JPS623408B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for driving an active matrix liquid crystal display device in which a switch element and a capacitive element are provided for each pixel. The present invention relates to an AC drive method that allows brightness control of a display screen using a voltage.

Recently, development of high-density active matrix type liquid crystal display devices using switch/capacitor arrays fabricated using semiconductor integrated circuit technology has been progressing. Since this type of display device includes a switch element and a capacitive element for each pixel, it is possible to obtain a display device with good volatility, contrast, and response.

FIG. 1 is an equivalent circuit diagram for explaining an example of the configuration of the above switch/capacitor array, in which 1 is a MOS type FET as a switch element, 2 is a MOS type capacitor as a capacitive element, and 3 is a display electrode that defines a unit pixel. The source or drain of FET 1 is electrically connected to one end of capacitor 2. The gates of FET1 are commonly connected for each row to provide address buses Y ₁ , Y ₂ ...... _Yo , and the drains or sources are commonly connected for each column to provide data buses X ₁ , X ₂ ...... ...X _n is provided. Said
The FET 1, capacitor 2, address and data bus are integratedly formed on, for example, a semiconductor substrate, and display electrodes 3 are further formed on the semiconductor substrate via, for example, an interlayer insulating film.
is formed and electrically connected to one end of the capacitor 2.

FIG. 2 is a cross-sectional configuration diagram for explaining an example of an active matrix type liquid crystal display device using the switch/capacitor array shown in FIG. , 5 is an interlayer insulating film, 6
7 is a reinforcing substrate, 7 is a common electrode made of a transparent conductive film, 8 is a transparent insulating substrate, 9 is a spacer and a sealing portion, and 10 is a liquid crystal material.

The operation of the liquid crystal display device shown in FIG. 2 when driven by direct current is performed as follows. That is, in FIG. 1, the address buses Y ₁ , Y ₂ ......Y _o are sequentially scanned and driven by scanning signals (address pulses) from the scan drive circuit, and the FET 1 is driven for a period of T _F /n for each row. sequentially brought into conduction. Here T _F
is the frame scanning period. When data, for example m parallel image signal voltages, are supplied to the data buses X ₁ , X ₂ . _{. .} . Accumulated and held over _F. This held signal voltage is guided to the display electrode 3, and excites the liquid crystal layer sandwiched between it and the opposing common electrode 7 in accordance with the signal voltage, thereby displaying an image. At this time, the brightness of the display screen can be controlled by adjusting the DC voltage supplied to the opposing common electrode 7.

However, it is well known that a liquid crystal display device driven by direct current has a short lifespan, and that driving by alternating current is preferable. A basic example of AC driving a matrix type liquid crystal display device is
It is disclosed in Publication No. 28117. In the case of the device shown in Fig. 1, AC driving is also possible by using the parallel image signal as a signal whose polarity is inverted every scan period of the address pulse with reference to the intermediate potential between the two potentials of the address pulse. be.

However, in AC drive of such a matrix type liquid crystal display device, it is not necessarily easy to control the brightness of the display screen. For example, it is conceivable to perform brightness control by changing the DC level of the parallel image signals as in television, but in this way, the data bus drive that drives the data buses X ₁ , X ₂ , ...... The IC must have a very high breakdown voltage. Further, brightness cannot be simply controlled by a DC voltage applied to the opposing common electrode as in the case of DC drive. For example, if the polarity of the DC voltage applied to the counter electrode is reversed in synchronization with the polarity reversal of the parallel image signal, the effective voltage applied to the liquid crystal cell changes depending on the address. In this case, it becomes dark and it is not possible to control the brightness uniformly over the entire surface.

The present invention has been made in view of the above points, and provides a method for driving a matrix-type liquid crystal display device using AC drive, which makes it possible to control the brightness of the display screen without increasing the withstand voltage of the data bus drive IC. .

That is, in the above-described matrix type liquid crystal display device, the present invention allows the parallel image signals supplied to the data bus to be adjusted to the address using an intermediate potential (not necessarily a strict midpoint) between both potentials of the address pulse as a reference. AC driving is performed as a signal whose polarity is inverted every pulse scanning period, and the polarity is inverted at a period that is an even multiple or an even fraction of the scanning period, with the intermediate potential as a reference, applied to the opposing common electrode of the liquid crystal cell. It is characterized in that a brightness control voltage is applied. According to the present invention, as in the case of direct current driving, it is possible to perform alternating current driving in which brightness can be controlled by the voltage applied to the facing common electrode of the liquid crystal cell. Also, unlike the method of adding DC voltage for brightness control to parallel image signals, the withstand voltage of the data bus driving IC can be lowered.

FIG. 3 is a voltage waveform diagram for explaining one embodiment of the present invention, where y ₁ is an address pulse supplied to address bus Y ₁ in FIG. 1, and y _j is an address pulse supplied to an appropriately selected address bus Y _j. This is the supplied address pulse, and shows the waveform when FET1 is a P channel. T _F is the frame scanning period. x _i is _the image signal voltage supplied to any one bus X _i of _the data buses X ₁ , It is shown as a thing. The polarity of this image signal x _i is inverted every scan period T _F with reference to the intermediate potential V _R between the high and low potentials of the address pulses (y ₁ , y _{j ,} etc.). V _COM is a brightness control voltage supplied to _the opposing common electrode 7 of the liquid crystal display device shown in _FIG .
The polarity is reversed every _2TF times. the above
y ₁ , y _j , x _i and V _COM are address buses y ₁ , y
_j , the data bus x _i and the opposing common electrode 7, respectively, the pulse bus Y ₁ and the data bus x _i
The liquid crystal cell of the pixel at the intersection of y ₁ −x _i in Figure 3
An alternating current voltage such as y j is applied, and a pulse bus y _j
An alternating current voltage such as y _j -x _i in FIG. 3 is applied to the liquid crystal cell of the pixel at the intersection of data bus x _i . However, these voltage waveforms are shown for the case where the current flowing through the liquid crystal cell is sufficiently small and the attenuation of the voltage accumulated in the capacitor 2 can be ignored. The voltage applied to these liquid crystal cells y ₁ −x _i
The effective value of y _{j −x i} is (a ² +b ² ) ^1/2 regardless of the address, and _{V COM}
By adjusting the value b of , it is possible to easily control the brightness uniformly over the entire surface in AC drive.

In the above embodiment, the polarity of the brightness control voltage applied to the opposing common electrode 7 is reversed at twice the scanning period _TF , but generally it is reversed at a period that is an even multiple or an even fraction of the scanning period _TF . If it is reversed, the effective value of the voltage applied to the liquid crystal cell becomes constant regardless of the address, and similar brightness control is possible.

As explained above, according to the present invention, the polarity of the parallel image signals supplied to the data bus of an active matrix type liquid crystal display device is determined every scanning period with reference to the intermediate potential between the high and low potentials of the address pulse supplied to the address bus. At the same time, by reversing the polarity of the brightness control voltage supplied to the opposing common electrode of the liquid crystal cell at an even number multiple or even fraction of the scanning period with reference to the intermediate potential, Similarly, AC driving can be performed in which the brightness can be controlled by the voltage of the opposing common electrode of the liquid crystal cell. Moreover, according to the present invention, there is an effect that the withstand voltage of the data bus driving IC can be lowered compared to the case where brightness control is performed by changing the DC level of the image signal.

[Brief explanation of the drawing]

FIG. 1 is an equivalent circuit diagram for explaining an example of the configuration of a switch/capacitor array, FIG. 2 is a cross-sectional configuration diagram for explaining an example of an active matrix liquid crystal display device using the array shown in FIG. The figure is a voltage waveform diagram for explaining one embodiment of the present invention. Y ₁ , Y ₂ , …………… Y _o ……address bus,
X ₁ , X ₂ , ......X _n ...Data bus, 1...
MOS type FET (switch element), 2... MOS type capacitor (capacitive element), 3... display electrode, 4...
Silicon substrate, 5... Interlayer insulating film, 6... Reinforcing substrate, 7... Opposing common electrode, 8... Transparent insulating substrate, 9... Spacer, 10... Liquid crystal substance, y ₁ , y
_i ... Address pulse, x ₁ ... Image signal, V _COM ...
...Brightness control voltage, V _R ...Intermediate potential, T _F ...Frame scanning period.

Claims (1)

[Scope of Claims] 1. A plurality of address buses to which address pulses are supplied and scanned sequentially and a plurality of data buses to which parallel image signals are supplied and driven simultaneously are wired in an intersecting manner. A pixel is provided, comprising a switch element controlled by a bus, a capacitor element to which parallel image signals are supplied from the data bus via the switch element, and a liquid crystal cell to which a voltage stored in the capacitor element is applied, and the liquid crystal In a driving method of a matrix type liquid crystal display device in which cells have opposing common electrodes, the parallel image signal is a signal whose polarity is inverted every scanning period of the address pulse with reference to an intermediate potential between both potentials of the address pulse, and a matrix type liquid crystal display characterized in that a brightness control voltage whose polarity is reversed at an even multiple or even fraction of the scanning period with respect to the intermediate potential as a reference is applied to the opposing common electrode. How to drive the device. 2. In a liquid crystal display device, a switch element, a capacitive element, an address bus, and a data bus are integrated and formed on a semiconductor substrate, and display electrodes are connected to the capacitive element for each pixel on the surface of this substrate via an interlayer insulating film. A matrix type liquid crystal display device according to claim 1, which is constructed by providing a transparent insulating substrate on which a common electrode made of a transparent conductive film is formed with a liquid crystal substance interposed therebetween. Driving method.