JPH03181915A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To integrate and miniaturize the circuits on a system side and to protect a liquid crystal display body from a DO drive by detecting the presence or absence of the input signal, such as data signal or control signal, from the system side, with a protective circuit and shutting down the liquid crystal voltage impressed to the liquid crystal display body at the time of a non-input signal state. CONSTITUTION:The presence or absence of the input signal, such as data signal 5 or control signal 7, from the system 11 side is detected with the protective circuit 2. The liquid crystal voltage impressed to the liquid crystal display body 1 is shut down when the non-input signal state is detected. The circuits on the system side are integrated and miniaturized in this way and the deterioration and damage of the liquid crystal display body and liquid crystal driving circuit by the non-input state of the data signal or control signal by the breakdown, disconnection, etc., of the system by a contingent accident are prevented in this way.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a liquid crystal display device.

[Prior Art] In conventional liquid crystal display devices, a liquid crystal voltage can be applied to a liquid crystal display by turning an external switch on or off, regardless of the presence or absence of input signals such as data signals and control signals.

[Problem to be solved by the invention] However, in a liquid crystal display, an alternating current voltage is always applied to the liquid crystal sealed in two pieces of glass called a cell from opposing electrodes on the surface of each glass. If a liquid crystal voltage is applied without inputting a liquid crystal alternating signal, which is a signal for an alternating voltage, a direct current voltage is applied to the cell, and a phenomenon called DC drive occurs. For example, when the Da middrive occurs, the cells deteriorate and deteriorate, resulting in deterioration of the display quality of the liquid crystal display device and shortening the life of the liquid crystal display. For this reason, conventionally, after outputting a protection circuit for the liquid crystal display or data signals and control signals to the system side,
Liquid crystal display devices were equipped with sequential circuits to apply liquid crystal voltage, but this meant that the system became larger and
This led to larger size.

Therefore, the present invention aims to provide a liquid crystal display device in which the load on the circuits on the system side is reduced by inserting a simple protection circuit into the liquid crystal display device side.

[Means for Solving the Problems] In order to solve the above problems, the liquid crystal display device of the present invention includes a liquid crystal display body and a liquid crystal drive circuit, and includes a protection circuit section, and the liquid crystal display device includes a protection circuit section. The circuit has a function of detecting the presence or absence of input signals such as data signals and control signals from the system side, and shutting down the liquid crystal voltage applied to the liquid crystal display when there is no input signal. .

[Function] In the liquid crystal display device configured as described above, since the liquid crystal voltage is switched by the protection device, it contributes to circuit integration and miniaturization on the system side, and also prevents system breakdown and disconnection due to accidental accidents. data signal, etc.
This has the effect of protecting the liquid crystal display from DC drive caused by no input signals such as control signals.

[Example] Examples of the present invention are shown below. FIG. 1 is a block diagram of a liquid crystal display device of the present invention, and FIG. 2 shows an example of a circuit diagram of a protection circuit section in FIG. 1.

In FIG. 2, the input signal serving as a trigger for applying a liquid crystal voltage to the protection circuit may be any appropriate signal, but here, a liquid crystal alternating current signal is used as an example. The liquid crystal alternating current signal has a duty ratio of 50% and a cycle of about 60.
This is a signal of ~70H3 and is a signal for applying an alternating current voltage to the liquid crystal display.

Here, the potential of GND, which is the reference potential, is V. , the potential of the liquid crystal voltage is vr, on, the potential of the power supply voltage is vDD, contact N
The gate voltage of vN1 T2, which has a potential of 1, is assumed to be ■T2. At this time, the range of the potential of VNI # ■T2 is O vN since the signal system fluctuates between the power supply voltages and the signal system fluctuates between the liquid crystal voltages.

It can be expressed as T2 < 1Vnn < IVLOD . . . ■ ■ . Also, the size relationship of ■DD and 'VLOD is IVDD Vol << IVLOD V
Assume that ol...■. Generally, the GND potential Vo is OV, and VDD is ■. +5■ based on VDD, VLOD is -20 to -30 based on VDD
It is V. From these facts and formula (■), it is impossible to drive N-type power MO3) transistor T2 with a different voltage system by changing the potential of N1, so a level shift circuit is inserted between N0 and m3J1 power MO8) transistor T2. I decided to do so.・As a result, when VDD and Vo are input to the input of the level shift circuit, respectively,
VDD and 'VLOD are output.

When the liquid crystal alternating current signal is in a non-input state, that is, at a constant value, the potential of contact N2 is the same as that of coupling capacitor C□
It is cut from the potential of the liquid crystal alternating current signal by R2, and pulled up by R2 to become Vnn. As a result, the P-type MOS transistor T1 is turned off, 0□ is not charged, and the potential of the contact N is also pulled down by R1. Then,
The N-type power transistor T2 (M, O8) is also turned off, and the liquid crystal voltage path becomes open in the liquid crystal display device. As a result, even if the external switch S1 in FIG. 1 is turned on for some reason when the liquid crystal alternating current signal is not input, the liquid crystal voltage path is cut off inside the liquid crystal display device, so the liquid crystal display is No liquid crystal voltage is applied, protecting against phenomena such as DC drive.

When the liquid crystal alternating current signal is input, the voltage 01 becomes short-circuited in an AO manner, and the potential of the N2 changes in an alternating current manner. The potential is applied to the T1, and the T1 repeats on and off, but if the value of the R1 is sufficiently large, the 0
Charge 2.

As a result, the potential of N1 becomes VDD. The potential is boosted by a level shift circuit and applied to the T2 to turn on the T2. This short-circuits the liquid crystal voltage path inside the liquid crystal display device. This allows sequential input of input signals and input voltages without the need for a sequential circuit for input signals on the system side.

In a liquid crystal display device, alternating current in the cell section is an important condition, and for this reason, a liquid crystal alternating signal is an absolute requirement. Impressing the liquid crystal voltage without the liquid crystal alternating signal is a fatal phenomenon for the liquid crystal display. Therefore, for example, laptop computers that use a liquid crystal display, it has been impossible to take measures such as a protection circuit, a facial sequence circuit, etc. on the system side. Therefore, the present invention reduces the burden on the circuits on the system side, and can contribute to system integration and miniaturization. Further, since the protection circuit can detect a system failure due to an accident or a no-input signal state such as a disconnection, it is possible to prevent DO drive due to an unexpected accident.

In addition, by creating a protection circuit by combining it with other control signals such as horizontal synchronization signals and vertical synchronization signals, and data signals, it is possible to protect not only the liquid crystal display but also the liquid crystal drive circuit. .

[Effects of the Invention] As explained above, the liquid crystal display device of the present invention contributes to circuit integration and miniaturization on the system side, and also prevents data signals and control signals from occurring due to system breakdown or disconnection due to accidental accidents. This prevents deterioration and damage to the liquid crystal display and liquid crystal drive circuit due to no-input conditions.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a liquid crystal display device of the present invention. Figure 2 shows
FIG. 3 is a circuit diagram of a protection circuit section of a liquid crystal display according to the present invention.

Claims (1)

[Claims] A liquid crystal display device consisting of a liquid crystal display body and a liquid crystal drive circuit has a protection circuit section, and the protection circuit detects the presence or absence of input signals such as data signals and control signals from the system side, and detects the presence or absence of input signals such as data signals and control signals from the system side. A liquid crystal display device having a function of shutting down a liquid crystal voltage applied to the liquid crystal display body when a state is detected.