JPH0580296A - Liquid crystal display device - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide an active matrix liquid crystal display device using thin film transistors, which has less flicker and afterimage and excellent display uniformity. [Structure] The gate voltage of a TFT driving a pixel and the gate voltage of a sampling (peripheral circuit) TFT driving a drain wiring have a bidirectional input configuration. [Effect] The bidirectional input cancels the jump-in voltage caused by the wiring delay, thereby improving the display uniformity and the flicker characteristic.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique effectively applied to a liquid crystal display device, for example, a liquid crystal display device having an active matrix structure in which a liquid crystal is driven by using a TFT (thin film transistor).

[0002]

2. Description of the Related Art As a liquid crystal display device having a TFT active matrix structure, there is, for example, Japanese Patent Publication No. 64-68724. In this example, T for driving the video signal line on the insulating substrate
Built-in FT. In this device, the scanning voltage for driving the gate of the pixel TFT is supplied from the Y driver, and the sampling (peripheral circuit) for driving the video signal line is also provided.
The voltage supplied to the gate of the TFT is supplied from L1 to L3. Here, the gate voltage of the pixel TFT and the gate voltage of the sampling TFT that drives the video signal line are both supplied from the left end of the display area, or the gate voltage of the pixel TFT is supplied from both sides. The delay time of the gate wiring of the sampling TFT and the pixel TFT is also increased from the left end to the right end or the center on the substrate.

[0003]

The TFT liquid crystal display device is mainly used as a monitor in a microcomputer as a small and low power consumption display device. As a problem in display quality of the active matrix liquid crystal display device for such an application, there are flicker which is a flicker of a screen, an afterimage which occurs when an image is switched, and display unevenness (nonuniformity). In particular, diagonal 10
A practical problem has been found in a TFT liquid crystal display device of inches or more.

FIG. 6 shows a constitutional view of a glass substrate on which a TFT is formed in a liquid crystal display device measured by the inventor. In the figure, the liquid crystal display unit 8 is provided with pixel TFTs for a plurality of liquid crystal cells (LC) arranged in a matrix, and each liquid crystal is driven by the switching operation of the TFTs. Here, the gate wiring G which is an electrode commonly drawn from the gates of the TFTs arranged in the horizontal direction
A gate voltage is supplied to 1, G2 and GN from a gate drive circuit 1 connected to one side of the substrate. On the other hand, the drain voltage is also supplied from the data drive circuit 2 to the drain wirings D1, D2 and DN which are electrodes commonly drawn from the drains of the TFTs arranged in the vertical direction. In this example, only the display region is formed on an insulating substrate such as glass, and the drivers 1 and 2 are connected from the outside. On the other hand, on the liquid crystal cell, for example, a Twisted Nematic type liquid crystal layer is sealed in a gap with the second counter glass substrate. A common electrode formed of a transparent electrode that applies a common voltage Vcom to the liquid crystal layer is formed on the counter glass substrate, and the common electrode is supplied with Vcom from a power supply circuit through a connection terminal in order to connect to the outside. ..

FIG. 7 shows a transmittance distribution measured along the gate wiring from the gate drive circuit 1 side when halftone display is performed in the liquid crystal display device of FIG. The liquid crystal display is driven by TFT and the screen size is 10 inches diagonal and the number of display dots is 48.
It is 0x640. The drain voltage supplied from the data drive circuit 2 is applied to all drain wirings so that the center of the screen has a transmittance of 50%. As a result, although the same voltage is supplied from the data drive circuit 2, the display unevenness occurs in which the transmittance increases along the direction of the gate wiring and tends to be saturated.

Next, the cause of the display unevenness will be described.

FIG. 8A shows line-sequential scanning of the gate voltage VG,
A drive waveform when the drain voltage VD is inverted for each frame and a single color is displayed is shown. The on and off voltages of the gate voltage are represented by VGH and VGL, respectively. On the other hand, the drain voltage is made alternating with the center voltage of VDH and VDL, and the signal voltage Vsig = (VDH-VDL) / is applied to the liquid crystal capacitance.
2 is applied to the pixel electrode and becomes VS.

Here, ΔVH and ΔVL are VG due to the influence of the parasitic capacitance CGS between the gate and source electrodes of the TFT.
From V to VGL, the jump voltage drops sharply. The subscripts H and L are jump voltage when the signal voltage is higher than the center voltage Vc of the amplitude, and jump voltage when it is low.

FIG. 9 shows the scanning line delay time tGF and the jump voltages ΔVH and ΔV in the scanning line direction from the gate drive circuit 1 side.
L is shown. The delay time was defined as the time when 90% of the voltage dropped from VGH to VGL. Although ΔVH is constant as the delay time increases, ΔVL decreases, and it can be seen that this decrease causes display unevenness.

FIG. 10 is a view for explaining the mechanism of ΔVL decreasing with the increase of the voltage delay time of the scanning wiring. The relationship between the scanning voltage VG, the signal voltage VD, and the source voltage VS applied to the pixel electrode when the scanning wiring delay is large is shown. VS decreases due to a decrease in VG. However, during this period (minute period Δt), since VG is larger than VD and VS, the TFT is turned on and the jumped voltage is V
Recharge to return to D. As a result, the actual jump-in voltage δV is smaller than that in the case without wiring delay. Therefore, ΔVL having a long ON period remarkably moves away from the gate driver 4 and decreases as the wiring delay increases.

This also deteriorates the flicker characteristic which is the flickering of the screen.

FIG. 11 shows the value of the common voltage Vcom applied to the counter glass substrate which minimizes the flicker in each pixel along the gate line from the gate drive circuit in the liquid crystal display section 8 of FIG. The liquid crystal display device has a diagonal of 10 inches, and the measurement is in a display mode in which a drain voltage having a transmittance of 50% is applied at each measurement point. From FIG. 11, it was found that the value of Vcom that minimizes the flicker is different in each liquid crystal cell and increases toward the center of the screen from the position where the gate drive circuit 1 is connected. From this fact, when a general driving method is used, only a constant Vcom is applied. Therefore, when Vcom that minimizes the flicker at the center of the screen is applied, the gate drive circuit 1
In a liquid crystal cell close to, there is a problem that flicker is large. As described above, it was found that the above display unevenness and flicker were caused by the large voltage delay of the scanning wiring. However, since the wiring material is already low-resistance aluminum, it is difficult to obtain a wiring resistance lower than this. On the other hand, in the conventional technique, the peripheral T that drives the gate wiring and the drain wiring of the pixel region TFT
Both gate voltages of FT are supplied from the left end of the display area. That is, the wiring delay time also increases from the left end to the right end on the substrate, and there is a problem that the drop in the jump voltage is superimposed and the display unevenness and flicker are further increased. Also, when the gate voltage of the pixel TFT is supplied from both sides of the screen, the wiring delay between the sampling TFT and the pixel TFT increases from the left end of the screen toward the center toward the center of the screen, resulting in non-uniform distribution on the substrate. In addition to the fact that the problem is not solved, the gate drive circuit is required twice, which causes a problem that the price of the liquid crystal display device increases.

An object of the present invention is to solve the above display unevenness and flicker and to provide a low cost liquid crystal display device.

[0014]

The object of the present invention is achieved by inputting the gate voltage of the pixel area TFT from the left end of the display area and the gate voltage of the sampling (peripheral circuit) TFT from the right end of the display area. ..

[0015]

For the purpose of the present invention, when the gate voltage of the TFT in the pixel region is inputted from the left end of the image display region, the jump voltage is lowered from the left end of the display region along the gate wiring. On the other hand, when the gate voltage of the peripheral circuit TFT is input from the right end of the display area, the jump voltage decreases from the right end of the display area along the gate wiring. Therefore, the voltage drop of both is offset and a uniform voltage is applied to the liquid crystal capacitor. Therefore,
It is possible to provide a liquid crystal display device having good display performance with less display unevenness and flicker in the entire screen area.

[0016]

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

FIG. 1 shows an embodiment of an active matrix type liquid crystal display device of the present invention.

In the figure, the liquid crystal display unit 8 is provided with TFTs (E) for a plurality of liquid crystal cells arranged in a matrix.
1, E2) are provided, and each liquid crystal cell is driven by the switching operation of this TFT. Here, a gate voltage is sequentially applied from the gate drive circuit 1 to the scanning lines G1 to GM, which are electrodes commonly drawn from the gates of the TFTs arranged in the horizontal direction, and the gates of the TFTs are opened for each gate line. Turn on.

On the other hand, drain lines D1 to D1 which are electrodes commonly drawn from the drains of the TFTs arranged in the vertical direction.
The data voltage is sequentially applied to the DN from the data driving circuit 2 through the sampling circuit 3 for each gate line to which the on-gate voltage is applied, and is applied to each liquid crystal cell. The sampling circuit 3 has a sampling TFT that constitutes a peripheral circuit with respect to the drain line, and while the pixel TFT gate-on voltage is applied to the gate terminal of the sampling TFT, a plurality of sampling voltages φ1 and φ2 are applied. Supply. However, this output voltage φ1,
Although φ2 is supplied from the sampling drive circuit 9, the screen control circuit 10 (which also transmits a control signal to the gate drive circuit 1 and the data drive circuit 2) determines a frame, and the polarity is supplied to the sampling drive circuit 9 for each frame. Issue a reverse command.
Further, since the drain signals input to the sampling circuit 3 can be put together according to the number of sampling signals, the number of drain lines connected from the sampling circuit 3 to the data driving circuit 2 can be reduced.

The feature of the present invention is that the gate-on voltage to the gate line of the pixel TFT is supplied from the left end of the display area by the gate drive circuit 1, while the sampling TF is used.
The sampling voltages φ1 and φ2 supplied to the gate of T are supplied from the sampling circuit 9 from the right end of the display area 8.

If the sampling circuit 3 among the above circuits can be formed on the substrate 4 made of glass or the like like the pixel TFT, the connection between the sampling circuit 3 and the data driving circuit 2 will be made according to the number of sampling signals of the sampling TFT. Since the number can be reduced, the connection line between the display device main body formed on the glass substrate 4 and the external drive circuit can be reduced and the data drive circuit 2 can be simplified. When the number of sampling signals is 2, as shown in FIG. 2, the drain lines D1 and D2 are grouped together and connected to the data driving circuit as DK1.
As a result, the number of connections between the data drive circuit 2 and the substrate on which the pixel TFTs and the sampling circuit 3 are formed can be reduced by half, that is, the number of driver ICs that form the data drive circuit 2 can be reduced by half. Since the sampling circuit 3 can be easily formed in the same process as the pixel TFT, the effect of halving the number of driver ICs has an effect of reducing the liquid crystal display cost. Of course, the gate voltage VG of the pixel TFT and the sampling TF
The sampling voltages φ1 and φ2 applied to the gates of T (TR1, TR2) are input bidirectionally, respectively.

Next, the operation of the first embodiment will be described with reference to FIG. 1A shows the E1 pixel in FIG. 1, and FIG. 1B shows EN.
-Driving waveform for 1 pixel, sampling TFT
, The drain voltage VDD supplied from the external driver IC, the output voltage from the sampling TFT, which is the drain voltage of E1 and EN-1 of the pixel TFT VD, and the TFTs of E1 and EN-1 are pixel electrodes. 7 shows a voltage waveform of the source voltage VS charged in the above manner. This waveform is for the first one, that is, G1 in the circuit of FIG. 2, and corresponds to the drive waveforms of the odd-numbered drain lines (here, the pixels E1 and EN-1 of the D1 line) for the pixel TFT. The operation will be described. VD for E1 pixel
When D is applied and the sampling voltage φ1 is on, FIG.
TR1 which is the sampling TFT is turned on and VDD is applied to the drain line D1. However, when φ1 switches from on to off due to the parasitic capacitance between the φ1 wiring and the D1 wiring in TR1, the voltage drops. The jump voltage at that time is ΔVGφL. Therefore, VDD-ΔVGφL is applied to the drain wiring D1. Since the gate voltage VG of the pixel TFT is on for about twice as long as φ1, the pixel TFT E1 charges the liquid crystal capacitance, and the source voltage VS reaches VDD−ΔVGφL. When the gate voltage VG is switched from on to off, the voltage drops due to the influence of the parasitic capacitance between the gate line G1 and the pixel electrode. The jump voltage at that time is ΔVGDL. Therefore, VS actually applied to the liquid crystal capacitance CL1 is VDD−
ΔVGφL−ΔVGDL.

Similarly, as shown in FIG.
V applied to the liquid crystal capacitor CLN-1 from the N-1 TFT
S becomes VDD-ΔVGφR-ΔVGDR. here,
VDD-ΔVGφL-ΔVGDL applied to the E1 pixel
And EN-1 VDD applied to the pixel VDD-ΔVG φR-ΔV
If the GDRs are almost equal, display nonuniformity and flicker do not occur. In the conventional method, both VG and φ are supplied from the left end of the screen, and the wiring delay time of each increases from the left end to the right end. Due to
VGφL> ΔVGφR, resulting in VDD−ΔVG
[phi] L- [Delta] VGDL> VDD- [Delta] VG [phi] R- [Delta] VGDR, resulting in screen nonuniformity and flicker.

On the other hand, in the present invention, VG and φ are bidirectionally input at the left end and the right end of the screen, respectively. Therefore, regarding VG, ΔVGDL>
ΔVGDR, but for φ, ΔVGφL <ΔVG
φR, and the jump voltages of both are canceled out, resulting in VD
D-ΔVGφL-ΔVGDL = VDD-ΔVGφR-ΔV
It becomes GDR, and it is possible to provide a liquid crystal display device having good image quality without uneven display and flicker. In order to obtain the effect of the present invention with high accuracy, ΔVGDR and ΔVGφL are equal to each other.
The wiring constant may be set so that VGφR and ΔVGDL are equal, and for that purpose, the product of the wiring resistance and the wiring capacitance of the pixel TFT, that is, the wiring to which VG is transmitted, and the sampling TF.
It suffices to set the product of the wiring resistance and the wiring capacitance of the wiring through which T, that is, φ, to be equal.

FIG. 4 is a schematic perspective view of an embodiment of a laptop type (or book type) microcomputer using the liquid crystal display device according to the present invention. A keyboard 5 is a main body, and a liquid crystal display device 6 serving as a display monitor is provided on the main body. The display monitor incorporates the liquid crystal display device of the present invention, and the signal of the internal microcomputer is input to the screen control circuit, and the display content is judged there, and the gate drive circuit, the data drive circuit, and the sampling drive circuit respectively receive signals. To send. As the driving method, the driving method of the first embodiment is used, and it is possible to realize an image monitor with excellent display quality, and a sampling circuit can be formed on the same substrate as the pixel TFT. Can be realized.

Next, a second embodiment of the present invention will be described. FIG. 5 shows a second embodiment of an active matrix type liquid crystal display device using the present invention.

In the figure, the operations of the liquid crystal display section 8 and the gate drive circuit are the same as in the first embodiment.

On the other hand, with respect to the drain lines D1 to DN commonly drawn from the drains of the TFTs arranged in the vertical direction, the data driving circuit 2 supplies the data voltage for each gate line to which the gate voltage of the pixel TFT is applied. The voltage is sequentially applied through the sampling circuit 3 and applied to each liquid crystal cell. In the present invention, the sampling circuit 3 comprises an IC chip formed on a silicon substrate as an integrated circuit (IC), and is mounted on the insulating substrate 4 to be formed. Further, the gate voltage VG input and the sampling voltage φ are bidirectional inputs, so that it is possible to provide a liquid crystal display device having good image quality without image unevenness and flicker. This IC chip formed on the insulating substrate has the function of not only the sampling circuit 3 but also the data driving circuit 2, so that it is possible to reduce the number of external connections and further improve the reliability. is there. The terminals on the IC chip and the wirings are connected by using, for example, a wire bonding technique using gold as a material.

[0029]

According to the present invention, it is possible to easily provide a voltage for reducing non-uniformity of images on the screen, flicker, and afterimage, which are problems in display quality of the liquid crystal display device. Therefore, the liquid crystal display device having excellent display quality is provided. Can be provided.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a transmissive circuit according to an embodiment of the present invention.

FIG. 3 is a diagram showing drive waveforms according to an embodiment of the present invention.

FIG. 4 is a perspective view of a microcomputer according to an embodiment of the present invention.

FIG. 5 is a configuration diagram of a liquid crystal display device according to an embodiment of the present invention.

FIG. 6 is a configuration diagram of a liquid crystal display device in a conventional method.

FIG. 7 is a diagram showing a transmittance distribution in a conventional method.

FIG. 8 is a diagram showing a drive voltage waveform in a conventional method.

FIG. 9 is a diagram showing a voltage delay characteristic of wiring in a conventional method.

FIG. 10 is a diagram showing a mechanism for causing characteristic nonuniformity in a conventional method.

FIG. 11 is a diagram showing a common voltage distribution in a conventional method.

[Explanation of symbols]

Vcom ... Common voltage, VG ... Gate voltage of pixel TFT, V
D ... Drain voltage of pixel TFT, VDD ... Drain voltage of sampling TFT, φ ... Gate voltage of sampling TFT, 1 ... Gate drive circuit, 2 ... Data drive circuit, 3 ...
Sampling circuit, 4 ... Substrate on which pixel TFTs are formed,
5 ... Keyboard, 6 ... Liquid crystal display device.

Claims (5)

[Claims] 1. A pixel formed of liquid crystal capacitors arranged in a matrix, a display region formed of a matrix of the pixel, a thin film transistor formed for each pixel to drive the pixel, and the thin film transistor. A substrate, a display region composed of a drain line connecting the drain terminals of the thin film transistors belonging to the same column, and a gate line connecting the gate terminals of the thin film transistors belonging to the same row,
In a liquid crystal display device in which a sampling TFT for supplying a voltage to the gate line or the drain line is formed and which has a gate wiring for controlling the sampling TFT, a voltage input terminal of a gate wiring of a TFT for driving a pixel and the sampling TFT 2. The liquid crystal display device, wherein the input terminal of the control gate wiring is input bidirectionally from a position facing each other on the substrate. 2. The T according to claim 1, which drives the pixel.
A liquid crystal display device characterized in that an FT and a sampling TFT for supplying a voltage to a drain or a gate wiring for supplying a voltage to the pixel are formed on an insulating substrate such as a glass plate. 3. The T for driving the pixel according to claim 1.
The FT is formed on an insulating substrate, a sampling TFT for supplying a voltage to a drain or a gate wiring for supplying a voltage to the pixel is formed on a silicon substrate, and the silicon substrate is cut into an appropriate size. A liquid crystal display device characterized by being adhered to the top. 4. A product of wiring resistance and capacitance of a gate wiring for supplying a voltage to a gate of a TFT for driving the pixel according to claim 1, 2 or 3, wherein a voltage is applied to a drain or a gate wiring for supplying a voltage to the pixel. Sampling T to supply
A liquid crystal display device characterized by being equal to a product of a wiring resistance and a capacitance of a control gate wiring for supplying a voltage to a gate of an FT. 5. A pixel formed to drive liquid crystal by a thin film transistor formed in a matrix, a gate drive circuit for driving the thin film transistor, a data drive circuit for applying a predetermined voltage to the liquid crystal, and the gate drive circuit. And a screen control circuit for giving a control code to the data drive circuit, a microcomputer for arithmetic processing and information input means, and the arithmetic processing result or information from the information input means is transferred to the screen control circuit via the microcomputer. In an information processing device for transmitting, a switching element for controlling a data signal is provided between the data driving circuit and the thin film transistor, and a direction for inputting a voltage from the gate driving circuit to a gate of the thin film transistor and a switching for controlling the data signal. The direction of inputting voltage to the gate of the device is bidirectional The information processing apparatus according to claim Rukoto.