JPH0364790A - Driving system for tft panel - Google Patents

Abstract

PURPOSE:To make the contrast constant at the upper and lower parts on a screen by switching the gate electrode driving signal of a TFT panel to one of plural levels in each field and holding charges implanted to each picture element constant. CONSTITUTION:The TFT panel is constituted by arraying plural gate lines G and drain lines D in matrix and connecting the liquid crystal display picture elements E to respective intersection parts through thin film transistors T for switching. A gate line driving means 21 applies the gate electrode driving signal to the gate lines G. A driving signal switching means 24 switches the level of the gate electrode driving signal every time constant lines are scanned to hold the charges implanted to each picture element E constant. A drain line driving means 22 supplies a video signal to the drain lines D in synchronism with the gate electrode driving signal. Consequently, the contrast of the TFT panel is made constant at the upper and lower parts on the screen.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a driving method for a TFT panel that displays a liquid crystal display using an active matrix driving method.

[Prior art] TFTs conventionally used as display devices for liquid crystal televisions, etc.
The panel, ie, an active matrix drive type liquid crystal display panel, is constructed as shown in FIG. As shown in the figure, gate lines Gl, G2 . . . . and drain lines DI, D2° . . . are arranged in a matrix, and a thin film transistor (TFT) Tit for switch ink is provided at each intersection.

T12. ...T21. T22. ... will be established. These thin film transistors Tll, T12.・・・
・, T21. T22°... is a gate line Gl to which the gate electrode corresponds.

G2. . . , and the drain electrodes are connected to the corresponding drain lines Di, D2 . . . and further connected to the source electrode of the pixel E11. E12. ...
E21°E22. ... is connected.

Each of these pixels Ell, E12. ...E21.
E22°... consists of a pixel electrode 11a and a liquid crystal element 11b, respectively, as shown in FIG.
1a is connected to the source electrode of the thin film transistor T, and one end of the liquid crystal element flb is connected to the common power supply 12 via a common line.

In the above configuration, gate lines Gl, C; 2°...
- and drain lines DI, D2. ... are driven by the signals shown in FIG. In this Figure 5, (a)
is the first half gate drive signal, (b) is the drain drive signal, (
c) is the common input signal, (d) is the second half gate drive signal,
(e) shows the waveform of the pixel charge Q in the first half of the screen, and (f) shows the waveform of the pixel charge Q in the second half of the screen.

The TFT panel configured as shown in FIGS. 3 and 4 has gate lines Gl, G2, . ...is the 511th
Selective scanning is performed sequentially by gate pulses shown in id(a) and id(d). Also, drain line DI.

D2. . . , the TV video signal shown in FIG. 5B is input, and this video signal is inverted in accordance with the TV field or frame period.

Therefore, the gate lines Gl, G2 . When a gate pulse is applied to . When the charge Q is exhausted, the voltage applied to the pixel E drops because the charge Q leaks through the off-resistance of the thin film transistor T or the liquid crystal element 11b. Furthermore, a voltage difference between the signal applied to the drain line D and the common signal and a gate signal differentiated by the capacitance Cgs between the gate and source of the thin film transistor T are applied to the pixel after being multiplied by ff1. Therefore, the charge Q in each pixel E differs slightly from scan line to scan line, and for example, in certain lines in the first half and the second half of the screen, the waveforms are as shown in FIGS. 5(e) and 5(f). Therefore, the contrast of the image displayed on the TFT panel differs between the upper and lower parts.

[Issues to be solved by the invention] As described above, in the conventional TFT panel driving method, the charge of each pixel is slightly different for each scanning line, and the charge is slightly different between the upper part and the lower part of the screen. This had the disadvantage of causing a difference in contrast.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a TFT panel driving method that can make the contrast of the TFT panel constant from top to bottom.

[Means and effects for solving the problem] The present invention provides TF
The gate electrode drive voltage of the T-panel is switched, for example, at the center of the screen, so that the charges injected into the pixels are constant at the top and bottom of the screen.

By switching the gate drive voltage of the TFT panel midway as described above, the charge injected into the pixel can be made constant at the top and bottom of the screen, and the contrast can be kept uniform over the entire screen.

[Example] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a gate electrode drive circuit for a TFT panel. In the figure, reference numeral 21 denotes a shift register, to which a timing signal φV synchronized with a vertical synchronization signal and a timing signal φh synchronized with a horizontal synchronization signal are manually input. The shift register 21 converts the vertical timing signal φV into a horizontal timing signal φ
Read in synchronization with h and shift sequentially. Then, each bit output of the shift register 21 is transferred to a level shifter 22.
sent to.

The above-mentioned level shifter 22 has first and second gate electrodes that apply reference potentials (low level) Va and Vb of the gate electrode drive signal.
power supplies 23a and 23b are selectively connected via a changeover switch 24. The first and second electricity [23a,
23b (D voltage Va, Vbl, t, %J Ever I
It is set to 20V and OV. The changeover switch 24 is controlled by a changeover signal Sa sent from a control section (not shown). This switching signal Sa is synchronized with, for example, the common signal, that is, the gate line is 1/2
The signal level is changed every time the screen is scanned, and the changeover switch 24 is controlled so that the first power source 23a is selected in the first half of each field, and the second power source 23b is selected in the second half of each field. . In addition, the level shifter 2
2 is connected to an operating power supply 25 of, for example, +5V, which provides a high-level potential Vdd of a gate electrode drive signal. The signal outputted from the level shifter 22 is applied as a gate electrode drive signal to the gate lines 1, G2, . ...is supplied to...

Next, the operation of the above embodiment will be explained with reference to the timing chart of FIG.

The shift register 21 converts the vertical timing signal φV given at the start of each field into the horizontal timing signal φh.
Read in synchronization with and shift sequentially.

Each bit output signal of this shift register 21 is then sent to a level shifter 22. The level shifter 22 is supplied with the output voltage Va of the first 71M23a selected by the changeover switch 24 in the first half of each field. Therefore, when a pulse signal is applied from the shift register 21, the level shifter 22 uses the voltage Va as a reference (low level) and sets the voltage Vdd supplied from the operating power supply 25 to a high level, as shown in FIG. 2(a). A gate electrode drive signal is applied to the gate line Gl of the TFT panel shown in FIG.

G2. Output to... The TFT panel also has drain lines DI, D2. ... are supplied with the video signal shown in FIG. 2(b), and the common power supply 12 is supplied with the common line.

When the first half of scanning for the TFT panel is completed, the level of the switching signal Sa sent from the control section (not shown) is inverted, and the changeover switch 24 is switched to the second power source 2ab.
Switch to the side. As a result, the changeover switch 24
The output voltage vb of the power supply 23b is selected and supplied to the level shifter 22. Therefore, the reference level of the gate electrode drive signal output from the level shifter 22 decreases from Va to Vb as shown in FIG. 2(a). Further, at this time, the signal levels of the drain drive signal and the common power supply 12 are inverted as shown in FIGS. 2(b) and 2(c). In this way, the level shifter 22 is synchronized with the level inversion of the common signal.
By changing the reference level of , charges Q are injected into the pixel E via the gate-source capacitance Cgs of the thin film transistor T. As a result, the parasitic charge Q to the pixel E is canceled and a constant charge Q is injected into the pixel E.

The level shifter 22 is connected to the shift register 21.
When a pulse signal is given from the operating power source 25, the voltage vb is used as a reference (low level) as shown in FIG. 2(a).
A gate electrode drive signal that sets the voltage Vdd supplied from the TFT panel to a high level is output to the gate line G in the latter half of the TFT panel. This gate electrode drive signal turns on the thin film transistor T, and the drain electrode drive signal applied to the drain line D is supplied to the pixel E, thereby driving the image *E to be displayed.

FIG. 2(d) shows the level change of the charge Q in the pixel E.

As described above, by canceling the parasitic charge Q to the pixel E and injecting a constant charge Q into the pixel E in the second half of the screen, the influence of the discharge of the charge Q is eliminated, and the contrast of the second half of the screen is changed from that of the first half. can be kept at the same level.

When the scanning of one field is completed, the switching signal S
The level of a is reversed, and the selector switch 24 is switched to the first power supply 2.
3a side to return to the initial state.

In the above embodiment, the level of the gate electrode drive signal is switched only once at the center of the screen, but the level of the drive signal may be switched a plurality of times at regular intervals.

[Effects of the Invention] As detailed above, according to the present invention, the gate electrode drive signal of the TFT panel is switched to a plurality of levels in each field, and the charge injected into each pixel is kept constant. It is possible to eliminate the influence of pixel discharge, keep the contrast constant at the top and bottom of the screen, and improve image quality.

[Brief explanation of drawings]

1 and 2 show one embodiment of the present invention, FIG. 1 is a block diagram showing the configuration of the gate electrode drive circuit portion, FIG. 2 is a timing chart for explaining the operation,
FIG. 3 is a diagram showing a schematic configuration of a TFT panel, FIG. 4 is a diagram showing details of one pixel portion in FIG. 3, and FIG. 5 is a timing chart for explaining a conventional TFT panel driving method. . Gl, G2. ..., ...gate line, DI, D2
゜... drain line, Tll, T12.・・・
・T21. T22,... Thin film transistor, Ell, E12. ...E21. E22. -,
---Pixel, l1a--Pixel electrode, llb--Liquid crystal element, 12--Common power supply, 21--Shift register, 22--Level shifter, 23a--First power supply, 23b-- ...Second power supply, 24...Selector switch, 25...Operating power supply. 1 2 3 4 Figure 4 Figure 1 Figure 2

Claims (1)

[Claims] A gate electrode drive signal is sequentially applied to a TFT panel in which a plurality of gate lines and drain lines are arranged in a matrix, and a liquid crystal display pixel is connected to each intersection point via a switching ink thin film transistor, and to the gate line. gate line driving means; drive signal switching means for switching the level of the gate electrode driving signal every fixed line scan to keep the charge injected into each pixel constant; and driving the drain line in synchronization with the gate electrode driving signal. A method for driving a TFT panel, comprising: drain line driving means for supplying a video signal to a TFT panel.