JPH0370279A - Drive method for tft active matrix liquid crystal panel - Google Patents

Abstract

PURPOSE:To reduce flicker by forming independent source bus lines with even and odd number lines, connecting an independent source driver to the even and odd number lines and supplying a signal whose AC polarity is inverted to the even and odd number lines. CONSTITUTION:X electrodes (source bus lines) are wired so as to be independent for the even and odd number lines and different source drivers 15, 16 are connected respectively to the even and odd number lines and the polarity of AC supply is made opposite to the even and odd number lines. Thus, the source lines are wired separately to the even and odd number lines and the divers are formed separately to the even and odd number lines, then 1H period drive is always attained with a driver IC of simple constitution. Thus, requirements to a TFT(Thin Film Transistor) are relaxed and even when the polarity of AC supply on the line period is inverted, since no inversion takes place on the source bus lines, a small drive capacity is enough.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is based on TFT (Thin Film Tra
This invention relates to a method for driving an active matrix liquid crystal panel.

[Conventional technology]

Fig. 3 is an equivalent circuit diagram of a conventional TFT active matrix liquid crystal panel. A field effect transistor (FET or TFT) is connected to one electrode (drain electrode or pixel electrode) of each liquid crystal cell, and these three elements constitute one pixel. . 4 is a plurality of Xt poles commonly connected to the input electrode (source electrode) of FET 3 for each column of the matrix; 5
are a plurality of Y electrodes commonly connected to the gate electrodes of the FETs 3 for each row of the matrix.

Further, 6 is a scanning circuit that sequentially applies scanning pulses to the Y electrodes 5, and 7 is a scanning circuit that samples and holds the video signal to convert the video signal for one horizontal scanning line into parallel video signals for the number of X electrodes. 4 is a serial/parallel conversion circuit that applies voltage to the serial/parallel conversion circuit 7, and 9 is an AC conversion circuit for each of R, G, and B that converts the video signal into AC in order to supply the AC video signal to the serial/parallel conversion circuit 7. A common electrode 8 is commonly connected to the other electrode of all liquid crystal cells 1.

FIG. 5 shows the shape and pixel arrangement of RlG and B pixels arranged on each liquid crystal cell in FIG. 3.

In this figure, the solid line frame indicates a unit (one pixel) that is sampled and displayed at approximately the same time, and this one driving unit (one pixel) is made up of one each of R, G, and B pixels. .

Next, a method for driving the display device shown in the figure will be explained.

Now, if the first row of Y electrodes is Yl, -Y electrode 5
For each electrode, for example, the electrodes Y1 to Y4, the Y l shown in FIG.
A waveform signal with a timing like ``' Y a is applied by the scanning circuit 6. When this scanning pulse is applied to the gate of the FET 3, all the FETs 3 in the selected row are turned on, and the signal from the X electrode 4 is turned on. A charge corresponding to the parallel video signal is charged to the storage capacitor 2 via the FET 3.Even if the FET 3 is turned off, the charge stored in the storage capacitor 2 causes the liquid crystal to have a voltage corresponding to the video signal. continues to be applied, the transmitted light of each liquid crystal cell can be controlled and displayed by the video signal.Also,
The method of sampling and displaying drive units such as R, G, and B at the same time as shown in FIG.
This can be controlled by how the sampling clock is applied to the serial/parallel conversion circuit 7.

Note that if the voltage of the same polarity is continuously applied to the liquid crystal, its lifespan will be shortened, so even if the polarity of the voltage applied to the liquid crystal is reversed, it has almost the same transmitted light characteristics. However, more precisely, when converting to AC,
There is a slight difference in transmitted light characteristics depending on the polarity, and as a result, a bright screen and a dark screen are repeated at a field period (60 Hz), resulting in flicker at a frame period (30 Hz).

Conventionally, as a countermeasure for this kind of flicker on large screens, for example, as shown in Figure 5, pixels driven with positive or negative polarity are divided into a shaded area and a non-shaded area to reduce the printing force on large screens. Was. In other words, if no measures are taken, the entire screen will change between bright and dark at 60Hz, but if the above measures are taken, the partial area of the screen will change from <60Hz.
The light/dark cycles are repeated at each frequency, but the bright/dark N
Since the area is dispersed within the screen, a visual LP (low pass) effect works, and it is perceived as the average brightness of bright/dark. However, with this kind of countermeasure, there is a problem in that when the object approaches the object a little, a regular vertical striped pattern appears, which is easily perceived. Therefore, as shown in Figure 2, it was considered to change the polarity of the alternating current for each gate line, but if the polarity was reversed in the gate line period in this way, the signal to be supplied to the X electrode would be IH (1 When the horizontal period is 2T, the period becomes 63.5 μ5 ec), and the fundamental frequency becomes extremely high from the conventional 30 Hz to 15 KHz. The Xt poles are wired from end to end as pass lines in the vertical direction of the panel, and their distributed capacitance is also considerable. Therefore, as the signal frequency increases as mentioned above, it is extremely difficult to drive within the IH period due to the distributed capacitance, and it is difficult to prevent flicker as shown in Figure 2. .

Next, the power of the serial/parallel conversion circuit 7 (source line driver) shown in FIG. 3 will be explained. Figure 6 shows its constituent countries, and the sample/hold circuit that divides one line of AC video signal into X number of electrodes and holds each potential.
S/H) 10 and the time-sharing type driver 11 that controls the drive of each output and increases the drive capability.Normally, with a source driver like the one shown in Fig. 6, the drive of one line is The video signal is the effective video period of IH, S/H
L, - will be driven simultaneously based on the control of the output enable signal OE supplied to the driver during the retrace period. Therefore, since the drive period indicated by the solid line is the retrace period, which is only about 10 μsec (in the case of a TV), it is necessary to charge or discharge the storage capacitor 2 during this period. A considerably high N (on current) was required. It has been difficult to achieve this on-current in TFTs formed using a-3i as a channel material, which is generally used and has the characteristics of low power consumption and a uniform bottom film.

In order to solve this problem, a driver having a configuration as shown in FIG. 7 can be considered. In this configuration, 378 circuits are connected to 1 circuit in the figure.
As shown in 2.13, it has two lines, and the output of each bit selects 1 and 2 of the 378 circuits based on the control signal, which is the SW signal, supplied to the selection type driver 14. Therefore, the I that S/H1 is sampling
During the H period, the result of S/H before that IH can be driven by S/H2, and furthermore, in the next IH period, the result of S/H can be driven by S/H1, and the result of S/H can be driven by S/H2. is always 1H3tJI by turning it for sampling.
You can drive for a while. As a result, restrictions on TFTs are relaxed, but such a configuration requires 378 circuits for two lines of source drivers, which is large-scale.

In addition to being complicated, the LCD display is its special feature.

Due to the requirement for a compact form, the source line driver has also become highly integrated, and by increasing the number of output bits, this is in conflict with the aim of reducing the number of driver ICs to be mounted. .

[Problem to be solved by the invention]

Conventional TFT active matrix liquid crystal panels have been driven using the methods described above, which have led to numerous problems such as noticeable flicker, strict specifications for TFTs, and difficulty in implementing LSI source drivers.

This invention was made in order to solve the above-mentioned problems, and it is a simple driver, the required specifications for TFT are not strict, and it is possible to drive a TFT active matrix liquid crystal panel that can effectively achieve flicker countermeasures. The purpose is to obtain a method.

[Means to solve the problem]

The method for driving a TFT panel according to the present invention is to wire X electrodes (source pass lines) so that they are independent on even and odd lines, and connect different source drivers to the even and odd lines, respectively. Furthermore, the polarity when converting to alternating current is such that the even numbered line and the odd numbered line have opposite polarity.

[Effect]

In this invention, the method of separating the source lines into even and odd lines and dividing the driver between the even and odd lines makes it possible to always drive during the IH period using a driver IC with a simple configuration. Therefore, the required specifications for the TFT can be relaxed, and furthermore, even if the polarity of the alternating current is reversed at the line period on the panel, it is not reversed on the source path line, so the drive capacity may also be small.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a configuration for realizing a driving method for a TFT active matrix liquid crystal panel according to an embodiment of the present invention, which corresponds to the conventional pixel arrangement pattern shown in FIG. As shown in Figure 0, which shows the panel structure regarding the wiring for the source electrode of the TFT 3 of each pixel (source pass line) along with the connection of the source line driver, each source pass line is an even line and an odd line, respectively. It is separated and pulled out to the upper side and lower side, and a separate source line driver 1 is attached to each of them.
5 and 16 are connected.

The configuration of the TFT panel and its surroundings other than this part is the same as that of the conventional example, so the explanation will be omitted.

Next, the operation will be explained.

First, source line drivers 15 and 1 in FIG.
6, a driver configured as shown in FIG. 6 may be used.
That is, for example, if a certain odd line is currently being driven by the upper source driver 15 for an IH period based on the result of S/H performed before IH, the video signal for this period is driven by the lower source line driver 16 for S/H. 6th order I
In the H period, the next line (even line) is driven by the result of S/H performed before IH by the lower source driver 16, contrary to the above, and the video signal in this period is driven by the upper source line driver 15. Therefore, S/H will be performed.

By repeating this process, even a driver with a simple configuration as shown in Figure 6 can always drive the TFT during the IH period, and the conditions regarding the specifications of the TFT, such as Ion, can be relaxed, and as a result, the yield of the panel can be improved. It also contributes to improvement.

On the other hand, regarding flicker countermeasures, even if one field of signals of the same polarity is applied to one source path line, the polarity of each color signal of R, G, or B corresponding to that line is changed by the upper driver 15 and the lower driver 16. VI so that the polarity is reversed.
By supplying the DEO signal, the phase of alternating current can be changed with the line period, eliminating the limitation due to the driving ability of the driver as in the conventional example. As a result, as shown in FIG. 2, the polarity of the alternating current can be reversed between the shaded area and the non-shaded area, which is highly effective in preventing flicker.

〔Effect of the invention〕

As described above, according to the present invention, independent source path lines are formed by even-numbered lines and odd-numbered lines, independent source drivers are connected for the even-numbered lines and odd-numbered lines, and the even-numbered lines and the odd-numbered lines Since signals with opposite polarities are supplied, it is possible to obtain a driver with a simple configuration, which can ease the specifications for the TFT and further reduce flicker to a large extent.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the wiring structure of the source path line and the connection form of the source driver according to an embodiment of the present invention, FIG. 2 is a diagram illustrating the flicker reduction effect according to the embodiment of the present invention, and FIG. 4 is a diagram showing an equivalent circuit of a conventional TFT liquid crystal panel, and FIG. 4 is a diagram explaining the operation of the scanning circuit in FIG. 3.
FIG. 5 is a diagram for explaining a conventional flicker countermeasure, and FIGS. 6 and 7 are diagrams for explaining the configuration of a source line driver. In the figure, 1 is a liquid crystal cell, 2 is a storage capacitor, and 3 is a liquid crystal cell.
is FET, 4 is X electrode, 5 is Y electrode, 6 is scanning circuit, 7
is a serial/parallel conversion circuit, 8 is a common electrode, 9 is an AC conversion circuit,
10 is a 1-line S/H circuit, 11 is a time division type driver,
12 is an upper 1-line S/H circuit 1, 13 is a lower 1-line S/H circuit 2, and 14 is a selective driver. In the drawings, the same reference numerals indicate the same or equivalent parts. Figure 1q

Claims (1)

[Claims] (1) In the driving method of a TFT active matrix liquid crystal panel, the data bus line connecting the data input electrodes of each TFT is
The arrangement is divided into even-numbered lines and odd-numbered lines, and each independent data bus line consisting of even-numbered lines and odd-numbered lines is driven by an independent drive circuit, and when AC driving the liquid crystal, the polarity is set to the even-numbered line. A TFT characterized by having opposite polarity on odd-numbered lines.
How to drive an active matrix liquid crystal panel.