JPS6275515A - Liquid crystal driving device - Google Patents

Abstract

PURPOSE:To prevent liquid crystal from deterioration due to the misconnection of a data line or abnormality of the data line by impressing a fixed DC bias to a common electrode of a panel and impressing a waveform of which panel width is modulated between segments while alternately inverting the waveform every modulation. CONSTITUTION:An LCD driver 1 is functioned as a liquid crystal driving device to control voltages to be impressed upon the common electrode 3 and the segment electrodes 4. A frame inverting signal is repeatedly turned to 'H' and 'L' at 60Hz so as to correspond to the change of 60 frames of a TV picture signal every second. A common voltage to be impressed to the common electrode is -3V DC voltage, and when black display is to be executed at a certain segment, -3V DC is impressed as the segment voltage of the segment electrode. At that time, the voltage impressed to the liquid crystal becomes OV and the liquid crystal interrupts light from a light source, so that black display can be attained. The impressed segment voltage is converted into a pulse alternately inverted every period on the basis of the 'H' and 'L' of the frame inverting signal and the pulse is impressed to the liquid crystal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a liquid crystal display device in which each segment of a liquid crystal panel having a plurality of segments arranged vertically and horizontally is spaced according to a predetermined brightness. ! ! I] Concerning escaping.

[Front of the Invention] In recent years, as display elements using liquid crystals have become more sophisticated, a wide variety of display devices using them have appeared. For example, a large color video device uses a liquid crystal display (LCD).
Some are constructed using a large number of panels. This liquid crystal panel has a liquid crystal sealed between a common electrode and a plurality of segment electrodes arranged vertically and horizontally, and has a light source on one side of the panel and an RG B on the other side.
Equipped with 3 primary color filters. Then, by applying a certain potential difference between the common mill and the segment electrodes according to the desired brightness to display, the liquid crystal is opened and closed as a shutter.
It indexes light from a light source to the outside through a filter.

By the way, when constructing a large display using a large number of LCD panels, the number of segments becomes extremely large, so it is possible to make a mistake in connecting the data line, which requires one per segment, or to disconnect the data line. Abnormalities often occur.

Problems caused when these connection errors occur will be explained below.

FIG. 5 is a time chart showing voltage applied to an LCD panel by a conventional liquid crystal driving device. In the figure, the common voltage indicates a clock applied to the common electrode. This is normally 60H2 and is synchronized with the image signal. When a certain segment is to be displayed in black, halftone, or white under this common voltage, segment voltages as shown in the figure are applied to the segment electrodes.

For example, when displaying black, a pulse having the same waveform as the common voltage is applied to the segment. A voltage equal to the difference between the common voltage and the segment voltage is applied to the liquid crystal, but in this case, since the potential difference between the common voltage and the segment voltage is O, the voltage applied to the liquid crystal is also O. Therefore, that segment will be displayed in black.

When displaying halftones, the voltage applied to the segments is supplied with the phase shifted from the common voltage. Thereby, the voltage difference is applied to the liquid crystal, and gradation control can be performed.

Furthermore, in the case of white display, a pulse having a phase opposite to that of the common voltage is applied to segments 1 to 1. In this case, the LCD will display
A pulse of V is applied repeatedly, and the liquid crystal displays white.

By the way, in the above-described gradation control, the voltage applied to the liquid crystal is alternately positive and negative. this is,
This is to prevent deterioration of the liquid crystal.

However, due to a data line connection error or data line abnormality, the segment voltage may be fixed at "l-1" or 'L.'In this case, the common voltage clock may be displayed on the LCD as it is or may be completely inverted. In other words, a direct current component in one direction is repeatedly applied, which has the disadvantage of deteriorating the liquid crystal.

Generally speaking, if the segment electrode terminal is disconnected, the segment A will light up in white, which has the disadvantage of making it difficult to see when displaying an image.

[Objective of the Invention 1] In view of the above-mentioned problems of the conventional type, the present invention provides a liquid crystal display device that opens and closes each segment of a liquid crystal panel formed by arranging a plurality of segments vertically and horizontally according to a predetermined brightness. In the IJ device, the purpose is to prevent deterioration of the liquid crystal due to data line connection errors or abnormalities in the data line for data provided to the segment side, and to improve system reliability.

1. Structure of the Invention] To achieve the above object, the present invention provides a liquid crystal drive device that opens and closes each segment of a liquid crystal panel formed by arranging a plurality of segments vertically and horizontally according to a predetermined brightness, which comprises: It is characterized in that a constant DC bias is applied to the common electrode, and a pulse width modulated waveform is applied between segments while roughly alternating forward and reverse at each modulation period.

[Description of Embodiment] FIG. 1 shows a connection diagram of a liquid crystal driving device and an LCD panel according to an embodiment of the present invention. FIG. 2 does not show a timing chart for receiving signals from each part of the device of this embodiment.

In FIG. 1, the LCD driver 1 functions as a liquid crystal driving device and controls the voltage applied to the common electrode 3 and segment 1 of the LCD panel 2.5
(5-1, 5, -?) is a power source for applying voltage to the electrodes 3 and 4.

In Figure 2, the frame inversion signal is 60)-12.
H" and "L" are repeated. This corresponds to the TV image signal changing by 60 frames per second.

The common voltage applied to the common electrode is a 13 DC voltage.

When a black display is to be performed in a certain segment, a DC voltage of 13cm is applied as a segment voltage for replacing that segment. At this time, the voltage applied to the liquid crystal becomes O, and the liquid crystal blocks light from the light source, resulting in a black display.

When displaying in intermediate gradations, the pulse width of the segment voltage is changed by pulse width modulation, and the brightness is changed based on the change. That is, the segment voltage changes the duty (t/T) according to the brightness of the image. Here, T is the pulse period of pulse width modulation, and 1 is the width of the pulse whose width is changed by modulation. The applied segment voltage is lHI+, 11111 of the frame inversion signal.
Based on this, the pulses are converted into alternating forward and reverse pulses every cycle and applied to the liquid crystal.

In other words, the segment voltage pulses are applied to the liquid crystal with positive and negative pulses of 50
The DC component is canceled out and applied in % increments. As a result, rather than applying a large amount of voltage to the liquid crystal in only one direction, the same amount of voltage is applied from both directions, thereby preventing deterioration of the liquid crystal. Therefore, the life of the liquid crystal can be extended.

If you want to display white, just set the above-mentioned t equal to T and shift the duty t/T to 1. At this time, the pulses are continuous, and a DC voltage of +Voo is applied while the segment voltage is - and white is displayed. This segment voltage is converted into a pulse that alternately repeats +8 and -8 V based on the frame inversion signal, and this pulse is applied to the liquid crystal. This results in white display.

FIG. 3 is a circuit diagram according to a roughly specific embodiment of the present invention. In the figure, a Toshiba IC (product name: T6961A) is used as a liquid crystal driving device.

FIG. 4 shows a circuit diagram and signal timing diagram 1- when the liquid crystal driving device of FIG. 3 is applied to a liquid crystal display device. This timing chart shows the case of 6-gradation display.

In this device, the common voltage is applied as DC and always kept at a constant level, and the DC component is canceled out using a frame inversion signal. Therefore, even if an abnormality occurs in the data line and a constant bias is output to the segment, no DC component will be applied due to the frame inversion signal. In other words, the segment voltage is fixed at either ゛)-1°'' or ``L'' (but since this segment voltage is always divided into positive and negative 50% by the frame inversion signal, it is difficult to apply direct current). No problem.

Effects of the Invention] As explained above, according to the present invention, in the liquid crystal driving device, a constant DC bias is applied to the common electrode,
Since a pulse width modulated waveform is applied to the segment side in alternating forward and reverse directions for each pulse period of this modulation,
Trusted in preventing LCD deterioration! /il't can be raised.

[Brief explanation of drawings]

FIG. 1 shows a liquid crystal driving device and an LC according to an embodiment of the present invention.
A connection diagram of the D panel; FIG. 2 is a time chart showing the voltage applied to each part of the above embodiment; FIG. 3 is a circuit diagram according to a more specific embodiment of the present invention; FIG. A circuit diagram and a signal timing chart when the liquid crystal driving device shown in the figure is applied to a liquid crystal display device. FIG. 5 is a time chart showing the voltage applied to an LCD panel in the conventional liquid crystal driving device. 1: LCD bar, z' bar, 2: LCD panel, 3: common electrode, 4: segment electrode, 5 (5-1,
5-2): Power supply. 18 Figure 8

Claims (1)

[Claims] 1. A liquid crystal driving device that opens and closes each segment of a liquid crystal panel formed by arranging a plurality of segments vertically and horizontally according to a predetermined brightness, the common electrode of the panel having a constant DC bias. A liquid crystal driving device characterized in that a pulse width modulated waveform is applied between segments while alternating forward and reverse at each modulation period. 2. The liquid crystal driving device according to claim 1, wherein the forward/reverse alternation of the waveform is performed based on a predetermined clock signal such that one cycle of the pulse width modulation corresponds to a half cycle thereof.