WO1995000874A1

WO1995000874A1 - Liquid crystal matrix display device and method of driving the same

Info

Publication number: WO1995000874A1
Application number: PCT/JP1993/000820
Authority: WO
Inventors: Masaaki Kitajima; Yasuyuki Mishima; Makoto Tsumura
Original assignee: Hitachi, Ltd.
Priority date: 1993-06-18
Filing date: 1993-06-18
Publication date: 1995-01-05
Also published as: KR950001375A

Abstract

The distortion state of waveforms of a scanning voltage and a common voltage applied to scanning lines and a common electrode of a liquid crystal matrix panel is detected to correct the external voltage to the liquid crystal matrix panel. Since fluctuation of brightness and a contrast ratio by a display pattern can be reduced, high quality color display can be accomplished. Deterioration of picture quality resulting from ON-state resistance of a driving LSI and a connection resistance between a circuit and the panel can also be prevented. Further, color display driving of a large and high precision panel becomes easy and moreover, the reduction of the size and simplification of the apparatus can be accomplished.

Description

Specification

Liquid crystal matrix display device and driving method thereof

Technical field

The present invention relates to a liquid crystal matrix display device and a driving method thereof, and in particular, to a liquid crystal matrix display device for realizing high-quality display realizing uniform brightness and contrast. The present invention relates to a device and a driving method thereof.

Background art

A liquid crystal active matrix display device that displays a surface image by driving a liquid crystal by a TFT (Thin Film Transistor) or MOS transistor is thinner than other flat displays. In recent years, it has become widely used for OA equipment such as personal computers because it can realize color display with light weight.

Display image quality is improving due to improvements in liquid crystal materials and TFT manufacturing processes.However, as panels become larger and have higher definition, uniform display of brightness and contrast ratio can be achieved. It will be difficult. Also, depending on the contents to be displayed, the distortion of the voltage waveform in the panel increases. Due to the distortion of the voltage waveform, there are problems such as uneven brightness in the panel surface and a decrease in contrast ratio.

In order to solve such a problem, Japanese Patent Application Laid-Open No. 60-14032 and Japanese Patent Application Laid-Open No. 62-21772 Drive system is adopted.

However, in such a method, the circuit scale of the control circuit becomes large, so that not only is it difficult to reduce the thickness, but also the power consumption is increased, and the price is also increased. In addition, since the parasitic capacitance between the TFT terminals differs from panel to panel, it was difficult to completely compensate for variations in brightness.

Disclosure of the invention

An object of the present invention is to reduce the size and simplification of a drive circuit that corrects variations in brightness and contrast ratio in the plane of a panel, and to make circuit constants such as parasitic capacitance in a panel fluctuate. Another object of the present invention is to realize a drive system which is not affected by this.

To achieve the above object, in a liquid crystal matrix panel using the following means, the state of the scanning voltage applied to the scanning line or the common electrode before the scanning line to be driven, and the waveform of the common voltage The voltage input to the external circuit panel is corrected based on the detection amount obtained by the detection means.

In addition, in order to correct the voltage input to all the scanning lines, the current flowing through each scanning line is detected, and the scanning voltage is corrected according to the detected amount according to the line-sequential timing.

When the current flowing through the scanning line, the signal line, and the common electrode is detected individually or in any combination, the state of the waveform of the scanning voltage of the driving scanning line is determined based on a preset correction amount. Is corrected.

In addition, the voltage waveform distortion caused by the current flowing into and out of the scanning line, signal line, common electrode, and common line of the storage capacitor is driven by applying the opposite voltage by predictive control by itself or in any combination. The state of the waveform of the scanning voltage of the scanning line is corrected.

With the above-described method, it is possible to prevent the display pattern, that is, the waveform distortion of the scanning voltage and the common voltage depending on the voltage level of the signal voltage. In particular, by correcting the waveform distortion of the scanning voltage, the voltage written to the pixel depends on the display pattern because the waveform distortion of the scanning line due to the storage capacitance and the parasitic capacitance between the pixel and the scanning line can be reduced. do not do. As a result, it is possible to prevent the dependence of the brightness and contrast ratio on the display pattern, thereby realizing a high-quality display. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic diagram of a display device according to the present invention.

Figure 2 shows the distortion of the scanning voltage waveform.

Figure 3 shows the configuration of one pixel of a liquid crystal panel.

FIG. 4 is a configuration of an embodiment for correcting the waveform distortion of the scanning voltage. FIG. 5 is a configuration diagram of a circuit for detecting a current flowing in the scanning line. FIG. 6 is a configuration diagram of a circuit for detecting a current flowing in the scanning line. 7 is a configuration diagram of another embodiment for correcting waveform distortion of a scanning voltage. FIG. 8 is a configuration diagram of an embodiment for correcting a common voltage.

FIG. 9 is a diagram showing waveforms at various points in FIG.

FIG. 10 is a configuration diagram of another embodiment of the present invention.

FIG. 11 is a configuration diagram of another embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 schematically shows the configuration of a liquid crystal display device according to the present invention. The device includes a liquid crystal panel 1, scanning voltage generating means 7, scanning side load detecting means 8, signal voltage generating means 9, common voltage generating means 11, It comprises common-side load detection means 12 and an image signal / control signal generation circuit 13. The liquid crystal panel 1 includes a TFT 2, liquid crystal pixels 3, a common electrode 4, a signal line 5, and a scanning line 6. The details of the scanning-side load detecting means 8 and the common-side load detecting means 12 will be described later. In the embodiment of the present invention, the above two load detecting means may be simultaneously included in the liquid crystal display device. It may be used alone or in an appropriate combination. The configuration is not particularly limited. The purpose of the embodiment shown in FIG. 1 is to prevent the degradation of the image quality peculiar to driving the liquid crystal by TFT. Therefore, before describing the embodiment of FIG. 1, the operation of the TFT and the deterioration of the image quality peculiar to the TFT driving will be described.

Figure 2 shows the scan voltages VGK and VGK + applied to the Kth scan line 6 and the K eleventh scan line 6 'of the liquid crystal panel. 1 and each voltage waveform of the signal voltage VD applied to a certain signal line 5 are shown. FIG. 3 shows a configuration of one pixel of the liquid crystal panel 1. The storage capacitor 14 is also formed between the output terminal S of the TFT and the scanning line 6. Note that the same reference numerals are used for the same parts as in FIG.

When the scanning voltage VGK + 1 becomes a high level VGH, TFT2 becomes conductive, and the signal voltage VD is written to the storage capacitor 14 and the liquid crystal pixel 3 through TFT2. Next, when the scanning voltage V G K + 1 becomes the low level V G L, the TFT 2 becomes non-conductive, and the written signal voltage is maintained as it is. These operations are generally repeated 60 times with a period of about 1 second.

In the figure, the waveform shown by the dotted line is an ideal scanning voltage waveform, but the waveform is a solid line due to the output resistance of the scanning voltage generating means 7, the connection resistance between the scanning voltage generating means 7 and the liquid crystal panel 1, and the like. Distorted like. Note that the waveform distortion is schematically shown. The waveform distortions (a) and (b) of the scanning voltage VGK shown in the figure are mainly caused by the parasitic capacitance between the scanning line and the signal line and the resistance described above. The waveform distortion (c) is caused by a current flowing into the scanning line 6 immediately before the driving scanning line 6 ′ via the storage capacitor CSTG 14 when the TFT 2 is turned on. When the polarity of the signal voltage VD is inverted, the polarity of the waveform distortion (c) is also inverted. Finally, the waveform distortion (d) is When the voltage VGK11 changes to the low level voltage VGL, the current is drawn from the scanning line 6 'via the parasitic capacitance and the storage capacitance CSTG between the S and G terminals of the TFT. .

At this point, if the waveform distortion (c) continues until the scanning voltage VGK + 1 falls near VGL, the voltage applied to the liquid crystal pixel 3 eventually fluctuates, and the brightness / contrast ratio fluctuates. Occurs. This waveform distortion changes depending on the amplitude value of the signal voltage, that is, the display pattern. Further, the waveform (d) also causes the above-described deterioration in image quality. Furthermore, since current also flows to the common electrode 4 via the liquid crystal pixels 3, distortion occurs in the voltage of the common electrode, that is, the common voltage. The waveform distortion of the common voltage also occurs due to the cutting due to the parasitic capacitance between the common electrode and the signal line. This waveform distortion causes image quality degradation similar to that described above. The feature of the present invention is that the deterioration of image quality is prevented by correcting such waveform distortion.

FIG. 4 shows a more specific embodiment relating to the correction of the scanning voltage by the scanning voltage generating means 7 and the scanning load detecting means 8 which are the correction circuits on the scanning side in the embodiment of FIG. This circuit corrects the distortions (c) and (d) of the waveform distortion shown in Fig. 2.

The scanning voltage generating means 7 comprises switch circuits 7a to 7e. To achieve. Each switch circuit has three input terminals, a, b, and c, and an output terminal, and is controlled by a control circuit (not shown) that controls the opening and closing of the switches. The a input terminal is connected to the power supply 31 that supplies the high-level voltage VGH, and the b input terminal is connected to the power supply 30 that supplies the low-level voltage VGL. The scanning load detecting means 8 shown in FIG. 1 includes a load current detecting means 28 and a scanning off voltage correcting means 32. The c input terminal is connected to the load current detecting means 28.

The liquid crystal panel 20 includes scanning lines 21 to 25, a signal line 26, a TFT 2, a liquid crystal pixel 3, a common electrode 4, and a storage capacitor 14. The liquid crystal panel 20 is driven by line-sequential driving, but details are omitted. Here, only the description relating to the present invention will be described.

The case where the scanning line 23 is driven as shown in the figure, that is, the case where the TFT connected to the scanning line 23 is turned on will be described as an example. At this time, the switch circuit 7c selects the scan-on voltage (high-level voltage) VGH input to the a input terminal. As a result, the TFTs connected to the scanning lines 23 are simultaneously turned on, and the signal voltage VD is simultaneously written to the storage capacitors 14 and the liquid crystal pixels 3. The switch circuit 7b connected to the scanning line 22 to which this storage capacitor is connected selects the c input terminal and flows to the scanning line 22. Output to the current detection line 29. Other switch circuits select the b input terminals so that the TFTs are turned off, and the scan off voltage (low-level voltage) VGL is applied to the scan lines connected to them. That is, the feature of the present embodiment is that the current flowing through the scanning line immediately before the driven scanning line can be detected so that the current flowing through the storage capacitor can be detected in line-sequential timing. It is to detect. As a matter of course, this operation is performed sequentially from the first scanning line of the liquid crystal panel to the subsequent scanning lines.

The detected current is converted to a voltage signal V CMP. This signal is the correction signal. This correction signal is input to the scan-off voltage correction circuit 32, which corrects the scan voltage applied to the liquid crystal panel so that the distortion does not occur. That is, the scan-off voltage correction circuit 32 inputs the correction signal VCMP and the scan-off voltage VGL as the reference voltage, outputs a scan voltage without distortion, and detects the current through the load current detection circuit 29. Apply to line 29.

FIG. 5 shows a specific configuration example of the load current detection means 28 in FIG. In the embodiment of FIG. 5, the current from the current detection line 29 is supplied to one input terminal (one input) of the operational amplifier 36, and the current detection circuit composed of the operational amplifier 36 and the resistor 35 supplies the current to the correction voltage VCMP. Convert. Then, the voltage VCMP and the scan-off voltage VGL are applied to the scan-off voltage correction circuit 3 2 The scan-off voltage correction circuit outputs the corrected voltages VVGL and VCMP, which depend on VGL and VCMP, and inputs them to the other terminal (ten inputs) of the operational amplifier. As a result, the potential of the current detection line 29 becomes equal to the corrected scan-off voltage (VVGL, VCMP), so that there is no particular problem in the operation of the TFT. Although the output voltage VCMP of the operational amplifier changes in proportion to the current flowing through each scanning line, the output voltage level may be adjusted by the resistor 35. Although not shown, a level adjusting circuit may be added after the current detecting means 28, and the configuration method is not particularly limited.

FIG. 6 shows another embodiment of the current detecting means 28. The current flowing through the current detection line 29 is detected by the current detection coil, and the correction voltage VCMP is output via the buffer circuit 38. EXAMPLE same voltage VCMP and scan-off voltage VGL of 5 input to the scan-off voltage correction circuit 3 2, scan-off voltage correction circuit corrected voltage V ₂ (VGL, VCMP) depends on VGL and VCMP output And apply it to the current detection line 29.

As described above, the correction signal VCMP obtained by the current detection means is input to the scan off voltage correction means 32, where the correction is made so as to eliminate the distortion of the scan off voltage VGL. In this case, the correction target is the scanning line shown in Fig. 4. 2 2. No other correction of the scanning voltage applied to the scanning line is performed. The scan-off voltage correction means 32 is configured using, for example, an operational amplifier. However, the scan-off voltage correction means 32 may be any device that inputs the voltages VGL and VCMP and performs the above-described calculation. Not limited.

FIG. 7 shows the configuration of another embodiment for correcting the scanning voltage. The scanning voltage generating means 40 comprises switch circuits 40a to 40c each having two input terminals a and b and an output terminal. The scan-off voltage correction means 42 includes current detection means and voltage correction means, and corrects this voltage in accordance with the current flowing in the scan-off voltage VGL. The details of the current detection means and the voltage correction means are the same as in FIG. 6, and are omitted here.

Note that the correction signal of the off voltage VGL of the scanning voltage can detect the current flowing through the scanning line, and the configuration method is not particularly limited. Also, in some cases, the scanning voltage itself of the scanning wiring in the liquid crystal panel is detected, and based on the detection result, the off-voltage VGL of the scanning voltage is input to each switch circuit of the scanning voltage generating means to form a waveform. The distortion may be corrected.

FIG. 8 shows another embodiment of the present invention. This corresponds to the common voltage generating means 11 and the common side load detecting means 12 shown in FIG. What is the voltage of the common electrode of the liquid crystal panel? The waveform is distorted by the resistance of the supply line or the connection resistance between the circuit and the panel. Then, as the size of the panel increases, and as the number of pixels increases, the amount of distortion increases.

When the common voltage is distorted, the brightness of the liquid crystal fluctuates. Since the amount of distortion of the waveform depends on the level of the signal voltage, the above-described image quality is degraded by the display pattern. Focusing on the fact that the amount of distortion of the common voltage waveform corresponds to the current flowing through the common voltage supply line, this current is detected, and the waveform of the common voltage input from the outside is compensated in advance from this detected amount. Correct and prevent waveform distortion in the LCD panel.

The current ICOM flowing through the common voltage supply line 48 is converted into a correction voltage VCMP2 by a current detection circuit composed of an operational amplifier 45 and a resistor 46. The converted correction voltage VCMP 2 is input to the common voltage correction means 47, is synthesized with the common voltage VCOM already input from the external circuit, and is output as a VCOMA waveform as shown in FIG. Thus, the waveform distortion of the common voltage in the panel can be corrected. Adjustment of the absolute level of the correction voltage may be performed by adjusting the value of the resistor 46 or in the common voltage correction means 47. This makes it possible to correct the waveform distortion of the common voltage that fluctuates according to the display pattern, that is, the load fluctuation, in real time.

The current detection circuit and the common voltage correction means 47 are What is necessary is just to achieve the function as described above, and the configuration is not particularly limited.

FIG. 10 shows still another embodiment of the display device according to the present invention. In one dot of the liquid crystal panel 50, the TFT 51, the pixel 52, and the common terminal 53 are arranged in a matrix. Further, a gate line 55 is connected to the gate terminal of each TFT, and a drain line is connected to the drain terminal.

A gate drive circuit 56 is connected to the gate line 55, which generates a gate voltage for controlling the TFT 51, and a drain line 54 is connected to the drain line 54. A drive circuit is connected, which generates a drain voltage that determines the brightness of the liquid crystal. Gate voltage level generating circuit 57 generates V GH for turning on TFT or V GL for turning off TFT.

The gate voltage level generation circuit 57 is connected to a correction voltage generation circuit-59. The correction voltage generation circuit 59 generates a correction voltage for correcting the waveform distortion of the gate voltage according to the state of the image signal. The correction amount VCMP at this time is a value corresponding to the brightness of all pixels for each horizontal line displayed on the LCD panel 50, but the value of the current flowing through the gate line or the gate It suffices if voltage waveform distortion can be predicted, and the method of calculating the correction amount is not particularly limited. The voltage amount may be divided into a plurality of levels.

FIG. 11 shows still another embodiment of the display device of the present invention. The display device includes a liquid crystal panel 60, a gate drive circuit 64, a drain drive circuit 65, and a gate voltage detection circuit. It is composed of circuits 68. One dot of the liquid crystal panel 60 includes a TFT 61, a liquid crystal pixel 62, and a common terminal 63.

One terminal of the TFT 66 a to 66 e is connected to the gate line 68 a to 68 e, and the other terminal is commonly connected to the input terminal of the gate voltage detection circuit 68. Have been.

The TFTs 66a to 66e are turned on and off according to the voltage state of the gate voltage VG, and select and output the preceding gate voltage. For example, when an on-voltage is applied to the gate line 68 b, the TFT of the pixel connected to this gate line is turned on. At the same time, the gate voltage (off voltage) applied to the gate line 68a in which the TFT 66a is also turned on is selected and output. Hereinafter, the same operation is performed for each line order. As a result, the output voltage VDT of the gate voltage detection circuit 68 becomes the gate voltage applied to each gate line. Based on the VDT obtained here, the gate voltage input to the liquid crystal panel is corrected to reduce waveform distortion.

The TFTs 66a to 66e may be amorphous silicon TFTs or polycrystalline silicon TFTs, and are not particularly limited. Further, it may be provided outside the liquid crystal panel. in this case, It is not necessary to use a TFT, and for example, a MOS transistor may be used.

Further, the combination of TFTs 66a to 66e is not limited to the configuration shown in FIG. 11, and may be divided into a plurality of blocks.

As a modified example of the present invention, in addition to correcting the gate voltage in accordance with the detection amounts of the gate voltage and the gate current, a common voltage or a current (not shown) is detected and the gate voltage is also detected. Alternatively, the common voltage may be corrected.

ADVANTAGE OF THE INVENTION According to this invention, since the fluctuation | variation of brightness and a contrast ratio resulting from the waveform distortion by a display pattern can be prevented and reduced, a high quality display apparatus can be implement | achieved. In particular, it is possible to prevent the image quality from deteriorating even when the display size or the number of pixels of the panel increases. Furthermore, the size and simplification of the device can be reduced.

Claims

The scope of the claims

1. A liquid crystal matrix comprising a scanning line, a signal line, a switching element connected to the scanning line and the signal line, a liquid crystal pixel driven by the switching element, and a common electrode connected to the liquid crystal pixel. In a trix display,

Detecting means for determining the state of the waveform of the scanning voltage of the scanning line preceding the scanning line to be driven; and voltage correction for correcting the state of the waveform of the scanning voltage of the scanning line to be driven based on the detection amount of the detecting means. And a liquid crystal matrix display device.

2. The liquid crystal matrix display device according to claim 1, wherein the state of the waveform of the scanning voltage is obtained from a current flowing in a scanning line before the scanning line to be driven.

3. Liquid crystal composed of a scanning line, a signal line, a switching element connected to the scanning line and the signal line, a liquid crystal pixel driven by the switching element, and a common electrode connected to the liquid crystal pixel In a matrix display device,

Detecting means for detecting the current flowing into and out of the scanning line; and voltage correcting means for correcting the state of the waveform of the scanning voltage of the scanning line to be driven based on the detection amount of the detecting means. Liquid crystal matrix display device.

4. Scanning and signal lines, switching elements connected to the scanning and signal lines, and driven by the switching elements In a liquid crystal matrix display device including a liquid crystal pixel and a common electrode connected to the liquid crystal pixel,

When the TFT is turned on, the scanning voltage waveform of the driving scanning line is corrected based on the waveform state caused by the current flowing from the scanning line to be re-driven to the previous scanning line via the TFT. A liquid crystal matrix display device comprising: a voltage correction unit.

5. The storage capacitor is provided in a circuit connecting the TFT and the preceding scanning line, and the preceding scanning line is connected to the scanning off voltage correcting means via the load current detecting means. The liquid crystal matrix display device described.

6. A liquid crystal matrix including a scanning line, a signal line, a switching element connected to the scanning line and the signal line, a liquid crystal pixel driven by the switching element, and a common electrode connected to the liquid crystal pixel. In a trix display,

A voltage that corrects the state of the scan voltage waveform of the drive scan line based on the state of the waveform caused by the current flowing from the scan line to be re-driven to the common electrode via the TFT through the TFT when the TFT is turned on. A liquid crystal matrix display device comprising: a correction unit.

7. The scanning line and the signal line, the switching element connected to the scanning line and the signal line, the liquid crystal pixel driven by the switching element, the common electrode connected to the liquid crystal pixel, In a driving method of a liquid crystal matrix display device for driving a matrix panel composed of a storage capacitor connected to a TFT and a storage capacitor common line connecting the storage capacitors in common, there may be used alone. Detects the current flowing into and out of the scanning line, the signal line, the common electrode, and the storage capacitor common line by an arbitrary combination, and detects the current flowing through the scanning line, the signal line, the common electrode, and the storage capacitor common line. A method for driving a liquid crystal matrix display device, characterized in that a state of an applied voltage is corrected.

8. A matrix including a scanning line, a signal line, a switching element connected to the scanning line and the signal line, a liquid crystal pixel driven by the switching element, and a common electrode connected to the liquid crystal pixel. In a method of driving a liquid crystal matrix display device for driving a liquid crystal panel,

When the current flowing through the scanning line, the signal line, and the common electrode is detected alone or in any combination, the state of the waveform of the scanning voltage of the driving scanning line is corrected based on a preset correction amount. A method for driving a liquid crystal matrix display device, comprising:

9. A scanning line, a signal line, a switching element connected to the scanning line and the signal line, a liquid crystal pixel driven by the switching element, and a common electrode connected to the liquid crystal pixel. In a method of driving a liquid crystal matrix display device for driving a matrix panel, The voltage waveform distortion caused by the current flowing into and out of the scanning line, the signal line, the common electrode, and the common line of the storage capacitor is driven by applying an opposite voltage by predictive control, alone or in any combination. A method for driving a liquid crystal matrix display device, comprising: correcting a state of a scanning voltage waveform of a scanning line.