JP2003222836A - Active matrix type liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an active matrix type liquid crystal display device of high picture quality by eliminating unevenness of a γ-characteristic at the time of turning on auxiliary illumination and turning it off. <P>SOLUTION: The active matrix type liquid crystal display device receives a selection signal corresponding to turning on/off the auxiliary illumination, and switches between the auxiliary capacitance voltages by a switch circuit 33 when the auxiliary illumination is turned on and turned off, to apply different voltages to liquid crystal pixels PIX via storage capacitance CS at the time of turning on/off, respectively. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix type liquid crystal display device, and more particularly to a storage capacitor driving technique for an active matrix type liquid crystal display device which independently drives storage capacitor lines.

[0002]

2. Description of the Related Art FIG. 4 shows an equivalent circuit of a conventional active matrix type liquid crystal display device. Here, 41 is a gate drive circuit that supplies a gate selection signal for controlling ON / OFF of the thin film transistor TFT, and 42 is a source that supplies an image signal to a pixel whose thin film transistor TFT is turned ON by the gate drive circuit 41. Drive circuit,
Reference numeral 43 is a storage capacitor drive circuit that independently supplies a voltage to the storage capacitor CS. Further, 45 is a storage capacity drive circuit 43
Is a circuit that generates a storage capacitor voltage supplied by the.

A conventional active matrix type liquid crystal display device is provided at a plurality of gate lines G arranged in rows, a plurality of source lines S arranged in columns, and the intersections of the gate lines and the source lines. An active matrix display portion including an LC, a storage capacitor CS, and a thin film transistor TFT for driving a pixel, and a wiring parallel to the gate line are provided.
It is composed of a plurality of storage capacitor lines C connected for each line. Further, the source line S is the source drive circuit 4
The image signal of the thin film transistor TFT is supplied from the source drive circuit 42. The gate drive circuit 41 is connected to the gate line G, and a gate selection signal is supplied from the gate drive circuit 41. The storage capacitance line C is connected to the pixel via the auxiliary capacitance CS and further connected to the storage capacitance drive circuit 43, and the voltage applied to the liquid crystal pixel is supplied from the storage capacitance drive circuit 43. In addition, a thin film transistor TFT provided in each pixel
Is connected to the counter electrode COM via the liquid crystal capacitance LC,
A constant DC voltage is applied.

Next, a general driving method of the active matrix type liquid crystal display device will be described.

FIG. 5 shows applied voltage waveforms at various parts in a conventional active matrix display device. VG in the figure
1 and VG2 are gate voltage waveforms sequentially output from the gate drive circuit 41, and data is in the range of VH potential to VL potential corresponding to the image signal during the period when the gate line is selected by the image signal from the source drive circuit 42. The voltage is the liquid crystal capacity LC
Write in. Further, VC1 and VC2 are storage capacitance voltage waveforms which are output signals from the storage capacitance drive circuit 43 to the storage capacitance line, and Vpix is an actual voltage waveform applied to the liquid crystal pixel. In the first one frame (odd), while the gate voltage VG1 is ON, the liquid crystal pixel rises to the VH potential, and when the gate voltage VG1 is turned OFF, the potential slightly drops due to the penetration of the thin film transistor TFT, but the storage capacitance voltage VC1 Storage capacity C at startup
The pixel potential increases by ΔVcs via S, and the potential is held until the next frame. Since the polarity is inverted in the next frame (even), VL is written in the liquid crystal pixel while the gate VG1 is ON, and the pixel potential drops by ΔVcs via the storage capacitor CS when the storage capacitor voltage VC1 falls. , The potential is held until the next frame.

Further, in reality, the opposite voltage Vcom is
Is the voltage written in the liquid crystal pixel. That is, ΔV + and ΔV− are voltages written in the liquid crystal pixels, and ΔV + and ΔV− are used to prevent liquid crystal deterioration.
The Vcom voltage is set so that the effective value of V- is made equal, and AC drive is performed.

In the driving method shown in this example, by independently driving the storage capacitor line C, it is possible to apply a sufficient voltage for driving the liquid crystal while reducing the amplitude of the image signal data.

[0008]

Next, the gamma characteristic of the active matrix type liquid crystal display device when the auxiliary illumination is turned on and off is described. The semi-transmissive / reflective active matrix liquid crystal display device is an auxiliary lighting lighting mode in which the auxiliary light is turned on when it is used in a dark place such as indoors and the light source is used for display, and in a bright place such as in sunlight. It is a technology of a liquid crystal panel having a mechanism of two modes, an auxiliary lighting non-lighting mode in which a display is performed by natural light without using auxiliary lighting at the time of all use.

In the display device, it is necessary to make the gamma characteristics uniform in the two modes. In a semi-transmissive active matrix liquid crystal display device, light from the backlight passes through the liquid crystal only once and goes out to the surface when transmitted, but when reflected, natural light enters from the surface of the liquid crystal display device and passes through the liquid crystal. However, the light reflected by the reflector in the device again passes through the liquid crystal and goes out to the surface. That is, at the time of reflection, light that has passed through the liquid crystal twice appears on the surface. The difference in light transmission during transmission and reflection makes it difficult to make the gamma characteristics equal.

Further, in the reflective active matrix type liquid crystal display device, since the light is guided through the front light guide plate, the light passes through the light guide plate only once when the front light is turned on, but when the front light is not turned on. Light guides 2
It will pass twice. The difference in light transmission when the front light is on and when it is off makes it difficult to make the gamma characteristics equal.

According to the present invention, by changing the configuration of the above-mentioned conventional liquid crystal display device, the difference in gamma characteristics between when the auxiliary lighting is turned on and when the auxiliary lighting is not turned on, which has been a problem in the prior art, is eliminated, and a high image quality is obtained. An object is to provide an active matrix liquid crystal display device.

[0012]

In order to achieve the above object, an active matrix type liquid crystal display device of the present invention comprises:
A plurality of gate lines laid out in rows, a plurality of data lines laid out in columns, an active matrix display portion including liquid crystal pixels, storage capacitors and pixel driving thin film transistors, and wirings parallel to the gate lines, With respect to the capacitance, a plurality of storage capacitance lines connected for each line, a horizontal drive circuit for controlling the supply of the image signal to the thin film transistor via the source line, a vertical drive circuit for controlling the gate line, and the storage capacitance are provided. A storage capacitor drive circuit for controlling the voltage applied to the liquid crystal pixel by the liquid crystal pixel, and a selection circuit for controlling different voltage to be applied to the liquid crystal pixel through the storage capacitor when the auxiliary lighting is turned on and off. Is characterized by.

The selection circuit receives a selection signal corresponding to lighting or non-lighting of the auxiliary lighting for the liquid crystal display device, and 2
It is characterized in that different kinds of voltages are switched by a switch circuit, and different voltages are applied to the liquid crystal pixels via the storage capacitors during transmission and during reflection.

[0014]

1 shows a circuit configuration of a transflective active matrix liquid crystal display device according to an embodiment of the present invention. Here, as in the conventional example, 41 is a gate drive circuit that supplies a gate selection signal for controlling ON / OFF of the thin film transistor TFT, and 42 is a pixel whose thin film transistor TFT is turned on by the gate drive circuit 41. It is a source drive circuit that supplies image signals,
Reference numeral 43 is a storage capacitor drive circuit that independently supplies a voltage to the storage capacitor CS. Reference numeral 14 is a selection circuit that supplies the storage capacitor drive circuit with a storage capacitor voltage according to whether the backlight is on or off.

The transflective active matrix type liquid crystal display device of the present invention comprises a plurality of gate lines G arranged in rows.
And an active matrix display portion which is provided at a crossing portion of a plurality of source lines S arranged in a row and the gate line and the source line, and which includes a liquid crystal pixel LC, a storage capacitor CS and a thin film transistor TFT for driving the pixel, It is composed of a plurality of storage capacitor lines C which are wired in parallel with the gate lines and connected to the storage capacitors CS line by line. The source line S is connected to the source drive circuit 42, and the source drive circuit 4
2 supplies the image signal of the thin film transistor TFT. The gate line G is connected to the gate drive circuit 41, and the gate drive circuit 41 supplies a gate selection signal.

The storage capacitance line C is connected to the pixel via the auxiliary capacitance CS and further connected to the storage capacitance drive circuit 43, and the voltage applied to the liquid crystal pixel is supplied from the storage capacitance drive circuit 43. However, the voltage to be supplied is selected by the selection circuit 14 connected to the storage capacitor drive circuit in correspondence with the backlight lighting and the backlight non-lighting.

Further, the thin film transistor TFT provided in each pixel is connected to the counter electrode COM via the liquid crystal capacitance LC, and a constant DC voltage is applied.

FIG. 3 shows the configuration of the transmission / reflection selection circuit of the transflective active matrix type liquid crystal display device according to the embodiment of the present invention. Here, 14 is a backlight lighting / non-lighting selection circuit, 32 is a storage capacitor voltage generation circuit, and 33 is a switch circuit. The switch circuit 33 is connected to the storage capacity voltage generation circuit 32, and is supplied with the storage capacity voltage VCT when the backlight is lit and the storage capacity voltage VCR when the backlight is not lit. Further, the switch circuit is connected with a signal indicating when the backlight is lit and when it is not lit. The signal selects the storage capacitor voltage when the backlight is lit and when the backlight is not lit, and the selected auxiliary storage capacitor VC is used as a supplemental storage capacitor. It is supplied to the drive circuit 43.

Next, a method of driving the transflective active matrix type liquid crystal display device having the above structure will be described.

FIG. 2 shows applied voltage waveforms of respective parts in the transflective active matrix display device of the present invention. In the figure, VG1 and VG2 are gate voltage waveforms sequentially output from the gate drive circuit 41, and data is the source drive circuit 42.
During the period when the gate line is selected by the image signal from, the voltage in the range of VH potential to VL potential corresponding to the image signal
Write to LC. Further, VC1 and VC2 are storage capacitance voltage waveforms which are output signals from the storage capacitance drive circuit 43 to the storage capacitance line, and Vpix is an actual voltage waveform applied to the liquid crystal pixel.

When the backlight is turned on, the first 1
In the frame (odd), the gate voltage VG1 is ON
, The liquid crystal pixel rises to the VH potential and the gate voltage V
When G1 is turned off, the potential drops slightly due to the penetration of the thin film transistor TFT, but the storage capacitor voltage VCT1
At the rising edge of, the pixel potential rises by ΔVcst via the storage capacitor CS, and the potential is held until the next frame. Since the polarity is inverted in the next frame (even), VL is written in the liquid crystal pixel while the gate VG1 is ON, and the pixel potential drops by ΔVcst via the storage capacitor CS when the storage capacitor voltage VCT1 falls. , The potential is held until the next frame. In addition, actually, the potential difference between the counter voltage Vcom and the above Vpix is the voltage written in the liquid crystal pixel. That is, ΔV +, Δ
V− is a voltage written in the liquid crystal pixel, and in order to prevent deterioration of the liquid crystal, the Vcom voltage is set so that the effective values of ΔV + and ΔV− are equal to each other, and AC driving is performed.

When the backlight is off,
Although the driving method is the same as that in the transmission mode, the storage capacitor voltages are different and VCR1 and VCR2 are set. Therefore, when the storage capacitor voltages VCR1 and VCR2 rise and fall, the pixel potential that rises and falls through the storage capacitor is ΔVc.
sr.

As described above, by using the active matrix type liquid crystal display device of the present invention, the pixel potentials ΔVcst and ΔVc when the backlight is lit and when the backlight is not lit.
sr is optimized so that ΔVcst <ΔVcsr or Δ
By making the value different from Vcst <ΔVcsr, the nonuniformity of the gamma characteristic when the backlight is lit and when the backlight is not lit, which is a problem in the prior art, is improved, and in the transflective active matrix liquid crystal display device. High quality image can be obtained. Even in the reflective active matrix liquid crystal display device, the pixel potentials ΔVcst and ΔVcsr when the front light is turned on and not turned on are optimized to obtain Δ
Vcst <ΔVcsr or ΔVcst <ΔVcs
By setting the value different from r, the same effect as the transmissive active matrix liquid crystal display device can be obtained.

[0024]

The active matrix type liquid crystal display device of the present invention is equipped with a selection circuit for applying different voltages to the liquid crystal pixels via the storage capacitors when the auxiliary lighting is turned on and when the auxiliary lighting is not turned on, thereby optimizing the gamma characteristic. It is possible to provide an active matrix liquid crystal display device having high image quality by improving the non-uniformity of gamma characteristics in two modes of lighting and non-lighting auxiliary lighting, which has been a problem in the prior art. Become.

[Brief description of drawings]

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

FIG. 2 is a diagram of a pixel voltage waveform of the active matrix type liquid crystal display device according to the embodiment of the present invention.

FIG. 3 is a configuration diagram of a transmissive / semitransmissive selection circuit of an active matrix type liquid crystal display device according to an embodiment of the present invention.

FIG. 4 is a configuration diagram of a conventional active matrix type liquid crystal display device.

FIG. 5 is a diagram of a pixel voltage waveform of a conventional active matrix type liquid crystal display device.

[Explanation of symbols]

41 Gate drive circuit 42 Source drive circuit 43 Storage capacity drive circuit 44 LCD panel 14 Auxiliary lighting ON / OFF lighting selection circuit 32, 45 storage capacity voltage generation circuit 33 switch circuit TFT thin film transistor CS storage capacity LC liquid crystal capacity PIX LCD pixel G gate line S source line VG gate output signal VC, VCR, VCT Auxiliary capacitance output signal VH, VL Image signal potential VCOM counter voltage

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G09G 3/20 624 G09G 3/20 624B 5C094 641 641C 641Q 3/34 3/34 J 3/36 3/36 F-term (reference) 2H091 FA23X FA23Z GA02 GA11 GA13 LA16 LA17 LA20 2H092 GA12 GA24 JA24 JB22 JB31 JB61 JB69 NA01 PA06 PA07 PA13 2H093 NC03 NC09 NC11 NC13 NC14 NC34 NC35 NC36 NC51 NC62 NC65 ND01 ND02 ND03 ND04 ND06 ND08 NE06 5C006 AA01 AA16 AF45 AF46 AF51 AF53 AF61 BB16 BB28 BB29 BC03 BC06 BC11 BF14 BF24 EA01 FA54 FA56 5C080 AA10 BB05 DD03 EE28 FF11 JJ02 JJ03 JJ04 5C094 AA03 AA55 BA03 BA43 CA19 EA04 EA07 FB19

Claims (3)

[Claims] 1. An active matrix type liquid crystal display device comprising a plurality of gate lines arranged in rows, a plurality of source lines arranged in columns, liquid crystal pixels, storage capacitors and pixel driving thin film transistors. A matrix display portion and a plurality of storage capacitance lines that are wired in parallel with the gate line and are connected to the storage capacitance for each line, and control the supply of an image signal to the thin film transistor through the source line. A horizontal drive circuit, a vertical drive circuit that controls the gate line, and a storage capacitor drive circuit that controls a voltage applied to the liquid crystal pixel via the storage capacitor; and a storage capacitor,
An active matrix type liquid crystal display device, comprising: a selection circuit for controlling different voltages to be applied to liquid crystal pixels when auxiliary lighting is used and when not used. 2. The active matrix liquid crystal display device according to claim 1, wherein the auxiliary illumination is a backlight, and the selection circuit receives a selection signal corresponding to lighting or non-lighting of the backlight. An active matrix type liquid crystal display device characterized in that two kinds of voltages are switched by a switch circuit, and different voltages are applied to liquid crystal pixels through the storage capacitor during transmission and during reflection. 3. The active matrix type liquid crystal display device according to claim 1, wherein the auxiliary lighting is a front light, and the selection circuit receives a selection signal corresponding to lighting or non-lighting of the front light. An active matrix type liquid crystal display device characterized in that two kinds of voltages are switched by a switch circuit, and different voltages are applied to liquid crystal pixels through the storage capacitor during transmission and during reflection.