JP3366437B2 - Driving method of liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] BACKGROUND OF THE INVENTION 1. Field of the Invention
Of display characteristics and long-term operation of a liquid crystal display device
-LCD DEVICE AND ITS DRIVING WITH IMPROVED RELIABILITY
About the method. [0002] 2. Description of the Related Art FIG. 10 shows a conventional gradation display thin film transistor.
(Hereinafter referred to as TFT) type twisted nematic
(Hereinafter referred to as TN) liquid crystal display (hereinafter referred to as LCD)
2) is a diagram of an example of a system configuration. Display of this system
The halftone display method of the circuit uses a gradation voltage selection method.
In this gray scale voltage selection method, a plurality of
The gray scale voltage is applied to the source drivers 17a and 17b (hereinafter, representatives).
And 17) according to the gradation data.
Input an image signal to the liquid crystal panel 18. This
Here, each data of R, G, B of the input signal is the display image
Red, green and blue color component data, CLK is dot
The clock, Hsync or Vsync, respectively, is used to level the display screen.
Or a vertical synchronization signal. The display circuit is a source dry
Data and timing to the gate 17 and the gate driver 16.
Timing control circuit 15 for inputting the
Voltage, counter electrode voltage, gate voltage, and auxiliary capacitance electrode voltage.
The gradation voltage circuit 11 and the counter electrode voltage circuit 1 which are respectively generated
2. Gate voltage circuit 13 and auxiliary capacitance electrode voltage circuit 1
4. Source driver 17 and game
The signal input from the display circuit in the driver 16 is
Generates an image signal and a scanning signal, and enters the liquid crystal panel 18.
Power. The counter electrode voltage and the auxiliary capacitance voltage are the respective voltages
The signals are directly input to the liquid crystal panel 18 from the circuits 12 and 14. FIG. 11 shows an example of the configuration of a source driver 17.
FIG. In this way, the sample pulse
Raw circuit 21, data sampling circuit 22, latch circuit 23
And a gradation voltage selection circuit 24. Figure
At 11, the data of CLK, RGB
STP is a start pulse,
V0 to V7 are the gradation voltages in the 8-gradation display. This
As shown in FIG.
The corresponding gray scale voltage based on the data signal input to
The voltage is selected by the voltage selection circuit 24. The selected gradation
The voltage is output as an image signal to the source signal line of the LCD panel
Is done. FIG. 12 shows a normally white (hereinafter referred to as NW).
TF in the case of 8 gradation display in the mode)
It is a figure of the example of the voltage-transmittance characteristic of T-LCD. TN type L
In order to perform multi-gradation display on a CD,
AC signal whose AC amplitude changes in the same way must be applied to the liquid crystal layer.
I have to. Therefore, the voltage in FIG.
It is. T is the transmittance of the liquid crystal panel. V0-V7
Is the gradation voltage for 8 gradation display, and is 100 to 0
% Transmission by inputting an intermediate voltage between
Display can be realized. FIG. 13 shows a conventional floor of a TFT-LCD.
FIG. 5 is a waveform diagram of a regulated voltage. V0 to V7 are for 8 gradation display
Each of the gradation voltage waveforms, where V00 is an AC signal of V0 to V7.
This is the heart voltage, and the conventional gradation voltage setting method uses all eight gradations.
And the center voltage was the same. FIG. 14 shows a liquid crystal panel of a TFT-LCD.
FIG. SL is the source line, GL is the gate line
IN and D are drain (pixel) electrodes, COM is a counter electrode,
STL is an auxiliary (accumulation) capacitance line. FIG. 15 is a diagram showing the electronic information communication on February 19, 1993.
IEICE Technical Report EID92-117, page 21
Of one pixel of a conventional TN-type LCD using a thinned TFT
It is a circuit diagram. S is a source electrode, G is a gate electrode, CO
M is a counter electrode, and ST is an auxiliary (accumulation) capacitance electrode. Ma
Clc is the liquid crystal capacitance, Cgd is the parasitic between the gate and drain.
The capacity, Cst, is an auxiliary capacity. That is, TFT-LC
D, the parasitic capacitance C between the gate and drain of the TFT
gd is known to occur. The auxiliary capacitance Cst is the liquid crystal capacitance.
Connected to the drain electrode in parallel with the quantity Clc
There may or may not be. Drain electrode, source electrode
The potential of the electrode, gate electrode, counter electrode, and auxiliary capacitance electrode.
These are Vd, Vs, Vg, Vcom, and Vst, respectively. As mentioned above
In the liquid crystal layer, the potential difference between the drain electrode and the counter electrode (Vd
-Vcom) is applied. FIG. 16 shows the waveform of each electrode voltage of the equivalent circuit.
FIG. Here, DC power is used for both Vcom and Vst.
The case where pressure is used is shown. Vgh and Vgl are
The on-voltage and off-voltage of the Vsa and
Vso is the AC amplitude voltage and the center voltage of the source signal.
You. Therefore, this Vsa value changes according to the display gradation.
You. During the ON period (period when the gate voltage becomes Vgh)
The video signal input from the source line is
And Vd matches Vs. Then the gate voltage
Parasitic capacitance between gate and drain in synchronization with falling
The drain voltage fluctuates due to the coupling effect via Cgd.
You. The fluctuating voltage ΔVd is expressed by the following equation (1). [0009] (Equation 1) Here, ΔVg represents a variation amount of the gate voltage Vg. In addition,
If there is no auxiliary capacity, Cst = 0 may be substituted. ΔV
Since g = Vgl−Vgh is always a negative value, ΔVd is also a negative value.
Becomes As a result, the drain AC
The center voltage of the signal decreases. This voltage difference is applied to the liquid crystal
Normally, Vcom is set to Vso so as not to be applied as a DC voltage.
It is adjusted to a value lower by ΔVd. That is, the drain
The voltage fluctuation is corrected by Vcom. However, in general, the relative dielectric constant of a TN liquid crystal
ε_lcVaries with the applied voltage Vsa value as shown in FIG.
I do. As a result, Clc changes and ΔV according to equation (1).
The d value also changes. Therefore, all display gradations, that is,
The effect of ΔVd on Vsa value cannot be removed
No. As one example, a liquid crystal having the characteristics shown in FIG.
Calculation result of change of ΔVd value to Vsa when using
Are shown in Table 1. Here, Cst = 0.8 pF, Cgd = 0.
1 pF and ΔVg = 25 V. In this way, temporarily Vcom
Is the average value of the maximum value and the minimum value of ΔVd.
Even if it is adjusted to 33V, at Vsa = 0V and 4V
DC voltage of + 0.13V and -0.13V respectively for liquid crystal
Join the layers. [0011] [Table 1] In addition, the change of the ΔVd value with respect to Vsa when no auxiliary capacitance is provided.
Table 2 shows an example of the calculation results of the conversion. Similarly, Cgd = 0.1p
F, ΔVg = 25V. In this way, if Vcom is complemented,
A positive value is 9.43 V which is an average value of the maximum value and the minimum value of Vd.
, Even at Vsa = 0V and 4V
DC voltages of + 2.04V and -2.05V are applied to the liquid crystal layer.
I will. Thus, in general, when there is no auxiliary capacity
DC voltage applied to the liquid crystal by the change of ΔVd
It is larger than when there is capacity. [0012] [Table 2] [0013] As described above, the conventional
In the halftone display method using the gradation voltage selection method, the gate
Drain voltage becomes signal voltage based on parasitic capacitance between rain
Shifts by ΔVd. Also, the drain voltage
The signal voltage varies depending on the voltage dependence of the liquid crystal capacitance.
The shift is ΔVd depending on the pressure. Therefore, the change in drain voltage ΔVd
DC voltage is applied to the liquid crystal layer, causing burning or flickering.
Display failure based on the
There is a problem in that the reliability of The present invention solves such a problem and solves this problem.
By changing the center voltage according to the pressure, the liquid crystal
LCD driving method in which no DC voltage is applied to the layers
The purpose is to provide. Another object of the present invention is to provide a gray scale voltage in an LCD.
The characteristic opposite to the change of the liquid crystal capacitance due to the voltage
A variable capacitance is added in parallel to cancel the above-mentioned change in ΔVd.
DC voltage is applied to the liquid crystal layer
It is an object of the present invention to provide an LCD that is not used. [0017] Means for Solving the Problems The present inventionGet involvedLCD
In the driving method, a thin film transistor is provided for each pixel.
AC applied to each pixel with respect to the liquid crystal display device
A plurality of exchanges having different amplitudes, which constitute the grayscale voltage signal.
The center voltage of the flowing voltage is set to a different value for each AC voltage.
Is defined. The plurality of thin film transistors may be provided at the source of the thin film transistor.
Of drain voltage when each AC voltage is input
Values for each of the two center voltages of the AC voltage.
The difference between the pressures is the difference between the variation values of the two arbitrary AC voltages.
Set each of the center voltages to be equal to
Reduces the DC voltage applied to the liquid crystal layer.
Is preferred. Further, a reference voltage generation circuit, an addition circuit,
Maximum with both positive and negative polarities by combining multiple subtraction circuits
Generates amplitude gradation reference voltage and minimum amplitude gradation reference voltage
Maximum and minimum amplitude gradation
Dividing between the quasi-voltages with a dividing resistor allows
Corresponding halftone gradation reference voltages, and
A current divider sets each gradation reference voltage corresponding to the polarity.
In addition, the gray scale voltage is converted to AC, and the AC gray scale voltage signal is
It can be used as a component to accommodate the center voltage of AC voltage.
Because it can easily be set to a different value for each AC voltage
preferable. The corresponding floor of each of the positive and negative polarities
In the division resistors that set the tuning reference voltage,
Different values of the resistors to achieve the above method
Preferred from the point. Further, the maximum swing having the positive and negative polarities is
Generate the width gradation reference voltage and the minimum amplitude gradation reference voltage
If the corresponding adder or subtractor circuit has a different addition coefficient
Or having a subtraction factor achieves the above method
Is preferred. LCD according to the present inventionDrive methodIs an individual
Another pixel electrode, wherein the individual pixel electrode is connected to a drain electrode;
Thin film transistor and the individual pixel electrode and the dielectric film
A storage capacitor electrode that forms a storage capacitor that faces
Insulating property in which a plurality of pixels are provided in a matrix
Second insulating transparent substrate provided with a transparent substrate and a counter electrode
And the first and second insulating transparent substrates
However, the plurality of individual pixel electrodes and the counter electrode are mutually
While being held so as to face each other, the first and second
Liquid in which a liquid crystal material is sealed between two insulating transparent substrates
Crystal display device, wherein the auxiliary capacitance depends on an applied voltage.
Variable capacity with variable capacitance valueAnd the auxiliary capacitance is applied.
A variable capacitor whose capacitance value decreases as the voltage increases,
The auxiliary capacitance is a p-type metal insulator semiconductor.
Diode and n-type metal insulator semiconductor
Of a liquid crystal display device configured by connecting
A driving method, comprising: a reference voltage generation circuit, an addition circuit,
Maximum with both positive and negative polarities by combining multiple subtraction circuits
Generates amplitude gradation reference voltage and minimum amplitude gradation reference voltage
Maximum and minimum amplitude gradation
Dividing between the quasi-voltages with a dividing resistor allows
Corresponding halftone gradation reference voltages, and
A current divider sets each gradation reference voltage corresponding to the polarity.
In addition, the gray scale voltage is converted to AC, and the AC gray scale voltage signal
Used as a componentIt is characterized by that. The storage capacity increases as the applied voltage increases.
The variable capacitance whose value decreases decreases the voltage of the liquid crystal capacitance.
This is especially useful for canceling dependencies. The auxiliary capacitance is a p-type metal insulator
Semiconductor diode and n-type metal insulator
If it is configured by connecting semiconductor diodes in series,
Easily obtain the capacity to cancel the voltage dependence of the liquid crystal capacity
Is preferred because [0025] [Action] The present inventionGet involvedAccording to the driving method of the LCD,
The center voltage of the gradation voltage of each gradation is
By setting according to the voltage fluctuation value, the drain voltage
DC voltage generated by fluctuations can be reduced
You. The present inventionGet involvedDepends on LCD driving method
For example, the liquid crystal capacitance with the increase of the AC amplitude voltage of the drain voltage
Since the auxiliary capacitance has a capacitance change characteristic contrary to the change characteristic,
The effect of the liquid crystal capacitance change is negated and the drain fluctuation voltage
The change due to the rain voltage can be suppressed. The result
As a result, the DC applied to the liquid crystal when the drain voltage is changed
Voltage can be reduced, and display defects such as flicker and burn-in
And at the same time improve reliability in long-term operation.
You. [0027] 【Example】 [Embodiment 1] FIG. 1 shows an eight gradation display TFT-LCD of the present invention.
FIG. 7 is a gradation voltage setting diagram for explaining an embodiment in the case of FIG.
You. The gradation voltages V0 to V7 in the figure are the same as those in FIG.
V00 to V70 are the central voltages of the gradation voltages V0 to V7, respectively.
Pressure. Here, the center voltage V00 to V70 of each gradation is set for each gradation.
(2) according to the fluctuation value of the drain voltage
Set. [0028]         Vi0 = Vd0 + (ΔVd (Vi) −ΔVd (Vj))                                       (I = 0-7) (2) Here, Vd0 is a reference voltage of the center voltage, ΔVd (Vi), ΔV
d (Vj) is the drain voltage of gray scale i and j, respectively.
It is a fluctuation value. j is one specific gradation of j = 0 to 7
You. Set the common voltage as shown in the following equation (3).
You. [0029]         Vcom = Vd0−ΔVd (Vj) (3) The gray scale voltage of the liquid crystal panel with the auxiliary capacitance shown in Table 1 above.
The present invention represented by the formulas (2) and (3) is used for the pressure setting.
Table 3 shows setting examples. [0030] [Table 3] Here, Vi0 is the center voltage of the gradation voltage of gradation i. First
A reference voltage Vd0 of the center voltage is set. Here, Vd0 = 9.
5V. Next, by selecting j = 7,
The following equation is derived from the equation (2). [0031]       Vi0 = Vd0 + (ΔVd (Vi) −ΔVd (V7)) (4) The following equation (5) is derived from the equation (3). [0032]       Vcom = Vd0−ΔVd (V7) (5) As a result, Vi0 is corrected according to the ΔVd value of the gray scale i.
It becomes the heart voltage. In this case, the center voltage of the drain voltage after fluctuation
The voltage is equal to Vcom, and the generation of DC voltage applied to the liquid crystal layer
Can be suppressed. The setting method of this gradation voltage will be described with reference to a flowchart.
As shown in FIG. First, Vsa dependence of ΔVd unique to the panel
Measurement or calculation is performed (see S1). That is,
[Delta] Vd is obtained by the equation (1). Next reference center
Calculation and setting of voltage Vd0, gradation j, and Vcom are performed (see S2).
See). That is, Vd0 is set, gradation j is selected, and (3)
The common voltage Vcom is calculated by the equation. Then, for each gradation
The center voltage Vi0 is determined (see S3). I.e. j
For example, it is set to 7, and Vi0 is calculated by the equation (2). Next
Then, a gradation voltage is calculated (see S4). That is, in S3
Using the center voltage Vi0 of each gray scale, the high-side voltage is Vsh
(I) = Vi0 + Vsa (i), and the low-side voltage is Vsl (i)
= Vi0-Vsa (i). Finally, set the circuit
(See S5). That is, a gradation voltage circuit described later (see FIG. 3)
Adjust the divided variable resistors VR1 to VR14
, The coefficients of the addition and subtraction circuits 4a, 4b, 5a and 5b are calculated.
Or set while observing with an oscilloscope
I do. The center voltage of the above-mentioned gradation voltage is given by the following equation.
Therefore, the same applies by setting Vi0 and Vcom.
Can be obtained. [0035]       Vi0 = Vd0 + {ΔVd (Vi) − (ΔVdmax + ΔVdmin) / 2}                                                             (6)       Vcom = Vd0− (ΔVdmax + ΔVdmin) / 2 (7) Here, ΔVdmax and ΔVdmin are the maximum of ΔVd, respectively.
Value, minimum value. Table 1
Equations (6) and (7) for the gradation voltage setting of the liquid crystal panel
Therefore, Table 4 shows a setting example using the present invention. [0036] [Table 4]Here, Vd0 = 9.5V. ΔVdmax = 2.46
V, ΔVdmin = 2.20V. Also in this case, Vi0
It becomes the center voltage corrected according to the ΔVd value of the gray scale i,
Generation of a DC voltage can be suppressed. Example 2 Auxiliary capacitance in Table 2 above
(4) for the gradation voltage setting of the liquid crystal panel without
Table 5 shows a setting example using the present invention represented by the expression (5).
You. [0038] [Table 5] Here, similarly to the first embodiment, the center voltage Vi0 of the gradation voltage is
It is set according to equation (4). Where Vd0 =
9.5V. The common voltage is set according to equation (5).
Is defined. As a result, Vi0 depends on the ΔVd value of the gradation i.
The corrected center voltage. In this case the fluctuating dray
The center voltage of the pixel voltage matches Vcom, and
The generation of the flowing voltage can be suppressed. The liquid crystal panel without the auxiliary capacitor shown in Table 2
Expressions (6) and (7) for the gray scale voltage setting
Table 6 shows an example of setting the center voltage of each gradation voltage. [0040] [Table 6]The center voltage Vi0 of the gradation voltage is set according to the equation (6).
Have been. Here, Vd0 = 9.5V. Common power
The pressure is set according to equation (7). And this
Even in the case where Vi0 is corrected according to the ΔVd value of gradation i
It becomes a cardiac voltage, and generation of a DC voltage can be suppressed.
Table 2 shows the difference in gradation because there is no auxiliary capacitance as described above.
Difference between V00 and V70 due to the
It is larger than Table 1, which is the case. However, in the present invention
Changing the center voltage on the gradation voltage setting for Vi0 setting
Suppresses DC voltage generation even without auxiliary capacitance
be able to. Therefore, by adopting the present invention,
The auxiliary capacity can be removed. [Embodiment 3] An example of a method of realizing Embodiments 1 and 2 will be described.
As shown in FIG. FIG. 3 is a circuit diagram of a gradation voltage circuit in an 8-gradation display.
It is a block diagram showing an example. As shown in the figure, the circuit
Voltage Vro generating circuit 1, reference voltage Vrb generating circuit 2, reference voltage
Vrc generation circuit 3, addition circuits 4a and 4b, subtraction circuit 5a,
5b, divided variable resistors VR1 to VR14,
It is configured. Output from reference voltage Vr0 generation circuit 1
The reference voltage Vr0 is generated by the reference voltage Vrb generation circuit 2
The positive / negative maximum is obtained by adding and subtracting the reference voltage Vrb
The amplitude gradation reference voltages V7U and V7L are generated. Further V
7U and V7L by subtracting / adding reference voltage Vrc.
To generate the positive and negative minimum amplitude gradation reference voltages V0U and V0L.
You. In addition, between V7U and V0U, and between V7L and V0U
L is divided by dividing variable resistors VR1 to VR14
To set a gray scale reference voltage for halftone. AC circuit
In step 6, the gray scale reference voltage of the positive and negative polarities of each gray scale is
By selecting and switching every period or every horizontal period.
A streamed gray scale voltage is generated. Conventional gradation voltage generation
On the road, the set values of the divided resistors VR1 to VR14 are VR1 and V
R14, VR2 and VR13, upper and lower in the figure
The center voltage of each gray level is
Set to the same value The value of this split resistor
Is adjusted, the difference of ΔVd between the gray scales of the present invention is adjusted.
It is easy to shift the center voltage of each gradation voltage according to
Can be realized. In addition, fixed resistors are used for VR1 to VR14.
Even if a divided resistor is configured by
Similarly, the above-mentioned gradation
Shift the center voltage of each gradation voltage according to the difference of ΔVd between
Settings can be realized. [Embodiment 4] In a conventional gradation voltage generating circuit,
The coefficients of the addition and subtraction circuits in FIG. 3 are the same on the positive polarity side and the negative polarity side.
The same. Adjust this coefficient between positive and negative polarity
In accordance with the difference in ΔVd between gradations of the present invention,
The setting in which the center voltage of the adjustment voltage is shifted can be easily realized. In each of the embodiments described above, eight gradations are displayed.
The method of setting the gradation voltage in the above has been described.
It is similarly effective for arbitrary gradation display. [Embodiment 5] In each of the above embodiments, the gradation voltage
Shift the center voltage of the
Although the change in the liquid crystal capacitance due to the voltage was suppressed, in this embodiment,
A variable capacitance auxiliary capacitor that changes in the opposite direction to the liquid crystal capacitance is set.
It is intended to improve the situation. FIG. 4 illustrates a first embodiment of the LCD of the present invention.
Circuit equivalent to one pixel of TN type LCD using TFT
FIG. Here, the capacitance value of Cstv changes depending on the voltage.
STV is a variable capacity auxiliary (accumulation) capacity.
This is an auxiliary capacitance electrode. Image of TN type LCD having equivalent circuit of FIG.
The element is shown, for example, by FIG. (A) is a plane
Fig. (B) shows the cross-section of the section cut by AA in the horizontal direction.
It is sectional drawing seen from. First and second insulating transparent groups
On the plates 31 and 32, a plurality of pixels shown in FIG.
Are arranged in a box shape. In FIG. 5, the source line SL
Part of the source electrode and part of the gate line GL as the gate
The drain electrode 36 of the thin film transistor as an electrode is
Connected to another pixel electrode 34. This individual pixel electrode 34
The pixel capacitance is opposed to the opposite electrode 37 via the liquid crystal material 33.
Form Clc. Further, the individual pixel electrode 34 is made of a dielectric material.
The storage capacitor electrode STV is opposed to the storage capacitor electrode
Form Cstv. In this embodiment, the auxiliary capacitance Cstv is
It is a variable capacitor whose capacitance value changes according to the applied voltage.
Although details are not shown in FIG. 5, the material of the dielectric film 35 is not shown.
Of the fee and the structure of the storage capacity Cstv itself
This allows a configuration of such a variable capacitance.
The design of the characteristics of the variable auxiliary capacitance Cstv is described below.
Will be described. In FIG. 5, 38 is a thin film transistor
A silicon layer to be a channel region of 40, a gate insulating film 40
Layers 39 and 41 are alignment film layers. Also, the auxiliary capacitance electrode
STV is the gate line of the pixel located in the next row or column.
It is also possible to use the same as the GL. FIG. 6 shows the relationship between the applied voltage of Cstv and the capacitance value.
FIG. Here, Co is the maximum value of capacity, and Cm is
The minimum value of capacitance, Vo is the voltage at which the capacitance takes the maximum value
The values Vm1 and Vm2 are the first and second values when the capacitance takes the minimum value.
2 voltage value. Vh1 is an intermediate voltage (Vh1) between Vo and Vm1.
= (Vo + Vm1) / 2), and Ch1 (Ch in the figure) is V
This is the capacitance value at h1. Vh2 is an intermediate voltage between Vo and Vm2
(Vh2 = (Vo + Vm2) / 2), and Ch2 (C in the figure)
h) is the capacitance value at Vh2. Here, the variable capacity compensation
Adjust by adjusting the material and structure of the auxiliary capacitor.
The voltage and capacitance values shown in FIG.
Is set to suppress the effect of. For example, Table 1 above
Characteristics of Cstv so as to suppress the effect of liquid crystal capacitance change
If set, it will be as follows. Co = 0.7 pF,
Ch = 0.65 pF, Cm = 0.6 pF, Vo−Vm
1 = Vm2-Vo = 4V. Then, V is applied to the STV in FIG.
By applying o, Vd-Vo is applied to Cstv.
It is. Calculation result of the drain voltage fluctuation value ΔVd at this time
Are shown in Table 7. [0048] [Table 7] Here, ΔVd is changed to Cst in equation (1) by Vd−Vo.
It was determined by substituting the value of Cstv to be converted. As shown in Table 7
The change in ΔVd is 0.08 V or less,
It was reduced to 1/3 or less compared to 0.26V. Accordingly
By setting Vcom to Vd0-2.7V,
The DC voltage applied to the liquid crystal layer by the change is 0.04 V
It can be suppressed below. The above-mentioned variable capacity auxiliary capacity has been implemented.
As a method of realizing this, an AC amplitude voltage Vsa as shown in FIG.
Dielectric constant ε with increasing_stvVsa-ε that reduces
_stvUse a material with properties as a dielectric for Cstv
No. This is the AC amplitude voltage dependency which is the exact opposite of the characteristics in Table 1.
is there. Also, such a variable capacity auxiliary capacitor is realized.
As shown in FIG. 8, n-type amorphous silicon
(A-Si (n)) film and silicon nitride (SiNx) film
Metal Insulator Semiconductor
MIS) and p-type amorphous silicon
(A-Si (p)) film and silicon nitride (SiNx) film
MIS diode composed of
Conceivable. Such a variable capacity auxiliary capacity is
One electrode is connected to the pixel electrode under the pixel electrode instead of the capacitor.
And providing the other electrode with a transparent conductive film such as ITO.
Does not affect the aperture ratio. Auxiliary case in this case
The quantity Cstv is determined by the capacitance Cn of the n-type MIS diode and the p-type M
The following formula (8) is used as the combined capacitance of the capacitance Cp of the IS diode.
It is represented by [0050] (Equation 2) FIG. 9 shows the Cstv characteristic shown in FIG. 6 in this structure.
FIG. 6 is a characteristic diagram for explaining a method of setting Cn and Cp values for setting.
As shown in FIG. 9, the voltage-capacitance characteristics of the MIS diode
The p-type shows a right-downward characteristic, and the n-type shows a left-downward characteristic. This
Thus, the maximum and minimum capacitance in p-type and n-type diodes
The values are identical and their values are designated C2 and C1.
You. Also, the voltage value at which the capacitance value starts to change matches Vo
are doing. As a result, the maximum value of the combined capacity is Co = C2 /
2. The minimum value is Cm = C1 / C2 / (C1 + C2).
You. The maximum value of the capacitance in both diodes is the value of the SiNx film.
Since the capacitance value is determined only by the dielectric properties,
By adopting the same structure and the same material SiNx film
It is possible to match C2 as shown in FIG. one
On the other hand, in both diodes, the minimum value of the capacitance is within the a-Si film.
Depletion layer is formed on the substrate and the dielectric characteristics of the a-Si film are SiNx film
And the combined capacitance value added to the characteristic of Again,
By adjusting the dielectric constant, film thickness, etc. of the a-Si film
As shown in FIG. 9, C1 can be matched. n-type
And the capacitance value start to change in the p-type diode
The voltage is controlled by the donor and acceptor in the a-Si film, respectively.
It can be adjusted by controlling the amount of impurities. Accordingly
Therefore, as shown in FIG. 9, the voltage at which both capacitances start to change is V
It is also possible to match o. In both diodes, for example, FIG.
In order to achieve the indicated Cm and Co values, the MIS
C2 = 1.6pF, C1 = 0.96pF
Just set it. This is the film thickness and electrode area of the diode.
Which structure and characteristics of SiNx film and a-Si film
It can be realized by adjusting. [0052] According to the gradation voltage setting method of the present invention, the direct
By reducing the current voltage, flicker,
Improves display defects and improves long-term display reliability
Can be made. Furthermore, by adopting the present invention,
To remove auxiliary (accumulated) capacity.
Cost can be reduced because the structure of the crystal panel can be simplified
It also leads to reduction. According to the LCD of the present invention, the drain
Liquid crystal capacitance change characteristics with increasing AC voltage
Since the auxiliary capacitance has the capacitance change characteristic of
Cancels out the effect of
The change due to this can be suppressed. And the drain
DC voltage applied to the liquid crystal layer when the pressure is changed
Wear. As a result, flicker and burn-in
Which display defects can be reduced and at the same time
Reliability can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram illustrating a gradation voltage of a TFT-LCD according to the present invention. FIG. 2 is a flowchart of a gradation voltage setting method as an embodiment of the LCD driving method according to the present invention. FIG. 3 is a gray scale voltage setting circuit diagram of an embodiment of the LCD driving method according to the present invention. FIG. 4 is an equivalent circuit diagram of one pixel of an embodiment of the LCD of the present invention. FIG. 5 is a plan view and a cross-sectional view of one pixel of one embodiment of the LCD of the present invention. FIG. 6 is a diagram illustrating a relationship between an applied voltage and a capacitance value of a variable capacitance auxiliary capacitor of the LCD of the present invention. FIG. 7 is a diagram showing a change in relative dielectric constant of a variable capacity auxiliary capacitor of an LCD according to the present invention with respect to an AC amplitude voltage. FIG. 8 is a configuration diagram of an example of a variable capacity auxiliary capacitor of the LCD of the present invention. FIG. 9 shows Cn and C for obtaining the Cstv characteristic shown in FIG. 6;
FIG. 4 is a diagram illustrating a method for setting a p-value. FIG. 10 is an example of a system configuration of a thin film transistor TN-LCD. FIG. 11 is a block diagram of a TFT-LCD source driver. FIG. 12 is a diagram showing a voltage-transmittance characteristic example of the NW mode TNLCD. FIG. 13 is a waveform diagram of a gradation voltage of a conventional TFT-LCD. FIG. 14 is an equivalent circuit diagram of a liquid crystal panel of a TFT-LCD. FIG. 15 is an equivalent circuit diagram of one pixel of the TFT-LCD. 16 is a waveform diagram of each electrode voltage of the equivalent circuit of FIG. FIG. 17 is a diagram illustrating a relationship between a relative permittivity and a voltage applied to a liquid crystal material. [Description of Signs] 1 reference voltage Vro generation circuit, 2 reference voltage Vrb generation circuit, 3 reference voltage Vrc generation circuit, 4a, 4b addition circuit, 5a, 5b subtraction circuit, 6 AC conversion circuit, 31 first insulating transparent Substrate, 32 second insulating transparent substrate, 3
3 liquid crystal material, 34 individual pixel electrodes, 35 dielectric film,
36 drain electrode, 37 counter electrode, VR1 to VR1
4 divided variable resistor, Cgd parasitic capacitance, Clc liquid crystal capacitance,
Cstv variable capacity auxiliary capacity.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-64-63996 (JP, A) JP-A-1-303882 (JP, A) JP-A-2-217894 (JP, A) JP-A-2- 309318 (JP, A) JP-A-3-198089 (JP, A) JP-A-5-203918 (JP, A) JP-A-5-27264 (JP, A) JP-A-5-188392 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) G02F 1/133 525 G02F 1/133 575 G02F 1/1368 G09G 3/36

Claims (1)

(57) Claims 1. An individual pixel electrode, a thin film transistor in which the individual pixel electrode is connected to a drain electrode, and an auxiliary capacitance formed opposite to the individual pixel electrode via a dielectric film. A first insulating transparent substrate in which a plurality of pixels each formed of an auxiliary capacitance electrode are provided in a matrix, and a second insulating transparent substrate in which a counter electrode is provided.
And the first and second insulating transparent substrates.
Insulating transparent substrate, while the plurality of individual pixel electrodes and the counter electrode are held so as to face each other,
A liquid crystal display device in which a liquid crystal material is sealed between the first and second insulating transparent substrates, wherein the auxiliary capacitance is a variable capacitance whose capacitance value changes depending on an applied voltage; Ri Ah variable capacity auxiliary capacitor decreases the capacitance value with increasing applied voltage, of the storage capacitor is p-type metal insulator semiconductor diode and the n-type metal insulator semiconductor diode liquid crystal display device constituted by serially connecting a
A driving method, comprising a plurality of combinations of a reference voltage generation circuit, an addition circuit, and a subtraction circuit.
The maximum amplitude gradation reference voltage with positive and negative polarities
And the minimum amplitude gradation reference voltage,
Between the maximum and minimum amplitude gradation reference voltage
By dividing, multiple halftones
Set the gradation reference voltage, and further use the AC
The gradation voltage is exchanged by combining the corresponding gradation reference voltages between
And use it as a component of the AC gradation voltage signal.
A method for driving a liquid crystal display device .