JPS62267725A - Driving method for display device - Google Patents

Abstract

PURPOSE:To easily adjust the displaying brightness, contrast ratio, visual angle, color tone, etc., of a display device, by changing the waveform of the voltage applied across a common electrode. CONSTITUTION:Display is performed by applying a scanning voltage Vscan, signal voltage Vsig, and common electrode voltage Vcom across an active- matrix liquid-crystal display which is equipped with scan wirings 2 that connect gate electrodes of TFT elements 1, signal wirings 3 that connect drain electrodes, and a liquid crystal layer 5 enclosed into the space between transparent electrodes 4 connected with a source electrode side and transparent electrodes 6 formed on a facing glass base plate. The reference frequency of an AC voltage Vcom is set by using the frequencies of selected periods t1 and t3 and the reference frequency is used as the frequency when the scanning voltage Vscan successively scans scanning lines. The waveform of the voltage applied across the liquid crystal layer becomes a waveform Vlc which is amplitude-modulated by the AC voltage Vcom. Voltages to be applied across a selected picture element and across a nonselected picture element are made different from each other in such way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to five driving methods for display devices, and particularly to a driving method suitable for active matrix liquid crystal displays using thin film transistors (TJ'T).

[Conventional technology]

In a conventional active matrix liquid crystal display, when the transparent common ti on the glass substrate facing the TPT substrate via the liquid crystal f- is at a common potential for the entire screen, ffH, fF is disclosed in Japanese Patent Publication No. 1983-28649. As described, the potential of the transparent common electrode is switched at a constant period, or Japanese Patent Application Laid-open No. 55-157795 VC
As mentioned above, the polarity of the signal voltage is reversed every 177 frames, and the common electrode substrate is correspondingly reversed every 1 frame.

In the above driving method, when changing the effective voltage ratio (hereinafter referred to as applied voltage ratio) of the voltage applied to the liquid crystal layer of the selected pixel and the non-selected pixel, the voltage level applied to the signal electrode is changed to VC. It's changing. In this way, for example,
Viewing angle of LCD panel? To adjust the display brightness, contrast ratio, etc., use the A1 signal lightning pressure V
S1g (7') voltage level? There is a costume that can be changed, and according to this, you can scan [Wing Vscan 5-Change ζ,
Also, the scanning voltage should be adjusted with a margin to match the conditions where the effect of the signal voltage is the greatest. It is necessary to set it. However, it is necessary to consider the withstand voltage of the TF'T element, and there is a power supply voltage limit for the peripheral drive circuit that operates the display section, so there is no method of using it by varying the signal voltage or scanning voltage. This cannot be said to be a desirable method.

[Problem that the invention seeks to solve]

For the purpose of the present invention, the viewing angle, contrast ratio, and each display factor of the liquid crystal display are determined by the TF'T element bottle of the display section. − is the operating condition f of the scanning full I drive circuit, signal side drive circuit, etc.
The present invention is to provide a method for driving an adjustable display without changing the display.

[Problem f - Strategies to solve the problem]

The above objective is achieved by utilizing the phenomenon that the transmittance (brightness) of the liquid crystal currently used in the active matrix liquid crystal display depends on the Higashide effective value marked 77D.

[Embodiment 1] Hereinafter, an embodiment using the method of dH will be described with reference to FIG. The signal wiring #j3 connects the scanning wiring 2 filled with the gate electrode of the TF'T element 1 and the drain electrode, and the transparent wiring connected to the source electrode side of the TF'T element.
For an active matrix liquid crystal display composed of tFi4 and a liquid crystal layer 5 sealed between a transparent electrode 6 formed on a counter glass substrate, a scanning voltage Vsc is applied.
An, signal voltage Vsig, and common electrode voltage Vcom are applied to perform display.

Scanning voltage vscan rt, selection period 'I*'S, voltage P higher than threshold voltage vth of TPT element is applied to turn on TPT (conducting state), non-selection period it and t4rc. The TPT'E-off state (blocking state) is set as a voltage lower than the threshold voltage of the rXTFT element.Periods t1 and tl constitute one frame.The signal voltage Vsig is set during the selection period t1.t of the scanning voltage Vscan. , the voltage value applied to the liquid crystal layer 5 is set in accordance with 11° The voltage is inverted T in the frame c of t2 (hereinafter referred to as an even frame for convenience) and the frame of period f3*'4 (hereinafter referred to as an odd frame).T, that is, \liquid crystal 7
#2 Voltage Tube Mark 7JI] In the case of vcrI even number frame v-h te Vs odd number 7V-me, VS is set, and when no voltage is applied to the liquid crystal layer, vc is even number frame, odd number frame tomo Vn
shall be.

Generally speaking, as the common electrode potential Vcom, conventionally a DC voltage equal to V4 of the signal voltage a:Vsig, or with a slight level difference from v4, has been applied, but in the present invention, the common electrode potential Vcom is applied as the common electrode potential Vcom. With respect to the potential vcom, the cross +5! as shown in FIG. It uses voltage.

Based on this AC' voltage, the selected periods tl and ts are
It is set as a quasi-frequency. That is, the common electrode potential Vcom
The frequency ヰ and the scanning voltage ``5can'' are the frequencies at which the scanning lines are sequentially scanned.

At this time, for example, the voltage waveform applied to the liquid crystal layer of the selected pixel has a vtc-like waveform, and a drum-shaped waveform that is modulated by the alternating current voltage of vcom. If the effective voltage applied 770 to the liquid crystal layer is Vtl, and the effective voltage applied by the frame signal voltage is Vtl, and the effective voltage applied by the common electrode voltage Vcom is Vt2, then Vlceff
= (Vjt ” + Vts ”) ” fk h
The ratio α of the effective voltages applied to the liquid crystal layer of the selected pixel and the non-selected pixel is expressed by the following equation.

That is, by adjusting the values of vtt and vtl, it is possible to change the value of α.

As mentioned above, by changing the voltage applied to the selected pixel and the non-selected pixel, the brightness of the selected pixel and the non-selected pixel can be changed, as shown in Figure 2, and the display adjustment of the brightness, g4 adjustment of the contrast ratio, and in the case of viewing angle dependent characteristics such as FFTN liquid crystal, vcα,
The optimum viewing angle can be set.

Here, what is the voltage component applied to the liquid crystal layer from the common voltage iEVcom? think. In Figure 3, the liquid crystal volume 11c
tc, the gate capacitance CgS and floating capacitance ics that exist between the source electrode 4 and the traveling electrode 2 are common depending on the value of the number of customers! The value voltage Vcom is divided to determine the voltage applied 710 to the liquid crystal layer. According to these capacities, common 1
The effective component of the voltage applied to the liquid crystal may be changed by adjusting 1r411tEEVcom.

FIG. 4 shows an example of the waveform of the common electrode voltage vCOm.

This is a waveform obtained by applying an alternating voltage to the center of the voltage level v4f of the signal voltage Vsig in (a). Three levels of voltage during period t1? is applied, but the last j within the period tl
li is set to v4, and when the signal voltage vsig is applied through the nocturnal layer KTF'T element at this time, the instantaneous applied voltage at the non-selected pixel is set to O.

The waveform in (b) shows that the bias value ■b is applied to the final value PV4 of the period t1, and that πv4rr is applied every l frame.
- The waveform switches to the center and is T-type. The value of vb is T in the selection period with respect to the signal voltage VSig K.
It acts as a bias voltage when F'T is in the on state 1'(1'), and it is possible to change the C pressure value of selected and non-selected pixels.

Waveform tsL in (C) This is an example of a waveform in which the brightness of each color is varied separately when the color filter arrangement t shown in FIG. 5 is striped in the m direction.

T, that is, red (R) scanning, vLr, green (G) scanning line Lg, and blue (B) scanning in the period @Lh, changing the final value of the voltage of each selection period, and making it roughly an even number. The voltage level is inverted around the voltage level v4F in the frame and the odd-numbered frame. Thereby, by adjusting the voltage level for each color, the display color parameters can be changed.

Although the above embodiment shows an example in which the signal voltage level is adjusted to the center voltage level, in order to reduce the DC voltage when the DC voltage is applied to the liquid crystal layer, Modifications such as changing the voltage level are also possible.

FIG. 6 shows a specific example in which this embodiment is applied to an active matrix liquid crystal display. backlight 8 upper vct
A panel with liquid crystal sealed between two substrates, the FT substrate 7 and the common polar substrate 8! This is a method in which the voltage level of the waveform generating circuit 0 is varied using a variable resistor 11 or the like with respect to this common electrode substrate. While using the display panel, the user [2] can adjust the value of the variable resistor [1] to obtain the optimum display condition.

〔Effect of the invention〕

According to the present invention, the voltage applied to the signal wiring and the short supply wiring is the same as the conventional method! Changing the voltage waveform applied to the pole has the effect of easily adjusting the display brightness, conotrast ratio, viewing angle, color tone, etc.

[Brief explanation of drawings]

f4L111 is a circuit diagram and a waveform diagram of an embodiment of the method of the present invention, FIG. 5AO color filter piping diagram, @Figure 6 is a t diagram of the display. 1... Thin film transistor, 2... Scan tL 3...
・Signal '1M pole, 4... Source Ntaku, 5... Liquid crystal,
6... Opposing common tti, 7... *til-lanogistor board, 9... Backlight. Figure 1 VC

Claims (1)

[Claims] 1. A substrate on which thin film transistors are arranged at each intersection of a plurality of scanning wirings and a plurality of signal wirings intersecting the scanning wirings, and a common electrode substrate facing the substrate and having a transparent electrode formed on a transparent insulating substrate; In an active matrix liquid crystal display in which liquid crystal is sealed between these two substrates, the display is characterized in that an alternating current voltage having a frequency that is an integral multiple of the frequency of the scanning voltage applied to the scanning wiring is applied to the common electrode substrate. How to drive the device.