JPH0510679B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improving the contrast of a time-division matrix display device, and more specifically, to improve the contrast of a time-division matrix display device, and more specifically, to improve the contrast of a time-division matrix display device, and more specifically, to improve the contrast of a time-division matrix display device. Regarding possible methods.

In recent years, development of high-density display panels using liquid crystals, EC, EL, etc. has been active. When performing high-density display using such a display element with poor time-division performance, the following two methods are used. The first method is called a passive matrix, in which the degree of time division is suppressed to an appropriate value and avoided by multiple wiring, etc. The second method is called an active matrix, in which active elements such as transistors and nonlinear resistors are formed as switches on the panel, and voltage is accumulated in each pixel.

The former panel is relatively easy to manufacture, but there is a limit to increasing the wiring multiplicity, and the display density cannot be increased that much. Although the latter can sufficiently increase display density, the technology to fabricate high-density, defect-free and uniform switching elements sufficient to store enough charge is extremely difficult, and has not yet been put into practical use as a large-area panel.

The present invention relates to a method of optimizing and using a nonlinear resistor conventionally used in an active matrix, not as a charge storage element, but as a voltage partial subtraction type element in a passive matrix. It can be used even with elements that do not have a passive matrix, and the time division degree of the passive matrix can be increased from several times to 10 times.

The description will be given below based on the drawings.

FIG. 1 is an equivalent circuit of a passive matrix. S is a row electrode, D is a column electrode, C(i,j)(i,
j is an integer) is a display element.

FIG. 2 is an equivalent circuit of a matrix having matrix elements M(i,j) to which nonlinear resistances NL(i,j) are added. Traditionally, it has been used as an active matrix, and details can be found in the paper by B. Lechner et al.
(1971)) and D. Castle berry's paper (IEEE
Trans., ED-26, p. 1123-1128 (1979)), the passive matrix according to the present invention can also be represented by the equivalent circuit shown in FIG.

FIG. 3 shows an example of the current I vs. voltage V characteristic of the nonlinear resistance element used in the present invention, and shows a curved characteristic that changes from off-resistance R _OFF to on-resistance R _ON before and after the threshold voltage V _th .

FIG. 4 is a block diagram of an embodiment of the matrix display device of the present invention. 151 is a display panel, 1
Reference numeral 52 denotes a row electrode driver 1 that applies scanning signals such as φ _o and φ _{o+1 in} FIG. 5 to the row electrodes S _I to S _N of the display panel.
54 connects the data signal as shown in FIG. 5 D _n to the column electrode D _I ~
A column electrode driver 153 that applies voltage to D _M is a controller that supplies display information 155, timing signals 158, 159, power supplies 156, 157, etc. to each driver.

FIG. 5 is a drive waveform diagram of an embodiment of the present invention. φ _o and φn+1 of a are scanning signals and selection phases
A voltage of ±a is taken at T _A , and a reference voltage of 0 is taken at the non-selected phase T _B. Dm in b is a data signal and takes a voltage of ±1 depending on the data. (Here, when the voltage amplitude of the data signal is V _p , each voltage is normalized by V _p . The shapes of both the scanning and data signals are exactly the same as the conventional passive matrix 1/a bias method. However, in order to apply this waveform to a matrix using nonlinear resistance elements, the driving voltage V _p
The relationship between and the threshold voltage V _th of the nonlinear resistance element and a
It is necessary to optimize the value of , and the present invention makes it possible to use even a nonlinear resistance element with a lower degree than the conventional one by adopting conditions different from the conventional one.

FIG. 6 is an example of the driving conditions shown in Castle Berry's paper (Fig. 7). According to him, the following two conditions must be met.

a-1< _th (where _th = V _th /V _p (1) 1+ _ON < _th (where _ON = V _ON /Vo (2) (1) and (2) are the necessary conditions for a charge storage type active matrix. be.

However, in the present invention, conditions (1) and (2) are not used, but the following condition (3) is used instead.

1 _th FIG. 5c and d are voltage waveforms applied to each matrix element when condition (3) is used. The shaded area is the voltage waveform applied to the display element. The characteristics of this waveform are that the absolute value of the voltage applied to the matrix element is approximately equal to or larger than V _th in most phases, and the absolute value of the voltage applied to the display element is
It is at a point that approximately corresponds to the voltage applied to the matrix element minus V _th . In other words, when conventional conditions (1) and (2) are used, the nonlinear resistance element acts as a charge storage switch, whereas when the present invention's condition (3) is used, the nonlinear resistance element acts as a simple voltage subtraction type resistance. It can be used as an element.

The effective values of the voltages applied to the display elements in Figures 5c and d are the on-voltage V _ON and the off-voltage, respectively.
For V _OFF , the number of time divisions n is expressed by the following equation.

V _ON =V _p √ [(+1- _th ) ² + (-1) (1-
_th ) ² ]/n(4) V _OFF = V _p √ [(-1- _th ) ² + (-1) (1-
_th ) ² ]/n(5) Here, in order to optimize a and _th, it is necessary to consider the following points. The first thing is to make the amount called drive margin M defined in (6) as large as possible.

M=V _ON /V _OFF (6) In liquid crystal, EL, etc., display quality such as contrast viewing angle improves as M increases.

Figure 7 shows equal M on the a- _th plane when n=400.
It is a line diagram. In the case of liquid crystals, at present M is at least
Since we want about 1.1, it is desirable that _th satisfy the following formula.

0.5∠〜V _th /Vo∠〜1 (7) The second point to consider is the variation in V _th .
This is a change in V _ON . In general, it is difficult to align the V _th of non-linear elements, and it is desirable for the driving method to minimize the effect of this. Defining the rate of variation m due to variation using the following formula: m = (rate of change in V _ON ) / (rate of change in V _th ) (8) In Castle Berry's driving method, m = 1.5. In the present invention, if the conditions are selected as shown in Fig. 8, m∠~0.2
It is also possible to use the curve at least outside the m1 curve.

The third point to consider is the absolute value of the threshold voltage V _th . Although a nonlinear resistance element with an ideal threshold value as shown in FIG. 3 does not actually exist, for example, an amorphous silicon (a-Si) diode ring shown in application number 57-167945 filed by the present applicant, etc. has similar characteristics. However, the drawback of this element is that V _th is low, with only 0.7 to 1.0 V in one stage, and if more is required, multiple stages must be connected, and the greater the number of stages, the more complicated the manufacturing becomes.

Therefore, it is desirable that V _th /V _ON normalized by the display voltage V _ON be as small as possible. FIG. 9 is an equal V _th /V _ON diagram in the a- _th plane. For LCD, V _ON
Since it is about 2V, if you use the outside of the curve of V _th /V _ON = 3, you can use an a-Si diode within 6 stages.

As is clear from the above description, compared to the conventional example, the present invention has the feature of only performing voltage subtraction without charge accumulation, and by optimizing the conditions, the driving voltage fluctuation rate with respect to threshold fluctuation is lower than the conventional m = 1.5 to less than m = 1.0~0.2, and it is also much smaller than the conventional passive matrix.
V _ON /V _OFF can be obtained, and high division of n400 to 1000 is also possible. Furthermore, since no charge is accumulated at all, the off-resistance R _OFF in the characteristics shown in FIG. 3 is not so large to be usable. That is, in the past _, it was necessary for the load capacity C _LC to satisfy the following formula, but in the present invention, the following formula is sufficient: _{R OFF > T A /} C _LC (10) n = 100 to 1000, the conditions are greatly relaxed. For example, when using an a-Si diode ring, this is possible even without suppressing the decrease in R _OFF due to external light, and it also makes it easier to control manufacturing conditions, improving yields and shortening the process. This is possible, and panel manufacturing costs can be significantly reduced compared to conventional methods.

Incidentally, the scanning signal φ _o and the data signal D _n of the embodiment shown in FIG. 5 have their reference levels shifted every T _A /2 from 0 in the first half to a-1 in the second half as shown in FIG. Of course, it will not change even if it is reduced.

In the embodiments, liquid crystal is used as the display element, and liquid crystal is most effective in the present invention, but other display elements such as electrochromism and electroluminescence may also be used.

[Brief explanation of the drawing]

Fig. 1 is an equivalent circuit diagram of a conventional passive matrix, Fig. 2 is an equivalent circuit diagram of a passive matrix of the present invention using a nonlinear resistance element, and Fig. 3 is a characteristic diagram of the nonlinear resistance element used in the present invention. FIG. 4 is a block diagram of the display device of the present invention, FIG. 5 is a drive waveform diagram of an embodiment of the present invention, FIG. 6 is a conventional drive waveform diagram, and FIGS. 7, 8, and 9 are drive waveform diagrams of the present invention. FIG. 10 is a characteristic diagram showing the relationship between driving conditions and evaluation parameters when the method is used, and FIG. 10 is a driving waveform diagram of another embodiment of the present invention. S, S _I ~ S _N ... Row electrode, D, D _I ~ D _M ... Column electrode,
C(i,j)...display element, NL(i,j)...nonlinear resistance element, M(i,j)...matrix element,
V _th ...Threshold voltage of the nonlinear resistance element, Vo...One side voltage amplitude of the data signal.

Claims (1)

[Claims] 1. Matrix elements in which a display element and a nonlinear resistance element are connected in series are arranged in a matrix, one end of the matrix element is connected to a row electrode, the other end is connected to a column electrode, and each row electrode is connected in sequence. In the method for driving a matrix display device that displays data on display elements based on signals applied to column electrodes, the nonlinear resistance A row electrode drive signal and a column electrode drive signal for which the absolute value of the voltage across the element is equal to or higher than the threshold voltage of the nonlinear resistance element are applied to each row electrode,
A method for driving a matrix display device, characterized in that a voltage is applied to column electrodes. 2 The drive signal applied to the row electrodes is a scanning signal having a selection phase and a non-selection phase, and the drive signal applied to the column electrodes is a data signal dependent on display data, with the scanning signal of the non-selection phase as a reference. 2. The method of driving a matrix display device according to claim 1, wherein the maximum absolute value of the data signal is approximately equal to or larger than the threshold voltage _Vth . 3 If the threshold value of the nonlinear resistance element is V _th and the maximum value of the voltage applied to the matrix element in the non-selected phase is V _p , then V _th /V _p is approximately 0.5 to 1.0.
2. The method of driving a matrix display device according to claim 1, wherein the driving method is between. 4. The method for driving a matrix display device according to claim 1, wherein the nonlinear resistance element is a forward-reverse parallel connected element of amorphous silicon diodes.