JP3079402B2 - Liquid crystal display - Google Patents

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, and more particularly to a method for reducing flicker of the liquid crystal display device.

[0002]

2. Description of the Related Art FIG. 5 shows a configuration of a conventional active matrix type liquid crystal display device. A large number of liquid crystal pixel portions 22 are arranged in a matrix on a transparent substrate 21 to form a liquid crystal display portion A having a desired size. In addition, each liquid crystal pixel section 22
The pixel switch 23 is formed small by TFT in the corner of the line buffer unit 2 disposed around the liquid crystal display unit A.
4, horizontal shift register 25, vertical shift register 26
And can be selectively driven.

As shown in FIG. 6, the liquid crystal pixel section 22 comprises a liquid crystal cell in which a liquid crystal material 33 is sealed between a common electrode 31 made of a transparent electrode ITO and each pixel electrode 34 with a protective layer 32 interposed therebetween. In addition, a layer including a color filter layer corresponding to each pixel and a light-shielding layer for shielding light between pixels is provided.

A luminance signal and an audio signal of a television are compressed to a certain band and sent to a line buffer unit 24 driven by a horizontal shift register 25 having a driving ability capable of following the frequency. Next, the vertical shift register 2
6, the signal is transferred to the liquid crystal while the pixel switch 23 is ON.

Normally, a recording signal is sequentially transferred from a signal input terminal 27 to each pixel or each line at a shifted timing by a line sequential driving method. That is, in FIG. 7, one line of the video signal VIN to be recorded on the liquid crystal is supplied to the line buffer unit 24 via the shift pulse switch 28 driven by the horizontal shift register 25 which outputs an output synchronized with the frequency of the video signal. Minutes are recorded. After the video signals of all the pixels in the n-th line are recorded in the line buffer unit 24, they are turned on by the output switch 29 of the line buffer unit 24 turned on by the signal S1 and the signal S2 from the vertical shift register 26. Each liquid crystal cell 2 of the line through the pixel switch 23
2, the pixel video signal VLCn is recorded. In general, signal transfer to each liquid crystal cell is performed collectively for a certain line during a blanking period during a horizontal scanning period. At the above timing, the pixel video signal V is sequentially applied to each line.
LCn, VLCn + 1... Are recorded.

[0006] With respect to the signal voltage thus transferred,
By the liquid crystal molecules constituting the cell move separately by the direction of the polarizing plate provided in the context of cross-polarizers, the transmittance of the liquid crystal cell changes. In this case, in order to prevent a DC component from being applied to the liquid crystal, a signal is applied with the polarity of the signal voltage changed every frame, and the liquid crystal itself operates according to the AC voltage component.

[0007]

However, in the above liquid crystal display device, the flicker of the screen occurs due to the fluctuation of the transmittance of the liquid crystal display panel. The cause of the flicker is a DC shift of the + -electric field in the liquid crystal generated when the liquid crystal is alternately driven. First, the DC shift occurs.
It is difficult to configure the liquid crystal display panel symmetrically, and it is inevitably an asymmetric panel structure.
This is due to the presence of contaminants and mobile ions in the liquid crystal.

Conventionally, as a countermeasure against the asymmetry of the first panel structure, an offset is fixed so that flicker is minimized, and the potential of the common electrode is fixed. As a countermeasure against contamination in the second liquid crystal, the liquid crystal material and the process have been improved. However, flicker has not yet been sufficiently reduced.

[0009] The present invention has been made in view of the above,
An object of the present invention is to apply a liquid crystal display device that can effectively reduce flicker on a screen caused by a change in transmittance or the like of a liquid crystal display panel.

[0010]

In order to achieve the above object, a liquid crystal display device according to the present invention comprises an active matrix type liquid crystal display.
A liquid crystal display panel provided with a common electrode potential control means ,
A signal source that has a light source and a photodetector that detects the amount of light transmitted through the liquid crystal display panel, and is applied to the liquid crystal for each frame.
The polarity of the positive and negative fields
Output fluctuations of the photodetector, and the output fluctuations
By changing the potential of the common electrode so that it becomes smaller,
This electric field is controlled.

[0011]

The flicker is caused by a change in the transmittance of the liquid crystal display panel due to a DC shift of the + -electric field in the liquid crystal generated when the liquid crystal is alternately driven. Therefore, the fluctuation of the transmittance of the panel, which is a cause of flicker, is detected by the photodetector as the fluctuation of the photocurrent, and the common electrode potential control means is used for the positive and negative fields of the video signal so that the fluctuation of the output is minimized. When that Gyosu control the potential of the common electrode, the liquid crystal within the + - DC lag field is minimized in steady state can be reduced flicker. Therefore, not only the flicker component generated from the initial stage due to the asymmetric structure of the liquid crystal display panel, but also the flicker component generated at the time of energization due to contamination and movable ions in the liquid crystal can be both reduced to a minimum. Can
You.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the illustrated embodiments.

FIG. 1 shows a conceptual configuration of a liquid crystal display device according to the present invention, which has a liquid crystal display panel 7 and a light source device 9. As a configuration for eliminating flicker on the screen, a photodetector 13 for detecting the amount of light transmitted through the liquid crystal display panel 7 and means for controlling the liquid crystal display panel 7 so that the output fluctuation of the photodetector is minimized. And 10.

In FIG. 2, the liquid crystal display has a liquid crystal display panel 7 and a light source device 9. LCD panel 7
A transparent substrate 1, a layer 2 composed of a color filter layer corresponding to each pixel and a light-shielding layer for shielding light between pixels, a common electrode 3 for applying a voltage to the liquid crystal, a liquid crystal layer 4, An SOI layer 5 provided with an electrode for applying a voltage to a liquid crystal, a transistor, and a driving circuit, and a transparent substrate 6 are provided in this order. Therefore, the liquid crystal material is the common electrode 3
And each pixel electrode 5 to form a liquid crystal cell. Reference numeral 8 denotes an optical system disposed on the front side of the liquid crystal display panel 7, and the light source device 9 is disposed on the back side of the liquid crystal display panel 7 as a so-called backlight.

Reference numeral 11 denotes a video signal VIN applied to the liquid crystal cell.
A video signal generating means for generating (see FIG. 7) 12 is layer 5
It is a drive signal generation means for generating drive signals S1 and S2 (see FIG. 7) for a transistor and the like provided together with electrodes therein.

Further, the liquid crystal display device shown in FIG. 2 has a liquid crystal display panel 7 as a structure for eliminating flicker on the screen.
And a voltage control circuit 14 for controlling a voltage applied to the common electrode 3 of the liquid crystal display panel 7 such that output fluctuation of the photodetector is minimized. And

Next, the operation of the above configuration will be described.

As already described with reference to FIG. 7, the video signal VIN from the video signal generating means 11 is transmitted through the shift pulse switch 28 driven by the horizontal shift register 25 which outputs an output synchronized with the frequency of the video signal. One line is recorded in the line buffer unit 24. After the video signals of all the pixels in a certain n-th line are recorded in the line buffer unit 24, they are turned on by the output switch 29 of the line buffer unit 24 turned on by the signal S1 and the signal S2 from the vertical shift register 26. Pixel switch 2
3, the pixel video signal VLCn is recorded in each liquid crystal cell 22 of the line. Signal transfer to each liquid crystal cell is performed collectively for a certain line during a blanking period during a horizontal scanning period.

As shown in FIG. 3, a video signal is transmitted to a liquid crystal by a D signal.
In order to prevent the C component from being applied, the polarity of the signal voltage is changed every frame, and the liquid crystal itself is applied with the AC voltage.
It operates according to the voltage component. Therefore, the photodetector 13
As shown in FIG. 3B, the detected output waveform repeatedly increases in one positive field of the video signal and gradually decreases in the next negative field.

The applied voltage control circuit 1 for the common electrode 23
Reference numeral 4 receives the video signal and the detection output of the photodetector 13, detects the output fluctuation of the photodetector in the positive field and the negative field of the video signal, and applies a signal to the common electrode 23 in a direction in which the output fluctuation decreases. Vary the applied voltage.
That is, the peak value of the current positive / negative field is compared with the peak value of the previous positive / negative field, and the voltage applied to the common electrode 23 is shifted in such a direction that the difference obtained as a result of the comparison in the next positive / negative field becomes smaller. Close. Specifically, PP of the detection output of the photodetector 13
The value (peak-to-peak value) is compared with the previous value, and the voltage applied to the common electrode 23 is shifted so that the difference as the result of the comparison becomes smaller as the result of the next comparison. By repeating the operation of shifting the applied voltage in the direction in which the PP value of the photodetector decreases, the positive and negative peak values of the video signal become constant, and the PP value of the photodetector 13 becomes as shown in FIG. To a minimum.

Therefore, when the liquid crystal display panel is energized, the peak value of the positive and negative fields of the video signal is, for example, larger on the positive side than on the negative side, thereby causing a DC-like shift of the + -electric field in the liquid crystal. However, the change in the transmittance of the panel due to this is detected as an increase in the photocurrent of the phototransistor as the photodetector. For this reason, the control circuit 14
The deviation control is performed so as to reduce the applied voltage in the positive field period of the video signal, and the DC shift of the + -electric field in the liquid crystal is minimized. Therefore, not only the occurrence of flicker due to the asymmetrical panel structure, but also the occurrence of flicker during energization due to contamination and movable ions in the liquid crystal is suppressed to a minimum.

In the case of the present embodiment, as shown in FIG. 3C, the deviation control amount of the applied voltage switches between the extremes in synchronization with the positive and negative fields of the video signal. However, it is not always necessary to perform the synchronization. As a result, the photodetector 1
This is because it is only necessary to settle down so that the output fluctuation of No. 3 is minimized .

[0023]

As described above, according to the present invention, the DC deviation of the +-electric field in the liquid crystal is minimized and the flicker can be reduced. Therefore, not only the flicker component generated from the initial stage due to the asymmetric structure of the liquid crystal display panel, but also the flicker component generated at the time of energization due to contamination and movable ions in the liquid crystal can be both reduced to a minimum. I can .

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic configuration of a liquid crystal display device of the present invention.

FIG. 2 is a diagram showing one embodiment of the liquid crystal display device of the present invention.

FIG. 3 is a diagram provided to explain an operation in the embodiment of FIG. 1;

FIG. 4 is a diagram showing a relationship between an output of a photodetector and a common electrode potential in the embodiment of FIG.

FIG. 5 is a diagram showing a configuration of a conventional liquid crystal display device.

FIG. 6 is a diagram showing a configuration of a liquid crystal cell of a conventional liquid crystal display panel.

FIG. 7 is a diagram illustrating a configuration of a driving circuit of a conventional liquid crystal display device.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 transparent substrate 2 layer composed of color filter layer and light-shielding layer 3 common electrode 4 liquid crystal layer 5 SOI layer provided with electrodes for applying voltage to liquid crystal for each pixel 6 transparent substrate 7 liquid crystal display panel 8 optical system 9 light source device DESCRIPTION OF SYMBOLS 10 Control means 11 Video signal generation means 12 Drive signal generation means 13 Photodetector 14 Applied voltage control circuit

Continuation of front page (56) References JP-A-61-269127 (JP, A) JP-A-61-256382 (JP, A) JP-A-1-136127 (JP, A) JP-A-4-20924 (JP) JP-A-61-250618 (JP, A) JP-A-52-142535 (JP, A) JP-A-3-166513 (JP, A) JP-A-4-147213 (JP, A) 50-120997 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/133 580 G02F 1/133 535 G02F 1/133 575

Claims (1)

(57) [Claims] 1. An active matrix type common electrode
A liquid crystal display panel having position control means , a light source, and a photodetector for detecting the amount of light transmitted through the liquid crystal display panel ,
The polarity of the signal voltage applied to the liquid crystal is inverted every frame.
The photodetectors in the positive and negative fields
Output fluctuations and minimize the output fluctuations.
The electric field applied to the liquid crystal is controlled by changing the potential of the common electrode.
A liquid crystal display device characterized by controlling .