signal of the output V _IF of F is a unipolar signal . Transis
Bias voltage variable circuit
Configure. The transistor 81 plays the same role as a diode that clamps the synchronization signal section S _y . When the volume 80 is changed, the clamp level V _L shown in Fig. 8 (b) changes.
It turned into, the changes input bias level to the amplifying transistor 84. That is, V _B is changed and the brightness of the display device is changed.
Can be adjusted.

Further , the resistor 88 and the volume 89 are
A variable width value circuit is configured. The volume 89 is made variable by changing the emitter resistance of the amplification transistor 84.
The output amplitude to the transistor 93 that inverts and amplifies the image signal is made variable. The transistor 93 and the resistors 91 and 92 are
It constitutes an inverting amplifier circuit. Emitter of transistor 93
When the output is taken from the side, the amplified signal is taken as it is.
Take out, take output from the collector side of transistor 93
Then, the inverted and amplified signal can be taken out. Of the inverting amplifier circuit
Output consists of transmission gates 94 and 95
Input to the selection circuit. The selection circuit uses the frame signal S _f
Transmission gate 94 for each field
95 is selected alternately, and the inverted signal for each field
select. The signal selected by the selection circuit is buffered.
It becomes the image signal VS through 96. The image signal VS is
2 is supplied to the display device.

Therefore, in changing the volume 80
The bias voltage VB changes and the brightness can be adjusted.
Amplitude A _V is changed by changing the volume 89
The contrast can be adjusted.

Another variable system of the present invention will be described. FIG. 9 is a characteristic example of a typical thin film transistor (TFT). The horizontal axis represents the gate voltage, and the vertical axis represents the drain current when the source / drain voltage is constant. In addition, FIG. 1
0 is a gate signal for selecting one scanning line. If the center value between fields of the image signal is assumed to be the GND potential, the potential of VW when selected and VH when not selected is applied to this potential. Then, depending on the value of VW , it will be ON when selected.
The current ION changes. This is the same as the change of RTR in FIG. If VW becomes smaller and RTR becomes larger, the signal on the data line cannot be sufficiently written in the pixel within the predetermined period TS, and the effective value of the pixel is lowered. This relationship is shown in FIG. Write voltage V on the horizontal axis
W , the vertical axis is the ratio of how much the potential of the data line is written in the pixel through the transistor. By varying VW from this curve, the effective value of the pixel can be varied even if the image signal is constant.

Further, the gate bias voltage V _H when not selected
In FIG. 9, the transistor resistance RTR at the time of non-selection can be made variable. If V _H (-) Taking large to side, the resistance value at the time of non-selection is lowered. As a result, the signal of the data line is slightly written in the pixel even when it is not selected. As a result, the discharge characteristic of the signal of each pixel shown in FIG. 4C becomes gradual, and the effective pixel value increases.

FIG. 12 shows a concrete example of this relationship, which is an example in which V _H is set to a potential at which the current of the transistor is minimized , and when such a setting is made, the effective value is almost minimized.

FIG. 13 shows an implementation example of this system, in which the power supply voltages VDD and VSS of the gate driver 103 directly determine the selection level and non-selection level of the selection signal of the gate output. The power supply circuit 100 inputs the VCC input to VDD
Convert to VSS potential. Volume 101 VSS, i.e. the non-selection level V _H, the volume 102 is VDD, that is, the selected level VW variable.

The bias voltage VB of the image signal to be sent out to the data line in the present invention, since the method for varying the amplitude A _V can be varied independently brightness and contrast respectively, especially LCD contrast curve as in FIG. 6 is not smooth Alternatively, it is effective when the video IF signal is unstable and easily changed.

On the other hand, the method of varying the selection level V _W and the non-selection level V _H of the gate signal has the convenience that the brightness and the contrast can be changed at the same time, and is easy to use under a relatively fixed contrast curve. Especially, V _W helps to raise the black level, V _H helps to raise the white level,
By using each nonlinearity, both can be used at the same time, and stable image quality can be obtained by properly using both. In addition, depending on the contrast curve, even if the image signal and the level of the gate line are mixed and used, it is naturally possible to perform better adjustment.

[0022]

As described above, according to the present invention, the bias value and the amplitude of the image signal input, the selection level and the non-selection level of the gate line, or the effective value given to each pixel can be changed by changing both of them. the optimum image quality is one that can easily obtained as adjusted in accordance with the wishes of the user in any conditions, by the method of the present invention, Oh Ru those that always can realize a good TV display. In particular, the voltage level when the gate signal is not selected is set to the phase of the data signal.
The source of the thin film transistor with respect to the center value of inversion
Select a via in the direction of the voltage to reduce the drain current.
Since it is set to the applied voltage,
You can control the degree and contrast.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of a liquid crystal display body using an active matrix substrate.

FIG. 2 is a circuit diagram thereof.

FIG. 3 is an equivalent circuit diagram of a cell.

FIG. 4 is a drive waveform diagram of the circuit of FIG.

5 is a drive waveform diagram of the circuit of FIG.

FIG. 6 is a diagram showing a contrast curve of a liquid crystal display element.

FIG. 7 is a waveform diagram showing variable portions V _B and A _V of an image input signal according to the present invention.

FIG. 8 is a diagram showing a specific circuit example thereof.

FIG. 9 is a base transistor characteristic diagram.

FIG. 10 is a waveform diagram showing a variable part of the level of the gate signal according to the present invention.

FIG. 11 is a graph showing a variable effect.

FIG. 12 is a graph showing a variable effect.

FIG. 13 is a diagram showing each of the examples.

[Explanation of Codes] . . Data side shift register 2. . . Sample hold transistor

Claims (1)

[Claims] 1. An active matrix panel in which an effective value of each pixel is obtained by writing an image signal to a predetermined pixel via a transistor when selected by a gate signal and holding the image signal when not selected, wherein the effective value at each pixel is
A method for driving an active matrix panel, characterized in that adjustment is performed by a change in a bias voltage of an image signal, an amplitude of an image signal, a selection level of a gate signal, and a non-selection level of a gate signal, singly or in combination.