JP3897454B2 - Display drive circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a display driving circuit, and more particularly to a display driving circuit for a matrix display device.
[0002]
[Prior art]
3 and 4 show a conventional matrix type liquid crystal display device. Reference numeral 30 in FIG. 3 denotes a TFT substrate constituting the liquid crystal panel. A TFT 35 is formed on the TFT substrate 30, and its gate is connected to the gate line 33 and its source is connected to the source line 34. A pixel electrode 32 and an auxiliary capacitor 36 are connected to the drain.
[0003]
FIG. 4 is a cross-sectional view of the liquid crystal panel 40, and the liquid crystal 47 is sandwiched between the glass substrate 49 having the transparent electrode 48 and the TFT substrate 30.
[0004]
A column of pixel electrodes 32 and a counter electrode 48 arranged horizontally via the TFT 35 connected to the gate line 33 in FIG. 3 serve as a scanning line for displaying a single horizontal image.
[0005]
In such a matrix type liquid crystal display device, when a television video signal interlaced at 2: 1 of the NTSC system is to be displayed, the following display method is known.
[0006]
The video signal to be displayed on the i-th scanning line in FIG. 5A in the odd field of the NTSC television signal is displayed on the i and i + 1th in FIG. 5B to display the NTSC television. There is a method of displaying the video signal to be displayed at the (i-1) th in FIG. 5 (c) in the even field of the signal at the (i-1) th and ith in the liquid crystal display of FIG. 5 (d).
[0007]
In this case, the drive circuit of the liquid crystal display device displays the liquid crystal display in FIG. 5B with the reverse polarity for each line, such as i-th positive polarity and i + 1-th negative video signal voltage. In FIG. 5D of the liquid crystal display, the i-1th is displayed with a positive polarity and the ith is displayed with a negative polarity video signal voltage with a reverse polarity. That is, in FIGS. 5B and 5D, the video signal voltage polarity is inverted every horizontal synchronization period of the liquid crystal display device 40 and further inverted every time one screen is displayed on the liquid crystal display device 40. This is to prevent a DC voltage from being applied to the liquid crystal for a long time. It is known that when a DC voltage is applied to the liquid crystal for a long time, polarization occurs and the characteristics of the liquid crystal change.
[0008]
FIG. 6 shows the configuration of the drive circuit. In the display method of this apparatus, a line memory is provided to display substantially the same video signal for every two scanning lines of the liquid crystal display device 40. The first line memory 1 and the second line memory 2 correspond to this. The video signal input to the signal switching device 7 is first stored in the first line memory 1 for one line. When this is completed in one horizontal synchronization period of the NTSC television signal, the NTSC television signal is stored. The connection between the video signal input and the line memory is switched by the memory switching signal for each horizontal scanning period, and the next one line starts to be stored in the second line memory 2. At the same time, the output side of the first line memory is connected to the signal polarity control device 3 by the line memory switch 9. From the first line memory 1, a video signal is read out during a period of ½ of one horizontal synchronization period of the NTSC television signal, and a video signal for two lines is supplied to the liquid crystal display device 40. Accordingly, on the liquid crystal display device 40, substantially the same signal is displayed on the two scanning lines from the second scanning line, as in the odd-field liquid crystal display video signal shown in FIG. At this time, the signal polarity control device 3 receives a polarity switching signal that is inverted in one horizontal scanning period of the liquid crystal display device 40 from the doubler 10 that has doubled one horizontal synchronization period of the NTSC television signal. The video signal polarity switching signal generator 73 inverts the polarity of the video signal voltage for each line. After the display of one surface of the liquid crystal display device 40 is made as described above, the connection between the video signal input and the line memory is switched by the memory switching signal for each horizontal synchronization period of the NTSC television signal. As described above, the video signal is read from the second line memory 2 in a half of one horizontal scanning period of one horizontal synchronization period of the NTSC television signal, and the video signal for two lines is liquid crystal. It is supplied to the display device 40. Then, the scanning line designating circuit 5 starts displaying substantially the same signal from the first scanning line to the two scanning lines, as shown by the liquid crystal display video signal in the even field in FIG. The polarity switching signal at this time is supplied to the signal polarity control device 3 so that the video signal voltages of the respective scanning lines are opposite in polarity to those in the first field of the previous field.
[0009]
[Problems to be solved by the invention]
In the driving circuit of the matrix type liquid crystal display device that supplies substantially the same video signal every two lines as described above and changes the display position in the odd field and the even field, different video signals in the odd field and the even field are on the same scanning line. In some cases, the panel is supplied. For this reason, in the liquid crystal display, flicker and burn-in may occur in the normal video signal voltage inversion for each line.
[0010]
[Means for Solving the Problems]
In the display driving circuit of the present invention, different interlace-driven video signals are input to the odd-numbered field and even-numbered field for each of the picture elements arranged in a matrix, and the video signals are substantially the same on the two scanning lines. A display driving circuit for a display device for displaying a signal, wherein a display scanning line position is shifted in the odd field and the even field,
Means for inverting the voltage polarity of the video signal for every two scanning lines of the odd field; means for inverting the voltage polarity of the video signal for every two scanning lines of the even field; and Means for shifting the voltage polarity inversion by one line in a period longer than one field .
[0012]
In the display driving circuit of the present invention, means for inverting the polarity of the video signal voltage every two horizontal scanning periods is provided to reduce the above-described flicker.
[0013]
Further, in the driving circuit of the matrix type display device that supplies substantially the same video signal every two lines as described above and changes the display position in the odd field and the even field, different video signals in the odd field and the even field are on the same scanning line. In some cases, the panel is supplied. For this reason, as shown in FIG. 7, a high DC voltage is applied in the combined period of the odd field and the even field at the boundary where the luminance difference of the NTSC video signal changes greatly. Therefore, this part is burned in or recognized as an afterimage.
[0014]
As a means for avoiding the application of a DC voltage generated by the reversal of the video signal voltage between the fields having different video signal voltages between the fields, as shown in Japanese Patent No. 2577796 of Nakamura et al. It is known to reverse the polarity relationship of the signal voltage. However, in this method, the luminance difference between the fields at the time of inversion is visually recognized due to the relationship between the applied voltage and the luminance of each scanning line of the liquid crystal display device 40 when the video signal is inverted between the fields.
[0015]
In view of the above, in the inversion of the video signal voltage for every two lines, the boundary DC voltage of the NTSC video signal generated by the inversion of the video signal voltage for every two lines between one field shown in FIG. Trying to compensate with a frame. Therefore, the video signal polarity inversion signal is shifted by one line as shown in FIG. 10 before and after the compensation time. As a result, the DC voltage superimposed by the liquid crystal display video signal before compensation is canceled out by the DC voltage superimposed after compensation. By the means for inverting the polarity of the video signal voltage every two horizontal scanning periods and the means for shifting the video signal polarity inversion signal by one line, the direct current component superimposed on the liquid crystal becomes almost zero, preventing burn-in and afterimage phenomenon. be able to.
[0016]
【Example】
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0017]
First, means for inverting the video signal voltage every two lines of each field will be described.
[0018]
FIG. 1 is a drive circuit diagram showing a reference example . In FIG. 1, the same components as those shown in FIG.
[0019]
The video signal input to the signal switching device 7 of FIG. 1 is first stored in the first line memory 1 for one line, and when this is completed in one horizontal synchronization period of the NTSC television signal, the NTSC The connection between the video signal input and the line memory is switched by the memory switching signal for each horizontal synchronization period of the television signal, and the next one line starts to be stored in the second line memory 2. At the same time, the video signal is read from the first line memory 1 in a half of one horizontal scanning period of the NTSC television signal, and the video signal for two lines is supplied to the liquid crystal display device 40. Is done. Accordingly, on the liquid crystal display device 40, substantially the same signal is displayed on the two scanning lines from the second scanning line as in the odd-field liquid crystal display video signal shown in FIG. At this time, the signal polarity control device 3 receives the signal from the video signal polarity switching signal generator 4 that is inverted in one horizontal synchronization period of the NTSC television signal, that is, in the two horizontal scanning periods of the liquid crystal display device 40. Thus, the polarity of the video signal voltage is inverted every two lines. After the display on one surface of the liquid crystal display device 40 is made as described above, the connection between the video signal input and the line memory is switched by the memory switching signal for each horizontal scanning period of the NTSC television signal. The video signal is read from the second line memory 2 in the half of one horizontal scanning period of the NTSC television signal as described above, and the video signal for two lines is supplied to the liquid crystal display device 40. Is done. However, the scanning line designating circuit 5 starts displaying substantially the same signal from the first scanning line to the two scanning lines, as shown by the liquid crystal display video signal in the even field in FIG. At this time, the signal from the video signal polarity switching signal generator 4 is supplied to the signal polarity control device 3 so that the video signal voltages of the respective scanning lines have opposite polarities to those of the first field of the previous field. The
[0020]
FIG. 11 is a cross-sectional view of the liquid crystal display device used in this reference example . The panel size is 0.6 inches and there are 460 scan lines. In the structure of this panel, 100 is a semiconductor substrate, and 103 is a transparent thin film such as SiO _{2 on the} surface of the semiconductor substrate. Reference numeral 104 denotes a spacer which is provided between the SiO ₂ and the glass substrate 105 with a color filter and maintains a gap of about 4.5 μm. 106 is a KN5015LA liquid crystal manufactured by Chisso, which is sandwiched between the SiO ₂ film and the glass substrate 105 with a color filter. Reference numeral 103 denotes a TFT corresponding to 35 in FIG. 3, and reference numeral 101 denotes a peripheral circuit composed of a MOS transistor or the like for driving the TFT.
[0021]
FIG. 12 shows a comparison of flicker levels when the video signal inversion is performed for each line in the odd field and the even field using the liquid crystal display device described above and when the video signal is inverted for every two lines. ing.
[0022]
From this result, it can be seen that the flicker level at the time of inversion of the video signal for every two lines is reduced to a level around 1/2 that at the time of inversion of the video signal for every line.
[0023]
Although the above liquid crystal display device is used in this reference example , the above effect can be applied to other liquid crystal display devices and display devices other than the liquid crystal display device that performs similar video signal inversion.
[0024]
Next, an embodiment of the present invention will be described in which means for inverting the polarity of the video signal voltage for every two scanning lines in the reference example is further added with means for shifting one line at a period longer than one field.
[0025]
Here, an example in which the polarity inversion of the video signal is shifted by one in one frame period will be described.
[0026]
FIG. 2 is a drive circuit diagram showing an embodiment of the present invention. In FIG. 2, the same components as those shown in FIG.
[0027]
In the present embodiment, in addition to the inversion every two scanning lines shown in FIG. 1, a one-line period delay device 12 is provided to shift the polarity inversion of the video signal voltage by one line every frame. The one-line period delay unit 12 receives a timing signal twice as long as the vertical synchronizing signal from the 2N frequency divider 13 (N = 1 here) and operates for each frame. The one-line period delay unit 12 receives a signal that is inverted in one horizontal synchronization period of an NTSC television signal as a processing signal, that is, two horizontal scanning periods of the liquid crystal display device 40, and outputs the signal to the NTSC television. One horizontal synchronization period of the John signal is delayed by one line of the liquid crystal display by the signal from the doubler 10.
[0028]
This signal relationship will be described with reference to the drawings. FIG. 9 is a signal diagram in the case where the video signal voltage inversion is performed for every two lines in the odd and even fields as in FIG. The difference between the two is that the video signal in FIG. 8 is for gradation display and the video signal in FIG. 9 is for repeated display of black and white blocks. FIG. 10 is a diagram in the case where the video signal polarity inversion signals of the odd and even fields in the signal of FIG. 9 are driven by a signal shifted by one line.
[0029]
Here, the liquid crystal display video signal at the NTSC boundary will be examined. The liquid crystal display video signal in the odd field in FIG. 9 immediately changes from a high voltage to a low voltage AC signal following the NTSC video signal input signal at the fall of the NTSC video input signal. In contrast, the even-field liquid crystal display video signal changes from a high voltage to a low voltage AC signal with a delay of one line from the NTSC video signal input signal at the falling edge of the NTSC video input signal. As a result, a positive voltage that is the difference between the odd field and the even field continues to be applied to the boundary unless the frame drive is changed. Next, consider FIG. 10 in which the video signal polarity inversion signal of the odd and even fields in the signal of FIG. 9 is driven by a signal shifted by one line. The relationship between the odd field and even field liquid crystal display video signals in FIG. 10 is the same as in FIG. However, since the video signal polarity inversion signal of FIG. 9 is driven by a signal shifted by one line, the polarity of the liquid crystal display video signal applied to the line next to the falling edge of the NTSC video input signal is an odd number. The field is negative and the even field is positive. As a result, the negative voltage of the difference between the odd field and the even field continues to be applied to this boundary portion.
[0030]
The combination of both frames cancels the DC voltage superimposed on the liquid crystal. This repetition period is determined by a period during which no image sticking or afterimage occurs due to the characteristics of the liquid crystal.
[0031]
The above-described embodiment for shifting the video signal polarity inversion signal by one line is not limited to the case where the voltage polarity of the video signal is inverted every two scanning lines, but the voltage polarity of the video signal is changed every three scanning lines or more. It can also be applied to the case of inversion.
[0032]
Further, the present invention is not limited to the liquid crystal display device, and can be applied to a display device that causes a problem when a DC voltage is applied to the display medium for a long time.
[0033]
【The invention's effect】
As described above, according to the present invention, in the case of displaying an image having a bright and dark luminance boundary or a still image, etc., flicker caused by display with the display scanning line position shifted in the odd field and the even field is displayed. The level can be reduced. Further, it is possible to cancel the DC voltage applied to the liquid crystal superimposed for the above driving, and it is possible to prevent the occurrence of image sticking or an afterimage phenomenon.
[Brief description of the drawings]
FIG. 1 is a block diagram of a drive circuit showing a reference example .
FIG. 2 is a diagram showing an embodiment having means for shifting a video signal polarity inversion signal by one line between frames.
FIG. 3 is a schematic plan view of a conventional liquid crystal panel.
FIG. 4 is a schematic cross-sectional view of a liquid crystal panel.
5A is a diagram of an odd field of an NTSC video signal, FIG. 5B is a diagram of an odd field of a liquid crystal video signal, FIG. 5C is a diagram of an odd field of an NTSC video signal, and FIG. 5D is a liquid crystal video signal. FIG.
FIG. 6 is a block diagram of a conventional circuit for inverting the polarity of a video signal voltage for each line.
FIG. 7 is a timing diagram of polarity inversion for each line of the gradation video signal voltage.
FIG. 8 is a timing chart of polarity inversion for every two lines of the gradation video signal voltage.
FIG. 9 is a timing diagram of polarity inversion for every two lines of a repetitive display video signal voltage of a black and white block.
FIG. 10 is a timing diagram when polarity inversion is performed by shifting one line between frames every two lines of a video signal voltage for repeated display of black and white blocks.
FIG. 11 is a cross-sectional view of a liquid crystal display device used in this example.
12 shows a comparison of flicker levels when the video signal is inverted for each line in the odd field and the even field using the liquid crystal display device of FIG. 11 and when the video signal is inverted for every two lines. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Video signal line memory 2 Video signal line memory 3 Video signal voltage polarity inverter 4 Video signal polarity switching signal generator 5 Scan line designation circuit 6 Image data transfer clock 7 Video input switching device 8 Signal inversion circuit 9 Line memory switching device 10 2 doubler 12 1 line period delay 13 2N frequency divider 30 TFT substrate 32 pixel electrode 33 gate line 34 source line 35 TFT
40 liquid crystal display device 47 liquid crystal 48 counter electrode 49 glass substrate 73 video signal voltage polarity inverter

Claims (1)

Video signals of different interlace drive in an odd and even fields for each of the picture elements arranged in a matrix is input, the video signal is displayed substantially the same signal at two scanning lines, the odd field And a display drive circuit for a display device in which the display scanning line position is shifted in the even field,
Means for inverting the voltage polarity of the video signal for every two scanning lines of the odd field; means for inverting the voltage polarity of the video signal for every two scanning lines of the even field; and Means for shifting voltage polarity reversal by one line over a period longer than one field .

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