JP3684611B2 - Liquid crystal drive device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a liquid crystal drive device, and more particularly, for example, to a liquid crystal drive device suitable for drive control of an active matrix LCD, in which a video input signal is inverted in polarity and a transistor for each pixel is AC driven.
[0002]
[Prior art]
Conventionally, when gradation display is performed using a liquid crystal display panel using TN (Twisted Nematic) liquid crystal, for example, the voltage applied to the liquid crystal is controlled according to the gradation data to be displayed. The control of the applied voltage is to control the effective voltage applied to the liquid crystal by changing the voltage application time or the applied voltage value according to the gradation data.
[0003]
In the case of multi-tone display by controlling the effective value of the applied voltage (Vop), when the voltage is gradually applied to the liquid crystal, the alignment vector of the liquid crystal molecules starts to rise so as to align in the electric field direction.
[0004]
FIG. 4 is a diagram showing the relationship between the effective voltage applied to the TN liquid crystal and the luminance. As shown in FIG. 4, when the threshold voltage (VOFF) is exceeded, the optical rotation is suddenly lost, the transmitted light is blocked, and a black display appears. Further, when the applied voltage is further increased, the luminance gradually increases, and by applying an effective voltage equal to or higher than the saturation voltage (VON), a good display with high contrast can be obtained. In the case of performing a gray scale display, by selecting a voltage application time obtained by dividing the threshold voltage (VOFF) to the saturation voltage (VON) (T1) into eight equal parts in the TN liquid crystal characteristic diagram of FIG. Each gradation can be displayed. Thus, in the conventional multi-gradation display, the voltage averaging method is used to control (PWM) the pulse width of the liquid crystal driving voltage pulse corresponding to the number of gradations of the video signal. Specifically, the pulse width of the liquid crystal drive pulse corresponding to the number of gradations is preset using the gradation control circuit 1 described below.
[0005]
Further, in a conventional liquid crystal driving device for driving an active matrix LCD, a video input signal input to each signal line is transmitted for one horizontal period in a TFT (Thin Film Transistor) connected to each intersection of a scanning line and a signal line. By performing AC driving in which the polarity is inverted every time or every frame, the DC component remains on the pixel electrode.
[0006]
[Problems to be solved by the invention]
However, in such a liquid crystal driving device for driving the conventional active matrix LCD, AC driving is performed to invert the polarity of the video input signal input to each signal line every horizontal period or every frame. This prevents the DC component from remaining on the pixel electrode, but the polarity inversion period is controlled so as to invert the polarity at equal intervals regardless of the gradation number data of the video input signal. When the inversion period is lengthened, flicker is generated, and when the polarity inversion period is shortened, power consumption is increased.
[0007]
An object of the present invention is to provide a liquid crystal driving device that variably controls the polarity inversion period when alternating driving a TFT according to the change in the number of gradations of a video input signal, thereby preventing flicker and reducing power consumption. Is to provide.
[0008]
[Means for Solving the Problems]
According to the first aspect of the present invention, the scanning line driving circuit scans each scanning line at a scanning timing according to the video input signal, and the video line input circuit inputs the video input signal to the signal line. In a liquid crystal driving device that alternately reverses the polarity of positive and negative video signals every predetermined period, the polarity inversion period of the video input signal supplied to the signal line differs depending on the magnitude of the video input signal. so that, by quickly polarity inversion cycle of a change amount steep region of luminance, providing the polarity inversion period control means for controlling the slow to so that the period of the polarity inversion at the variation is gentle region of luminance It is characterized by.
[0009]
In this case, as described in claim 2, the polarity inversion cycle control means stores inversion cycle setting for storing setting data for setting the polarity inversion cycle and the drive voltage in accordance with the number of gradations of the video input signal. It is effective to provide means.
[0010]
[Action]
According to the first aspect of the present invention, the scanning line driving circuit scans each scanning line at the scanning timing corresponding to the video input signal, and the video input signal input to each signal line is signal-driven. In a liquid crystal driving apparatus that alternately reverses the polarity of positive and negative video signals every predetermined period by a circuit, the polarity inversion period control means supplies the signal lines with the magnitude of the video input signal. with different polarity inversion period of the video input signal, and quickly the polarity inversion cycle of a change amount steep region of the luminance is controlled to slow to so that the period of the polarity inversion at the variation is gentle region of luminance The
[0011]
Therefore, the polarity inversion period when transferring display data with a large amount of luminance change is optimized (not too long) compared to the control with a constant polarity inversion period regardless of the conventional gradation, and flicker is generated. It is possible to prevent power consumption and to reduce power consumption by optimizing (not shortening too much) the period for changing the voltage level when transferring display data with a small amount of change in luminance.
[0012]
According to invention of Claim 2,
The polarity inversion period control means includes inversion period setting means for storing setting data for setting the polarity inversion period and the drive voltage in accordance with the number of gradations of the video input signal, and therefore corresponds to the number of gradations to be displayed. Thus, the polarity inversion period can be easily set.
[0013]
【Example】
Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS.
1 to 3 are diagrams showing an embodiment of a liquid crystal display device to which the present invention is applied.
[0014]
First, the configuration will be described.
FIG. 1 is a diagram showing a main block configuration of a liquid crystal display device 1 of the present embodiment.
In FIG. 1, a liquid crystal display device 1 includes a signal source 2, an A / D conversion circuit 3, a data conversion circuit 4, a control circuit 5, an interface circuit 6, a scanning side driving circuit 7, a signal side driving circuit 8, and an active matrix type. The liquid crystal display panel 9 is used.
[0015]
The signal source 2 outputs the video signal D1 obtained by separating the synchronization signal from the video signal including the synchronization signal input from the outside to the A / D conversion circuit 3, and outputs the video signal S1 including the synchronization signal to the control circuit 5. .
[0016]
The A / D conversion circuit 3 performs A / D (analog / digital) conversion (sampling) on the video signal D1 input from the signal source 2 based on the timing signal S2 input from the control circuit 5, and the digital video signal D2 is output to the data conversion circuit 4. The data conversion circuit 4 converts the digital video signal D2 input from the A / D conversion circuit 3 into a data format that can be held by the signal side drive circuit 8, and outputs the digital video data D3 to the signal side drive circuit 8. .
[0017]
That is, for example, the data conversion circuit 4 sequentially reads the digital video signal D2 input from the A / D conversion circuit 3 by the timing signal S2 input from the control circuit 5, and reads the digital video signal D2 for one line. Thereafter, a gradation signal is generated in accordance with the digital video signal D2, and is output to the signal side drive circuit 8 as display data D3.
[0018]
Further, in the data conversion circuit 4 of this embodiment, in order to generate the display data D3, a data conversion table as shown in FIG. 2 is stored, and the input digital video signal D2 is stored by this data conversion table. The polarity inversion period and the voltage level when AC driving the corresponding eight gradation data are set, and the gradation is determined based on this data conversion table by the count signal S3 input from the control circuit 5 every horizontal period. A signal is generated and the display data D3 is output to the signal side drive circuit 8.
[0019]
The data conversion table of FIG. 2 is the setting content when the number of gradations of the video displayed on the LCD 9 is “8”, and the gradations “0” to “7” of the input digital video signal D2 are 8 The amplitude of the setting voltage for AC driving for each gradation is set to 16 levels from “0” to “15”, and the polarity inversion period is input from the control circuit 5 every horizontal period. The count signal S3 is set so that the above or below a predetermined gradation is different from the other gradations.
[0020]
In the case of this embodiment, the polarity inversion period is set such that the polarity is inverted every two horizontal periods when the gradation of the digital video signal is “0”, “1” and “6”, “7” When the gradation is “2” to “5”, the polarity is inverted every horizontal period. The basis for setting the polarity inversion period is based on the characteristic curve of the liquid crystal of this embodiment shown in FIG.
[0021]
That is, in FIG. 3, the vertical axis indicates the luminance of the liquid crystal, and the horizontal axis indicates the effective value of the applied voltage (Vop). The luminance is near the threshold voltage (VOFF) and slightly before the saturation voltage (VON). Changes gradually, and the amount of change in brightness is steep in the middle part. Therefore, as shown in FIG. 3, when this characteristic curve is divided equally into 8 gradations, in this embodiment, the gradations “0” and “1” in which the amount of change in luminance is moderate are shown in FIG. For “6” and “7”, the AC drive cycle is set to be long (for example, at gradation 0, the voltage levels “0” and “15” are inverted every two horizontal cycles), and the amount of change in luminance is steep. In the gradations “2” to “5”, the AC drive cycle is set to be short (for example, in the gradation 2, the voltage levels “2” and “13” are inverted every horizontal cycle).
[0022]
In this way, flicker can be suppressed by increasing the polarity inversion period in a region where the luminance change amount is steep, and the region in which the luminance change amount is gentle has a high drive voltage. Power consumption can be reduced by delaying the polarity reversal period at.
[0023]
The control circuit 5 generates a timing signal S2 based on the synchronization signal included in the video signal S1 input from the signal source 2 and outputs the timing signal S2 to the A / D conversion circuit 3, and from the synchronization signal, the horizontal synchronization signal S4 and The vertical synchronization signal S5 is separated and output to the interface circuit 6. The control circuit 5 has a built-in counter that counts up every horizontal period from the synchronization signal separated from the video signal, and outputs the count signal S3 to the data conversion circuit 4.
[0024]
The interface circuit 6 generates a scanning side display control signal S6 and a signal side display control signal S7 based on the horizontal synchronizing signal S4 and the vertical synchronizing signal S5 input from the control circuit 5, and scans the scanning side display control signal S6. In addition to outputting to the side drive circuit 7, the signal side display control signal S 7 is output to the signal side drive circuit 8.
[0025]
The scanning side driving circuit 7 sequentially drives and drives a predetermined number of scanning lines in the active matrix liquid crystal display panel 9 based on the scanning side display control signal S6 input from the interface circuit 6. Further, the signal side drive circuit 8 sequentially selects a predetermined number of signal lines in the active matrix liquid crystal display panel 9 based on the signal side display control signal S 7 input from the interface circuit 6, and from the data conversion circuit 4. The input display data D3 is sequentially transferred to the selected signal line.
[0026]
In the active matrix liquid crystal display panel 9, liquid crystal is sealed between a pair of transparent glass substrates, and a plurality of scanning lines and signal lines are formed in a matrix on opposite surfaces of the pair of transparent glass substrates. A display dot made up of the TFT 10 and the liquid crystal 11 connected to the TFT 10 is formed at each intersection between the scanning line and the signal line, and the scanning line and the signal line are sequentially switched by driving control by the scanning side driving circuit 7 and the signal side driving circuit 8. The charge is accumulated in the liquid crystal 11 at the intersections that are selected and driven sequentially, based on the display data (gradation data), but characters and images based on the display data are displayed in gradation.
[0027]
Next, the operation of this embodiment will be described.
When a main power supply (not shown) of the liquid crystal display device 1 of this embodiment is turned on, a power supply voltage is supplied to each block shown in FIG. 1 by a power supply circuit (not shown), and the operation of each block is started.
[0028]
When the output of the video signal S1 including the synchronization signal from the signal source 2 to the control circuit 5 is started and the output of the video signal D1 separated from the synchronization signal to the A / D conversion circuit 3 is started, In the control circuit 5, a synchronization signal is separated from the input video signal S1, a timing signal S2 is generated based on the synchronization signal and output to the A / D conversion circuit 3, and a horizontal synchronization signal is generated from the synchronization signal. S4 and the vertical synchronization signal S5 are separated and output to the interface circuit 6.
[0029]
In the control circuit 5, a counter built in every horizontal period is counted up from the synchronization signal separated from the video signal S 1, and the count signal S 3 is output to the data conversion circuit 4.
[0030]
In the A / D conversion circuit 3, the video signal D 1 is A / D converted based on the timing signal S 2 input from the control circuit 5, and the A / D converted digital video signal D 2 is converted into the data conversion circuit 4. Is output.
[0031]
Then, in the data conversion circuit 4, the digital video signal D2 input from the A / D conversion circuit 3 is sequentially read for each line by the timing signal S2 input from the control circuit 5, and according to the digital video signal D2 Tones are generated. At this time, according to the data conversion table shown in FIG. 2, the voltage amplitude (“0” to “15” stage) for AC driving is set by the number of gradations corresponding to the digital video signal D2, and the number of gradations is set. In response to the count signal S3 input from the control circuit 5, the set voltage is switched at the set polarity inversion period, and is output to the signal side drive circuit 8 as display data D3.
[0032]
In the interface circuit 6, a scanning side display control signal S6 and a signal side display control signal S7 are generated from the horizontal synchronizing signal S4 and the vertical synchronizing signal S5 input from the control circuit 5, and the scanning side display control signal S6 is generated. In addition to being output to the scanning side driving circuit 7, the signal side display control signal S 7 is output to the signal side driving circuit 8.
[0033]
Then, the scanning side driving circuit 7 sequentially scans and drives a predetermined number of scanning lines in the active matrix liquid crystal display panel 9 based on the scanning side display control signal S6 input from the interface circuit 6 to drive the signal side. The circuit 8 sequentially selects a predetermined number of signal lines in the active matrix liquid crystal display panel 9 based on the signal-side display control signal S 7 input from the interface circuit 6, and displays data input from the data conversion circuit 4. By transferring D3 to the sequentially selected signal lines, in the active matrix liquid crystal display panel 9, charges are accumulated in the liquid crystal at the sequentially selected intersections based on the display data (gradation data). The characters and images based on them are displayed in gradation.
[0034]
As described above, in the liquid crystal display device 1 of the present embodiment, the polarity reversal period when the TFT 10 in the active matrix type liquid crystal display panel 9 is AC driven in the data conversion circuit 4 is the same as that of the active matrix type liquid crystal display panel 9. Since the gradation control of the liquid crystal characteristic curve is variably controlled for each gradation, that is, in gradations “0”, “1” and “6”, “7” where the luminance change amount is gradual. The AC driving cycle is set to be long (for example, polarity is inverted every two horizontal cycles), and the AC driving cycle is shortened (for example, one horizontal) for the gradations “2” to “5” where the change in luminance is steep. Since the polarity is inverted every cycle), it is possible to prevent the occurrence of flicker when transferring display data with a large amount of luminance change compared to the control with a constant polarity inversion cycle regardless of the conventional gradation, Brightness change The amount smaller display data thereby reducing power consumption and slow changes in the voltage level at the time of transfer.
[0035]
As a result, it is possible to improve the display capability and reduce the power consumption of the liquid crystal display device 1 employing the AC driving method.
In the above embodiment, the case where the polarity inversion period is controlled according to the display data in the display data of 8 gradations has been described. However, in the display data of other gradation numbers, for example, 16 gradations or 24 gradations. Similarly, it is of course possible to variably control the polarity inversion period. That is, it is possible to easily cope with this by changing the setting contents of the data conversion table shown in FIG. 2 optimally in accordance with the required number of display gradations.
[0036]
Further, the present invention is not limited to the active matrix type and can be applied to a simple matrix type liquid crystal display panel. Furthermore, in the above embodiment, the case where the polarity inversion period is controlled according to the number of gradations has been described. However, in recent years, the liquid crystal birefringence characteristics are used without using a color filter, and the liquid crystal driving voltage is controlled. A liquid crystal display panel for color display has been developed, but it can be applied to such a liquid crystal display panel.
[0037]
【The invention's effect】
According to the first aspect of the present invention, the polarity reversal cycle when transferring display data having a large luminance change amount is optimized (not too long) compared to the control with a constant polarity reversal cycle regardless of the conventional gradation. In addition, the occurrence of flicker can be prevented, and the cycle for changing the voltage level when transferring display data with a small luminance change is optimized (not too short) to reduce power consumption. be able to.
[0038]
According to the second aspect of the present invention, it is possible to easily set the polarity inversion period corresponding to the number of gradations to be displayed.
[Brief description of the drawings]
FIG. 1 is a block diagram of a main part of a liquid crystal display device to which the present invention is applied.
FIG. 2 is a diagram showing an example of a data conversion table stored in the data conversion circuit of FIG. 1;
FIG. 3 is a diagram illustrating a characteristic curve of liquid crystal of the LCD according to the present embodiment.
FIG. 4 is a diagram showing a characteristic curve of a conventional TN liquid crystal.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Liquid crystal display device 2 Signal source 3 A / D conversion circuit 4 Data conversion circuit 5 Control circuit 6 Interface circuit 7 Scanning side drive circuit 8 Signal side drive circuit 9 Active matrix type liquid crystal display panel

Claims (2)

The scanning line driving circuit scans each scanning line at a scanning timing according to the video input signal, and the video line input circuit inputs the video input signal to the signal line driving circuit to generate positive and negative video signals. In the liquid crystal driving device that alternately displays the polarity reversed every predetermined period,
Depending on the magnitude of the video input signal, the polarity inversion period of the video input signal supplied to the signal line is made different, the polarity inversion period in the region where the luminance change amount is steep, and the luminance change amount is slow. a liquid crystal driving device which is characterized in that the provided polarity inversion period control means for controlling the period of the polarity inversion slow to so that in a region.   2. The polarity inversion cycle control means comprises inversion cycle setting means for storing setting data for setting the polarity inversion cycle and drive voltage in accordance with the number of gradations of a video input signal. Liquid crystal drive device.

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