JP2504105B2 - Driving method for active matrix liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention provides a switching element for each pixel,
The present invention relates to a so-called active matrix type liquid crystal display driving method.

[Prior Art] In recent years, research and development of so-called active matrix type liquid crystal displays, in which a switching element is provided for each pixel, have been conducted in various places aiming at a liquid crystal display of high display quality. The main application of this active matrix type liquid crystal display device is television display. The NTSC system is widely used for television display, and one field consists of 60 hertz. When this is used in the above active matrix type liquid crystal display, since the liquid crystal needs to be AC-driven from the viewpoint of stability over time and the like, the frequency of AC driving of the liquid crystal is 30 hertz. However, the limit is usually around 40 Hertz, and flicker occurs at frequencies below that,
There is a problem that the display quality is deteriorated.

As means for solving the above problems, for example, Japanese Patent Laid-Open No. 62-17
There is a driving method disclosed in No. 5074, which can double the frequency of AC driving of liquid crystal.

FIG. 3 is a time chart showing the driving method,
FIG. 4 shows the electric circuit. The driving method will be described below with reference to FIGS. 3 and 4.

In FIG. 4, S1 ... Sn are switching elements by MIS transistors, C1 ... Cn are liquid crystal layers, X1 ... Xn are scanning signal lines that determine selection (ON) or non-selection (OFF) of the switching elements, Y1 ... Yj ... Is an image signal line for supplying an image signal to a pixel electrode (not shown) through the switching element. The scanning signal driver 9 is a circuit that receives a signal from the control circuit 10 and supplies a signal to the scanning signal lines X1 ... Xn.
The image signal driver 11 is a circuit that receives a signal from the selection circuit 12 and selects two types of image signals described below. The counter electrode is an electrode formed on the counter substrate provided via the liquid crystal layers C1 ... Cn with respect to the substrate on which the switching elements S1 ... Sn are formed, and due to the voltage difference between the counter electrode and the pixel electrode. , The liquid crystal layers C1 ... Cn are changed in light transmittance to perform display. In FIG. 3, TV is a vertical period corresponding to one field period, and TVf and TVs are a first half period and a second half period in which the above vertical period TV is equally divided. TH is a horizontal period obtained by dividing one vertical period by the number of scanning signal lines n, and TH = TV / n.

THf and THs are a first half period and a second half period in which the above horizontal period TH is equally divided. χ1 ... χn are scan signals applied to the scan signal lines X1 ... Xn. Vj is an image signal applied to the image signal line Yj, which is a positive polarity real-time image signal VS.
It is composed of IG and a predetermined negative DC signal VDC. Although the image signal is different on each image signal line Y1 ... Yj ..., VSIG and VDC are supplied at the same timing as Vj in the above description. Therefore, in the following description, Vj is referred to as an image unless otherwise specified. Treat as a signal representative.

The operation in TVf during the first half of the vertical period Tv is as follows. Horizontal period TH first half period THf → second half period THS → first half period
Scan signal line X1 → Xn / 2 + in synchronization with the timing of THf ...
1 → X2 ... is selected by the scan signal driver and the scan signal χ
1 → χn / 2 + 1 → χ2 ... Becomes “1” and the switching elements S1, Sn / 2 + 1, S2 ... sequentially turn on.

At this time, the image signal Vj supplied from the image signal driver 11 to the image signal lines Y1 ... Yj in synchronization with the above timing is
VSIG → VDC → VSIG ... and these signals are supplied to each pixel electrode through the switching elements S1, Sn / 2 + 1, S2 ..., and due to the voltage difference between the pixel electrode and the counter electrode, the liquid crystal layers C1, Cn /
Display is performed by changing the light transmittance of 2 + 1, C2 .... The voltage difference between the pixel electrode and the counter electrode depends on the capacitance component of the liquid crystal layers C1, Cn / 2 + 1, C2 ... It is the same scan signal line X1, Xn / 2 +.
It is held until 1, X2 ... is selected. The operation in the second half period Tvs of the vertical period Tv is as follows. The scanning signal line Xn / 2 + is synchronized with the timing of the horizontal period THf → the second half period THS ...
1 → X1 is selected, the scanning signal χn / 2 + 1 → χ1 becomes “1”, and the switching elements Sn / 2 + 1, S1 ... sequentially turn on.
At this time, the image signal Vj supplied from the image signal driver 11 to the image signal line in synchronization with the above timing is VSIG → VDC.
... and these signals are switching elements Sn / 2 + 1,
It is supplied to each pixel electrode through S1 .... The operation described above is repeated with the vertical period TV as a cycle.

As can be seen from the above, the scanning signals χ1 ... χn supplied to the scanning signal lines X1 ... Xn are selected at every cycle corresponding to approximately 1/2 TV, and at this time, are supplied to the pixel electrodes through the switching elements S1 ... Sn. The generated image signal has an opposite polarity in every cycle corresponding to approximately 1/2 TV. That is, the liquid crystal layer
Since the polarities of the voltages applied to C1 ... Cn are reversed in every cycle corresponding to approximately 1/2 TV, the liquid crystal layers C1 ... Cn are set in the vertical period TV.
AC drive will be performed at a cycle corresponding to. Applying this to the NTSC system TV display, the frequency of AC drive is increased to 60 hertz, and flicker is greatly reduced.

Note that the DC signal VDC is used as the image signal Vj in the second half period THs of the horizontal period TH, in order to reduce the circuit cost by not installing a memory circuit or the like.

[Problems to be Solved] According to the above-described driving method, the positive-polarity real-time image signal VSIG is always supplied to the pixel electrode in the first half period THf of the horizontal period TH, and always in advance in the second half period THs of the horizontal period TH. The determined negative DC signal VDC is supplied to the pixel electrode.
Therefore, the voltages applied to the liquid crystal layers C1 ... Cn are asymmetrical in positive and negative, and as a result, a DC bias is applied to the liquid crystal layers C1 ... Cn, which causes a problem of accelerating the deterioration of the liquid crystal panel. This is an unavoidable problem as long as the signal supplied to the pixel electrode in the second half period THs of the horizontal period TH is a DC signal of a predetermined level.

An object of the present invention is to provide a method for driving an active matrix type liquid crystal display, which can increase the frequency of AC driving of liquid crystal and can prevent a DC bias from being applied to the liquid crystal.

[Means for Solving the Problems] A method of driving an active matrix type liquid crystal display according to the present invention includes a plurality of switching elements arranged in an array and a plurality of scanning signal lines for supplying a scanning signal to each of the switching elements. A driving method of an active matrix type liquid crystal display having a plurality of image signal lines for supplying an image signal to each of the switching elements selected by the scanning signal, one vertical scanning period is divided into an odd number of divided periods. A scanning signal is supplied to each of the switching elements through the scanning signal line for each of the divided periods to select each of the switching elements for each of the divided periods,
A signal whose polarity changes through the image signal line is supplied to each of the selected switching elements through the image signal line, and each polarity changing signal supplied to each of the switching elements corresponds to one vertical scanning period. And an even number of pre-fixed signals whose polarities change in a cycle corresponding to one divided period between adjacent image signals supplied to the switching elements. It is characterized by being.

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

In FIG. 2, S1 ... Sn are switching elements by MIS transistors, C1 ... Cn are liquid crystal layers, X1 ... Xn are scanning signal lines for selecting (ON) or non-selecting (OFF) the switching elements, and Y1 ... Yj are An image signal line for supplying an image signal line to a pixel electrode (not shown) through the switching element. 1 is a timing circuit, which is the period TV, TV shown in FIG.
A timing pulse having a cycle corresponding to 1, TV2, TH, TH1, TH2, TH3 is generated. The scanning signal driver 2 receives the above-mentioned timing pulse and sends it to the scanning signal lines X1 ... Xn in FIG.
The scanning signal of 1 ... χn is supplied. Reference numeral 3 denotes a gate circuit which receives each of the above timing pulses as an input, and generates a signal for sequentially selecting signals VSIGP, VSIGN, VDCP, VDCN described later. Reference numerals 4 ... 7 are analog switches, and 8 is an image signal driver, which receives the signals selected by the analog switches 4 ... 7 and selects four types of image signals described later. The counter electrode 9 is an electrode formed on the counter substrate, which is installed via the liquid crystal layers C1 ... Cn with respect to the substrate on which the switching elements S1 ... Sn are formed.

In FIG. 3, TV is a vertical period corresponding to one field period, and TV1, TV2, and TV3 are a first period, a second period, and a third period obtained by dividing the vertical period TV into three equal parts. TH is the horizontal period obtained by dividing the vertical period TV by the scanning signal line n, and TH = TV
/ n. TH1, TH2, and TH3 are a first period, a second period, and a third period obtained by dividing the horizontal period TH into three equal parts. χ1 ... χn are scan signals applied to the scan signal lines X1 ... Xn. Vj is an image signal applied to the image signal line Yj, and this is the positive and negative polarity real-time image signals VSIGP and VSIGN,
Pre-fixed positive and negative DC desired signals
It consists of VDCP and VDCN. The image signal is different for each image signal line Y1 ... Yj.
Since the timings at which IGN, VDCP, and VDCN are supplied are the same as Vj, Vj will be treated as a representative of image signals in the following description unless otherwise specified.

The operation in the first period TV1 of the vertical period TV is as follows. Horizontal period TH first period TH1 → second period TH2 → third period
The scanning signal line X1 → Xn / 3 + 1 → X2n / 3 + 1 → X2 ... Is selected by the scanning signal driver in synchronization with the timing of TH3 → first period TH1 ..., and the scanning signal χ1 → χn / 3 + 1 → χ2n / 3 + 1
→ χ2… becomes “1” and switching elements S1, Sn / 3 + 1, S
2n / 3 + 1, S2 ... Turn on sequentially. At this time, from the image signal driver 8, the image signal lines Y1 ...
The image signal Vj supplied to Yj ... is VSIGP → VDCN → VDCP → V
SIGN… changes, and these signals are switching elements S1, S
It is supplied to each pixel through n / 3 + 1, S2n / 3 + 1, S2 ... And due to the voltage difference between the pixel electrode and the counter electrode, the liquid crystal layers C1, Cn / 3 + 1, C2n / 3
Display is performed by changing the light transmittance of +1, C2 ....

The operation in the second period TV2 of the vertical period Tv is as follows. Horizontal period TH first period TH1 → second period TH2 → third period
Scan signal line in synchronization with the timing of TH3 → first period TH1 ...
X1 → Xn / 3 + 1 → X2n / 3 + 1 → X2 ... Is selected, the scan signal χ1 → χn / 3 + 1 → χ2n / 3 + 1 → χ2 ... becomes “1”,
The switching elements S1, Sn / 3 + 1, S2n / 3 + 1, S2 ... Turn on sequentially. At this time, the image signals supplied from the image signal driver 8 to the image signal lines Y1 ... Yj ... In synchronization with the above timing.
Vj changes in the order of VDCN → VSIGP → VDCN → VDCP ... And these signals are supplied to each pixel electrode through the switching elements S1, Sn / 3 + 1, S2n / 3 + 1, S2.

The operation in the third period TV3 of the vertical period TV is as follows. Horizontal period TH first period TH1 → second period TH2 → third period
In synchronization with the timing of TH3 → first period TH1 ..., the scanning signal line X1 → Xn / 3 + 1 → X2n / 3 + 1 → X2 ... Is selected and the scanning signal χ1 → χn / 3 + 1 → χ2n / 3 + 1 → χ2 ... is "1". become,
The switching elements S1, Sn / 3 + 1, S2n / 3 + 1 → S2 ... sequentially turn on. At this time, the image signal Vj supplied from the image signal driver to the image signals Y1 ... Yj ... in synchronization with the above timing.
Changes from VDCP → VDCN → VSIGP → VDCN ... And these signals are supplied to each pixel electrode through the switching elements S1, Sn / 3 + 1, S2n / 3 + 1, S2. Next vertical period TV first period
The operation on TV1 is as follows. The first period T of the horizontal period TH
The scanning signal line X1 → Xn / 3 + 1 → X2n / 3 + in synchronization with the timing of H1 → second period TH2 → third period TH3 → first period TH1 ...
1 → X2 ... is selected, and scanning signal χ1 → χn / 3 + 1 → χ2n /
3 + 1 → χ2 ... becomes "1" and switching elements S1, Sn / 3
+1, S2n / 3 +1, S2 ... Turn on sequentially. At this time, from the image signal driver 8 in synchronization with the above timing, the image signal line
The image signal Vj supplied to Y1 ... Yj ... is VSIGN → VDCP → VDC
Change from N → VSIGP…, these signals are switching elements
It is supplied to each pixel electrode through S1, Sn / 3 + 1, S2n / 3 + 1, S2 .... In this way, similar operations are sequentially performed.

Here, for example, the scanning signal χ supplied to the scanning signal line X1
Focusing on the image signal Vj supplied by the switching element S1 selected by 1, the VSI is generated at a cycle corresponding to 1/3 TV period.
GP → VDCN → VDCP → VSIGN ... Although the other switching elements S2 ... Sn have different phases, the above-mentioned image signal sequences are sequentially supplied. That is, since the image signal Vj supplied to the pixel electrode is a signal of opposite polarity in a cycle corresponding to 1 / 3TV period, the liquid crystal layers C1 ... Cn are
AC drive will be performed at a cycle corresponding to the 2/3 TV period. When this is applied to the NTSC system TV display, the liquid crystal
It will be driven at 90 Hertz, and almost no flicker will occur.

On the other hand, focusing on the real-time image signals VSIGP and VSIGN, VSIGP and VSIGN are alternately supplied to the pixel electrodes in a cycle corresponding to one vertical period TV. Therefore, the disadvantage that the real-time image signal is biased to only one polarity, which has been conventionally seen, is removed, and a DC bias is not applied to the liquid crystal layers C1 ... Cn.

In the above embodiment, one vertical period TV is divided into three,
In the present invention, the number of divisions is not limited to this, and may be odd divisions such as 5 divisions, 7 divisions. Further, each divided period does not have to be equally divided, and for example, in the case of three divisions, it may be divided into 2: 1: 1.

EFFECTS OF THE INVENTION According to the present invention, since the liquid crystal is driven by an alternating current with a cycle shorter than a cycle corresponding to one vertical scanning period, display with almost no flicker can be obtained, and an image signal can be displayed in one vertical scanning period. Since the voltage is alternately applied to the liquid crystal layer in a corresponding cycle, it is possible to prevent the direct current bias from being applied to the liquid crystal layer, and it is possible to significantly suppress the deterioration of the liquid crystal panel.

[Brief description of drawings]

FIG. 1 is a time chart of a driving method showing an embodiment of the present invention, FIG. 2 is an electric circuit diagram for realizing the driving method of FIG. 1, FIG. 3 is a time chart of a driving method of a conventional example,
FIG. 4 is an electric circuit diagram of the above conventional example. S1 to Sn …… Switching elements X1 to Xn …… Scanning signal lines

Claims (1)

(57) [Claims] 1. A plurality of switching elements arranged in an array, a plurality of scanning signal lines for supplying a scanning signal to each of the switching elements, and an image signal to each of the switching elements selected by the scanning signal. In a driving method of an active matrix type liquid crystal display having a plurality of image signal lines, one vertical scanning period is divided into an odd number of divided periods, and each switching element is scanned through the scanning signal line in each of the divided periods. A signal is supplied to select each of the switching elements for each of the divided periods, and a signal whose polarity changes through the image signal line for each of the divided periods is supplied to each of the selected switching elements. The signals whose polarities change are supplied to the switching elements are the image signals whose polarities change in a cycle corresponding to one vertical scanning period. An active matrix type characterized in that it is composed of an even number of pre-fixed signals whose polarities change in a period corresponding to one divided period between adjacent image signals supplied to the respective switching elements. Liquid crystal display driving method.