JPH01147525A - Driving method for liquid crystal display panel - Google Patents

Abstract

PURPOSE:To adjust contrast to the contrast meeting a user's desire and to prevent overlap of images by the shadows of black display picture elements by varying the amplitudes of source impression voltages and the pedestal level. CONSTITUTION:A reference voltage Vr and voltages V1-V4 are generated from a voltage source 21 and the relations expressed by the equation are given between the voltages. The magnitudes of V1 and V4, V2 and V3 with respect to Vr are varied by a variable resistor RV to adjust the level. A decoder 17j (j=1, 2,...) selects switching elements Sj1-Sj4 in the combination modes of '1' and '0' of a command signal M for conversion of current to AC and a picture element array signal DSj. The V2 or V3 is impressed to the corresponding picture element electrodes and the picture elements show the gray color between black and white in the case of the picture element array signal DSj=0. The density of the gray color varies with the magnitude of the V2 or V3. Namely, the background is displayed gray and the density thereof is regulated by the variable resistor RV. The double images are then invisible even if the liquid crystal panel is obliquely viewed. The shadows of the picture elements are substantially inconspicuous and the image quality is improved if the density of the background is adjusted.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" This invention relates to an improvement in a method for driving an active liquid crystal display panel.

"Prior Art" In an active liquid crystal display panel, as shown in FIG. 5, pixel electrodes 2 are arranged in a matrix of m rows and n columns in the display panel l, and each pixel electrode 2 has one TPT).
A transistor 3 is correspondingly provided, and the drain of the TPT transistor 3 is connected to the pixel electrode. One gate bus 4 corresponding to any i row and column of the above matrix.
1 and l'') (7) A source bus 5j is provided, and the gate of the corresponding TPT is connected to the gate bus 41,
The source of the corresponding TPT is connected to the source bus 5j.

An n-stage shift register 1 corresponding to the n columns of the display panel 1
1 is provided, and the terminal 12 is connected to the data input terminal of the first stage.
When a pulse-like horizontal start signal 5TH (Fig. 6A) is supplied, and then a horizontal dot clock CPH for one horizontal time is applied from the terminal 13 to the clock terminal CK of each stage, the horizontal start signal STH becomes horizontal. The output pulses of each stage are shifted to the right by one stage for each dot clock CPH, and the output pulses of each stage are sequentially output during one horizontal time (IH), and the clock terminals CK of the first latch circuits 14j (j = 1 to n) are respectively output. given to. On the other hand, a data signal DS for one horizontal time, that is, one row, is applied from the terminal 15 to the data input terminal of each first latch circuit 14j, and is sequentially corresponding to the output pulse of each j stage of the shift register 11. Pixel data DSj of stage j is latched.

Almost at the same time as the pixel data DSj of each column is latched by each first latch circuit 14j, it is outputted to the data input terminal of each corresponding second latch circuit 16j, and is simultaneously latched to the second latch circuit 14j by the next horizontal activation signal STH. It is latched into circuit 16j. Almost simultaneously, the pixel data DSj of each column latched is outputted and applied to one input terminal of each corresponding decoder 17j. The pixel data DSj of each column is also called a pixel column signal, and has a waveform as shown in FIG. 6B, for example. The other input terminal of each decoder 17j has a terminal 18.
An alternating current command signal M (FIG. 6C) is given.

Liquid crystal elements cannot be driven with direct current due to their lifespan, so when the pixel data is 1, the AC command signal M (1 on the display screen)
It is necessary to apply a positive or negative voltage (equal in magnitude) to the pixel electrode with respect to the reference voltage Vr according to the value of the binary code (1 or O alternately taken for each field). Note that the reference voltage Vr is applied to a common electrode (not shown) of the pixels.

In order to drive each source bus 5j, the liquid crystal drive circuit is provided with a voltage source 21 that outputs a first voltage Vl, a second voltage v8, and a third voltage V. Here T! Vl>Vx>V
s, Vr-(V+ +Vs)/2,
The voltage v8 is the reference voltage Vr mentioned above.

One end of switch elements 5JII 5JII S2 is connected to each source bus 5j led out from the display panel 1, and the other ends of these switch elements are connected to a first voltage v1 and a second voltage v of a voltage source 21, respectively. Wealth and third voltage V,
connected to the output terminal of

When the alternating current command signal M is M-1, each decoder 173 turns on the switch element Sj1 or Sjt in accordance with DSj-1 or 0, respectively. As a result, the voltage V or V! is applied to the source bus 5j, respectively. is given.

Further, each decoder 17j receives an AC conversion command signal M from M-0.
In this case, the switch element Sj3 or Sjl is controlled to be turned on depending on DSj=1 or O, respectively. As a result, the voltage V or v8 is applied to the source bus 5j, respectively. Pixel data for one horizontal time, that is, one row, is sequentially latched by the first latch circuits 14+ to 1411, and in response to the next horizontal activation signal STH, each of the latched pixel data is transferred to the second latch circuit 16. ~16. Then, the pixel data of the next row is latched in the first latch circuit 141.
~14. are latched sequentially. Thereafter, the above steps are repeated. In this way, pixel data for each row is transmitted to the source buses 51 to 5 for each horizontal activation signal STH. - Output simultaneously.

As already mentioned, the signal level is selected to be V, v8 or ■, vS depending on the value of the AC command signal M. For example, a source bus drive signal VSj shown in FIG. 6 is outputted to the source bus 5j in accordance with the value of the pixel column signal DSj.

Each bit of the source bus drive signal vSj is converted into a horizontal activation signal S.
The gate bus 4. ~4. A gate bus drive circuit 30 is provided to sequentially drive the gate bus. That is, the gate bus drive circuit 30 is given the vertical synchronization signal S from the terminal 31 and the horizontal activation signal STH from the terminal 12, and the gate bus drive circuit 30 synchronizes with vS and controls the gate bus for one vertical time. 41-4. are sequentially driven one horizontal time at a time in synchronization with STH. As a result, the TPTs in rows 1 to m are sequentially turned on, and the voltages V, , V, or vS corresponding to each bit of the pixel column signal VSj are applied to the corresponding pixel electrode 2 in column j.
The 0 pixel column signal DSj sequentially applied to 1j to 2m7 is D
The pixel to which the source bus drive signal VSj equal to the reference voltage vP (""Vt) is applied to the pixel electrode 2 at Sj-0 is as follows.
The magnitude of the voltage applied between the common electrode of the 0 pixel and the pixel electrode, which displays white (black) in a normally white (black) mode LCD, and therefore the background color of the screen is white (black). Since the contrast strength of the screen is determined by
Alternatively, the magnitude of the third voltage V, with respect to the reference voltage Vr is determined experimentally in advance at the design stage, and in the commercialized circuit, the magnitude of V,, V, is fixed to that value, and especially adjustment is not required. It has no function.

``Problems to be Solved by the Invention'' In active liquid crystal display panels driven by conventional liquid crystal driving circuits, the contrast of the display screen is fixed and cannot be changed by the user. In addition, when the liquid crystal display panel is viewed diagonally from the front, there is a problem in that the displayed characters and lines are cast in shadows and appear double, degrading the image quality.

As shown in FIG. 7, the liquid crystal display panel has a glass plate 41 superimposed on a reflecting plate 40, and pixels 42 are formed on the glass plate 41. One of the pixels is shown. Now, parallel incident light! ,~j! , is incident on the display panel from the front obliquely.1. The light between 1I and 1I is reflected by the reflection plate 40, passes through the pixel 42, and reaches the front. l,~l! The light between them enters the pixel 42, part of which is reflected by the surface, and the other light passes through the pixel, is reflected by the reflector 40, passes through the pixel again, and reaches the front *Between Ilt and I8 Part of the light is reflected by the surface of the pixel, and the other light passes through the pixel and is reflected by the reflector 40, reaching the front. When the pixel 42 is currently displaying black, a shadow 43 of the pixel is created on the reflector 40, and among the light reflected by the shadow, the light that passes through the pixel again is reflected by the pixel (real image). ) is not a problem because it overlaps with the light reflected on the surface of It will be sensed, and the image will be 2
This causes it to look heavy.

An object of the present invention is to vary the amplitude and pedestal level of the source applied voltage so that when the display screen of the panel is in the normally white mode, (a) black display pixels and other pixels, that is, background pixels, both display color; from (b) where the display color of the black display pixels is dark and the display color of the background pixels is light (therefore, the screen contrast is high), and further (C)
The contrast can be adjusted to the user's preference by continuously changing the screen density, such as the black display pixel and the background pixel displaying a dark color (thus, the screen contrast is low). to prevent the image from appearing double due to the shadow of the black display pixel.
This is an attempt to improve the liquid crystal driving method.

``Means for solving problems'' According to this invention, the reference voltage Vr and the first voltage vI.

Second voltage v! , the third voltage V, and the fourth voltage v4 (V, >V, ≧Vr≧V, >V, ,Vt shelf (vt 10V
4)/2-(V+Vl)/2) is provided, and a first set of the first voltage vl and the second voltage v8 is set depending on the value of the alternating current command signal. or fourth
Each voltage of the second set consisting of the voltage v4 and the third voltage Vs is selected, and depending on the value of the pixel data signal, either the first set or the second set of two voltages is applied to the corresponding source bus. and a first voltage vl and a fourth voltage v4 of the voltage source
゜ and/or the reference voltage V of the second voltage ■ and the third voltage V
The magnitude of r is adjusted by the level adjustment means.

Embodiment An embodiment of the drive circuit of the present invention is shown in FIG. 1, with the same reference numerals assigned to parts corresponding to those in FIG. 5, and redundant explanation will be omitted. A reference voltage Vr is supplied from the voltage source 21.

A first voltage vl, a second voltage Vt+a third voltage ■, and a fourth voltage v4 are generated. (hereinafter simply vr, vlVz,
) However, between these voltages there is V, >V, ≧Vr ≧v 3> v a
(A relationship D is given. An example of the magnitudes of Vr and Vl-Va is shown on the voltage axis in Fig. 2. With Vr as the reference, the magnitudes of vl and v4 are equal and the polarities are opposite. , vyo and V.

By varying the variable resistor RV, V with respect to Vr
, and ■4 and ■2 and V can be varied. That is, in this example, the variable resistor RV constitutes the level adjustment means.

The reference voltage Vr is supplied to the common electrode of the liquid crystal display panel l as in the conventional case. Voltages V and -V4 are respectively applied to switch elements SJI +SJ! +Sj2 +Sja (j = 1
% n ) to a common source bus 5j.

As shown in FIG. 3, the decoder 17j turns on the first switch element Sjl when (al) AC conversion command signal M-L pixel column signal DSj=1, and (a8) turns on the first switch element Sjl when M=1. DS
When j −0(7), the second switch element sno! is turned on, (bt)M=0. When n5j=t, the fourth switch element Sj4 is controlled to be on, and (bri M=O, DSj
When =O, the third switch element Sj3 is turned on.

For example, a source bus drive signal VSj shown in the second diagram is applied to each source bus 5j. Figure 2 A, B, C
6 respectively indicate a horizontal activation signal 5TH1 pixel column signal DSj and an AC conversion command signal M, which are similar to those shown in FIG.

As already mentioned, when the pixel column signal DSj is DSj-〇, the corresponding pixel electrode has 2 or V.

is applied. Therefore, that pixel displays gray between white and black. The density of gray is changed by ■ or the magnitude of Vl. That is, the background color is gray, and its density is adjusted by the variable resistor RV. As already mentioned, when the LCD panel is viewed diagonally, the shadow of the real image can be seen along with the actual image, causing the image to appear double. With this adjustment, the shadows are almost invisible (but the contrast of the screen is somewhat lowered, so the variable resistor RV is used to adjust the screen so that it is most easily seen as a whole).

Although the embodiment shown in FIG. 1 is constructed using the decoder 17j and the first to fourth switch elements 3H to SJ4, it is also possible to construct the system as shown in FIG. 4 without using these. In other words, the switch element S.
are switched to select the voltage V I +v2 or Vs, Va, respectively, and the switch element Sj is switched to the voltage Vl (
or v4).

■! (or Vs) is switched to the selection side.

[Effects of the Invention] According to the present invention, it is possible for the user to adjust the contrast of the liquid crystal display panel to his or her preference using the level adjustment means. In addition, by adjusting the density of the black display pixels on the screen displayed by the liquid crystal display panel, or by setting the background color of the screen to gray and adjusting its density, the screen will appear black when viewed from an angle. By making pixel shadows less noticeable, image quality can be significantly improved compared to conventional technology.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the liquid crystal drive circuit of the present invention, FIG. 2 is a waveform diagram of the main parts of the signals in FIG. 1, and FIG.
FIG. 4 is a circuit diagram showing main parts of another embodiment, FIG. 5 is a circuit diagram of a conventional liquid crystal drive circuit, and FIG. Figure 5 is a waveform diagram of the main part of the signal, and Figure 7 is a theoretical cross-sectional diagram to explain how black display pixels (real images) and their shadows appear double when the liquid crystal display panel is viewed from an angle. be. Patent applicant: Hoshi Denki Manufacturing Co., Ltd. Agent: Takashi Kusano 2
Illustrated figure 3/7 figure both OvI anti-JH board

Claims (1)

[Claims] A plurality of source buses and a plurality of gate buses are formed by crossing each other, and one source bus and one gate bus are driven to display an active liquid crystal display at the intersection of the source bus and the gate bus. A method of driving a liquid crystal display panel for driving pixels, the method comprising: a reference voltage Vr, a first voltage V_1, a second voltage V_2, a third voltage
voltage V_3 and fourth voltage V_4 (however, V_1>V_
2≧Vr≧V_3>V_4, Vr=(V_1+V_4)
/2=(V_2+V_4)/2) A voltage source is provided that generates the voltage V_1 and the second voltage V_1 according to the value of the alternating current command signal.
select each voltage of the first set consisting of the voltage V_2 or the second set consisting of the fourth voltage V_4 and the third voltage V_3;
the first voltage V_1 and the fourth voltage V_4 of the voltage source;
Alternatively, a method for driving a liquid crystal display panel, comprising adjusting the magnitude of the second voltage V_2 and the third voltage V_3 with respect to the reference voltage Vr using a level adjusting means.