JPH09269477A - Driving method for liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely adjust a liquid crystal impression voltage corresponding to the maximum multilevel value by impressing a modulation voltage in accordance with a multilevel value on a signal line corresponding to a pixel while making voltages larger than the maximum value of the range of working voltages of liquid crystal amplitude voltages. SOLUTION: An amplitude voltage Va in performing a pulse width modulation control and the maximum amplitude voltage Vb in performing a pulse amplitude modulation control are set so as to become larger than voltage in the range of normal operation of liquid crystal. Then, it is possible to control a voltage to be impressed on liquid crystal to zero surely by making the amplitude voltage Va of a data line electrode in a selection period larger than the voltages in the range of the normal operation of liquid crystal. Consequently, it is possible to make a voltage value to be impressed on liquid crystal zero in accordance with the maximum multilevel value by making the maximum multilevel value correspond to a maximum ON time in the case of performing a pulse width modulation and also by making the maximum multilevel value correspond to a maximum amplitude voltage Vb in the case of performing a pulse amplitude modulation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving method of a liquid crystal display device which performs gradation display using a two-terminal active element.

[0002]

2. Description of the Related Art In an active matrix type liquid crystal display, an active element is provided for each pixel on a display surface, the active element is turned on during a writing period to write a data voltage, and turned off during other periods to hold the voltage. By doing, the display is performed. The display surface of the liquid crystal display is formed by intersecting the scanning line electrodes and the data line electrodes facing each other in a matrix, and defining these intersections as one pixel, a plurality of pixels are provided on a plane. Then, by controlling the voltage applied to each electrode in a time-division manner, ON / OFF of each active element is controlled. As the active element, there are a three-terminal element represented by an amorphous silicon TFT element and a two-terminal element represented by an MIM (conductor-insulator-conductor) element.

The two-terminal type element includes the MIM element described above, a back-to-back diode element, a diode ring element, a varistor element, and the like, all of which have nonlinear current-voltage characteristics. There is. FIG. 4 is a diagram showing current-voltage characteristics of the MIM element most widely used as the two-terminal active element. The horizontal axis represents the voltage applied to the MIM element and the vertical axis represents the current, and it can be seen that the current-voltage characteristics are non-linear. FIG. 5 is a diagram showing an equivalent circuit of one pixel of the liquid crystal display device using the MIM element. The drive voltage is V _D , the voltage applied to the liquid crystal layer is V _LC , MI
The voltage applied to the M element is V _MIM . R _LC and C _LC represent the resistance value and the capacitance value of the liquid crystal layer, respectively, and R _MIM and C _MIM
Indicates the resistance value and the capacitance value of the MIM element. In the liquid crystal display device, the equivalent circuit shown in FIG. 5 is arranged in a matrix. Any one of the plurality of scanning lines and data lines is connected to each equivalent circuit, and a pixel to be driven is selected by selecting a predetermined scanning line and data line. .

FIG. 6 shows a time variation of an applied voltage of an arbitrary pixel on a display surface and corresponding scanning line electrodes and data line electrodes when an MIM diode (metal / insulator / metal diode) is used as an active element. FIG. 4 is a waveform diagram showing an example of the above. In the case shown in this diagram, the voltage V _D applied to the pixel is controlled by pulse width modulation. The pixel applied voltage V _D is determined by the voltage difference between the scan line electrode voltage and the data line electrode voltage. In this case, the voltage of the scan electrode in the selection period is adjusted to a voltage obtained by adding the threshold voltage of the MIM diode and the maximum operating voltage of the liquid crystal. Therefore, the period during which the diode turns on is determined according to the voltage waveform of the data line electrode. When performing pulse width modulation, when the voltage of the data line electrode is at ground potential, the liquid crystal applied voltage V _LC becomes the maximum operating voltage, the applied voltage V _LC of the liquid crystal by the time the data line electrode is the ground potential Decided. Note that, in this figure, the case where the voltage applied to the pixel is controlled by pulse width modulation is shown, but unlike this, the voltage applied to the pixel is controlled by changing the voltage value of the data line electrode during the selection period. You can also

Next, the relationship between the applied voltage V _{LC of the} liquid crystal and the transmittance τ will be described with reference to FIG. FIG. 7 shows a liquid crystal applied voltage V in a normally white liquid crystal display.
FIG. 6 is a diagram showing the relationship between _LC and transmittance τ, in which the horizontal axis represents the liquid crystal applied voltage V _LC and the gradation value when gradation control of 16 gradations is performed, and the vertical axis represents the transmittance τ. Liquid crystal displays have different characteristics of change in transmittance τ depending on the viewing angle. FIG. 7 shows the viewing angle with respect to the liquid crystal display 1 divided into the vertical direction, the clear viewing direction, and the reverse clear viewing direction shown in (a), and the change in the transmittance in each direction is shown in (b). . As shown in this figure, compared with the change in transmittance in the vertical direction, a decrease in transmittance occurs in the clear vision direction with a smaller applied voltage, while in the reverse clear vision direction, a larger decrease in transmittance is applied. It is generated by voltage. Further, in the clear viewing direction, inversion occurs in a portion where the applied voltage is low, in which the transmittance decreases as the voltage increases. The change in the transmittance in the clear viewing direction and the reverse clear viewing direction changes depending on the size of the viewing angle. Similarly, the position of reversal in which the order of transmittance is reversed in the clear viewing direction and the magnitude of the maximum value at that time also change according to the viewing angle.

The gradation values of 16 gradations of 0 to 15 and the liquid crystal applied voltage V _LC are set in accordance with the characteristics of the change of the transmittance in the vertical direction.
Each gradation value is set so as to correspond to a predetermined voltage within the operating voltage range of the liquid crystal applied voltage V _LC . Since the change in transmittance has a non-linear characteristic, the setting of each gradation value has a non-uniform interval accordingly.

[0007]

By the way, in the conventional liquid crystal display driving method, the conversion characteristic between the gradation value and the liquid crystal applied voltage is set in the region in which the change width of the transmittance can be used most effectively. The gradation value is not necessarily set in correspondence with the liquid crystal voltage that maximizes the transmittance of the liquid crystal. However, particularly in a liquid crystal display used for a personal computer, complete white data is often required, and it is necessary to secure the maximum transmittance corresponding to the maximum gradation value, for example, with other gradation values. It is often more important than maintaining a uniform change in transmittance with. In this case, the liquid crystal applied voltage corresponding to the maximum gradation value may be set to the voltage that maximizes the transmittance. However, M
In a liquid crystal pixel using a two-terminal non-linear active element such as an IM element, the applied voltage V _{LC of the} liquid crystal cannot be directly controlled and the applied voltage V _D of each pixel is controlled. There is a problem that it is difficult to control only V _LC with high accuracy, and it is difficult to appropriately adjust the liquid crystal applied voltage V _LC corresponding to the maximum gradation value.

The present invention has been made under such a background, and a liquid crystal capable of reliably adjusting the liquid crystal applied voltage corresponding to the maximum gradation value in a liquid crystal display device using a two-terminal active element. It is an object to provide a driving method of a display device.

[0009]

SUMMARY OF THE INVENTION The present invention has a plurality of pixels each of which is formed by connecting a liquid crystal and a two-terminal type active element in series with each other, and one terminal of each pixel is connected to a predetermined scanning line and the other terminal. In a liquid crystal display device that connects a predetermined signal line to form a display surface by arranging a plurality of scanning lines and a plurality of signal lines and displays a predetermined video signal on the display surface in a plurality of gradations. , A gradation value corresponding to each pixel is obtained according to the video signal, a voltage larger than the maximum value of the operating voltage range of the liquid crystal is set as an amplitude voltage, and a value corresponding to the gradation value is set as a modulation rate. A pulse width modulation is performed to obtain a modulation voltage, and the modulation voltage is applied to a signal line corresponding to the pixel in a predetermined selection period to control the display gray level of the pixel on the display surface. There is.

[0010]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a liquid crystal drive device using an embodiment of the present invention. In FIG. 1, 1 is a liquid crystal panel having a plurality of liquid crystal pixels, 2 is a data line driving unit that drives a plurality of data line electrodes, 3 is a scanning line driving unit that drives a plurality of scanning line electrodes, 4
Is a liquid crystal display module in which the liquid crystal display unit 1, the data line driving unit 2, and the scanning line driving unit 3 are configured as one unit. In this embodiment, a MIM element is used as a two-terminal type active element that constitutes each pixel. Each pixel is connected to a data line electrode and a scanning line electrode, respectively, and is formed at each intersection of the data line and the scanning line arranged in a matrix on the display panel 1. 5
Is an A / D converter, which converts an analog video signal supplied from the outside into a digital value.

A timing controller 6 inputs a digital value of a video signal and a synchronizing signal, and supplies a plurality of timing pulses to the liquid crystal display module 4, the liquid crystal driving power supply 7, and the data electrode power supply circuit 8. In the timing controller 6, a step size setting unit 6a for selectively setting the step size of the gradation when performing the gradation control is provided for each pixel based on the video signal according to a selection signal supplied from the outside (not shown). The step size of the gradation value corresponding to is selected and set.
The liquid crystal driving power supply circuit 7 and the data electrode power supply circuit 8 are
Power is supplied to the scanning line driving unit 3 and the data line driving unit 2 in accordance with the timing pulse supplied from the timing controller 6.

Next, referring to FIG. 2, the pixel output voltage and the data line electrode voltage applied to each pixel during the selection period by the voltage output from the scanning line driving unit 3 and the data line driving unit 2. The waveform will be described. In the present embodiment, the pattern of the voltage waveform applied to the scanning line electrode and the data line electrode is the same as the conventional one described with reference to FIG. In the present embodiment, the relationship between the maximum value of the voltage applied to the data line electrode in the selection period and the voltage or time width corresponding to each gradation value is different from the conventional one. The scanning voltage waveform is the same as that shown in FIG. 6 and is not shown.

FIG. 2A shows a selection period when the data line voltage is controlled by the pulse width modulation control, and FIG. 2B shows a selection period when the data line voltage is controlled by the pulse amplitude modulation (or pulse height modulation) control. The voltage waveform of the data line electrode and the waveform of the pixel applied voltage V _D are shown respectively.
When the pulse width modulation control is performed, the voltage applied to the data line electrode is the voltage Va controlled as the amplitude voltage and the time width Ta controlled according to the gradation value. Further, when the pulse amplitude modulation control is performed, the voltage value itself applied to the data line electrode changes with the maximum voltage amplitude being Vb.

In the present embodiment, the amplitude voltage Va in the case of performing the pulse width modulation control and the maximum amplitude voltage Vb in the case of performing the pulse amplitude modulation control are set to be larger than the voltage in the normal operation range of the liquid crystal. . Therefore, when the amplitude voltage Va or the amplitude voltage Vb is applied to the data line electrode, the pixel voltage V _D determined by the difference voltage between the scanning line electrode voltage and the data line electrode voltage becomes smaller than the threshold voltage of the MIM element, and the MIM element is selected during the selection period. The element cannot be turned on and the voltage applied to the liquid crystal is 0V. As described above, by making the amplitude voltage of the data line electrode in the selection period larger than the voltage in the normal operation range of the liquid crystal, the voltage V _LC applied to the liquid crystal can be controlled to 0V without fail. Therefore, when performing pulse width modulation, the maximum gradation value and the maximum on-time are made to correspond, and when performing pulse amplitude modulation, the maximum gradation value and the maximum amplitude voltage are made to correspond, The voltage value applied to the liquid crystal corresponding to the maximum gradation value can always be 0V.

When the maximum gradation value and the maximum on-time are associated with each other when performing pulse width modulation, or when the maximum gradation value and the maximum amplitude voltage are associated with each other when performing pulse amplitude modulation. FIG. 3 shows an example of the relationship between the gradation value, the liquid crystal applied voltage, and the transmittance according to this embodiment. Each condition in FIG. 3 is the same as that in FIG. 7. As shown in this figure, the liquid crystal applied voltage corresponding to the maximum gradation value 15 is 0V.
Correspondences between other gradation values and applied voltages are set in the same manner as in FIG. When the amplitude voltage is set higher than that of the conventional one, in order to make the relationship between the grayscale value other than the maximum grayscale value, the liquid crystal applied voltage, and the transmittance the same as the conventional one, it corresponds to each grayscale value. By making the ON time or voltage value shorter or smaller than the case of using a normal amplitude voltage, it is possible to obtain the same relationship between the gradation value and the liquid crystal applied voltage and the transmittance as in the normal case as shown in FIG. Becomes

The relationship between the gradation value and the time width is set in the step size selection setting unit 6a shown in FIG. It is effective to make the applied voltage 0V of the liquid crystal correspond to the maximum gradation value, especially when displaying for a personal computer or displaying a character image. However, for example, when displaying a normal TV image, it is considered that it is better not to make such a setting. For this, the step size selection setting unit 6
If a selection signal is externally supplied to a, and the setting is switched between the normal data line voltage and the setting of the step size, and the setting of the data line voltage larger than the operation voltage of the liquid crystal according to the present invention and the step size for it. The same display device can perform the gradation control suitable for both.

[0017]

As described above, according to the present invention, in the liquid crystal display device using the two-terminal active element,
Since the voltage larger than the maximum value of the operating voltage range of the liquid crystal is used as the amplitude voltage and the modulation voltage according to the gradation value is applied to the signal line (data line) corresponding to the pixel, be sure to turn off the voltage applied to the liquid crystal. It becomes possible to control the transmittance of the liquid crystal in a wider range than before by including the voltage that can be applied. Therefore, there is an effect that the image can be surely displayed because the complete white data used in a personal computer or the like is required.

[Brief description of drawings]

FIG. 1 is a block diagram of a liquid crystal display device using an embodiment of the present invention.

FIG. 2 is a waveform diagram of a data line applied voltage and a pixel applied voltage in a selection period according to an embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between a pixel applied voltage, a gradation value and a transmittance in the liquid crystal display device according to the embodiment of the present invention.

FIG. 4 is a diagram showing current-voltage characteristics of an MIM element.

FIG. 5 is a diagram showing an equivalent circuit of a liquid crystal pixel using an MIM element.

FIG. 6 is a diagram showing current-voltage characteristics of an MIM element.

FIG. 7 is a diagram showing a relationship between a pixel applied voltage, a gradation value and a transmittance in a conventional liquid crystal display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Liquid crystal panel 2 ... Data line drive unit 3 ... Scan line drive unit 4 ... Liquid crystal display module 5 ... A / D converter 6 ... Timing controller 7 ... Liquid crystal drive power supply circuit 8 ... Data electrode power supply circuit

Claims (1)

[Claims] 1. A plurality of pixels each of which is formed by connecting a liquid crystal and a two-terminal type active element in series to each other, and one terminal of each pixel is connected to a predetermined scanning line and the other terminal is connected to a predetermined signal line. hand,
In a liquid crystal display device in which a display surface is configured by arranging a plurality of scanning lines and a plurality of signal lines, and a predetermined video signal is displayed on the display surface in a plurality of gradations, a gradation value corresponding to each pixel is displayed. Determined according to the video signal, a voltage larger than the maximum value of the operating voltage range of the liquid crystal is an amplitude voltage, and a value according to the gradation value is amplitude or pulse width modulated as a modulation rate to obtain a modulation voltage. A driving method of a liquid crystal display device, wherein the modulation voltage is applied to a signal line corresponding to the pixel during a predetermined selection period to control a display gradation of the pixel on the display surface.