JPH03172085A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To improve vertical resolution and to prevent flicker from being generated by inverting a polarity for every two fields concerning a video signal to be supplied to a data signal line and applying the signal to the data signal line while further changing the polarity for each horizontal scanning period as well. CONSTITUTION:A polarity inversion reference signal generating circuit is provided in a timing control circuit 12 so as to output an inversion reference signal to a polarity inversion timing control signal line 17 and to control the operation of a video signal polarity inverting circuit 11. A flip-flop 22 divides the frequency of a horizontal synchronizing signal and outputs a signal inverting the polarity for each horizontal scanning period. Parts 23 and 24 twice divide the frequency of the vertical synchronizing signal and output the signal inverting the polarity for each frame. These two signals are inputted to an exclusive OR gate 25 and the signal inverting the polarity for each horizontal scanning period and each frame can be obtained. Thus, a required data signal can be obtained on a data signal line 7 and a picture can be displayed without flicker.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a display device for a color television receiver using a liquid crystal panel.

Conventional technology A television receiver using an active matrix liquid crystal panel includes a number of scanning signal lines (approximately 220 to 240 in the Japanese domestic standard NTSC system) equal to the number of effective scanning lines for one field of television signals. Display devices using liquid crystal panels have already been developed.

FIG. 6 shows a block diagram of the structure of this liquid crystal television display device. The active matrix liquid crystal panel 5l used in this device has a number corresponding to approximately the number of effective scanning lines in one field, that is, approximately 2 in an NTSC standard television.
It has 20 to 240 (7) scanning signal lines 55 (the number is N), and each line and a plurality of data signal lines 5
57 independent pixels (MXN in total) are formed at the intersections of 4 (M pixels). Each pixel 57 is connected to a data signal line 54 and a running I signal line 55 through a switching element 56, and a voltage is applied to each pixel 57 independently. A segment driver 52 and a scan driver 53 are used to drive this liquid crystal panel/L5l.
The data signal line 54 is connected to the segment driver 52, and the scan code line 55 is connected to the scan driver 5.
A signal voltage is given from 3.

Of these, the scan driver 53 is driven by a shift register that operates in the horizontal scanning period of the video signal, and the segment driver 52 also repeats signal sampling, internal transfer, and output operations in synchronization with the same horizontal scanning period. As a result, when the signal on one scanning signal line 55 is in the selected state, the segment driver 52 controls the M pixels 57 in the I row connected to that signal line 55 for a period of one line. M signal voltages obtained by sampling the video signal are applied through respective data signal lines 54 to drive the liquid crystal. In other words, 1 pixel 57 in one row
Display of video signals for lines is performed. This operation is sequentially repeated N times in the vertical direction for each horizontal scanning period to display one image.

Each of these operations is performed by a timing control circuit 59 that operates based on a synchronization signal input from the synchronization signal line 6l.
is controlled through the driver control signal line 62.

Further, the polarity inversion circuit 58 is a circuit that inverts the polarity of the video signal input from the video signal line 6o for the purpose of AC driving the liquid crystal. , an alternating current data signal is obtained from the segment driver 52, and the liquid crystal can be driven with alternating current. The polarity inversion circuit 58 also controls the timing control a- through the polarity inversion timing control signal line 63.
control circuit 59.

Problems to be Solved by the Invention However, in the case of a liquid crystal display device z that has only a number of scanning signal lines corresponding to the number of effective scanning lines in one field, the CR
The displayed image is slightly different from that of a television receiver using a T-ray tube.

The signals that make up television images are produced according to a method called interlaced scanning. When transmitting a television screen that is made up of many scanning lines, this means that instead of transmitting one scanning line from the top of the screen to the bottom one by one, the scanning lines are first transmitted in odd fields as shown in Figure 7. This method sends half of the total scanning lines (solid lines in the figure) every other line from the top to the bottom of the screen, and sends the remaining half of the scanning lines (broken lines in the figure) to the subsequent even fields. The numbers attached to the left and right sides of the figure represent the order in which the scanning lines are transmitted. Therefore, in a television receiver that receives this signal and reproduces an image, it first creates a coarse screen consisting of half the scanning lines, and then scans it in the second vertical scan to fill in the gaps between the first scanning lines. An image reproduction process is required to complete the entire screen. In fact, television receivers using CRTs perform interlaced scanning.

However, when performing screen playback using a conventional LCD panel,
This liquid crystal panel has only the number of scanning signal lines for 17 yields of video signals, so the signals of the two odd and even fields, which should be reproduced at different positions, are reproduced according to their original positional relationship. Therefore, as shown in FIG. 8, both odd and even field signals are applied to the same display pixel row 62, and the signals of both fields are displayed in a superimposed manner.

Therefore, it has the disadvantage that its vertical resolution is inferior to that of a CRT television receiver that performs interlaced scanning according to the standard.

The present invention was created in view of the above points, and CR
The object of the present invention is to obtain a liquid crystal display device that has a vertical resolution equivalent to or higher than that of a T-TV receiver and is free from flicker.

Means for Solving the Problems The liquid crystal display device of the present invention will be explained. In the present invention,
At least the number of scanning signal lines corresponding to the number of effective scanning lines for one frame of television signal (approximately 440 to 480 in the NTSC system)
A liquid crystal panel driven by an active matrix method is used. In addition, as a means for driving this liquid crystal panel, an activation signal is simultaneously applied to two adjacent scanning signal lines, scanning is performed in units of two scanning signal lines by a register operation, and two scanning signal lines are activated simultaneously. A circuit is used that performs scanning by changing the combination of book scanning signal lines for each field. Furthermore, the polarity of the data signal supplied to the data signal line is changed every horizontal scanning period and also every frame including odd and even fields to eliminate flicker in image display.

Operation The driving of the scanning signal line in the liquid crystal display device of the present invention will be explained using the time chart shown in FIG.

First, in an odd field, the first
A selection signal is simultaneously applied to the th scanning signal line and the second scanning signal line, and a video signal is written to the pixel group corresponding to two rows through the TPT connected to both signal lines. Then, in the next horizontal scanning period, the third and fourth scanning signal lines are selected, and in the next horizontal scanning period, the fifth and sixth scanning signal lines are selected, and thereafter, two lines are selected in order. (Perform scanning) All scanning signal lines are scanned within the period of l7 yield. On the other hand, in even fields, scanning is performed by applying selection signals to two scanning signal lines at a time, but the combination of these two lines is different from that in odd fields.

That is, in the first horizontal scanning period, a selection signal is applied only to the first scanning signal line, in the next horizontal scanning period, the selection signal is applied to the second and third scanning signal lines, and in the next horizontal scanning period, the selection signal is applied to the fourth and third scanning signal lines. With the fifth scanning signal line in the selected state, all the scanning signal lines are scanned within the l field period.

When the scanning signal lines are operated in this manner, an image is displayed on the liquid crystal panel 4l with the positional relationship as shown in FIG.

The number attached to the right side of each pixel row 42 in the panel is the line number of the original video signal, that is, the number of the horizontal scanning period counted from the beginning of the field. In the even number 7 field, the display position is shifted by one pixel row from the odd number field, so that the display is performed as if it were stitched between the rows displayed in the odd number 7 field. In other words, display conforming to the original interlacing becomes possible.

On the other hand, by reversing the polarity of the applied voltage of the video signal supplied to the data signal line every horizontal scanning period, the effect of eliminating flicker in image display on the liquid crystal panel is produced. Generally, it is necessary to apply an alternating current voltage to a liquid crystal, and in a liquid crystal display device (conventional example) for displaying on a television, a voltage with a polarity opposite to the previous voltage is applied every 17 yield, that is, every 1/60 seconds.

At this time, if there is even a slight difference between the positive and negative polarity voltage values, a time fluctuation with a period of 30 Hz appears in the liquid crystal transmitted light. Therefore, if a video signal that maintains a constant polarity during the 17 yield period and inverts the polarity for each field is applied to the liquid crystal panel, the time changes in the applied voltage to each pixel row in the liquid crystal panel will all be in the same phase, and the liquid crystal panel In the transmitted light, the 30 Hz light intensity fluctuation of each pixel is emphasized, resulting in a 7-color pattern. However, if the polarity of the video signal voltage is reversed every horizontal scanning period and applied to the liquid crystal panel, the time change in the voltage applied to each pixel row in the liquid crystal panel will differ from pixel row to pixel row. In this case, the time-varying light intensity fluctuations with the opposite characteristics are canceled out, and flicker is no longer visible.

However, if the scanning signal line driving method according to the present invention is adopted and the video signal voltage polarity of the data signal line is inverted every horizontal scanning period, the liquid crystal of each pixel will be reduced to 17 yield (
It is not possible to drive by reversing the applied voltage polarity every 1/60 second). That is, in the first field 2
If you simultaneously write the same video signal, that is, a signal with the same polarity, to a group of pixels in a row (let's say pixel row 1 and pixel row 2),
In the next field, pixel row l of the pixel group in the two rows
Since the timing of writing a video signal to pixel row 2 is shifted by one horizontal period, video signals of opposite polarity are inevitably written to pixel row 1 and pixel row 2. Therefore, pixel row l
, it is unavoidable that a signal of either positive or negative polarity is written to one of the pixel rows 2 for two consecutive fields.

Therefore, in the present invention, the polarity of the video signal supplied to the data signal line is inverted every two fields (17 frames), and the polarity is also changed every horizontal scanning period, and the video signal is added to the data signal line. In this case, the time transition of the polarity of the signal voltage applied to the pixel liquid crystal of each pixel row is shown in FIG.
Either of the two cases b) will occur. Which of the two cases is selected depends on the structure of the circuit that produces the inverted reference signal used for inverting the video signal.

In the present invention, the time variation of the liquid crystal transmitted light of each pixel is 15
Hz, but when viewing multiple lines at the same time, there are four phases of light intensity fluctuations that differ in phase by 90 degrees, and these cancel each other out.

Therefore, the fundamental frequency of light intensity fluctuation is 60Hz,
7 licker becomes almost invisible.

Embodiment FIG. 1 shows the structure of a liquid crystal display device using a TPT liquid crystal panel, which is an embodiment of the present invention.

A TPT (thin film transistor) 9 is used as a switching element for switching each pixel of the active matrix driven liquid crystal panel, and the gate electrode of each TFT 9 is connected to the scanning signal line 8 and the source electrode to the data signal line 7. Further, the drain electrode of the TFT 9 is connected to the pixel electrode 10.

Data signal line 7, scanning signal line 8, TFT 9. Pixel electrode 1
0 are formed on the TFT side glass substrate 1. The TFT side glass substrate 1 and the counter electrode side glass substrate 2 face each other across a liquid crystal layer (not shown), and a voltage is applied between the pixel electrode 10 and a counter electrode (not shown) formed on the counter electrode pixel glass substrate 2. The state of the liquid crystal changes depending on the
The amount of transmitted light is controlled.

Now, when the voltage level of a certain scanning signal line 8 becomes high enough, the TFT 9 connected to that scanning signal line 8 is turned on, and a current flows between the source electrode and the drain electrode.
Charge is stored in the pixel electrode 10. Thereafter, when the voltage level of the scanning signal line 8 returns to its original low value, the TFT
9 changes to the OFF state, the resistance between the source and drain becomes high, and the charges stored in the pixel electrode 10 are retained as they are. Then, a voltage difference between the pixel electrode potential and the counter signal potential applied to the counter electrode from the counter electrode line 19 is applied to the liquid crystal layer for a period of time until the TFT 9 is turned on again. By repeating this operation sequentially in the vertical direction, T
The image is displayed on the PT liquid crystal panel.

In order to drive the scanning signal line 8 around the liquid crystal panel, the first
As shown in FIG. 3B, the scanning signal lines 8 are taken out alternately one by one from the left and right ends, and the scanning signal lines 8 are driven by two systems of scan driver circuits 5.6. The scan driver circuits 5 and 6 each output signals according to a simple shift register operation. The scan driver 6 that drives the numbered scan signal line 8 is an even driver. These two drivers are operated simultaneously in one of the two fields, 7 yields, and in the other 7 fields, the even-numbered driver is activated one horizontal scanning period later than the odd-numbered driver. In this way, the signal voltage applied to the scanning signal line 8 in the liquid crystal panel becomes as shown in FIG. 3, and the liquid crystal panel is scanned.

Regarding the connection between the data signal line 7 and the segment driver 3.4, it is possible to take out the data signal line 7 one by one on both the upper and lower sides and provide the segment driver 3.4 on both the upper and lower sides as shown in FIG. However, all the signal lines may be taken out to one side and the segment drivers 3.4 may be provided only on one side.

The segment driver 3.4 generates signal samples in synchronization with the horizontal scanning period, similar to conventional liquid crystal display devices. It may be one that repeats internal transfer and output operations. The above control is performed by the timing control circuit 12 through the segment driver 3.4 and the scan driver control signal line 15 and through the scan driver control signal line 16, respectively.

FIG. 2 is an example of a reference signal generation circuit for inverting the polarity of a data signal. This circuit is included in the timing control circuit 12 of FIG. 1 and outputs an inversion reference signal to the polarity inversion timing control signal line 17 to control the operation of the video signal polarity inversion circuit 1l. The synchronization separation circuit 21 receives the composite synchronization signal line (group) 14 as an input,
A horizontal synchronizing signal is output to the horizontal synchronizing signal line 26, a vertical synchronizing signal is output to the vertical synchronizing signal line 27, and a field signal for determining odd and even fields is output to the field signal line 28. 7
The flip-7log 22 divides the horizontal synchronization signal and outputs a signal whose polarity is inverted every horizontal scanning period, and the flip-7log 23 and 24 divide the vertical synchronization signal twice.
Outputs a signal whose polarity is inverted every frame. This 2
By inputting the two signals to the exclusive OR gate 25, a signal that is inverted every l horizontal scanning period and l frame is obtained. This signal causes the video signal polarity inversion circuit 11 to invert the video signal input from the RGB signal lines (group) 13, and liquid crystal application RGB signal lines (group) 18
output to segment driver 3.4 through. As a result, a required data signal is obtained on the data signal line 7, and flicker-free video display becomes possible.

Effects of the Invention As described above, according to the liquid crystal display device of the present invention, when displaying a television image signal produced in accordance with the interlaced scanning method, a high-definition liquid crystal television display with excellent vertical resolution and no flicker can be achieved. can be realized.

[Brief explanation of the drawing]

FIG. 1 is a structural diagram of a TPT active matrix liquid crystal display device according to an embodiment of the present invention, in which (a) is an overall view, (b) is an explanatory diagram showing how to connect scanning signal lines and scan drivers, (c) is a structural diagram of the inside of the TFT side glass substrate. Figure 2 shows a configuration of the liquid crystal display device shown in Figure 1. 2 is a diagram illustrating a configuration of a polarity inversion reference signal generation circuit used for data signal polarity inversion among the elements to be used. FIG. FIG. 3 is an output signal time chart of the scan driver of the liquid crystal display device according to the present invention, in which (a) is a time chart for an odd number 7 field, and (b) is a time chart for an even number 7 yield. FIG. 4 is an explanatory diagram showing video signals and their display positions in the liquid crystal display device according to the present invention, where Od indicates odd number 7 yields and Ev indicates even number 7 yields. FIG. M5 is an explanatory diagram showing the time transition of the polarity of the voltage applied to the liquid crystal in the liquid crystal display device according to the present invention. FIG. 6 is a block diagram of a conventional liquid crystal display device.
(a) is an overall view, and (b) is a II precept view of the liquid crystal panel. FIG. 7 is an explanatory diagram of the interlaced scanning method, in which the solid lines indicate the scanning signal lines of the odd 7-yield fields, and the broken lines indicate the scanning signal lines of the even-numbered fields. FIG. 8 is an explanatory diagram showing video signals and their display positions in a conventional liquid crystal display device, where Od is an odd field, E
v is an even field. l...TFT side glass substrate, 2... Counter electrode side glass substrate, 3.4... Segment driver, 5, 6...
・Scan driver, 7...Data signal line, 8...
Scanning signal line, 9...TPT (thin film transistor),
10... Pixel electrode, l1... Video signal polarity inversion circuit, l2... Timing control circuit, 13...
RGB signal line (group), 14... composite synchronization signal line, l5
...Segment driver control signal line (group), l6...
・Scan driver control signal line (group), l7...Polarity reversal timing control signal line, l8...Liquid crystal application RGB
Signal line (group), 19... Opposite signal line, 2l...
Synchronization separation circuit, 22.23.24...Flip-flop, 25...Exclusive OR gate, 26...Horizontal synchronization signal line, 27...Vertical synchronization signal line, 28...Field signal line , 41.71...Liquid crystal panel display section, 4
2.72... Pixel row, 51... Liquid crystal panel, 52... Segment driver, 53... Scan driver, 54... Data signal line, 55... Scanning signal line, 56... switching element, 57... pixel, 58... polarity inversion circuit, 59.
...Timing control circuit, 60...Video signal line, 6l...Synchronization signal line, 62...Driver control signal line, 63...Polarity inversion timing control signal line,

Claims (1)

[Scope of Claims] In a liquid crystal display device whose display is driven by an active matrix method in which pixels are switched by scanning signal lines and data signal lines, the scanning signal lines have a number corresponding to the number of effective scanning lines for one frame of a television signal. and a scanning signal line drive circuit that simultaneously applies an activation signal to the two adjacent scanning signal lines and performs scanning in units of two scanning signal lines by shift register operation. scanning signal line selection means for changing the combination of scanning signal lines for each field; and scanning signal line selection means for changing the combination of scanning signal lines for each field; A liquid crystal display device comprising: a data signal line drive circuit that supplies data signal lines.