JPH1020278A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To mitigate light display on the extension of consecutive selective picture elements by efficiently compensating transmission loss or the like at the time of driving a simple matrix having extremely large display capacity. SOLUTION: A scanning circuit 2 and a signal circuit 3 are connected to a liquid crystal cell 1 having electrode groups mutually nearly orthogonal. A power source circuit 4 supplying positive and negative scanning voltage as scanning voltage and signal voltage in the vicinity of the the intermediate value of the scanning voltage is provided. Though the power source circuit 4 outputs a selection signal and the signal voltage in accordance with voltage average addition, bias voltage is corrected in terms of bias by detecting the potential fluctuation of the nondisplay electrode of the liquid crystal cell 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal display device suitable for so-called simple matrix driving.

[0002]

2. Description of the Related Art Conventionally, in driving a liquid crystal cell having electrode groups that are substantially orthogonal to each other, that is, a so-called simple matrix drive, a voltage of a higher voltage level is sequentially applied to the electrodes of one of the electrode groups (scanning side). Line-sequential scanning is performed in which a voltage corresponding to an image signal is applied to the other electrode group (signal side) when a high voltage level is applied. Further, in order not to apply a direct current to the liquid crystal, as shown in Japanese Patent Publication No. 57-57718, the polarity is inverted based on a polarity signal.

For example, in a case where AC driving is performed by inverting the polarity for each frame, the polarity signal is inverted and provided for each frame. This polarity signal is an alternating signal (M)
Also called. V0 is applied to the scanning electrode during the scanning time of the first frame, V1 is applied to the other signal electrode when display is desired (selected pixel), and voltage is selected so that the applied voltage is reduced when display is not desired. Then, in the next frame, V1 is applied to the scanning electrode, and V0 is applied to the signal electrode in the selected pixel.

[0004]

However, in such a so-called simple matrix drive, as shown in two display forms on the right side of FIG. 2, a light color is added to a bar graph, a frame, or an extension of a simple linear drawing. Or a whiter color than the background color appears, which is called crosstalk, and the display quality is significantly reduced.

There are various theories about the cause.
For example, when driving a liquid crystal cell, so-called alternating current is performed, but analysis such as that caused by the difference in the liquid crystal response between the positive cycle and the negative cycle or the rounded waveform of the driving voltage of the liquid crystal has become effective. I have. In particular, 640 × 480 pixels (V
GA) or 1024 RGB x 768 pixels (color XGA)
This is remarkable in a large-scale high-density display such as (the number of pixels per signal side 3072). In such a large-sized, high-density display, a high-speed and high-withstand-voltage integrated circuit is required, and high-speed and high-withstand-voltage integrated circuits have conflicting specifications.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points. First, a liquid crystal cell having a group of electrodes that are substantially orthogonal to each other and one of the group of electrodes of the liquid crystal cell are provided. A scanning circuit for applying a scanning voltage, a signal circuit for applying a signal voltage to the other electrode group of the liquid crystal cell in accordance with an image signal, and a power supply circuit for applying a bias voltage to the scanning circuit and the signal circuit according to a voltage averaging method. And a correction circuit for detecting a potential change of a non-display electrode of the liquid crystal cell and outputting a bias correction signal.

Second, the present invention provides a scanning circuit for applying a scanning voltage to one electrode group of a liquid crystal cell having electrode groups substantially orthogonal to each other, and a signal circuit for applying a signal voltage to the other electrode group in accordance with an image signal. A power supply circuit for supplying, as a bias voltage, a signal voltage near an intermediate value between the positive and negative scanning voltages applied to the scanning circuit and the positive and negative scanning voltages applied to the signal circuit, and scanning by detecting potential fluctuations of non-display electrodes of the liquid crystal cell A circuit, a signal circuit, or a power supply circuit is provided with a correction circuit for supplying a bias correction signal. The non-display electrode is, for example, a mesh-like metal thin film provided on substantially the entire display surface. And
Preferably, the correction circuit detects a potential change of a non-display electrode provided so as to have a portion stacked with any one of the orthogonal electrode groups provided in the liquid crystal cell and supplies a bias correction signal. Upon receiving the signal, the signal circuit outputs substantially the same voltage as the voltage applied to the non-scanning electrode of the liquid crystal cell.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram of a liquid crystal display device according to an embodiment of the present invention. Reference numeral 1 denotes a so-called simple matrix type liquid crystal cell having electrode groups that are substantially orthogonal to each other. Field effect type liquid crystal such as a nematic liquid crystal display can be used. The electrodes of the liquid crystal cell 1 are made of, for example, transparent electrodes arranged in stripes and have no active elements at pixel intersections.

Reference numeral 2 denotes a scanning circuit for applying a scanning voltage to one electrode group of a liquid crystal cell having an electrode group orthogonal to each other. In order to perform line-sequential scanning, a high peak voltage is sequentially applied to the scanning electrodes during one frame. Is to give. Here, one of the positive and negative voltages -VL, + VH and the intermediate voltage Vm is selected and supplied to a predetermined electrode.
L and + VH are scanning voltages in the sense that they are bias voltages applied to the scanning-side electrodes selected for scanning, and the intermediate voltage Vm is a non-scanning voltage applied to other scanning-side electrodes not selected for scanning.

On the other hand, reference numeral 3 denotes a signal circuit for applying a signal voltage to the other electrode group of the liquid crystal cell having mutually orthogonal electrode groups in accordance with an image signal. When the positive and negative voltages -VL and + VH are used as the scanning voltage, the signal voltage includes two types of bias voltages -Vb and + Vb near an intermediate value between the positive scanning voltage + VH and the negative scanning voltage -VL and a bias correction signal. A signal voltage is selectively supplied to the electrodes of the liquid crystal cell 1 in accordance with the polarity signal M and the image signal (data). The voltage applied to the signal side electrode of the liquid crystal cell 1 in response to the bias correction signal is the intermediate voltage Vm in this embodiment.

A power supply circuit 4 applies a bias voltage to the scanning circuit 2 and the signal circuit 3 in accordance with the voltage averaging method.
When a positive or negative scanning voltage is used, the positive or negative scanning voltage −V
L, + VH and a signal voltage − near an intermediate value of the scanning voltage.
Vb, + Vb, and the intermediate voltage Vm output from the scanning circuit during the non-scanning time are supplied as bias voltages.

The power supply circuit 4 converts the voltages VDD and VEE (= GND) supplied from, for example, a personal computer in which the display device is incorporated into a voltage generation circuit (DC).
/ DC converter) 41 and outputs a positive / negative voltage −VL,
+ VH is generated. The term "positive / negative" herein means not an absolute potential, for example, a potential specified for a power supply of a personal computer in which this display device is incorporated, but a potential with respect to a scanning voltage (intermediate voltage) Vm during non-scanning. expressing.

The voltage generating circuit 41 more preferably generates and supplies a driving voltage for the scanning circuit 2 and the signal circuit 3, furthermore, a signal transmitting and receiving circuit 6 and a buffer circuit.
The signal transmission / reception circuit 6 shifts the drive transmission level to the supply power level as necessary when transmitting signals corresponding to various timing signals and image signals supplied to the signal circuit 3 through the buffer, This is a circuit to which an additional signal is given.

On the basis of the scanning voltage generated by the voltage generating circuit 41, a voltage having a predetermined bias value, that is, signal voltages −Vb and + Vb and an intermediate voltage Vm are obtained by a resistance dividing circuit 42, and these are passed through a buffer circuit 43. Output.

The magnitudes of the scanning voltages + VH, -VL and the signal voltages -Vb, + Vb are basically obtained according to the voltage averaging method. For example, when the XGA screen is divided, the number of scanning lines is 384 ( 1/384 duty), the optimum bias value is 1: 20.6, and the intermediate voltage Vm and G
When the ND levels are matched, the scan voltage ± 30.0 volts and the signal voltage ± Vb is ± 1.53 volts.

Reference numeral 5 denotes a correction circuit for detecting a potential change of a non-display electrode of the liquid crystal cell 1 and outputting a bias correction signal.
The non-display electrode is a conductor in a liquid crystal cell to which a voltage for display is not applied. The correction circuit 5 detects the potential change of the non-display electrode and supplies bias correction signals W and P to the signal circuit 3. The signal circuit 3 uses these signals, the polarity signal M and the image signal D to generate a signal. An intermediate voltage Vm is output instead of the signal voltages -Vb and + Vb for a predetermined change time.

The non-display electrodes are preferably orthogonal electrode groups (scanning electrodes and signal electrodes) provided in the liquid crystal cell.
It is preferable to provide a portion to be laminated with any one of the above electrodes. In this example, as shown in FIG. 4, the black matrix 13 of the color filter 12 provided on the inner surface of the liquid crystal substrate 11 is used as a non-display electrode.
Since the black matrix 13 of the color filter is formed of a metal thin film provided in a mesh pattern over substantially the entire display surface, it is easy to respond to the application of an abnormal voltage. That is, when the voltage is imbalanced, the excess or deficiency acts as a capacitor sandwiching a dielectric such as an alignment film or a filter, and a change in potential can be extracted.

The correction circuit 5 may detect a change in the potential of an electrode which is not used directly for display and is provided substantially in parallel with, for example, a stripe-shaped display electrode.
In this case, the potential of the non-display electrode substantially perpendicular to the signal side electrode is used when correcting the scanning side bias voltage, and the potential of the non-display electrode substantially perpendicular to the scanning side electrode is used when correcting the signal side bias voltage. May be. This is because the potential change of many counterpart electrodes is targeted, but the feedback side may be set according to the positive or negative of the detected signal without taking such a special consideration.

The bias correction signals P and W are directly introduced into the signal circuit 3, and the intermediate voltage is selected by the same number of drivers as the signal side electrodes. However, the present invention is not limited to this. . For example, in the scanning circuit 2,
When the positive and negative scanning voltages -VL and + VH rise or fall, the intermediate voltage is maintained for a certain period of time according to the potential change of the non-display electrode, or the intermediate voltage at the non-selected electrode is slightly changed to the positive side or the negative side. You may. Alternatively, a bias correction signal is supplied to the power supply circuit 4 so that a positive scanning voltage + VH, a negative scanning voltage -VL, a bias voltage -Vb, +
Either Vb or the intermediate voltage Vm may be slightly fluctuated.

Note that such correction is based on an analysis that the cause of display crosstalk is waveform distortion. To explain this, as shown in the waveform diagram on the left side of FIG. 2, during the non-scanning period, an intermediate voltage Vm is applied from the scanning circuit, and one of the signal voltages is applied from the signal circuit. M switches to the other signal voltage. Then, when the polarity of the signal voltage is inverted, waveform rounding occurs. Thereby, the effective value of the voltage applied to the liquid crystal cell decreases or increases. At this time, all the pixels on the signal electrode of the non-selected pixel (foreground) on the extension of the continuously selected pixel than the selected pixel are affected. FIG.
In the case of, in the black bar display on the white background shown in the upper half, even if the luminance of the foreground slightly changes, there is no comparison, so that it is not observed as crosstalk. On the other hand, in the display of black or white or coloring shown in the lower half, other non-selected pixels (background) are to be compared, and are recognized as crosstalk.

Accordingly, in the present invention, of the waveform distortions,
As shown in FIG. 3, in order to make the applied voltage substantially zero only when the direction of the distortion does not match the change in the signal-side voltage, the increase in the applied voltage is reduced to reduce the crosstalk displayed in white. Things. Accordingly, on the right side of FIG. 3, the area of the pattern portion and the back portion of the hatched portion, that is, the effective value of the applied voltage becomes substantially equal.

FIG. 4 is a circuit diagram showing a specific example of such a correction circuit 5. In this figure, black matrix 1
An operational amplifier 51 is connected to 3 by a capacitor coupling. The operational amplifier 51 has two inputs connected to each other with a diode interposed therebetween, and detects a positive potential fluctuation and a negative potential fluctuation. An exclusive OR circuit 52 for extracting the time of the potential change from the output of the operational amplifier 51
And a flip-flop 53 that generates a polarity display signal from the output of the operational amplifier 51. From the output of the exclusive OR circuit 52, a time width corresponding to the time of occurrence of distortion is generated as a signal w, and a signal p indicating the direction of occurrence of distortion is generated from the flip-flop 53.

FIG. 5 shows an example of such a signal waveform. The image signal D, which is data, is provided from an image controller or a microcomputer via a signal transfer circuit 6, and the polarity signal M may be provided from an image controller or a microcomputer. Good. In synchronization with the latch pulse (a), the scanning voltage (b) is a scanning signal applied to one scanning electrode, and the signal voltage (c) is a conventional signal applied to one signal electrode. Voltage. Conventionally, the signal circuit 3 outputs a signal voltage (c) based on the current image signal and the polar base signal M.

Signals (d0), (d1) and (d2) indicate the detected voltage and the output voltage of the operational amplifier 51 in FIG. The signals (P) and (W) are a signal w indicating a time width corresponding to the above-described distortion occurrence time and a signal p indicating the direction in which the distortion occurs, and are output signals of the correction circuit 5. According to the present invention, when the polarities of the signal P and the signal w indicating the distortion group do not coincide with each other with respect to the conventional signal voltage (c), the signal voltage is originally + Vb or −V during that period. Vb
The signal voltage (f) that has output any one of the above is substantially equal to the intermediate voltage Vm which is a voltage when the scanning signal is not selected.

In this embodiment, positive and negative scanning voltages -VL and + VH are used for the scanning signal. However, the present invention can be applied to a display drive according to a voltage averaging method in principle. In the driving of the general voltage averaging method as described in the prior art of the present application, since the scanning circuit and the signal circuit handle the same voltage, the non-display mode (D
Due to isp-off), the output fluctuates as a large voltage fluctuation near 30 volts. Therefore, if an appropriate value is not prepared, a new waveform distortion may occur due to the voltage fluctuation.

When the scanning signals -VL and + VH are used as the scanning signal, the output stage of the integrated circuit of the scanning circuit 2 requires a withstand voltage which is approximately twice as high as that of the conventional scanning circuit. Since the output stage selects one of the three potentials at the output stage, no large current is generated when the AC signal is switched. On the other hand, the signal circuit 3 handles only a low voltage of only 5 volts or less in the above-described example, and is not only suitable for high-speed driving but also has less waveform collapse. As for the unbalanced voltage that still occurs, the effective value is adjusted by using half the voltage of the signal voltage as described above, so that a small voltage can be switched smoothly and the influence on other pixels is small. In addition, large-capacity display can be performed with high display quality without increasing the number of switching transistors and without increasing the load on the integrated circuit for signal circuits. Therefore, the present invention is particularly effective when using positive and negative scanning voltages -VL and + VH.

[0027]

As described above, according to the present invention, the scanning circuit uses the positive and negative high voltages as the scanning voltage, uses three types of signal voltages near the intermediate value of the scanning voltage in accordance with the image signal, and responds to the image signal. Thus, even if the display capacity is increased and the image signal is significantly increased, the signal circuit can be easily driven at a high speed because of the low voltage driving.

[Brief description of the drawings]

FIG. 1 is a block diagram of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of display crosstalk.

FIG. 3 is a waveform diagram for comparison between the embodiment of the present invention and a conventional example.

FIG. 4 is a circuit diagram of a correction circuit according to the embodiment of the present invention.

FIG. 5 is a waveform diagram of a main part of the embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 liquid crystal cell 2 scanning circuit 3 signal circuit 4 power supply circuit 5 correction circuit

Claims (3)

[Claims] 1. A liquid crystal cell having electrode groups substantially orthogonal to each other, a scanning circuit for applying a scanning voltage to one electrode group of the liquid crystal cell, and a signal voltage applied to the other electrode group of the liquid crystal cell in accordance with an image signal. A power supply circuit for applying a bias voltage to the scanning circuit and the signal circuit according to a voltage averaging method, and detecting a potential change of a non-display electrode of the liquid crystal cell and outputting a bias correction signal. A liquid crystal display device comprising: 2. A liquid crystal cell having electrode groups substantially orthogonal to each other, a scanning circuit for applying a scanning voltage to one electrode group of the liquid crystal cell, and a signal voltage applied to the other electrode group of the liquid crystal cell according to an image signal. A power supply circuit for supplying, as a bias voltage, a signal voltage near an intermediate value between the positive and negative scanning voltages applied to the scanning circuit and the positive and negative scanning voltages applied to the signal circuit, and a non-display electrode of the liquid crystal cell. A liquid crystal display device comprising: a correction circuit for detecting a potential fluctuation of the pixel circuit and supplying a bias correction signal to the scanning circuit, the signal circuit, or the power supply circuit. 3. A liquid crystal cell having electrode groups substantially orthogonal to each other, a scanning circuit for applying a scanning voltage to one electrode group of the liquid crystal cell, and applying a signal voltage to the other electrode group of the liquid crystal cell in accordance with an image signal. A signal circuit for receiving a bias correction signal and outputting a voltage substantially the same as the voltage applied to the non-scanning electrode of the liquid crystal cell, and a power supply circuit for supplying a plurality of bias voltages to the scanning circuit and the signal circuit And detecting a potential change of a non-display electrode provided so as to have a portion laminated with any one of the electrodes of the substantially orthogonal electrode group provided in the liquid crystal cell, and supplying a bias correction signal to the signal circuit. A liquid crystal display device comprising: a correction circuit that supplies the liquid crystal.