JPS62262028A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To reduce an undesirable influence of a parallax exerted on a display characteristic of a liquid crystal display panel, and to obtain a uniform and good contrast characteristic, by providing a luminance correcting circuit for varying successively a selective voltage value of a scan driving waveform, by following a line sequential scan in one constitution screen. CONSTITUTION:In a liquid crystal display device which is an XY matrix type in which plural signal electrodes and plural scan electrodes are opposed to each other in a matrix shape, and provided with a multiplex driving circuit by a voltage averaging method, a luminance correcting circuit for varying successively a selective voltage value of a scan driving waveform by following a line sequential scan in one constitution screen is provided. Since the luminance correcting circuit for varying successively a scan voltage is added, unevenness and a fall of a contrast caused by a parallax in one screen are prevented, and even in case of a large-sized liquid crystal display panel, an image which is uniform and has a high quality can be obtained extending over the whole screen.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a liquid crystal display device, and particularly relates to a liquid crystal display device for displaying graphics,
The present invention relates to a liquid crystal display device suitable for large-sized liquid crystal display elements with a large number of time divisions, such as character display.

<Prior art> In recent years, in the field of liquid crystal display devices, there has been a demand for an increase in the amount of displayed information, and in matrix displays,
Furthermore, in order to diversify display information, it is required to realize a large display device in which the multiplex frequency N (number of scanning electrodes) in matrix drive is increased.

In order to realize this, optimization of driving methods, liquid crystal materials, polarizing plates, etc. has been actively studied in various fields. The biggest challenge in this large display device is how to obtain a wide viewing angle, a high contrast ratio, and a uniform display within the screen.

<Problem to be solved by the invention> By the way, the XY matrix type liquid crystal display panel is
When driving with the optimum voltage averaging method, as is known, the peak voltage of the scanning pulse V, the peak voltage of the emitting signal pulse V,
When there is a relationship between V1=$V, (1), the maximum contrast ratio is obtained, and at that time, it is expressed as the effective voltage Von at the lit pixel, and as the frequency N increases, Von and The difference with Voff decreases.

Furthermore, as the size of the panel increases, the parallax on one screen increases. That is, LCD (liquid crystal display)
If the viewing angle θ is defined as shown in Fig. 3, then T N (
The viewing angle dependence of the electro-optical characteristics of the twisted nematic)-L CD is shown in FIG.

For example, when viewing a screen measuring 150m5+ in the vertical direction from a distance of 500mm as shown in Figure 5, there will be a parallax of approximately 15° in the vertical direction.
The transmittance intensity differs at point b (see Figure 4). Also, as the ratio α between Von and Voff becomes smaller,
This phenomenon is even more important.

This problem essentially occurs in conventional matrix drive waveforms, and is one of the reasons for preventing the enlargement of liquid crystal display elements.

The present invention was made in view of the above circumstances, and aims to reduce the adverse effects of parallax on the display characteristics of a liquid crystal display panel, and to provide uniform and good contrast characteristics even in a liquid crystal display device. It is said that

Means for Solving the Problems First, the principle of the invention will be explained. Figure 8 is XY
FIG. 8(a) shows an example of the voltage applied by the voltage averaging method in a mamatrix liquid crystal display device, and FIG. 8(a) shows the voltage applied to the scanning electrode Y1, and FIG. 8(b) and FIG.

In the figure, (d) is a voltage waveform applied to a lit pixel, and (e) is a voltage waveform applied to a non-lit pixel. In addition, time [ is the ON period of one scanning electrode, time T is the frame period, voltage 1 is the peak voltage applied to the scanning electrode, and voltage V
! is the peak voltage applied to the signal electrode.

By the way, as mentioned above, the voltages V, , V, are the same as the above (1)
When the relationship is as shown in the formula (in this case, Vl and V.

are V 10pt and V zOpt), XY? Trix type LCD panel provides maximum contrast ratio,
At that time, the ratio αopt of the effective voltage applied to the lit pixel and the non-lit pixel is expressed by equation (2).

Moreover, the effective value voltage van(ri
s), the effective value voltage Vofr(r
Ills) is expressed by the following formula.

However, T=2Nt This means that Von (rms) and Vofr (rms) are ■
1 and Vl, and the second
In the figure, as an example, when N=120, the voltage V is set to a constant value (
Vtopt) and V on(
rms), Vorr(rms) and α. Moreover, the dotted line in the figure indicates the case where the relationship of equation (1) is not satisfied. From this, when vl is changed from the optimal drive fa V +opt, V on (rms), V .

It can be seen that rf (rms) can be increased at the same time, and even if v1 changes somewhat, the value of α hardly changes.

Therefore, the contrast ratio difference due to the above-mentioned parallax in the vertical direction of the screen can be solved by gradually changing IVll with line-sequential scanning and adjusting V on (rms) to the optimum value of the viewing angle characteristics at each display location on the LCD. It can be improved. That is, in FIG. 5, first, the transmitted light intensity of the non-lit pixel at point b is calculated as 1 as shown in FIG.
By adjusting v11, V below the threshold voltage
Set to 'off'. At this time, IV and l are assumed to be 1v and b+.

Furthermore, the transmitted light intensity TO corresponding to van' is obtained for the lit pixel at point b by driving using the optimal voltage averaging method. In this state, at point a, by setting 111 to a voltage 1V1a1 lower than the above-mentioned IVlbl, the transmitted light intensity of the lit pixel can be made to be the same To as the transmitted light intensity at point b.

Moreover, the effective value voltage VolT(r
ms) is applied. The rise of the transmitted light intensity at point a is sharper than that at point b, and as shown in Figure 2, even if V is slightly changed, the operating margin α hardly changes (between points a and b). can be considered to be almost the same), Vof'4 becomes a voltage lower than the threshold voltage at point a +1), and as a result, even at point a, b
The same contrast ratio as a point will be obtained. Using this principle, by gradually changing IV, l from point a to point b according to line-sequential scanning (IV, al
≦IV, l≦lv+”1), contrast unevenness due to parallax can be effectively improved even in large screen display.

Note that the operating margin α depends on the number N of scanning lines, and as shown in FIG. 7, as N increases, the operating margin α approaches the operating margin α opt of the optimal voltage averaging method.

Also, as is clear from this figure, when N is approximately 60 or more,
There is almost no problem with the decrease in the operating margin α.

Therefore, the driving according to the present invention exhibits a very remarkable effect in an XY matrix liquid crystal display device in which N is approximately 60 or more.

The above is the principle of the present invention. Note that the basic principle of the present invention can basically be applied to other multiplex drive waveforms.

Based on the above principle, the present invention provides an XY matrix type liquid crystal display device in which a plurality of signal electrodes and a plurality of scanning electrodes are opposed to each other in a matrix, and is equipped with a multiplex drive circuit using a voltage averaging method. A brightness correction circuit is provided that sequentially changes the selected voltage value of the drive waveform in accordance with line-sequential scanning within one constituent screen.

<Embodiment> FIG. 1 shows a liquid crystal display device according to an embodiment of the present invention. The XY matrix type car-type liquid crystal display panel 2 is a multiplex scanning side drive circuit, 3 is a multiplex signal side drive circuit, 4 is a scanning voltage IV consisting of an integrator 41 and inverting amplifiers 42 and 43 as a brightness correction circuit; 5 is an inverting amplifier 51 and a voltage follower 5.
This is a power supply circuit for signal voltages IV and l consisting of 2 and 2. The integrator 41 is provided with a field effect transistor (FET) 44 that resets the integrated value.

The scanning voltage V and the signal voltage V having waveforms based on the voltage averaging method shown in FIG.
120, an 8-inch leaf-sized liquid crystal panel was driven at a frame frequency of 60 Hz.

Here, the scanning voltage IV is applied over the entire liquid crystal display panel l.
, l, signal voltage IV, l to a constant value (V, opt.

V*opt), a change in contrast was observed from the top to the bottom of panel l, with the top being bright and the bottom being dark. Therefore, using the power supply circuit 4 incorporating the integrator 41 described in this embodiment, adjustments were made so that the scanning voltages IV and l exhibited changes as shown in FIG. 9(b). Regarding this setting, the optimum value was calculated in advance from the electro-optical characteristics of the liquid crystal display panel 1. Further, a pulse as shown in FIG. 9(a) is applied to the gate of FET 44 of the integrator 41, and a
Driving waveforms shown in FIGS. 9(c) and (d) are applied to the scanning side at point and b. As a result of such adjustment,
It was confirmed that the brightness unevenness within the liquid crystal display panel 1 was corrected, a substantially uniform screen with no contrast unevenness was obtained overall, and the contrast was corrected. Furthermore, similar effects can be expected if the present invention is applied in a case where cell thickness unevenness occurs in the vertical direction within a liquid crystal display panel and the threshold pressure of electro-optical characteristics varies.

<Effects of the Invention> According to the present invention, in a multiplex drive type XY matrix liquid crystal display device, a brightness correction circuit that sequentially changes the scanning voltage is added, so that unevenness or reduction in contrast due to parallax on one screen can be prevented. This makes it possible to obtain uniform, high-quality images over the entire screen on large liquid crystal display panels.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a liquid crystal display device according to an embodiment of the present invention.
2 and 7 are graphs explaining the invention in detail,
Figure 3 is an explanatory diagram showing the definition of viewing angle characteristics, Figure 4 is a graph explaining viewing angle characteristics of transmitted light intensity with respect to applied voltage, Figure 5 is a diagram explaining parallax occurring on a liquid crystal display panel, and Figure 6 is a liquid crystal display. FIG. 8 is an explanatory diagram showing the waveform of the applied voltage in an embodiment of the present invention, and FIG. 9 is a graph explaining the transmitted light intensity with respect to the applied voltage at each point on the display panel.
It is an explanatory view of pressure. 1.Liquid crystal display panel, 2.Scanning side drive circuit, 3..
・Signal side drive circuit, 4...Scanning voltage power supply circuit, 5.
... Signal voltage power supply circuit, 41... Integrator. Patent applicant: Sharp Corporation Agent
Patent attorney, previously mentioned, 2 people's hats @Kasho Seten J4; Nishikicho

Claims (1)

[Claims] (1) In a liquid crystal display device of an XY matrix type in which a plurality of signal electrodes and a plurality of scan electrodes are opposed to each other in a matrix, and is equipped with a multiplex drive circuit using a voltage averaging method, the selection voltage value of the scan drive waveform is determined. 1. A liquid crystal display device comprising a brightness correction circuit that sequentially changes brightness in line-sequential scanning within one constituent screen.