JPH05346771A - Method for driving liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain the drive method of a liquid crystal display device reducing display unevenness by expanding the range of the source potential of an OP amplifier wider than the drive potential of an LCD. CONSTITUTION:Source voltage VDD-VZZ is voltage-divided by resistors R1, R1, R2, R1, R1 and an emitter follower transistor 11, and the potential of respective voltage-divided points of the resistors are outputted through the voltage followers 13-16 of the OP amplifier and made the potential of V2-V5 respectively. The range VCC-VBB of the source potential is set wider than the range V1-V6 of the drive potential of a liquid crystal, and V1, V6 and the output potential V2-V5 of the OP amplifiers 13-16 are stabilized between with the source potential VCC by a capacitor C1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a simple matrix type liquid crystal display device used in computers, word processors and the like.

[0002]

2. Description of the Related Art FIG. 8 is a block diagram of a pixel of a simple matrix type liquid crystal display device, including (I, J) to (I + 1, J +).
4) of 1) is shown. Liquid crystal 6 of (I, J) pixel
3 is sandwiched between a row electrode 61 and a column electrode 62 arranged orthogonally. A plurality of transparent row electrodes parallel to the row electrode 61 are formed on one glass substrate, and a plurality of transparent column electrodes parallel to the column electrode 62 are formed on the opposing glass substrate, and between the both substrates. An image is displayed by controlling the voltage for each pixel with a row electrode and a column electrode intersecting the enclosed liquid crystal. R (I), R (I +
1) is the signal of the row electrodes of the I row and (I + 1) row, S (J),
S (J + 1) is a signal of the column electrodes of the J column and the (J + 1) column.

FIG. 9 is a screen view of a liquid crystal display device for explaining display unevenness. 71 and 72 are row electrodes of the liquid crystal display device,
A row-side drive circuit that sends a potential signal that selects and deselects pixels for each row, and columns 73 and 74 that are column-side drive circuits that send lighting and non-lighting signals to the column electrodes.

On the screen, in addition to a pattern in which the horizontal stripes of the white part 75 and the black part 76 are repeated, black vertical stripes 78 and white vertical stripes 79 are displayed, and white parts 80, 81 and 82 are provided on the upper side. From the white portion 82 that is continuous with the white vertical stripes, the white portion 81 that is above the black vertical stripes,
The white part 80 on the upper side of the pattern in which the black and white horizontal stripes are repeated becomes dark in order. Even in the black portion, the black portion 76 in the pattern in which the black and white horizontal stripes are repeated is darker than the black vertical stripe 78. Each of white and black has "unevenness of display" in which the density varies depending on the pattern.

FIG. 10 is a liquid crystal driving signal diagram for explaining display unevenness, and shows the signal of the row electrode and the potential of lighting and non-lighting of the column electrode related to the liquid crystal in the portion 75 of FIG. The signals of the row electrodes change to 91, 92, and 93, and take the non-selection potential V ₅ , the selection potential V ₁ , and the non-selection potential V ₅ , respectively, and in the next frame in which the polarities are inverted for AC driving of the liquid crystal, 9
6, 97, and 98, and correspondingly become the non-selection potential V ₂ , the selection potential V ₆ , and the non-selection potential V ₂ . The lighting potential of the column electrode is V ₆ , the non-lighting potential is V ₄ , and the lighting potential V ₁ and the non-lighting potential V ₃ in the frame in which the polarity is inverted.
V _K −V _{K + 1} = V (K = 1, 2, 4, 5).

In the screen 94 of FIG. 9, reference numeral 94 designates the liquid crystal row in the portion 76 at the selection potential, and the signal of the column electrode on the left half surface becomes the lighting potential V.
_This is a spike generated in the non-selection potential V ₅ of the row electrode through the capacitance of the liquid crystal in which the potential of the column electrode changes when changing from ₆ to the non-lighting potential V ₄ . In the case of 95, when the selection is moved to the liquid crystal row of the 77 portion, the signal of the column electrode on the left half surface is the non-lighting potential V ₄
Is a spike generated by changing from the lighting potential V ₆ to the lighting potential V ₆ . Similarly, 99 and 100 at the time of polarity inversion in the next frame are spikes corresponding to 94 and 95, respectively. The recovery time t _B of the spikes 94, 99 in the non-lighting potential direction is longer than the recovery time t _W of the spikes 95, 100 in the lighting potential direction.

11 (a), 11 (b) and 11 (c) show the voltage applied to the liquid crystal at the portions 82, 81 and 80 in FIG. 9 during the period indicated by T in FIG. The voltage between the electrodes of the liquid crystal, which is | the electric potential of the column electrode−the electric potential of the row electrode |
The time product is (a)>(b)> (c). The effective voltage applied to the liquid crystal is high in the white part (a) 82 connected to the white vertical stripes, the white part (b) 81 on the upper side of the black vertical stripes, and the white part (c) 80 on the upper side of the pattern in which the black and white horizontal stripes are repeated. It is getting lower in order. This situation depends on that t _B is longer than t _{W, the} direction in which the non-selective potential spike of the row electrode appears, and the way of taking the potential of the column electrode.

FIG. 12 is a power supply circuit diagram for producing a liquid crystal drive potential in a conventional liquid crystal display device. Between power supply voltage V _DD -V _ZZ, resistors _{R 1, R 1, R 2} , R 1, R 1 and divided by the emitter follower transistor 111, the potential of each dividing point of the resistors of the operational amplifier voltage follower 113, 11
It outputs through 4, 115 and 116, and V ₂ and V respectively
The potentials are ₃ , V ₄ , and V ₅ . V _DD = V ₁ , V ₂ ,
V ₃ is a lighting potential, a non-selection potential, and a non-lighting potential, respectively. The emitter potential of the transistor 111 V _EE = V ₆
And V ₅ and V ₄ are a lighting potential, a non-selection potential and a non-lighting potential, respectively, which are inversion potentials of V ₁ , V ₂ and V ₃ , respectively. The selection potentials with respect to the non-selection potentials V ₂ and V ₅ are V ₆ and V ₁ , respectively, and are used in common with the lighting potential. The capacitor C ₁ is for stabilizing each drive potential of the liquid crystal. The drive potential of the liquid crystal is adjusted by changing the base potential V _B of the transistor 111 within the power source of V _DD -V _ZZ .

Operational amplifier 11 of the power supply circuit of the liquid crystal display device
As 2, a μPC4741 type IC with four operational amplifiers is used. The power supply circuit shown in FIG. 12 is used in two sets with the same constant. _One supplies the drive potentials V _{1 to} V ₆ of the liquid crystal to the row side and column side drive circuits 71 and 73 shown in FIG. It is supplied to the row side and column side drive circuits 72 and 74. V _DD and V _EE are the positive and negative power supply potentials of the ICs of the row side and column side driving circuits. Another power supply potential V _SS for the logic signal is supplied at a voltage of 5 V inside the positive or negative power supply potential.

The output of the operational amplifier is an emitter follower in which NPN and PNP transistors are connected in a complementary manner. Operational amplifier 11 for non-selection potentials V ₂ and V ₅
When spikes in the non-lighting potentials V ₃ and V ₄ are applied to the outputs of ₃ and 116, respectively, the negative feedback of the voltage follower functions to change the base of the emitter follower in the positive and negative power supply directions of the operational amplifier. Then, the original non-selection potentials V ₂ and V ₅ are restored. In the circuit of FIG. 12, the positive and negative power supply potentials V _DD and V _EE of the operational amplifier are equal to the lighting potentials V ₁ and V ₆ , respectively, and | lighting potential-non-selection potential | is 1.
It is about 5v.

The change in the base potential of the emitter follower of the operational amplifier, which recovers the spike in the non-lighting potential direction, is within 1.5 V and does not change sufficiently rapidly, and the spike recovery in the lighting potential direction is suppressed. Like a large current cannot be applied to the load. Therefore, as shown in FIGS. 10, t _B , and t _W , the recovery of the spike in the non-lighting potential direction is delayed from the lighting potential direction, which causes display unevenness.

In recent years, liquid crystal display devices, which have become increasingly large in area and have high definition, use a super twist type liquid crystal display system having a steep transmittance-voltage curve. As the number of row electrodes increases, the selection period becomes shorter and the drive effective voltage for distinguishing between lighting and non-lighting becomes closer. Display unevenness caused by a spike in the non-selective potential of the row electrode due to the collective change of the signal of the column electrode described above and a change in the effective voltage is displayed on a screen including a graph with a standard pattern of lines, horizontal stripes, dots, blocks, etc. Then
It came to be recognized as a fault.

[0013]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and display unevenness can be obtained by using an improved driving method which has not been known. It is intended to newly provide a reduced liquid crystal display device.

[0014]

The present invention has been made to solve the above-mentioned problems, and a liquid crystal is provided between a substrate having a plurality of row electrodes and a counter substrate having a plurality of column electrodes. A liquid crystal that sandwiches and sends to the row electrodes a potential signal that selects and deselects pixels for each row from the row side drive circuit, and sends to the column electrodes a lighting or non-lighting signal from the column side drive circuit for display. In the display device, the drive potential of the selected, non-selected, lit, and non-lit liquid crystal that is supplied to the row-side and column-side drive circuits is created by dividing the power supply voltage with a resistor, and through it the voltage follower of the operational amplifier is used. With respect to the output potential, the range of the power supply potential of the operational amplifier is set wider than the range of the drive potential of the liquid crystal to stabilize it, and a method of driving a liquid crystal display device is provided.

[0015]

According to the present invention, the range of the power supply potential of the operational amplifier is made wider than the range of the drive potential of the liquid crystal so that the recovery speed is almost the same regardless of the direction of the spike so that the state of lighting and non-lighting can be achieved. The fluctuation of the effective voltage of a certain liquid crystal is reduced to reduce the display unevenness.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a drive signal diagram of a liquid crystal of a liquid crystal display device of the present invention, showing a signal of a row electrode related to the liquid crystal and a lighting / non-lighting potential of a column electrode. The signals of the row electrodes of the frame shown in the figure change to 1, 2, 3 to take the non-selection potential V ₅ , the selection potential V ₁ , and the non-selection potential V ₅ , respectively, and the lighting potential is V ₆ and the non-lighting potential is V. _{Is 4} . As will be explained later, the recovery speed is set regardless of the direction of the spikes generated in the non-select potential by setting the range of the power supply potential of the operational amplifier that is wider than the drive potential range of the selected, non-selected, lit, and non-lit liquid crystals. We are trying to be as fast as possible. The spikes indicated by 4 and 5 correspond to the spikes indicated by 94 and 95 in FIG. 10 of the conventional example, and the recovery time t _B of the spike 4 in the non-lighting potential direction.
Is close to the recovery time t _W of the spike in the lighting potential direction.

In the present invention, the voltage applied to the liquid crystal corresponding to the portions 82, 81 and 80 in FIG. 9 during the period shown in T of FIG.
(A), (b), (c). The voltage-time product of the voltage between electrodes of the liquid crystal and the period of T is (a) ≈ (b)>
Although it is (c), the difference between (a), (b) and (c) is based on the difference between (a) and (b) and (a) and (c) of the conventional example FIG. Much smaller. When a repeating pattern of horizontal stripes of white and black portions, vertical black stripes, and vertical white stripes are displayed on the screen as shown in FIG. 9, the difference in brightness of the upper white portions 80, 81, 82 and white The difference in darkness between the black portion 76 and the black vertical stripe 78 in the repeating pattern of horizontal stripes of the black and white portions is smaller than in the conventional case, and display unevenness is reduced.

FIG. 3 shows changes in the recovery time of spikes generated in the non-selection potential when the range of the power supply potential of the operational amplifier is made larger than the range of the drive potential of the liquid crystal. 12
The positive power supply potential of the operational amplifier shown in ( ₁₎ is set to V _CC , which is higher than the lighting potential V ₁ , and the negative power supply potential is V _BB , which is set to be lower than the lighting potential V ₆ . ΜPC47 as an operational amplifier
41, the capacitance C ₁ is 3.3 μF, and the average capacitance between the all-row electrodes and all-row electrodes of the liquid crystal display body is 0.3.
It is a measurement example in the case of μF. As the voltages V _CC -V ₁ and V ₆ -V _BB between the power supply potential and the lighting potential increase,
The recovery time t _B of the spike in the non-lighting potential direction approaches the recovery time t _W of the spike in the lighting potential direction, and is almost equal to that of 5 v.

FIG. 4 is a power supply circuit diagram according to the driving method of the liquid crystal display device of the present invention, which is the first embodiment. Power supply voltage V _DD
The voltage between −V _{ZZ is divided} by resistors R ₁ , R ₁ , R ₂ , R ₁ , R ₁ and the transistor 11 of the emitter follower, and the potential at each voltage dividing point of the resistor is divided by the voltage follower 13 of the operational amplifier.
It outputs through 14, 15 and 16, and V ₂ and V respectively
The potentials are ₃ , V ₄ , and V ₅ . V _DD = V ₁ , V ₂ ,
V ₃ is a lighting potential, a non-selection potential, and a non-lighting potential, respectively, and the emitter potential V _EE = V _{6 of} the transistor 11
V ₅ and V ₄ are inversion potentials of V ₁ , V ₂ and V ₃ , respectively, and are a lighting potential, a non-selection potential and a non-lighting potential, respectively. The selection potentials for the non-selection potentials V ₂ and V ₅ are V ₆ and V ₁ , respectively, which are common to the lighting potential.

The base of the transistor is a potential obtained by dividing V _DD -V _ZZ by resistors R ₄ and R ₆ and a variable resistor R ₅ . By adjusting the variable resistor R ₅ , each drive potential V _{1 of} liquid crystal
V ₆ and the driving voltage V _K −V _{K + 1} = V applied during the non-selection period
Adjust (K = 1, 2, 4, 5). Voltage follower 1
The positive power source potential of the operational amplifier circuits 12 of 3 to 16 is V
_{At CC} , the power supply potential V _{BB, which} is higher than the lighting potential V _{1 and} lower than the lighting potential V ₆ , is equal to V _ZZ .

Range of power supply potential of operational amplifier V _CC -V
_BB is set wider than the drive potential range V ₁ -V ₆ of the liquid crystal, and V ₁ and V ₆ and the output potential V _{2 of the} operational amplifiers 13 to 16 are set.
The ~V _5, is stabilized with the power source potential V _CC by the capacitance C _1. Capacitance C ₂ connected to the power supply potential V _DD
Is for stabilizing the base potential of the transistor 11. As shown in FIG. 3, the voltages V _CC -V ₁ and V ₆ -V _BB between the power supply potential and the lighting potential are set to be larger than 5 v, and as shown in FIGS. First, the recovery speed is made nearly equal and the display unevenness is reduced. The potentials of V _DD and V _EE , which are equivalent to the lighting potentials V ₁ and V ₆ , are the positive and negative power source potentials of the ICs of the drive circuits on the row side and the column side, and the power source potential V _SS for the logic signal of this IC. Is V
_DD- V _SS = 5v or V _SS -V _EE = 5v.

FIG. 5 is a power supply circuit diagram according to the driving method of the liquid crystal display device of the present invention, which is a second embodiment. Power supply voltage V _CC
Between -V _ZZ , Zener diode 21, resistors R ₁ , R
₁ , R ₂ , R ₁ , R ₁ , the Zener diode 22, and the emitter-follower transistor 23 are used for voltage division, and the potential at each voltage division point of the resistor is divided by the voltage follower 25 of the operational amplifier.
It outputs through 26, 27, 28, respectively, V ₂ , V
The potentials are ₃ , V ₄ , and V ₅ . Voltage follower 25
The positive power supply potential of the operational amplifier circuit 24 of ~ 28 is V _CC ,
The negative power supply potential V _BB is connected to the emitter of the transistor 23. The potentials lower than V _CC by the voltage of the Zener diode 21 are V _DD and V _1, and the potentials higher than V _BB by the voltage of the Zener diode 22 are V _EE and V ₆ .

The voltage between V _{CC and} V _{ZZ is divided} by the resistor R ₄ and the variable resistor R ₅ to obtain the base potential of the transistor 23.
The respective potentials of V _CC , V _BB , V _ZZ , V _DD , V _EE and V _{1 to} V ₆ correspond to the potentials of the same sign in the first embodiment. The capacitors C ₁ and C ₂ are connected between the power source potential V _CC and each potential,
The potential is stabilized. Range V of power supply potential of operational amplifier
The _CC -V _BB, than the range V ₁ -V ₆ of the liquid crystal drive potential, and voltage of widely setting Zener diode 21 and 22. Zener diodes of 5 V or more are used for 21 and 22.

FIG. 6 is a power supply circuit diagram according to the driving method of the liquid crystal display device of the present invention, which is a third embodiment. Power supply voltage V _CC
Between -V _ZZ , resistors R ₃ , R ₁ , R ₁ , R ₂ , R ₁ , R
₁ , R ₃ and emitter follower transistor 31
The voltage at each voltage dividing point of the resistor is output through the voltage followers 33, 34, 35, 36, 37, 38 of the operational amplifier, and V _DD = V ₁ , V ₂ , V ₃ , V ₄ , V
₅ , V ₆ = V _EE potential. Voltage follower 33
The positive power supply potential of the operational amplifier circuit 32 of ~ 38 is V _CC ,
The negative power supply potential V _BB is connected to the emitter of the transistor 31.

The base potential of the transistor 31 is V _CC
The _voltage between −V _{zz is divided} by the resistance R ₄ and the variable resistance R ₅ to determine. The respective potentials of V _CC , V _BB , V _ZZ , V _DD , V _EE and V _{1 to} V ₆ correspond to the potentials of the same sign in the first embodiment. The capacitors C ₁ and C ₂ are connected between the power supply potential V _CC and each potential to stabilize the potential. The power supply potential range V _CC -V _BB of the operational amplifier is set wider than the liquid crystal drive potential range V ₁ -V ₆ by the two voltages of the resistor R ₃ . The Zener diodes 21 and 22 in the circuit of FIG.
Replaced by ₃ .

FIG. 7 is a power supply circuit diagram according to the driving method of the liquid crystal display device of the present invention, which is a fourth embodiment. Power supply voltage V _CC
Zener diode 41 and diode 4 between -V _ZZ
2, resistors R ₁ , R ₁ , R ₂ , R ₁ , R ₁ , diode 4
3. Zener diode 44 and emitter follower transistor 45 divide the voltage, and the potential at each connection point is the voltage follower 47, 48, 49, 50, 51 of the operational amplifier.
It outputs through 52, 53 and 54, and V _DD and V respectively
The potentials are ₁ , V ₂ , V ₃ , V ₄ , V ₅ , V ₆ , and V _EE . Operational amplifier circuit 46 of voltage followers 47-54
The positive power supply potential of V _CC is V _CC , and the negative power supply potential V _BB is connected to the emitter of the transistor 45.

The base of the transistor 45 is V _CC -V
_The potential between _{ZZ is divided} by resistance R ₄ and variable resistance R ₅ . The respective potentials of V _CC , V _BB , V _ZZ , V _DD , V _EE and V _{1 to} V ₆ correspond to the potentials of the same sign described in the first embodiment. Capacitors C ₁ and C ₂ connected to the power supply potential V _CC stabilize each potential. Range V of power supply potential of operational amplifier
_CC -V _BB, from range V ₁ -V ₆ of the liquid crystal drive potential is voltage of wide set of zener diodes 41 and 44 and a diode 42, 43. In this embodiment, the power supply potential range V _DD -V _EE of the ICs of the row side and column side drive circuits is set wider than the drive potential range V ₁ -V ₆ of the liquid crystal by the voltage of the diodes 42 and 43. .. If necessary, a plurality of diodes 42 and 43 can be connected in series, or a low voltage Zener diode can be used instead.

[0028]

According to the present invention, in a simple matrix type liquid crystal display device in which a liquid crystal is sandwiched between orthogonal row electrodes and column electrodes, the range of the power supply potential of the operational amplifier outputting the drive potential of the liquid crystal is defined by the liquid crystal. The drive potential of the liquid crystal is wider than that of the column, and the spikes that occur in the non-selective potential due to the collective change of the signal of the column electrodes are quickly recovered to near the same regardless of the direction and the polarity, and the liquid crystal in the lighting and non-lighting states is effective. The fluctuation of the voltage is reduced, and the polarity of the drive signal is inverted at the frame cycle to perform AC driving.

According to the present invention, the display unevenness occurring on the screen is reduced by the pattern formed by characteristically collecting black and white pixels.
With a histogram or the like, a clear display with a higher white / black contrast than before can be obtained.

[Brief description of drawings]

FIG. 1 is a drive signal diagram of a liquid crystal of a liquid crystal display device of the present invention.

2A and 2B are voltage diagrams showing that display unevenness is reduced. FIG. 2A is a voltage diagram of a liquid crystal corresponding to a portion 82 of FIG. 9, and FIG. 2B is a voltage diagram of a liquid crystal corresponding to a portion 81 of FIG. Such a voltage diagram, (c) is a voltage diagram applied to the liquid crystal corresponding to the portion 80 in FIG. 9.

FIG. 3 is a diagram showing a relationship between a range of a power supply potential of an operational amplifier and a recovery time of a spike generated in a non-selection potential.

FIG. 4 is a power supply circuit diagram of a first embodiment according to the driving method of the liquid crystal display device of the present invention.

FIG. 5 is a power supply circuit diagram of a second embodiment according to the driving method of the liquid crystal display device of the present invention.

FIG. 6 is a power supply circuit diagram of a third embodiment according to the driving method of the liquid crystal display device of the present invention.

FIG. 7 is a power supply circuit diagram of a fourth embodiment according to the driving method of the liquid crystal display device of the present invention.

FIG. 8 is a configuration diagram of a pixel of a simple matrix type liquid crystal display device.

FIG. 9 is a screen diagram of a liquid crystal display device for explaining display unevenness.

FIG. 10 is a liquid crystal drive signal diagram for explaining display unevenness.

11A and 11B are voltage charts for explaining display unevenness, where FIG. 11A is a voltage chart applied to the liquid crystal in the portion 82 in FIG. 9, and FIG.
Of the voltage applied to the liquid crystal at the portion 81 in FIG.
The voltage figure which applies to the liquid crystal of the 0 part.

FIG. 12 is a power supply circuit diagram for producing a drive potential of liquid crystal in a conventional liquid crystal display device.

[Explanation of symbols]

V _1: Selection for lighting voltage and V ₅ potential V _2: non-selection potential V _3: non-lighting voltage V _4: non-lighting voltage and V ₃ and the polarity inversion V _5: V ₂ and the non-selected polarity by inverting the potential V _6: Lighting potential whose polarity is inverted from V ₁ and selection potential with respect to V ₂ t _B : Recovery time of spike in non-lighting potential direction in non-selection potential t _W : Recovery time of spike in lighting potential direction in non-selection potential V _CC : Positive power supply potential of operational amplifier circuit V _BB : Negative power supply potential of operational amplifier circuit V _ZZ : Negative power supply potential V _DD : Positive power supply potential of IC on the row side and column side V _EE : Row side and column side Negative power supply potential of IC

Claims (1)

[Claims] 1. A liquid crystal is sandwiched between a substrate on which a plurality of row electrodes are formed and a counter substrate on which a plurality of column electrodes are formed, and a row-side drive circuit selects a pixel for each row. In a liquid crystal display device that displays an unselected potential signal and a column-side drive circuit sends a lighting / non-lighting signal from a column-side drive circuit, selection / non-selection supplied to the row-side and column-side drive circuits The driving potential of the liquid crystal of lighting, non-lighting is made by dividing the power supply voltage by using a resistor, and the potential output through the voltage follower of the operational amplifier is within the range of the power supply potential of the operational amplifier. The method for driving a liquid crystal display device is characterized in that it is set wider than the range and stabilized.