JP2005260329A - Display device and display method - Google Patents

Abstract

Provided are a display device and a display method capable of displaying an image with good contrast without increasing power consumption and bit accuracy for signal processing.
Two types of LUTs are provided for gamma correction, an average value MV of signal values for one field of an input digital video signal is calculated, the brightness level of the entire screen is grasped, and A video signal processing unit 2 that selects an LUT and performs gamma correction on the video signal according to the brightness level, and a timing generator 3 that generates various timing signals based on the horizontal synchronization signal HSYNC and the vertical synchronization signal VSYNC. And an LCD driver 4 that generates a 1H inverted analog video signal level-converted to suppress the amplitude according to the brightness level of the entire screen, and the analog video signal to the LCD panel based on the timing signal An LCD panel module 5 for writing.
[Selection] Figure 1

Description

  The present invention relates to a display device such as a liquid crystal display device (LCD) and a display method that can change the display gradation of an image according to an applied voltage.

  As a driving method for a display device in which pixels are arranged in a matrix, for example, a liquid crystal display device (LCD driver), individual pixel electrodes are arranged for each of the pixels, and each of these pixel electrodes is arranged. There is known a so-called active matrix drive system in which a switching element such as a thin film transistor (TFT) is connected to a pixel to selectively drive a pixel.

  In an active matrix 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 overlapped, and a liquid crystal is sealed between these substrates. Is configured. In this liquid crystal panel, liquid crystal orientation is controlled by switching control using a thin film transistor and voltage application based on a video signal, and video display is performed by changing light transmittance.

In the drive system of an active matrix type liquid crystal panel, generally, a video signal and horizontal and vertical synchronization signals are received by a timing generator and an LCD driver, and various timing signals are received from the timing generator and AC driving is performed from the LCD driver. Display driving is performed by supplying analog video signals to the respective liquid crystal panels.
Here, the AC-driven analog video signal is a reference voltage Vcom in order to prevent the specific resistance (substance specific to the substance) of the liquid crystal from being deteriorated by continuously applying a DC voltage of the same polarity to the liquid crystal. An analog video signal whose polarity is inverted at a predetermined cycle.

  Further, 1H inversion driving (1H is one horizontal scanning period) is known as a driving method using the analog video signal that is AC driven. The 1H inversion driving is a driving method in which the polarity of the analog video signal is inverted for each line in the horizontal direction (horizontal direction) and further inverted for each field.

Conventionally, in a display device such as a liquid crystal display device as described above, in order to improve contrast, which is a ratio of maximum luminance to minimum luminance, an application that can be input to a display device regardless of the display level of the entire image. An analog video signal having a large amplitude as much as possible is supplied to the display device within the voltage range.
For this reason, there is a problem that the power consumption of the display device increases, and at the same time, in order to obtain a large amplitude analog video signal, it is necessary to use a relatively large transistor process. There is also a problem that the chip size of the driver IC becomes large and it is difficult to reduce the cost.

  In addition, since an analog video signal with a large amplitude is displayed in gradation using digital data, the accuracy per unit gradation deteriorates, and if the display device has a large variation characteristic of display brightness with respect to applied voltage, There is a problem that the display becomes rough.

  On the other hand, in the liquid crystal display device, since the VT characteristic (voltage-transmittance characteristic) of the liquid crystal has a steep curve in the halftone, the transmittance fluctuation in the halftone even if the voltage fluctuation is several mV. There is a feature that is large. Conventionally, the bit accuracy of digital signal processing has to be increased in consideration of the VT characteristics of the liquid crystal, and as a result, there is a problem that cost reduction is difficult.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a display device and a display capable of displaying an image with good contrast without increasing power consumption and bit accuracy for signal processing. It is to provide a method.

  In order to achieve the above object, a first aspect of the present invention is a display means for changing a gradation of video display according to an applied voltage, and a gamma correction according to display characteristics of the display means by inputting a video signal. Based on the gamma correction means for performing, an average video calculation means for calculating an average video signal value that is an average of the video signals in a unit frame, a video signal that has been gamma corrected by the gamma correction means, and the average video signal value And a display driving means for generating an applied voltage to be applied to the display means.

  Preferably, the display driving means limits an applied voltage according to the average video signal value.

  Preferably, the gamma correction unit has a plurality of correction conversion tables set in accordance with display characteristics of the display unit, and is selected from the plurality of correction conversion tables in accordance with the average video signal value. Gamma correction is performed based on the one correction conversion table.

  In order to achieve the above object, a first aspect of the present invention is a display method of a display unit that changes a gradation of video display according to an applied voltage, the step of inputting a video signal, and the input video signal Calculating an average video signal value that is an average of the unit frames, performing gamma correction on the input video signal in accordance with display characteristics of the display unit, and converting the gamma-corrected digital video signal And a step of limiting an applied voltage applied to the display unit according to the average video signal value.

  According to the display device of the first aspect, the gamma correction unit inputs the video signal, performs gamma correction according to the display characteristics of the display unit, and the average video calculation unit calculates the video signal in the unit frame. An average video signal value that is an average is calculated, and the display driving unit generates an applied voltage to be applied to the display unit based on the video signal that has been gamma corrected by the gamma correction unit and the average video signal value. An optimum applied voltage can be supplied to the display means while maintaining a good contrast according to the overall brightness.

  According to the display device according to the first aspect, the display driving unit limits the applied voltage in accordance with the average video signal value, so that power consumption can be reduced.

  According to the display device of the first aspect, the gamma correction unit has a plurality of correction conversion tables set according to display characteristics of the display unit, and the plurality of correction conversion tables are set according to the average video signal value. Since the gamma correction is performed based on one correction conversion table selected from the correction conversion tables, a natural gradation display suitable for the display characteristics of the display means is possible.

  According to the present invention, since the power consumption and the bit accuracy for signal processing are not increased, it is possible to display an image with good contrast, and there is an advantage that both low cost and high display performance can be achieved.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a block diagram showing a configuration example of an active matrix type liquid crystal display device 1 according to an embodiment of the present invention. As is apparent from the figure, the liquid crystal display device 1 has a video signal processing unit (2, a timing generator (TG) 3, an LCD driver 4, and an LCD panel module 5, and allows light to pass therethrough without applying an electric field. The panel configuration is normally white mode.
Hereinafter, each component of the liquid crystal display device 1 having the above configuration will be described.

The video signal processing unit 2 inputs RGB digital video signals and executes signal processing for adjusting image quality such as white balance adjustment and gamma adjustment.
In general, the display output corresponding to the input signal of the video display device does not appear to be linearly changing for the human eye, so gamma correction is performed to adjust this. That is, the RGB video signal input from the outside is output after being subjected to gamma correction matching the voltage-transmittance characteristics (VT characteristics) of the liquid crystal mounted on the LCD panel module 5.

The video signal processing unit 2 calculates the average value (MV) of the video signal per screen of the input video signal, that is, per field, and DC corresponding to the calculated average value MV of the video signal per field. A level control signal CTRL is supplied to the LCD driver 4.
Here, the reason why the average value MV of the video signal per field is calculated is that the voltage level of the analog video signal generated by the LCD driver 4 is adjusted according to whether the entire screen is bright or dark, as will be described later. Because.

The video signal processing unit 2 changes the correction coefficient for gamma correction according to the calculated average value MV of the video signal per field.
The video signal processing unit 2 is provided with two types of correction conversion tables (hereinafter referred to as LUTs), and applies gamma correction by applying one of the two types of LUTs to the input digital video signal. I do.

FIG. 2 is an example of gamma correction using two types of LUTs prepared in the video signal processing unit 2. FIG. 2A shows the voltage-transmittance characteristics (VT characteristics) of the liquid crystal, and FIGS. c) shows the characteristics of gamma correction determined by the two types of LUTs.
In FIG. 2A, since the VT characteristic differs greatly between the case where the voltage applied to the liquid crystal is in the voltage range RV1 and the case where it is in the voltage range RV2, a curve (gamma curve) that matches the display characteristics of the liquid crystal. ) To perform gamma correction, and two types of LUTs are set so that the gamma curves shown in FIGS. 2B and 2C can be obtained.

  In FIG. 2, the video signal processing unit 2 has a voltage range RV1 in which the voltage applied to the liquid crystal is low (relatively bright as the entire screen), that is, the calculated average value MV of the video signal per field is a predetermined threshold value (Dth In the above case, an LUT that can obtain a gamma curve as shown in FIG. 2B is selected. On the other hand, when the voltage applied to the liquid crystal is high in the voltage range RV2 (relatively dark as a whole screen), that is, when the calculated average value MV of the video signal per field is equal to or less than a predetermined threshold value (Dth), FIG. An LUT that provides a gamma curve as shown in 2 (c) is selected.

  As described above, the video signal processing unit 2 calculates the average value MV of the video signal per screen of the input video signal, that is, per field, and calculates the calculated average value MV and a predetermined threshold value (Dth). The digital video signal output S2 in which the gamma correction is performed by the LUT according to the comparison result and the DC level control signal CTRL corresponding to the calculated average value MV are output to the LCD driver 4 (see FIG. 1). .

The timing generator 3 generates a control signal (1HC) for 1H inversion based on the horizontal synchronization signal HSYNC and the vertical synchronization signal VSYNC and outputs the control signal (1HC) to the LCD driver 4, and also includes a vertical start pulse VST, a vertical clock pulse VCK, Various timing signals such as a horizontal start pulse HST and a horizontal clock pulse HCK are generated and output to the LCD panel module 5.
The timing generator 3 generates a sample hold pulse (SHP) for sampling processing executed in the LCD driver 4.

The LCD driver 4 performs control for 1H inversion on the RGB video signal output from the video signal processing unit 2 based on the 1H inversion control signal (1HC) supplied from the timing generator 3. Thereby, the LCD driver 4 outputs an analog video signal that is AC driven in a 1H cycle.
As a result, it is possible to prevent the deterioration of the specific resistance of the liquid crystal (substance value specific to the substance) caused by the continuous application of the DC voltage to the liquid crystal of the LCD panel module 5.

FIG. 3 shows an example of the waveform of an analog video signal that is AC driven by the 1H period output from the LCD driver 4.
As shown in FIG. 3, the analog video signal output from the LCD driver 4 is inverted in polarity for each line in the horizontal direction (horizontal direction) around the reference voltage Vcom, and further, for each field (1F), The signal on the same line is inverted. The LCD driver 4 generates an analog video signal that is AC driven in this way.

  The LCD driver 4 includes a D / A conversion circuit and a sample / hold circuit, converts the digital video signal from the video signal processing unit 2 into an analog signal, and a sample / hold pulse (SHP) supplied from the timing generator 3. Based on the above, a signal sampled at a constant interval is generated, and the AC processing as described above is performed.

As described above, the LCD driver 4 basically generates and outputs an analog video signal that is AC-driven as described above. At this time, the LCD driver 4 generates a control signal CTRL supplied from the video signal processing unit 2. In response, the generated analog video signal is level-converted and output to the LCD panel module 5.
4A and 4B are waveform diagrams showing level conversion processing of an analog video signal performed in the LCD driver 4. FIG. 4A shows a case where level conversion is not performed, and FIG. 4B shows a case where level conversion is performed on the bright side. (C) shows a case where level conversion is performed on the dark side.

For example, when an analog video signal is generated based on a video signal subjected to 10-bit digital signal processing, in FIG. 4A, the digital value “000h” of the digital video signal is Vn4 on the non-inversion side. The level is Vr4 on the inversion side. The digital value “3FFh” of the digital video signal has a level of Vn1 (> Vn4) on the non-inversion side and a level of Vr1 (<Vr4) on the inversion side.
Therefore, in FIG. 4A, the operation range of the analog video signal is a range of Vn4 to Vn1 (non-inversion side) and Vr1 to Vr4 (inversion side) in the drawing.

The LCD driver 4 is supplied with the control signal CTRL having a DC level corresponding to the average value of the video signal per field calculated by the video signal processing unit 2, that is, the brightness of the entire screen, so that the supplied control is performed. Based on the signal CTRL, the operation range of the analog video signal to be output is level-converted.
That is, when the control signal CTRL based on the result of the video signal processing unit 2 determining that the entire screen is relatively bright is given, the analog video signal is Vn3 to Vn1 (non-inversion side) as shown in FIG. ) And Vr1 to Vr3 (inversion side).
Further, when the control signal CTRL based on the result of the video signal processing unit 2 determining that the entire screen is relatively dark is given, the analog video signal is Vn4 to Vn2 (non-inverted side) as shown in FIG. ) And Vr2 to Vr4 (inversion side).

As described above, when level conversion is performed on an analog video signal, the black level shifts to the bright side in the case of FIG. 4B, but generally the sensitivity of the human eye is relative to the amount of light. Therefore, in the case of a bright image as a whole screen, even if the black level is slightly shifted to the bright side, the contrast does not look bad.
In the case of FIG. 4A, the white level shifts to the dark side. However, in general, in the case of a dark image as a whole screen, the human eye has sufficient contrast even if the white level is somewhat dark. There seems to be no problem.

The LCD panel module 5 is driven for video display in synchronization with a predetermined timing signal from the timing generator 3 by an analog video signal supplied from the LCD driver 4.
FIG. 5 shows an example of the circuit configuration of the LCD panel module 5.
Here, for simplification of the drawing, a pixel arrangement of 3 rows (n−1 rows to n + 1 rows) and 4 columns (m−1 columns to m + 2 columns) is shown as an example.

  In FIG. 5, in a display area (effective pixel area) 51, unit pixels 52 each including a thin film transistor TFT which is 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 a thin film transistor TFT and a counter electrode formed opposite to the pixel electrode.

In the pixel structure described above, the thin film transistor TFT has a gate electrode connected to the vertical scanning lines 53n-1, 53n, 53n + 1, and a source electrode connected to the signal lines 54m-1, 54m, 54m + 1, 54m + 2.
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 55. 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 that is a reference voltage is applied to the common line 25.

  One end of each of the vertical scanning lines 53n−1, 53n, 53n + 1 is connected to each output end of the corresponding row of the vertical drive circuit 56. One end of each of the signal lines 54m-1, 54m, 54m + 1, 54m + 2 is connected to each output end of the corresponding row of the horizontal drive circuit 57.

The vertical drive circuit 56 is supplied with a vertical start pulse VST and a vertical clock pulse VCK as timing signals from the timing generator 3 shown in FIG.
The vertical driving circuit 56 starts vertical driving (vertical scanning) in response to the vertical start pulse VST, sequentially outputs the scanning pulses φVn−1, φVn, φVn + 1 in synchronization with the vertical clock pulse VCK, and the vertical scanning line 53n. Applied to −1, 53n, 53n + 1.

An analog video signal from the LCD driver 4 shown in FIG. 1 is supplied to the horizontal drive circuit 57, and a horizontal start pulse HST and a horizontal clock pulse HCK are supplied as timing signals from the timing generator 3.
The horizontal drive circuit 57 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.

As a driving method of the horizontal driving circuit 57, there are a dot sequential driving method and a line sequential driving method.
In the case of the dot sequential driving method, analog video signals for 1H are sequentially sampled and output to the signal lines 54m-1, 54m, 54m + 1, 54m + 2 as they are. As a result, video signals are sequentially written to the pixels 52 in the line (row) selected by the vertical drive circuit 56.

  In the case of the line sequential driving method, analog video signals are sampled sequentially, and video signals for one line (1H) are once latched. Then, the latched video signals for one line are collectively output to the signal lines 54m-1, 54m, 54m + 1, 54m + 2. As a result, video signals for one line are simultaneously written to the pixels 52 of the line (row) selected by the vertical drive circuit 56.

  In the liquid crystal display device 1 according to the present embodiment, it does not matter whether the horizontal drive circuit 57 is driven by a dot sequential drive system or a line sequential drive system. That is, the present invention can be applied to the horizontal drive circuit 57 of any drive system.

In the above, each component of the liquid crystal display device 1 was demonstrated.
Next, the operation of the liquid crystal display device 1 according to this embodiment having the above-described configuration will be described with reference to FIG.
When a digital video signal is input, the video signal processing unit 2 calculates an average value MV of signal values for one field of the input video signal, and compares the average value MV with a predetermined threshold (Dth). The brightness level is ascertained and gamma correction is performed on the input video signal in accordance with the calculated average value MV.
At that time, two types of correction conversion tables (hereinafter referred to as LUT) are prepared for gamma correction, the calculated average value MV is compared with a predetermined threshold value (Dth), and the liquid crystal V V is determined according to the comparison result. Since the LUT that matches the -T characteristic is selected and gamma correction is performed, the video signal S2 having a natural gradation for the human eye is generated.

The video signal processing unit 2 supplies the LCD driver 4 with information on the brightness level of the entire screen ascertained based on the average value MV of the signal values for one field of the video signal as a DC level control signal CTRL. The LCD driver 4 generates an analog video signal for 1H inversion driving on the basis of the gamma-corrected video signal S2, and limits the operation range of the analog signal according to the control signal CTRL. Level conversion.
That is, when the entire screen is relatively bright, the analog signal is level-converted so that the black level voltage value shifts to the bright side. When the entire screen is relatively dark, the analog signal is level-converted so that the white level voltage value shifts to the dark side.

  The LCD panel module 5 sequentially writes data based on a predetermined timing signal supplied from the timing generator 3 by an analog video signal supplied from the LCD driver 4.

  As described above, according to the liquid crystal display device 1 according to the embodiment of the present invention, there are two types of LUTs for gamma correction, and the average value of the signal values for one field of the input digital video signal. The MV is calculated, the brightness level of the entire screen is grasped, the video signal processing unit 2 that selects the LUT and performs gamma correction on the video signal according to the brightness level, the horizontal synchronization signal HSYNC, and the vertical A timing generator 3 that generates various timing signals based on the synchronization signal VSYNC, and an LCD that generates an analog video signal that is inverted by 1H and is level-converted to suppress the amplitude according to the brightness level of the entire screen. A driver 4 and an LCD panel module 5 for writing an analog video signal to the LCD panel based on the timing signal; Since, it is possible to obtain the following effects.

  That is, in general, since the sensitivity of the human eye is not linear with respect to the amount of light, in the case of a bright image as a whole screen, the contrast does not look bad even if the black level is slightly shifted to the bright side, Also, in the case of a dark image on the entire screen, paying attention to the fact that the human eye appears to have sufficient contrast even if the white level appears somewhat dark, Thus, the amplitude of the analog video signal can be suppressed. As a result, it is possible to achieve both low power consumption and video display with a good contrast feeling.

At that time, when the analog video signal is level-converted according to the brightness level of the entire screen, the VT characteristics of the LCD differ depending on the applied voltage range, so two types set according to the brightness level of the entire screen. By performing gamma correction selectively from the LUT, it is possible to display gradations naturally.
As described above, according to the liquid crystal display device 1 according to the present embodiment, it is possible to display an image with a good contrast feeling while reducing power consumption without increasing the bit accuracy of digital signal processing.

The embodiment of the present invention is not limited to the above-described content, and various modifications can be made without departing from the scope of the present invention.
For example, in the content of the above-described embodiment, two types of LUTs for gamma correction are set in the video signal processing unit 2. However, the number of LUTs is not limited to two, and more if the storage capacity is allowed. A type of LUT may be set. In that case, the level conversion of the analog signal output in the LCD driver 4 can be set more finely according to the number of LUTs.

It is a block diagram which shows the structural example of the liquid crystal display device which concerns on one Embodiment of this invention. It is a figure for demonstrating two types of gamma curves set by LUT in a video signal processing part, (a) is VT characteristic of liquid crystal, (b) and (c) are two types set. The gamma curves are shown respectively. It is a wave form diagram which shows the analog video signal by 1H inversion drive. It is a wave form diagram which shows the level conversion process of the analog video signal performed in a LCD driver, (a) is a case where level conversion is not performed, (b) is a case where level conversion is performed on the bright side, (c) Indicates the case where level conversion is performed on the dark side. It is a circuit diagram which shows the circuit structural example inside a LCD panel module.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display device, 2 ... Video signal processing part, 3 ... Timing generator, 4 ... LCD driver, 5 ... LCD panel module.

Claims (5)

Display means for changing the gradation of the video display according to the applied voltage;
Gamma correction means for inputting a video signal and performing gamma correction according to the display characteristics of the display means;
Average video calculation means for calculating an average video signal value that is an average of the video signals in a unit frame;
And a display driving unit that generates an applied voltage to be applied to the display unit based on the video signal that has been gamma corrected by the gamma correction unit and the average video signal value. The display driving means includes
The display device according to claim 1, wherein an applied voltage is limited according to the average video signal value. The gamma correction means includes
A plurality of correction conversion tables set in accordance with display characteristics of the display means;
The display device according to claim 2, wherein gamma correction is performed based on one correction conversion table selected from the plurality of correction conversion tables according to the average video signal value. A display unit display method for changing a gradation of video display according to an applied voltage,
Inputting a video signal;
Calculating an average video signal value that is an average of unit frames of the input video signal;
Performing gamma correction according to the display characteristics of the display unit on the input video signal;
A display method comprising: generating a voltage to be applied to the display unit based on a gamma-corrected digital video signal and the average video signal value. The display method according to claim 4, wherein when the applied voltage is generated, the applied voltage is limited according to the average video signal value.

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