JP2002132227A - Display device and driving method for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the sacrifice of contract characteristics to some extent which is inevitable when 1H inversion drive to make flicker hardly recognizable is used. SOLUTION: Respective control signals for 1H inversion control and 1F (field) inversion control are outputted in accordance with a horizontal synchronizing signal and a vertical synchronizing signal. An analog video signal made into AC at a 1H period and an analog video signal made into AC at a 1H period are formed in signal drivers 12 and 13 in accordance with these control signals. A detection section 15 detects that the level of the inputted video signals is at a black level or near the same. One of the two analog video signals made into AC is selected in accordance with the detection signal of the detection section 15 and is supplied to a liquid crystal panel 17, by which the IF inversion drive is carried out during the black display and the 1H inversion drive is carried out at the times other than the same.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device and a method of driving the same, and more particularly, to a display device and a method of driving a display unit using an analog video signal which is AC driven.

[0002]

2. Description of the Related Art As a driving method for a display device in which pixels are arranged in a matrix, for example, a liquid crystal display device, individual independent pixel electrodes are arranged for each pixel, and a thin film transistor (TFT) is arranged for each of these pixel electrodes. TFT; Thin Fil
A so-called active matrix driving method (hereinafter, simply referred to as an active matrix type) in which a switching element such as an m-transistor is connected and pixels are selectively driven is known.

In an active matrix type liquid crystal display device, for example, a TFT substrate on which a thin film transistor is formed as a switching element and a counter substrate on which a color filter, a counter electrode and the like are formed are overlapped, and liquid crystal is sealed between these substrates. Constitutes a liquid crystal panel. In this liquid crystal panel, the liquid crystal orientation is controlled by switching control by a thin film transistor and voltage application based on a video signal, and video display is performed by changing light transmittance.

In an active matrix type liquid crystal panel,
In a state surrounding each of the pixels arranged in a matrix, a film having an excellent light-shielding property called a black matrix is formed in a pattern on the substrate. The black matrix is indispensable to prevent light from leaking from the vicinity of the periphery of the pixel electrode, that is, a region of an alignment defect called a so-called reverse tilt domain, which is generated between pixels, as the definition of the liquid crystal panel increases. By preventing this light leakage, the contrast characteristics of the liquid crystal panel can be improved.

In a drive system for an active matrix type liquid crystal panel, a timing generator and an analog signal driver generally receive a video signal and a horizontal and vertical synchronizing signal (or a composite video signal including a horizontal and vertical synchronizing signal). The display drive is performed by supplying various timing signals from a timing generator and an analog video signal converted into an AC signal from an analog signal driver to a liquid crystal panel.

[0006] The analog video signal driven by AC is used to prevent the specific resistance (specific resistance of a substance) of the liquid crystal from deteriorating due to the continuous application of a DC voltage of the same polarity to the liquid crystal. Reference voltage (signal center) Vco
An analog video signal whose polarity is inverted at a certain cycle around m.

As shown in FIG. 2, 1F (1F is one field period) inversion drive (A) and 1H (1H is one horizontal scanning period) inversion drive (B) are performed according to the inversion timing of the analog video signal. Are roughly divided into The 1F inversion drive (A) is a driving method in which after writing an analog video signal of a certain polarity to all pixels, the polarity of the analog video signal is inverted. On the other hand, 1H inversion driving (B) is a driving method in which the polarity of an analog video signal is inverted for each horizontal line (horizontal direction), and the polarity is further inverted for each field.

[0008]

FIG. 6 shows the polarity of the pixel potential in the case of the 1F inversion drive (A) and the case of the 1H inversion drive (B). As can be seen from the figure, in the 1F inversion drive (A), no electric field is applied in the vertical direction (vertical direction) on the black matrix between the pixels, so that the liquid crystal alignment does not disturb in this portion. Therefore, high contrast can be achieved because there is no light leakage at the time of black display. On the other hand, at the intermediate signal level, the luminance level difference between the High side (+ side) and the Low side (− side) causes flicker (image flicker). It is visually recognized as.

Conversely, in the 1H inversion drive (B), the flicker is less visible because the pixel potentials on the high side and the low side are adjacent to each other at the intermediate signal level. However, on the black matrix, an electric field is applied in the vertical direction, so that light leakage occurs due to disorder in liquid crystal alignment, and the contrast characteristics are reduced. Normally, display driving is performed using 1H inversion driving in which flicker is hardly visually recognized. However, as apparent from the above description, this impairs contrast characteristics to some extent.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a display device capable of improving a contrast characteristic of a liquid crystal panel while realizing an image display with less flicker, and a display device therefor. It is to provide a driving method.

[0011]

In order to achieve the above object, according to the present invention, in a display device having a display unit in which pixels are arranged in a matrix, the level of an input video signal is a black level or a black level. The display unit is driven (1F inversion driving) by a video signal whose polarity is inverted around a reference voltage in a 1F cycle when the level is near, and 1H when the level of the input video signal is other than the black level or its vicinity
The display unit is driven (1H inversion driving) by a video signal whose polarity is inverted around a reference voltage in a cycle.

When a level of an input video signal is at or near a black level, 1F inversion driving is performed on a display unit in which pixels are arranged in a matrix, so that color loss in a black matrix of the display unit is achieved. Since the area is suppressed and the luminance at the time of black display decreases, high contrast can be obtained. On the other hand, by performing 1H inversion driving except for black display, it is possible to realize video display with less flicker.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram showing a configuration example of an active matrix type liquid crystal display device according to one embodiment of the present invention. As is clear from the figure, the active matrix type liquid crystal display device according to the present embodiment includes a video signal processing unit 11, signal drivers 12, 13, a control unit 14, a detection unit 15, a switching element 16, and a liquid crystal panel (display unit). 17) and has a normally white mode panel configuration in which light passes without applying an electric field.

In the active matrix type liquid crystal display device having the above configuration, the video signal processing section 11 performs signal processing for performing normal image quality adjustment such as white balance adjustment and gamma correction on the input video signal, The signal is supplied to the signal drivers 12 and 13. Control unit 12
Receives a horizontal synchronizing signal and a vertical synchronizing signal, generates and outputs various timing signals based on these synchronizing signals, and generates respective control signals for performing inversion control of 1H inversion and 1F inversion. Signal driver 1
Give to 2,13.

The signal driver 12 performs 1H inversion control on the video signal passed through the video signal processing unit 11 based on the 1H inversion control signal supplied from the control unit 14. The signal driver 13 controls the 1F inversion on the video signal that has passed through the video signal processing unit 11 based on the 1F inversion control signal provided from the control unit 14. Thereby, the signal driver 12,
From 13, analog video signals that are AC-driven in each of the 1H cycle and the 1F cycle are output.

That is, as shown in FIG. 2, a signal driver 12 outputs a reference voltage (signal center) Vco.
An analog video signal (B) is output in which the polarity is inverted at a cycle of one line (1H) around m and further inverted for each field. Further, the signal driver 13 outputs an analog video signal (A) whose polarity is inverted in a cycle of one field (1F) around the reference voltage Vcom. These analog video signals that have been AC driven are supplied to the switching element 16.

The detecting section 15 has a function as a detecting means for detecting whether the level of the input video signal is at or near the black level or other levels. That is, the detection unit 15 has a black level detection (judgment) threshold value. For example, as shown in the waveform diagram of FIG. 3, when the input video signal level is equal to or higher than the black level detection threshold value, the low level and the black level When the voltage falls below the detection threshold, a high-level detection signal (detection signal) is output. The boundary between the black level or its vicinity and the other levels, that is, the black level detection threshold can be arbitrarily adjusted (set).

The detection signal output from the detection section 15 is supplied to a switching element 16. Switching element 16
Is a signal driver 12 based on a detection signal output from the detection unit 15.
An analog video signal output in the 1H cycle and output from the analog driver or an analog video signal output in the 1F cycle and output from the signal driver 13 is selected and supplied to the liquid crystal panel 17.

FIG. 4 shows an example of a circuit configuration inside the liquid crystal panel 17. Here, for simplification of the drawing, three rows (n
A case of a pixel array of four rows (−1 row to n + 1 row) and 4 columns (m−1 to m + 2 columns) is shown as an example.

In FIG. 4, in a display area (effective pixel area) 21, unit pixels 22 each having a thin film transistor TFT as a pixel transistor, a liquid crystal cell LC, and a storage capacitor Cs are arranged in a matrix. here,
The liquid crystal cell LC means a capacitance generated between a pixel electrode formed by the thin film transistor TFT and a counter electrode formed to face the pixel electrode.

In this pixel structure, the thin-film transistor TFT has a gate electrode having vertical scanning lines..., 23n-1,
3n, 23n + 1,..., And the source electrode is connected to a signal line..., 24m-1, 24m, 24m + 1, 24m + 2,.
It is connected to the. In the liquid crystal cell LC, the pixel electrode is connected to the drain electrode of the thin film transistor TFT, and the counter electrode is connected to the common line 25. The storage capacitor Cs is connected between the drain electrode of the thin film transistor TFT and the common line 25. A common voltage Vcom, which is a reference voltage, is applied to the common line 25.

Vertical scanning lines..., 23n-1, 23n, 23
Each end of n + 1,... is connected to each output end of the corresponding row of the vertical drive circuit 26. Signal line ..., 24
One end of each of m-1, 24m, 24m + 1, 24m + 2,... is connected to the output end of each corresponding column of the horizontal drive circuit 27.

The vertical drive circuit 26 is supplied with a vertical start pulse VST and a vertical clock pulse VCK as timing signals from the control section 14 of FIG.
The vertical driving circuit 26 starts vertical driving (vertical scanning) in response to the vertical start pulse VST, and scan pulses..., ΦVn−1, φV in synchronization with the vertical clock pulse VCK.
n, φVn + 1,... are sequentially output, and vertical scanning lines.
n-1, 23n, 23n + 1,...

The horizontal drive circuit 27 is supplied with the analog video signal selected by the switching element 16 in FIG. 1, and receives a horizontal start pulse HST and a horizontal clock pulse HCK as timing signals from the control unit 14. The horizontal drive circuit 27 starts horizontal drive in response to the horizontal start pulse HST, and sequentially samples the analog video signal every 1H in synchronization with the horizontal clock pulse HCK.

The horizontal driving circuit 27 can be driven by a point-sequential driving method or a line-sequential driving method. In the case of the point-sequential driving method, analog video signals for 1H are sequentially sampled, and the signal lines are sequentially and directly sequenced as they are, 24m-1,.
24m, 24m + 1, 24m + 2,... As a result, the video signal is sequentially written to the pixels 22 on the line (row) selected by the vertical drive circuit 26.

In the case of the line-sequential driving method, an analog video signal is sequentially sampled, and a video signal for one line (1H) is temporarily latched. And this latched 1
24m-1,
24m, 24m + 1, 24m + 2,... As a result, video signals for one line are simultaneously written to the pixels 22 on the line (row) selected by the vertical drive circuit 26.

In the active matrix type liquid crystal display device according to the present embodiment, it does not matter whether the horizontal driving circuit 27 is driven by a point-sequential driving method or a line-sequential driving method. That is, the present invention is applicable to the horizontal drive circuit 27 of any drive method.

Next, the operation when the active matrix type liquid crystal panel 17 according to the present embodiment is driven will be described.

The input video signal is supplied to signal drivers 12 and 13 after signal processing for normal image quality adjustment in a video signal processing circuit 11 and is also supplied directly to a detection unit 15. From the control unit 14,
Each control signal for 1H inversion / 1F inversion is generated and output based on the horizontal synchronization signal and the vertical synchronization signal, and the vertical start pulse VST, the vertical clock pulse VCK, the horizontal start pulse HST, and the horizontal clock pulse HCK are generated. Are generated and output.

The detector 15 monitors the level of the input video signal. For example, when the input video signal level is equal to or higher than the black level detection threshold, as shown in the waveform diagram of FIG.
H when the level is below the low level and black level detection thresholds.
A high-level detection signal is output, and the switching element 1
Give to 6. Then, based on the detected signal, the switching element 16 selects an analog video signal output from the signal driver 12 and converted into an AC signal in a 1H cycle or an analog video signal output from the signal driver 13 and converted into an AC signal in a 1F cycle. And supplies it to the liquid crystal panel 17.

Specifically, the detection signal of the detection unit 15 is Hi.
gh level, that is, when the input video signal is not at or near the black level, the signal driver 12
And outputs the analog video signal converted into AC signals at the 1H cycle from the LCD panel 17 to the liquid crystal panel 17. When the detection signal of the detection unit 15 is at the low level, that is, when the input video signal is at or near the black level, the analog video signal output from the signal driver 13 and converted into AC at the 1F cycle is selected and the liquid crystal panel is selected. 17.

Thus, 1F inversion driving of the liquid crystal panel 17 can be realized when the input video signal level is at or near the black level, and 1H inversion driving can be realized at other input video signal levels.

As described above, by performing the 1F inversion drive on the analog video signal only when displaying black, the liquid crystal panel 1
Since no electric field is applied in the vertical direction on the black matrix between the pixels 7, the liquid crystal alignment does not disturb in this portion. Therefore, a color loss area in the black matrix is suppressed, and the luminance at the time of black display is reduced, so that high contrast can be obtained. In addition, except for black display,
By making the analog video signal 1H inversion drive, FIG.
As can be seen from (B), at the intermediate signal level, H
Since the pixel potentials on the high side and the low side are adjacent to each other,
Flicker is hardly visually recognized, and an image display with less flicker can be realized.

In other words, the 1H inversion driving method with less flicker can be realized in the same liquid crystal panel 17 for a halftone image signal and the 1F inversion driving method with a high contrast for a black image signal.

In the above embodiment, the switching element 16 is arranged at the subsequent stage of the signal drivers 12 and 13,
Although the analog video signal output from the signal driver 12 and converted in the 1H cycle or the analog video signal output in the 1F cycle and output from the signal driver 13 is selected and supplied to the liquid crystal panel 17, The signal driver 12, based on the detection signal of the detection unit 15,
13 in an operable state, 1H cycle or 1
It is also possible to configure so as to alternatively generate an analog video signal that is AC-converted in the F cycle. Thereby, there is an advantage that the switching process at the subsequent stage of the signal drivers 12 and 13 becomes unnecessary.

In the above-described embodiment, the switching element 16 is arranged after the signal drivers 12 and 13. However, as shown in FIG. 5, the switching element 19 is arranged before the single signal driver 18. The switching element 19 selects one of the control signals for controlling the 1H inversion and the 1F inversion output from the control unit 14 based on the detection signal of the detection unit 15 and supplies the selected signal to the signal driver 18. Such a configuration is also possible.

In the case of this modification, the signal driver 18 controls the video signal that has passed through the video signal processing section 11 based on a control signal for inversion control of 1H inversion or 1F inversion provided from the switching element 19. Inversion control of 1H inversion or 1F inversion is performed. Then, the signal driver 18 outputs an analog video signal that has been converted into an AC signal at a 1H cycle or a 1F cycle.
7 will be supplied.

In this modification, a control signal for 1H inversion or 1F inversion is selected by the switching element 19 and applied to the signal driver 18 to control the driver 18, so that the number of signal drivers 18 is Since only one switching element is required as in the case of normal driving and only the switching element 19 needs to be added, there is an advantage that the intended purpose, that is, high contrast in black display can be achieved with a simple circuit configuration. is there.

In the above embodiment, the case where the present invention is applied to a liquid crystal display device has been described as an example. However, the present invention is not limited to this, and a pixel unit in which pixels are arranged in a matrix is used. Can be applied to all display devices configured to be driven by an analog video signal converted to AC.

[0041]

As described above, according to the present invention,
When the level of the input video signal is at or near the black level, 1F inversion driving is performed, and in other cases, 1H inversion driving is performed. With a video signal, video display with less flicker can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of an active matrix liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a waveform diagram showing an analog video signal in the case of 1F inversion driving (A) and in the case of 1H inversion driving (B).

FIG. 3 is a waveform chart for explaining the operation of a detection unit.

FIG. 4 is a circuit diagram showing an example of a circuit configuration inside a liquid crystal panel.

FIG. 5 is a block diagram illustrating a configuration example of an active matrix liquid crystal display device according to a modification of the present invention.

FIG. 6 is a diagram showing the polarity of a pixel potential in the case of 1F inversion drive (A) and in the case of 1H inversion drive (B).

[Explanation of symbols]

11: video signal processing unit, 12, 13, 18: signal driver, 14: control unit, 16, 19: switching element, 17: liquid crystal panel

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H093 NA16 NA32 NA33 NA42 NA43 NC16 NC26 NC34 ND04 ND10 ND49 5C006 AB01 AB03 AC02 AC27 AC28 AF42 AF44 BB16 BC06 BC16 FA23 5C080 AA10 BB05 DD06 DD30 FF07 JJ02 JJ04

Claims (7)

[Claims] 1. A display unit in which pixels are arranged in a matrix, a detection unit that detects that the level of an input video signal is at or near a black level and outputs a detection signal, When a video signal is received and a detection signal is output from the detection means, a video signal whose polarity is inverted around a reference voltage is generated in a cycle of one field period to drive the display unit, and the detection signal is output. A display device comprising: a driving unit that generates a video signal whose polarity is inverted around a reference voltage in a cycle of one horizontal scanning period when the signal is not output, and drives the display unit. 2. The driving unit generates a first inversion control signal having a period of one field period and a second inversion control signal having a period of one horizontal scanning period based on a horizontal synchronization signal and a vertical synchronization signal. Control signal generating means, and when the detection signal is output, one based on the first inversion control signal.
A video signal whose polarity is inverted in a cycle of a field period is generated. When the detection signal is not output, a video signal whose polarity is inverted in a cycle of one horizontal scanning period is generated based on the second inversion control signal. The display device according to claim 1, further comprising: a video signal generating unit that performs the operation. 3. The first video signal generating means generates a video signal whose polarity is inverted in a cycle of one field period based on the first inversion control signal;
A second signal generation unit configured to generate a video signal whose polarity is inverted in a cycle of one horizontal scanning period based on the second inversion control signal; and a first signal generation unit when the detection signal is output. And selecting means for selecting the video signal generated by the means, and otherwise selecting the video signal generated by the second signal generating means, and supplying the selected video signal to the display unit. Display device. 4. The video signal generating means selects the first inversion control signal when the detection signal is output,
Otherwise, selecting means for selecting the second inversion control signal, and a period of one field period or one horizontal period based on the first inversion control signal or the second inversion control signal selected by the selection means. The display device according to claim 2, further comprising: a signal generation unit configured to generate a video signal whose polarity is inverted in a cycle of a scanning period and supply the video signal to the display unit. 5. The display device according to claim 1, wherein a display element of each pixel of the display section comprises a liquid crystal cell. 6. A method of driving a display device having a display section in which pixels are arranged in a matrix, wherein the level of an input video signal is at or near a black level, and is equal to the period of one field period. The display unit is driven by a video signal whose polarity is inverted around the reference voltage, and when the level of the input video signal is other than the black level or its vicinity, the display is driven around the reference voltage in a cycle of one horizontal scanning period. A method for driving a display device, wherein the display unit is driven by a video signal whose polarity is inverted. 7. The method of driving a display device according to claim 6, wherein a display element of each pixel of the display section comprises a liquid crystal cell.