JPS62223728A - Driving method for active matrix type liquid crystal display - Google Patents

Abstract

PURPOSE:To display a picture image having high quality and less tendency for generating flicker by driving plural address lines in a line sequential system, when the image data are transferred corresponding to the address line in one scanning period. CONSTITUTION:A selecting signal is sent to a liquid crystal display X1 via a shift register A from a video signal in the first half of the scanning period. Simultaneously, the signal which is sample-holded in the scanning period is output to Y1-Yn. And, the signal is written in the display electrode connected to the X1 line by the action of a switching transistor connected to the address line X1. In the latter half of the scanning period, buffer of the analog memory is activated, and the signal corresponded to the line X4 is output to Y1-Yn. Simultaneously, the video signal is stored to the display electrode connected to the line X4 by the selecting signal sent to the line X4 from the shift resistor B. Intermittently, the signal corresponding to the address line X3 which sent from an outside is set to the sample hold 1 and the sample hold 2 as a reversed signal respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a method for driving an active matrix liquid crystal display using switching transistors.

[Technical background of the invention and its problems]

2. Description of the Related Art In recent years, a method of realizing a thin display device by configuring switching transistors in a matrix array has been attracting attention. In this method, image information is accumulated in each dot of a switching transistor matrix provided on a substrate, and this image information is applied to each dot of a liquid crystal layer, EL layer, or EC layer provided on a matrix array. This method attempts to obtain a single screen by displaying a display at a certain position, and compared to the method using CRT, which was the mainstream of conventional display devices,
In principle, a much thinner display device can be realized. Also, C
The display principle of RT is that high-energy electrons collide with a fluorescent substance to emit light, so the light emission time is on the order of milliseconds, so the entire screen is not always displayed, and it utilizes the afterimage phenomenon of one person's vision. However, there were problems with visibility due to flicker noise and the like. On the other hand, a display device using a transistor matrix displays information almost the entire time, as described below, and can provide a more natural screen than a CRT. Furthermore.

Compared to a CRT, it has the following characteristics: it provides a flat screen, does not require a high-voltage power supply, does not require a vacuum area, and is an all-solid-state device, so it is small and lightweight and has sufficient strength.

FIG. 4 is a schematic diagram showing the operating principle of a transistor matrix array. The six display screens are divided into a matrix of m vertically and n horizontally, and are divided into m/n unit side lines in total. . Intersection of each matrix C, □, C12・
...CL + J...C1,. consists of a memory circuit using switching transistors, which stores the image information of each pixel, and according to this information displays are realized in the area corresponding to each pixel of the LC layer used on the matrix circuit. It has become.

A specific memory circuit having a simple configuration as shown in FIG. 5 is used. This is because in order to obtain a high-definition display screen, the matrix size m'n must be very large, so in order to create a matrix circuit with high yield, a simpler circuit is desired. It's for a reason. In FIG. 5, 21 is a switching transistor;
22 is a liquid crystal layer, and 23 is a capacitor for storing image signals.

The gate of the transistor 21 is connected to the first X address line, and the source electrode is connected to the jth Y address line.The eX1 address line and the Yj address line are V(X, ) and v(Yj), respectively. power is connected. Turn on the transistor on the X1 line
When the signal to set the state is input, the transistor T1J2
1 channel becomes conductive, and at this time, the image signal prepared for the Yj line is accumulated in the capacitor C, 23, and while the gate voltage V (XL) is zero, the signal is stored in C8. The liquid crystal 22 is driven in accordance with this accumulated image signal. Note that X, the transistor on the line T Lx r
T i□..., T,, are simultaneously turned on, and the signals v(yl), v(y,)-v(yn) used on the Y address line at that time are applied to each pixel circuit Ci.
l + CL□...Accumulated in ctn. Similarly, X, +1. The image signals on each X line are accumulated one after another in the manner of xi, . . . , and the signals of the entire screen are written.

FIG. 6 schematically shows the timing at which the image signals V, . In the image signal C1JyPL+xeJ of FIG. 6, the solid line shows a timing chart during ideal operation.

That is, writing of the image signal of pixel CtJ starts from time '1-i1, and writing ends at t1□+ΔT. At the same time, the gate voltage V (Xz) becomes zero, and then at time tL2, the image signal is written to CtJ again. Until signal writing is performed, φlJ is held at the image signal v,1.

The above is the operating principle of the flat display device using the transistor matrix array shown in FIG. 4.

Semiconductor materials for transistors include S x y Cd S e g T in crystalline, polycrystalline and amorphous states.
A polycrystalline material such as e+CdS is used. Particularly in recent years, polycrystalline semiconductor materials, amorphous Si, and the like, which can be produced by low-temperature processes, have been attracting attention in order to realize larger area and lower cost of the matrix array.

As active liquid crystal display panels have become larger, the number of lines in the X and Y directions has increased, resulting in higher definition. However, with the increase in definition, a problem has arisen in that flickers appear when displaying television signals. FIG. 7 schematically shows this situation. Normally, for the video signal 41 of a TV, a vertical synchronization signal is sent every 16.7 msec (60 Hz), but a full screen video signal is sent at 33.3 msec Tframes (30 Hz), and the first frame (
In field A (16.7 msec) and the next frame field B, signals are sent by interlace operation. The video signals of these two frames are approximately 5 in terms of the number of scanning lines.
There are 00 episodes. In a small active matrix liquid crystal display with about 250 X address lines,
An image can be displayed by writing the signals of frame A and frame B to the same X address line. Furthermore, for the reliability of the liquid crystal, it is generally desired that the liquid crystal layer be operated by AC drive, and in the small LCD, by changing the direction of the electric field applied to the LC layer between frame A and frame B, it is possible to drive the liquid crystal layer at 30 Hz. 42.44° On the other hand, if the number of X address lines is so large that such a driving method is impossible, that is, the number is 400 or 500, frame A
The video signals of frame A and frame B are completely different and must be written to f and the X address line (actually, the signals of frame A and frame B are applied to every other line). Furthermore,
When the above AC drive is applied to the LC, this frequency is 15Hz.
(66,7m5ec) 43.45. in general.

Due to leakage in the liquid crystal layer, the voltage applied to the liquid crystal layer gradually decreases (44.45 dacay), and the contrast changes. This change is caused by the above 15Hz (66,
7m5ec) cannot be ignored, and
Since the frequency of 15 Hz can be sufficiently responded to even by human visual sense, there is a problem in that flicker is visible in such large panels.

[Purpose of the invention]

In view of the above points, the present invention provides a method for driving an active matrix liquid crystal display, which is driven substantially at the frame frequency of a display signal or at a frequency higher than that so that flicker is not perceived.

[Summary of the invention]

In an active matrix liquid crystal display in which a video signal is sent over multiple frames and written to display electrodes on independent X address lines, when the video signals being received are sequentially displayed on the active matrix liquid crystal display. At the same time, it is stored in analog or digital memory. Furthermore, in this frame, the video signal of another frame, which has already been stored in the memory, is also displayed on the liquid crystal display. In this way, all matrix cells within a frame are driven for display.

In the next frame, all cells are similarly driven to display, but by reversing the polarity of the voltage applied to the liquid crystal layer for each frame, the liquid crystal layer is driven with alternating current, and the actual frame frequency is lower than the conventional method. This makes it possible to achieve good liquid crystal display characteristics with no perceptible flicker.

〔Effect of the invention〕

According to the present invention, by using an external memory, images with excellent display quality can be obtained without making any structural improvements to conventional liquid crystal display panels.

[Embodiment of the Invention] FIG. 1 shows an embodiment of the present invention. In Figure 6,
The X address line of the liquid crystal display is connected to two shift registers A and B, and also.

Y data line is sample hold 1 and 2 dimensional CCD
connected to the buffer output of the analog memory consisting of A video signal adjusted to a display voltage is directly input to the sample hold 1. on the other hand.

Data in the analog memory is input from sample hold 2, and an inverted video signal is sent to sample hold 2. The video signal uses a regular television signal,
The data for the planning section is sent in two frames separated by a vertical synchronization signal. The number of X address lines on the LCD display is 480, and the odd number address lines are 240.
The book is placed in shift register A and also on even address line 24.
0 is connected to shift register B. Half of the video signal is sent to frame A, and these scanning line positions correspond to odd address lines, and the remaining half of the video signal sent every frame is data corresponding to even address lines.

The drive circuit system shown in FIG. 1 is operated by the method shown in FIG. First, in frame A, address line x
During the first half of the scanning period during which data corresponding to 3 is sent, a selection signal is sent from shift register A to X□, and at the same time the video signal sampled and held during the previous scanning period is transferred to These video signals are output to Yn and are written to the display electrodes on this X1 address line by the operation of the switching transistor on the X air address line. Next, in the latter half of this scanning period, the analog memory buffer becomes active, and the video data corresponding to A video signal is stored in each display electrode on the address line x4. Also, within this scanning period, the video signal corresponding to the address line X3 sent from the outside is set in sample hold 1 and sample hold 2 as an inverted video signal.

Φ and θ in the figure indicate the polarity with respect to the potential of the liquid crystal counter electrode.

The video signal set in sample hold 2 is taken into the two-dimensional analog memory of the COD, and at the same time the internally stored signal is also transferred in synchronization with the horizontal synchronization signal. Since a video signal corresponding to one frame (the same amount as frame A or frame B) is stored in the memory, the signal to be output next is set in the buffer stage.

・If we focus on one display electrode, the cell written from sample hold 1 (positive polarity) in frame A is 1
In the next frame B, data will be written from the analog memory (negative polarity), and if the counter electrode potential of the liquid crystal layer is effectively set to the average Ov for signals of both polarities, then in frame A, the negative polarity will be written. Bias, in frame B, AC drive with positive bias can be realized. This AC driving is performed for all pixels. Furthermore, the frequency of this AC drive is equal to the period of two frames (frame A + frame B), which is equivalent to a conventional compact accedip matrix type liquid crystal display with 240 X address lines, and is effectively driven by an AC drive. The driving frequency can be reduced to half that of the conventional method.

FIG. 3 shows another embodiment of the present invention, in which a digital memory is used instead of the analog memory described above, and the video signal is binarized through an AD converter and transferred to the memory. Further, desired video data is set in the sample hold 2 from the memory through the DA converter. The basic driving method is the same as that shown in FIG. 2, and it is possible to reduce the AC driving frequency of the liquid crystal to half of the conventional one.

It should be noted that the present invention is not limited to the above embodiments9
For example, it is possible to write to three or more X address lines within the -horizontal synchronization period, and in this case, by constantly reversing the polarity of each display electrode potential, the AC drive frequency of the liquid crystal can be effectively made higher than the frame frequency. , the influence of the drop in display electrode voltage through the liquid crystal layer can be substantially improved, and a clear display screen with high contrast can be obtained. In this case, the COD analog memory only needs to have the transfer lock frequency higher than the horizontal synchronization frequency, and this method can also be applied to small-sized accu-dip matrix type liquid crystal displays. Then, an image with higher display quality can be obtained. Furthermore, if a video signal is given as a composite signal of three colors of RGB, color display is also possible by using a color filter or the like.

[Brief explanation of drawings]

1 to 3 are diagrams for explaining the present invention in detail,
FIGS. 4 to 7 are diagrams for explaining conventional examples. Agent Patent Attorney Nori Ken Yudo Chika Tomihisa Takehana Figure 1 Figure 3 Figure 4 Figure V (Xn) Figure 5 Shigogo Nmon rshi 4/Figure 7

Claims (1)

[Claims] (1) When driving multiple address lines and data lines line-sequentially, drive multiple address lines line-sequentially within one scanning period in which image data corresponding to one address line is transferred. A driving method for active matrix liquid crystal displays.