JPH04247424A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To prevent the impression of a DC voltage which deteriorates a liquid crystal panel by starting the impression of a driving voltage to the liquid crystal panel upon lapse of a specified period of time after a display timing signal is started. CONSTITUTION:The control signal to prohibit the impression of the voltage to the liquid crystal panel during the time after the transfer of the display timing signal FLM is started upon turning on of a power source before scanning electrodes are scanned for one screen is created on the bases of the display timing signal FLM. The control signal to prohibit the voltage impression is created on the bases of the display timing signal CL1 even if the transfer of the display timing signal is suspended while the power source is held turned on. The circuit for controlling the voltage impression to the liquid crystal panel is built in a liquid crystal display module.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device used as a display terminal for handheld computers, laptop computers, notebook computers, word processors, measuring instruments, and the like.

0002

[Prior Art] A liquid crystal display module normally has a built-in scanning electrode drive circuit and a signal electrode drive circuit in accordance with display control signals (display timing signals and display data) transferred from a microcomputer circuit and a liquid crystal display control circuit. generates a liquid crystal drive waveform, and various displays corresponding to the display data are displayed on the liquid crystal display panel.

The above-mentioned liquid crystal display module generally has a circuit configuration shown in FIG. 2, in which the scanning electrode driving IC and the signal electrode driving IC operate according to display control signals (display timing signals and display data) transferred from the outside. ,
A liquid crystal drive waveform is generated from six levels of reference voltage to drive the liquid crystal panel.

0004

[Problem to be Solved by the Invention] However, after the entire system including the microcomputer circuit, liquid crystal display control circuit, liquid crystal display module, etc. is powered on, the liquid crystal display control circuit is initialized and starts normal operation. During this period, no proper display control signal is input to the liquid crystal display module, and only the power is turned on, and generally a DC voltage is applied to the liquid crystal panel. In addition, even if a display control signal is started to be input, a normal liquid crystal driving waveform is not applied to the entire display screen of the liquid crystal panel until the scanning electrode has finished scanning over at least one screen, so unnecessary scanning electrodes are is selected and a DC voltage is applied, or a pattern that is not supposed to be displayed is displayed. Additionally, if the display system is compatible with display devices other than liquid crystal display modules, such as CRTs, the display control signals for the liquid crystal display module and CRT are significantly different, so it is generally necessary to select one display device by switching. However, if the CRT is selected and the display control signal is no longer transferred to the liquid crystal display module while the power remains on, a DC voltage will be applied to the liquid crystal panel.

[0005] When a DC voltage is applied to a liquid crystal panel, an abnormal pattern with very sharp shading different from the normal display state may be displayed, or an electrochemical reaction may proceed inside the liquid crystal panel, causing the liquid crystal panel to This causes the problem of deterioration.

[0006]

[Means for Solving the Problems] The means adopted by the present invention to solve the above problems is a liquid crystal display device consisting of a dot matrix liquid crystal display panel, a scanning electrode drive circuit, and a signal electrode drive circuit. The application of drive voltage to the liquid crystal panel is prohibited until a certain period of time has elapsed after the transfer of the display timing signal has started, and the drive voltage to the liquid crystal panel is prohibited when the transfer of the display timing signal is stopped while the power is on. The liquid crystal display panel is equipped with a circuit that generates a signal to cut off the application of the .

[0007]

[Operation] With the above configuration, the present invention transfers a display control signal, applies voltage to the liquid crystal display panel only during a period when proper display is possible, and prohibits the application of voltage to the liquid crystal display panel during other periods. Therefore, application of DC voltage to the liquid crystal display panel can be prevented.

[0008]

[Examples] Examples of the present invention will be described below. In the present invention, a circuit as shown in FIG. 1 is used to prevent voltage from being applied to the liquid crystal panel until at least one screen worth of scanning is completed after the power is turned on and the display timing signal begins to be transferred. As soon as the transfer of the display timing signal is stopped while the power is on, voltage application to the liquid crystal panel is prohibited.

The operation of FIG. 1 will be explained below with reference to the time charts of FIGS. 4 to 6. After the power is turned on, 1
An FLM signal, which is a screen synchronization signal (frame start signal), is transferred to the monostable multivibrator 11. At this time, the time constant T1 (=C1 R1) of the monostable multivibrator 11 is TFLM <T1
<2TTLM (TFLM is the period of the FLM signal). For this reason, its output

0010

[Outside 1]

[0011] (Hereinafter, in this specification, overlined characters (used in the drawings) such as [O1] will be used as (Q1).
) is written as (H) when the FLM signal is transferred.
-) to (L-) and becomes (H-) again within 2TFLM after the transfer of the FLM signal is completed. on the other hand,
After (Q1 -) is inverted to L, the D-type flip-flop 13 receives the next FLM signal and its output (
Q2-) becomes (L-), and thereafter maintains the output of (L-) regardless of the inversion of (Q1-). (See Figure 4).

Furthermore, the monostable multivibrator 12 has a time constant T2 (=C2 R2) of TCL
1 < T2 < 2TCL1. Therefore, as shown in Figure 5, the output (Q3 -) becomes (L-) at the same time as the CL1 signal (synchronizing signal for one scan) starts transfer after the power is turned on, and the CL1 signal is transferred. It maintains the (L-) value until the T2 period has elapsed after the end of the period, and then changes to (H-).

[0013] These two outputs (Q2 -), (Q3 -)
is introduced into the OR gate 4 as shown in FIG. 1, and is output as the OR output (Q4 -). The above relationship is shown in FIG. When the power is turned on at time A, the synchronization signal CL1 for one scanning line and the synchronization signal FLM for one screen are sequentially transferred after a slight delay. Accordingly, the D-type flip-flop 3
The output (Q2-) is inverted to (L-) with the arrival of the second pulse of the FLM signal, and maintains this state thereafter.

The output (Q3-) of the monostable multivibrator 12 changes (H-
) becomes (L-), the transfer of the CL1 signal is completed, and T
After 2 hours, it will turn back to (H-). This (Q2
-), (Q3 -) are the logical sum gate 4 as mentioned above.
It becomes a logical sum output (Q4 -), which is input to the base of the transistor 5 that controls the output of the liquid crystal drive voltage shown in FIG. 1, and connects and disconnects the liquid crystal drive power supply.

In FIG. 1, the timing of starting voltage application to the liquid crystal panel is created based on the FLM signal, whereas the timing of ending voltage application is created based on the CL1 signal, which is the display timing signal. This is to prohibit the application of voltage to the liquid crystal panel as soon as possible after the transfer of the data is stopped. Therefore, the timing for ending voltage application to the liquid crystal panel can be created based on the display data shift clock CL2 from among the general display timing signals shown in FIG. 3. Further, the timing for starting voltage application can also be created based on the M signal, which is a liquid crystal drive waveform alternating signal, from among the display timing signals shown in FIG.

[0016]

Effects of the Invention As described above, the present invention prevents the voltage from being applied to the liquid crystal panel after the power is turned on and after the transfer of the display timing signal is started until the scanning electrodes have been scanned over at least one screen. A control signal to prohibit is created based on the display timing signal FLM or M signal, and even if the transfer of the display timing signal is stopped while the power is on, voltage application to the liquid crystal panel is immediately prohibited. The control signal to be displayed is the timing signal C.
By incorporating a circuit in the LCD module that generates the L1 or CL2 signal as a reference and controls the voltage application to the LCD panel using these control signals, it is possible to prevent the application of DC voltage to the LCD panel without external control. did.

[Brief explanation of the drawing]

FIG. 1 is a diagram of a liquid crystal drive voltage control circuit according to the present invention.

FIG. 2 is a general circuit configuration diagram of a liquid crystal display module.

FIG. 3 is a diagram showing general display timing signals of a liquid crystal display module.

FIG. 4 is a timing chart for starting voltage application to the liquid crystal panel according to the present invention.

FIG. 5 is a timing chart for ending voltage application.

FIG. 6 is a timing chart showing the timing of a comprehensive voltage application prohibition period.

[Explanation of symbols]

1 Liquid crystal display panel 2 Scanning electrode driving IC 3 Signal electrode driving IC 4 Reference voltage generation circuit 11, 12 Monostable multivibrator 13
D-type flip-flop 14 OR gate

Claims (5)

[Claims] [Claim 1] A dot matrix liquid crystal display panel;
In a liquid crystal display device consisting of a scanning electrode drive circuit and a signal electrode drive circuit that receive display timing signals and display data as input, after a certain period of time has elapsed after the power is turned on and the display timing signal is started, a signal is sent to the liquid crystal display panel. 1. A liquid crystal display device comprising a signal generating circuit that starts applying a driving voltage. [Claim 2] A dot matrix liquid crystal display panel;
In a liquid crystal display device consisting of a scanning electrode drive circuit and a signal electrode drive circuit that input display timing signals and display data, when the transfer of the display timing signal is stopped while the power is on, the drive to the liquid crystal display panel is performed. A liquid crystal display device comprising a signal generation circuit that prohibits the application of voltage. 3. The signal generating circuit for starting the application of the drive voltage to the liquid crystal display panel is generated based on a synchronization signal for one screen among the display timing signals. LCD display device. 4. The signal generating circuit for inhibiting the application of a driving voltage to the liquid crystal display panel is generated based on a synchronization signal for one scan among the display timing signals. LCD display device. [Claim 5] A dot matrix liquid crystal display panel;
In a liquid crystal display device consisting of a scanning electrode drive circuit and a signal electrode drive circuit that receive display timing signals and display data as input, after a certain period of time has elapsed after the power is turned on and the display timing signal is started, a signal is sent to the liquid crystal display panel. The liquid crystal display panel is characterized by comprising a signal generation circuit that starts applying the driving voltage to the liquid crystal display panel and prohibits the application of the driving voltage to the liquid crystal display panel when the transfer of the display timing signal is stopped while the power is on. LCD display device.