JPH01289918A - Active matrix type liquid crystal display device and its driving method - Google Patents

Abstract

PURPOSE:To decreases factors which decreases impedance and to realize high picture quality and high yield by equipping a transistor (TR) array substrate with source lines arranged in parallel to gate lines and equipping a counter substrate with counter electrodes which are arrayed in stripes at right angles to the gate lines. CONSTITUTION:This display device has source electrodes 10 connected to a common voltage, gate electrodes 11 connected in common by columns, drain electrodes 12, TFTs 13, liquid crystal 14, and counter electrodes 15 which are connected in common by rows and input signals. Namely, the TR array substrate is equipped with the source lines arranged in parallel to the gate lines and the counter substrate is equipped with the counter electrodes 15 which are arrayed in stripes at right angles to the gate lines. Thus, a display voltage input part is composed of the counter substrate in simple structure, so the factors which decrease the impedance are decreased to realize the high picture quality and high yield.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to field effect thin film transistors (hereinafter referred to as TP).
The present invention relates to an active matrix liquid crystal display device using an active matrix type liquid crystal display device (referred to as T) and a method for driving the same.

[Conventional technology]

FIG. 3 shows a circuit for driving a conventional active matrix liquid crystal display device disclosed in, for example, Japanese Patent Laid-Open No. 55-59494, and FIG. 4 shows its driving waveform. Although only four elements are shown, by arranging them in the X-Y direction and connecting them appropriately, a multi-line matrix display becomes possible.

In FIG. 3, 1 is a source electrode, 2 is a gate electrode, 3 is a drain electrode, 4 is a TPT, 5 is a liquid crystal, and 6 is a counter electrode. When applying source voltage 2 from source electrode 1 and gate voltage v1 from gate electrode 2 in FIG. 3, T'FT3
becomes conductive (ON), and the source electrode 1 to TPT3
The liquid crystal 5 is charged through the ON resistance (Ron). Next, when the gate voltage of gate electrode 2 is made zero, TPT4
is in the cut-off (OFF) state, and the capacitance (C1c) of the liquid crystal 5
The electric charge charged in 5 is the cutoff resistance of TPT4 (
Roff) and the liquid crystal resistor (Rlc). The voltage waveform of each electrode at this time is shown in FIG.
ff) I? on, Rlc>Roff, so even though the duty of the voltage applied to the source electrode 1 is small and the effective voltage is extremely small, the effective voltage generated at the drain electrode, that is, the effective voltage applied to the liquid crystal element is extremely small. The duty factor is small (but a high contrast display is performed).

[Problem to be solved by the invention]

Since the conventional liquid crystal display device is configured as described above, it has the following problems.

■ Due to the configuration of current drive circuits, high impedance is particularly required for the source line. This is because the circuit is active for about 10% of one scan time and then disabled. In current arrays, gate lines and source lines have a two-layer structure, or TPTs are connected, forming a complex circuit. Therefore, the impedance of the source line tends to drop, which hinders improvement in image quality.

■ Conventional active matrix liquid crystal display devices are
TF because the source voltage is not constant with respect to the gate voltage.
There is a problem that the Id-Vg characteristic surface of T is not fully utilized. In FIG. 5, 7 is a gate voltage, 8 is a source voltage, and 9 is a counter electrode voltage. For example, when looking at the relative value of the source voltage to the gate voltage when each voltage in an even frame is set as shown in Figure 5, when the gate voltage is 2°V, it is vgs - 15V, and when the gate voltage is OV, it is Vgs -
-5V, but in odd frames the gate voltage is 20V
Sometimes Vgs = 5V, when gate voltage is OV Vg
s --15V. Next, TPT generally shows Id = vg characteristics as shown in Figure 6, but here, the drain current 1d at each relative value in the odd-numbered frame mentioned above is 6th
The value of point A (OFF) and point B (ON) in the diagram is normally 1.
Rof f/Ron, which is said to require more than 00000
The ratio will be 1000 or less. As described above, depending on the voltage conditions, the Roff/Ron ratio may deteriorate, making it impossible to obtain good voltage holding characteristics, which is the lifeblood of an active matrix liquid crystal display device, and possibly resulting in poor image quality.

■ Also, TPT has a parasitic capacitance Cg between the gate and drain.
d exists and affects image quality. FIG. 7 is an equivalent circuit diagram for one pixel, and FIG. 8 is a partial chart diagram. Here, C1c is the capacitance of one pixel of liquid crystal. Even if the gate of TPT is opened and C1c is charged with Vd, when the gate is closed, it will be blown by ΔVd, and only Vd-ΔVd will be maintained between frames. The magnitude of ΔVd is determined by the following equation.

△Vd = (Cgd/C1c) x Vg or Vgs
If ΔVd is large, ΔVd also becomes large, and the effective value per frame becomes small. As described above, it has already been made clear that this ΔVd is caused by the influence of the parasitic capacitance 51cgd between the gate and the drain, and its magnitude is determined by the balance between Cgd, Cd, and Vgs. With conventional technology, the same ON,
In order to obtain a FF ratio of 10, a higher Vgs must be applied, which adversely affects image quality.

This invention was made in order to solve the above-mentioned problems, and it is hoped that the characteristics of TPT can be maximized, thereby providing a high-quality active matrix liquid crystal display device and its driving method. purpose.

[Means for Solving the Problems] In an active matrix liquid crystal display device according to the present invention, the transistor array substrate has a plurality of source lines arranged in parallel to the gate line, and the counter substrate has a plurality of source lines arranged in a direction perpendicular to the gate line. It is equipped with counter electrodes arranged in stripes.

Further, in the method for driving an active matrix liquid crystal display device according to the present invention, a common DC voltage is applied to all the source lines, and the display voltage is inputted from the counter electrode.

[For production]

The active matrix liquid crystal display device according to the present invention fixes the source voltage and always maintains constant Vgson and Vgson.
By setting gsoff, the TPT can always be used at a constant operating point. For example, the TPT characteristics can be changed to Vg as shown in Figure 9.
sof This is a dispute in which the f point was shifted from the 0 point to the D point.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure is a circuit diagram for driving the active matrix type liquid crystal display device of the present invention, and FIG. 2 shows its driving waveform. In FIG. 1, 10 is a source electrode connected to a common voltage;
Reference numeral 11 designates a gate electrode commonly connected for each column, 12 a drain electrode, 13 a TPT, 14 a liquid crystal, and 15 a counter electrode commonly connected for each row to which a display signal is input.

Next, the operation will be explained.

A common voltage Vcom is applied to the source electrode 10,
When the display signal voltage V2 is applied from the counter electrode 15 and the gate voltage ■1 is applied from the gate electrode 11, the TFT 4 becomes conductive (ON).
) state, and the 'l' FT4 is turned on from the source electrode 10.
The liquid crystal 14 is charged through a resistor (Ron). Next, when the gate voltage of the gate electrode 11 is reduced to zero, the TFT 4 enters the cut-off (OFF) state, and the capacitance (C1c) of the liquid crystal 14 decreases.
The electric charge charged in 14 is transferred to the cutoff resistance (
Roff) and the liquid crystal resistor (Rlc). Display signal voltage v1 from the counter electrode 15 in the next frame
, when a voltage v1 is applied to the gate electrode 11, T
The FT 4 becomes conductive (ON) again, the liquid crystal 14 is discharged from the counter electrode 15 through the ON resistance (Ron) of the TFT 4, and a voltage of Vl is applied to the liquid crystal layer 14. The same charging and discharging process is repeated for the liquid crystal layer 14 thereafter. On the other hand, while the gate voltage is zero, even if the display signal voltage of the counter electrode 15 changes, charging and discharging are blocked by the cutoff resistor (Roff), so the display is not affected.

〔Effect of the invention〕

As explained above, according to the present invention, the transistor array substrate includes a transistor array substrate having a plurality of source lines arranged in parallel with a gate line, and has counter electrodes arranged in stripes in a direction perpendicular to the gate line. (1) Since the display voltage input section is a simple-structured counter substrate, there are few factors that reduce impedance, achieving high image quality and high yield.

(2) Since the source voltage is fixed, it is possible to obtain a high 0N10FF ratio and good image quality by fully utilizing the TPT characteristics.

(3) In other words, the gate voltage can be lowered, which reduces the influence of Cgd on the gate voltage and contributes to low voltage design of the circuit.

(4) Since it is possible to create a structure in which the gate wiring and the source wiring do not intersect, there is no short circuit at the crossing part of the wiring part, and the yield is improved.

(5) Since the operating range is fixed, it is sufficient to manufacture a TPT with characteristics that match the operating range, leading to improved quality and yield.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram for driving an active matrix type liquid crystal display device according to an embodiment of the present invention, FIG. 2 is a drive waveform diagram of gate voltage, counter electrode voltage, and drain voltage, and FIG. 3 is a diagram of a conventional active matrix liquid crystal display device. Figure 4 is a waveform diagram of the gate voltage, source voltage, and drain voltage of the drive circuit diagram of Figure 3, and Figure 5 is a waveform diagram of the gate voltage, source voltage, and counter electrode voltage. , Fig. 6 is an Id-Vg characteristic diagram, Fig. 7 is an equivalent circuit diagram of one pixel, and Fig. 8 is an Id-Vg characteristic diagram.
The figure is a partial chart of gate voltage and drain voltage, No. 9.
The figure is a characteristic diagram of TPT. 10... Source electrode, 11... Gate electrode, 12.
...Drain electrode, 13...TFT, 14...Liquid crystal, 15...Counter electrode. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (2)

[Claims] (1) A transistor array substrate including a plurality of gate lines, a source line, a plurality of field effect transistors connected to the gate line and the source line, a counter substrate including a conductive thin film electrode, and an electrode of the counter substrate. In an active matrix type liquid crystal display device comprising a liquid crystal material sandwiched between the transistor array substrates, the transistor array substrate has a plurality of source lines arranged parallel to the gate line, and the counter substrate has a plurality of source lines arranged parallel to the gate line. An active matrix liquid crystal display device characterized by having counter electrodes arranged in stripes in the right angle direction. (2) a transistor array substrate including a plurality of gate lines, a source line, a plurality of field effect transistors connected to the gate line and the source line; a counter substrate including a conductive thin film electrode; and an electrode of the counter substrate. In an active matrix type liquid crystal display device comprising a liquid crystal material sandwiched between the transistor array substrates, a common DC voltage is applied to all the source lines, and the display voltage is input from the counter electrode. A method for driving a matrix type liquid crystal display device.