JP3227208B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device,
In particular, the present invention relates to an active matrix type liquid crystal display device.

[0002]

2. Description of the Related Art In an active matrix type liquid crystal display device, a liquid crystal is sandwiched between a pixel electrode and a common electrode, and the transmittance of the liquid crystal is changed according to the potential difference between the two electrodes. Corresponds to the luminance information of the display data, it is possible to obtain an arbitrary display luminance. [First Conventional Example] FIG. 5 is a basic voltage assignment diagram for a pixel electrode and a common electrode. In this figure, V ₀
ＶV ₇ and (V ₀ ) 〜 (V ₇ ) are a voltage for a pixel electrode having a constant potential difference (hereinafter, a reference voltage), V _COM is a voltage for a common electrode (hereinafter, a common voltage), and M is an inversion control signal. is there.
In a period (B) where the signal M is at L logic, V _{0 to} V ₇ are used,
In the H logic period (A), (V ₀ ) to (V ₇ ) are used. For example, in the case of a normally white type liquid crystal in which the light transmittance is maximum (white level) when the potential difference between both electrodes is minimum, as shown in FIG. 6, V ₀ (or ( V ₀ )), the white level, V ₇ (or (V
₇ )), the black level can be displayed.
_When an arbitrary voltage between ₀ (or (V ₀ )) and V ₇ (or (V ₇ )) is given, an intermediate level corresponding to that voltage can be displayed. That is, according to FIG. 5, V ₀ (or (V ₀₎₎ show the number and eight gradations of the same number of up to V ₇ (or (V ₇₎₎ from. Table 1 below summarizes the operation of selecting a reference voltage in the first conventional example.

[0003]

However, such basic voltage allocation
FIG. 7 shows an example of the reference voltage generating circuit.
As shown in FIG._DDAnd low-potential-side power supply V_LOWBetween
It is necessary to divide the potential difference into 8 × 2 resistance steps.
Both 8 × 2 resistors R₀ ~ R _Fifteen8 x 2
FA AMP B₀~ B_FifteenMust be provided.
The disadvantage that a double reference voltage generation circuit is required
is there. Power supply V_DDAnd V_SSAt least the potential difference between
16 steps or more (1 step is the potential difference between reference voltages)
And requires a high-potential power supply voltage.
There is a condition. [Second Conventional Example] FIG. 8 is a diagram showing a voltage split in which the above problem is solved.
FIG. 9 is a diagram showing a common voltage synchronized with the inversion control signal M.
V_COMPolarity is alternately reversed.
You.

FIG. 9 shows a second conventional reference voltage generating circuit.
FIG. In this example, V_DDAnd V_SSPotential difference between
With eight resistors R₂₀~ R₂₇And divide the pressure by 8
B ₂₀~ B₂₇8 kinds of reference voltages V through₀~ V₇Take
It is protruding. These reference voltages are
Data driver (see Fig. 3).
One reference voltage is applied to the contents of the display data signal.
It is selected according to. According to this, times
It is possible to avoid the increase of the road scale, and the step of resistance partial pressure
The number of power supplies can be reduced by reducing the number.

The following Table 2 summarizes the operation of selecting the reference voltage in the second conventional example. Therefore, in the first conventional example, 16 types of reference voltages are generated and input to the data driver, but in the second conventional example, only half of the 8 types are required.

[0007]

SUMMARY OF THE INVENTION
In the second conventional example, the potential difference between the reference voltages is constant.
For example, in the vicinity where the transmittance of the liquid crystal becomes minimum,
The problem is that the gradation change
You. That is, for example, the transparency of normally white liquid crystal
Excess rate (see Fig. 6)
Is linear, but the linearity near the black level is poor.
The reference voltage V₀~ V₇Is constant.
And V₀-V₁, V ₁-V_Two, ..., V_Five-V₆Between each
V for the difference in transmittance₆-V₇The difference in transmittance of
And the gradation change near the black level is not clear.
U. [Purpose] Therefore, the present invention optimizes the voltage applied to the liquid crystal.
By doing so, the liquid crystal transmittance is minimized
To improve the display quality
aimed to.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a reference voltage having a potential between a predetermined high potential and a predetermined low potential, each of which is equally divided into a plurality of parts.
One according to the display data, applying the selected voltage to the pixel electrode of the liquid crystal, applying a common voltage of which polarity alternates to the common electrode of the liquid crystal, and according to the potential difference between the pixel electrode and the common electrode. A first voltage having a higher potential than the high potential and a second voltage having a lower potential than the low potential. When the common voltage has a negative polarity, the first voltage is used instead of the reference voltage having the highest potential among the plurality of reference voltages, while when the common voltage has a positive polarity, It is characterized in that the second voltage is used in place of the reference voltage having the lowest potential among the reference voltages.

[0009]

According to the present invention, for example, in the black level display in the case of a normally white liquid crystal, the first voltage and the second voltage are alternately selected for each polarity of the common voltage. Here, the first voltage is a voltage higher than a predetermined high potential,
The second voltage is a voltage lower than a predetermined low potential. Therefore, the transmittance of the liquid crystal greatly changes by the potential difference between the first voltage and the predetermined high potential or the potential difference between the second voltage and the predetermined low potential. The change of the gradation in the vicinity of becomes clear.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings.
I do. 1 to 4 show one embodiment of a liquid crystal display device according to the present invention.
It is a figure showing an example. In FIG. 1, V_COMIs the inversion control signal
The common voltage whose polarity is alternately inverted in synchronization with the signal M
This common voltage V_COMIs applied to the common electrode of the liquid crystal
You. Also, V ₀~ V₇’ And (V₀) To (V₇’)
Are eight gradation voltages selected according to display data.
These voltages are generated by the reference voltage generation circuit of FIG.
Made

[0011] The reference voltage generating circuit of this embodiment, between the high-potential power supply V _DD and the low potential side power source V _SS, nine resistors R ₃₀ to R ₃₈ via the transistor Tr for switching in series Connected, and a total of 10 divided voltages V _A , V _B , V _C , V _D , V _E , V _F , V _G , V _H , V
_I and V _J are taken out. Here, the value of seven resistors R ₃₁ to R _37, excluding the two resistors R _38, R ₃₀ at both ends are equal, the potential difference from V _B to V _I is constant. Therefore, V _B , V _C , V _D , V _E , V except for V _A and V _J
F, V _G, the voltages V _H and V _I is the period from V _B as a predetermined high potential to V _I as a predetermined low potential 7
V _A is a first voltage having a potential higher than a predetermined high potential (V _B ), and V _J is a predetermined low potential (hereinafter referred to as a reference voltage). a second voltage having a potential lower than V _I).

SW1 to SW4 are analog switches which are turned on by H logic control input, G is an inverter gate, LS
1, LS2 is a level shift circuit, and an inversion control signal M
And the signal S _MX reverse phase with giving the SW1 and SW3, controls the on / off of each switch giving a signal S _M-phase to SW2 and SW4. In L logic period of the signal M is SW1 and SW3 are while V _A and V _I turned on is selected, the H logic period SW2 and SW4 are V _B and V _J is selected turned on.

V _A (or V _B ), V _I (or V _J )
The reference voltages V _{C and} V _H are applied to the data driver of the liquid crystal display device as shown in FIG. The data driver selects a data line of the liquid crystal panel line-sequentially in accordance with a control signal from the control circuit, and drives the selected data line with one reference voltage. (Gradation signal) and the inverted control signal M in the control signal.

Table 3 below summarizes the operation of selecting the reference voltage in the data driver of FIG.

As can be understood from Table 3, the inversion control signal M is in the period of L logic (in other words, the common voltage V _COM
When the black level is displayed during the negative polarity period), V _{B to} V _I
Instead of the reference voltage (V _B ) having the highest potential, a first voltage _VA having a higher potential is used.
Alternatively, when the inverted control signal M to display the black level during the H logic (positive polarity period of the common voltage V _COM other words) is, V _B ~V reference voltage (V _I having the lowest potential in the _I ), A lower potential second voltage V _J is used.

[0016] Therefore, as shown in FIG. 4, V ₆ and V
The potential difference between the ₇ 'potential difference between the and the _{(V 6) (V 7'} ) is, V ₀ ~V ₆ and (V ₀₎ ~ results is enlarged than the potential difference between (V _6), linear The amount of change in transmittance near a black level (however, in the case of a normally white liquid crystal) which has a problem in terms of characteristics can be increased in accordance with the potential difference, and the gradation of the gray level near the black level can be increased. The change can be clarified.

In this embodiment, eight gradations are taken as an example, but it is needless to say that the number of gradations is not limited.
Needless to say, it can be applied to a normally black type.

[0018]

According to the present invention, since the voltage applied to the liquid crystal is optimized, the gradation change near the minimum transmittance of the liquid crystal can be made clear and the display quality can be improved.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of voltage assignment according to one embodiment.

FIG. 2 is a configuration diagram of a reference voltage generation circuit according to one embodiment.

FIG. 3 is a block diagram of a liquid crystal display device according to one embodiment.

FIG. 4 is a transmittance-voltage (TV) characteristic diagram of an example.

FIG. 5 is a conceptual diagram of voltage allocation according to a first conventional example.

FIG. 6 is a transmittance-voltage (TV) characteristic diagram of the first conventional example.

FIG. 7 is a configuration diagram of a reference voltage generation circuit of a first conventional example.

FIG. 8 is a conceptual diagram of voltage allocation according to a second conventional example.

FIG. 9 is a configuration diagram of a second conventional reference voltage generation circuit.

[Explanation of symbols]

V _B: divided voltage (a predetermined high potential) V _I: divided voltage (a predetermined low potential) V _B ~V _I: reference voltage V _COM: the common voltage V _A: the first voltage V _J: second Voltage

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Katsuhiko Kishida 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside Fujitsu Limited (58) Field surveyed (Int.Cl. ⁷ , DB name) G09G 3/36 G02F 1 / 133 520 G02F 1/133 550 G02F 1/133 575 G09G 3/20

Claims (1)

(57) [Claims] 1. A method for selecting one of reference voltages having respective potentials equally divided into a plurality of portions from a predetermined high potential to a predetermined low potential according to display data, and selecting the selected voltage with a pixel electrode of a liquid crystal. And a common voltage whose polarity changes alternately is applied to a common electrode of the liquid crystal, and a change in transmittance according to a potential difference between the pixel electrode and the common electrode is caused in the liquid crystal between the two electrodes. Generating a first voltage having a higher potential than the high potential and a second voltage having a lower potential than the low potential; and when the common voltage has a negative polarity, among the plurality of reference voltages, While the first voltage is used instead of the reference voltage having the highest potential, when the common voltage has a positive polarity, the second voltage is used instead of the reference voltage having the lowest potential among the plurality of reference voltages. Configured to use The liquid crystal display device, characterized in that.