JPH0736132U - Liquid crystal display - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to provide a liquid crystal display device that can be used in a wide temperature range and can always maintain a constant contrast ratio. A liquid crystal panel 1 is formed with a transmissive portion 6 that holds liquid crystal so that light always passes through the liquid crystal regardless of a display image, and a non-transmissive portion 7 that holds liquid crystal so that light does not pass through the transmissive portion. The amount of light transmitted through the non-transmissive portion 6 and the non-transmissive portion 7 is measured by the photo interrupters 8 and 9, and the drive voltage for driving the liquid crystal panel 1 is switched to a high voltage or a low voltage in accordance with the measured amount to keep the contrast ratio constant. Control so that

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device used in a wide temperature range.

[0002]

[Prior art]

FIG. 3 shows a block diagram of a conventional example. In the figure, 11 indicates a liquid crystal panel. The drive voltage V _D is supplied from the drive voltage switching circuit 22 to the liquid crystal panel 21. Generally, when the temperature of the liquid crystal panel 21 decreases, the change in the state of the liquid crystal becomes small, and the contrast ratio of light and dark decreases. Therefore, the drive voltage is changed according to the temperature to deal with this.

A thermistor R is provided around the liquid crystal panel 21._THWith the thermistor R_THChange the resistance value due to the temperature change of the resistance R₁₁~ R₁₃And the comparator 23. The output signal of the comparator 23 is supplied to the drive voltage switching circuit 22. The drive voltage switching circuit 22 outputs the high drive voltage V by the output of the comparator 23._D1Or low drive voltage V _D2 I was switching to.

[0004]

[Problems to be solved by the device]

However, the conventional liquid crystal display device detects the ambient temperature of the liquid crystal panel with a thermistor or the like, and determines the drive voltage V _DD of the liquid crystal panel according to the detected temperature. The ambient temperature is not necessarily the temperature of the liquid crystal panel. Therefore, when the ambient temperature and the temperature of the liquid crystal panel are different, there is a problem that the contrast ratio is not compensated or, on the contrary, the one having a good contrast ratio is deteriorated.

The present invention has been made in view of the above points, and an object of the present invention is to provide a liquid crystal display device capable of always maintaining a constant contrast ratio.

[0006]

[Means for Solving the Problems]

 The present invention is a liquid crystal display device comprising a liquid crystal panel for displaying an image in which a drive voltage is applied to a position according to a display image, the liquid crystal panel being formed on the liquid crystal panel and keeping light in a transmissive state regardless of the display image. A transmissive part, which is formed on the liquid crystal panel and holds the light in a non-transmissive state regardless of the display image, and a certain amount of light is radiated to the transmissive part to transmit the light of the transmissive part. A first transmitted light detecting means for detecting an amount; a second transmitted light detecting means for irradiating the non-transmissive portion with a certain amount of light to detect the amount of light transmitted through the non-transmissive portion; The driving voltage is set in accordance with the difference between the amount of transmitted light detected by the transmitted light detecting means and the amount of transmitted light detected by the second transmitted light detection. Drive voltage control means for controlling so that the difference with the transmission amount of It becomes Te.

[0007]

[Action]

 According to the present invention, a liquid crystal panel is provided with a transmissive portion and a non-transmissive portion, and the amount of light transmitted through the transmissive portion and the non-transmissive portion is detected by the first and second light transmission detecting means to control the drive voltage. By calculating the difference in the amount of light transmitted between the transmissive part and the non-transmissive part according to this detection result and controlling the drive voltage so that this difference becomes constant, the transmissive part is not affected by the ambient temperature. The drive voltage is controlled so that the difference in the amount of light transmitted between the non-transmissive part and the non-transmissive part is constant, and therefore the contrast ratio of the image displayed on the liquid crystal panel can be always constant, improving the image quality. Can be done.

[0008]

【Example】

 FIG. 1 shows a block diagram of an embodiment of the present invention. In the figure, 1 indicates a liquid crystal panel. The liquid crystal panel 1 has a structure in which liquid crystal is enclosed between glass substrates 3 and 4 which are held at a constant interval by spacers 2 which are continuously arranged on the periphery.

A display unit 5 that displays an image on the liquid crystal panel 1 by applying a drive voltage V _D to the liquid crystal according to the image to be displayed and changing the state of the liquid crystal to change the light transmission state. A transmissive portion 6 in which the liquid crystal state is controlled so that light is always transmitted, and a non-transmissive portion 7 in which the liquid crystal state is controlled so that light is always non-transmissive are formed.

Pixel electrodes are formed in, for example, n rows × m columns in a portion corresponding to the display portion 5 of the glass substrate 4, and a switching element is provided in each pixel electrode. The switching element is switched according to an image. By controlling the supply of the drive voltage V _D to each pixel electrode is controlled. Further, an electrode having a size corresponding to the size of the non-transmissive portion 7 to be formed is formed in a portion corresponding to the non-transmissive portion 7 of the glass substrate 4, and the drive voltage V _D is constantly applied to this electrode. It A common ground electrode is formed on one surface of the glass substrate 3.

In the display unit 5, a driving voltage is applied between the pixel electrode of the glass substrate 4 and the common electrode of the glass substrate 3 according to an image, the state of the liquid crystal in the portion to which the driving voltage is applied changes, and Is no longer transmitted, light and dark are formed corresponding to the pixel electrodes, and an image is displayed.

Further, the drive voltage V _D is constantly applied to the non-transmissive portion 7, and the liquid crystal is held in a state in which light is not transmitted to be in a non-transmissive state. Since the driving voltage V _D is not applied to the transmissive portion 8, the liquid crystal is always held in a state of transmitting light, and the transmissive portion is in the transmissive state. Photo interrupters 8 and 9 are installed so as to sandwich the transmissive portion 6 and the non-transmissive portion 7 of the liquid crystal panel 1 from the front and back surfaces.

The photo interrupters 8 and 9 are composed of light emitting elements 8a and 9a and light receiving elements 8b and 9b. The light emitting elements 8a and 9a are connected to the light emission voltage supply means 10 and emit light according to the voltage supplied from the light emission voltage supply means 10. The light emitted from the light emitting elements 8a and 9a is supplied to the light receiving elements 8b and 9b via the transmissive portion 6 and the non-transmissive portion 7.

The light receiving elements 8 b and 9 b receive the light transmitted through the transmissive portion 6 and the non-transmissive portion 7, and supply the drive voltage control means 11 with a detection signal corresponding to the amount of the received light.

FIG. 2 is a block diagram showing the essential parts of an embodiment of the present invention. The driving voltage control means 11 comprises detection resistors R ₁ and R ₂ , amplification circuits 12 and 13, a comparator 14, and a switching means 15.

A constant voltage V _CC is applied to the collector of the light-receiving element 8b, and the emitter is grounded via the detection resistor R ₁ . A connection point P ₁ between the emitter of the light receiving element 8b and the detection resistor R ₁ is connected to the amplifier circuit 12.

The amplifier circuit 12 constitutes a non-inverting amplifier circuit by the operational amplifier 12a and resistors R ₃ , R ₄ etc., and amplifies and outputs the detection signal supplied from the connection point P ₁ . The output of the amplifier circuit 12 is supplied to the inverting input terminal of the comparator 14.

The light receiving element 9b has a collector to which a constant voltage V _CC is applied, and an emitter which is grounded through a detection resistor R ₂ . A connection point P ₂ between the emitter of the light receiving element 9b and the detection resistor R ₂ is connected to the amplifier circuit 13. Amplifying circuit 13 constitutes a non-inverting amplifier circuit by the operational amplifier 13a and resistors R _5, R _6, amplifies and outputs the detection signal supplied from the connection point P _2. The output of the amplifier circuit 13 is connected to the non-inverting input terminal of the comparator 14.

The comparator 14 compares the output signal of the amplifier circuit 12 and the output signal of the amplifier circuit 13, and when the output signal of the amplifier circuit 12 is larger than the output signal of the amplifier circuit 13, outputs a high level signal and amplifies the signal. When the output signal of the circuit 12 is smaller than the output signal of the amplifier circuit 13, a low level signal is output. The output signal of the comparator 14 is supplied to the switching means 15.

The switching means 15 is supplied with the normal contrast ratio drive voltage V _D1 and the low contrast ratio drive voltage V _D2 at the terminals T ₁ and T ₂ , and the contact 15 according to the output signal of the comparator 14. It is configured to switch to T ₁ or terminal T ₂ . The normal contrast ratio drive voltage V _D1 to the terminal T ₁ of the switching means 15 is applied, to the terminal T ₂ are applied teichoic Ntorasu ratio during driving voltage V _D2, the contact 15a is the output signal of the comparator 14 Is at the high level, it is connected to the terminal T ₁ , and at the low level, it is connected to the terminal T ₂ . The output drive voltage V _D of the switching means 15 is applied to the liquid crystal panel 1 as a drive voltage.

Here, the amplification factors of the resistors R ₁ and R ₂ or the amplification circuits 12 and 13 are set according to the contrast ratio to be obtained. That is, the output of the comparator 14 is set to a high level when the contrast ratio is normal temperature, and is set to a low level when the contrast ratio is low.

Here, for example, when the liquid crystal panel 1 is driven at room temperature, the amount of light transmitted through the transmissive portion 6 of the liquid crystal panel 1 is sufficiently larger than the amount of light transmitted through the non-transmissive portion 7, and therefore the light receiving element 8 b Is sufficiently larger than the output signal of the light receiving element 9b. Therefore, the signal supplied to the non-inverting input terminal of the comparator 14 is sufficiently larger than the signal supplied to the inverting input terminal, so that the output of the comparator 14 becomes high level, and the contact 15a of the switching means 15 is connected to the terminal. It is connected to T ₁ and a normal contrast ratio drive voltage V _D1 is supplied to the liquid crystal panel 1.

When the temperature of the liquid crystal panel 1 decreases and the change in the liquid crystal state decreases, the light transmittance of the transmissive portion 6 decreases and the contrast ratio deteriorates, so that the output signal of the light receiving element 8b decreases. . As a result, the signal supplied to the non-inverting input terminal of the comparator 14 becomes lower than the signal supplied to the inverting input terminal, the output of the comparator 14 becomes low level, and the contact 15a of the switching means 15 becomes the terminal T. ₂ , the low contrast ratio drive voltage V _D2 (> V _D1 ) is applied to the liquid crystal panel 1.

For this reason, the drive voltage V _D of the liquid crystal panel 1 is increased as compared with the normal state, the change in the state of the liquid crystal is increased, and the contrast ratio can be increased. Therefore, the contrast ratio rises when the temperature is low, and the same contrast ratio as in the normal time can be obtained.

As described above, according to this embodiment, the contrast ratio is controlled according to the actual contrast ratio, not the ambient temperature of the liquid crystal panel 1. Therefore, the temperature of the liquid crystal panel 1 itself and its surroundings are controlled. Even if there is a difference in temperature, regardless of this, if the contrast ratio decreases, the drive voltage V _D can be increased, and the contrast ratio can be increased, and control according to the actual display can be performed. In addition, it can handle not only temperature changes but also drive voltage changes.

In this embodiment, the configuration is such that the drive voltage can be switched between two levels according to the contrast ratio, but the present invention is not limited to this, and a configuration is possible in which a larger number of drive voltages are prepared and switched. The drive voltage may be continuously controlled according to the contrast ratio.

The transmitted light detecting means is not limited to the photo interrupter, and may be a combination of discrete electronic components such as a light emitting diode and a phototransistor. It is sufficient that the amount of light transmitted through the portion 6 and the non-transmissive portion 7 can be detected.

Further, although the liquid crystal panel which is in the transmissive state when not driven is used in the present embodiment, the present invention is not limited to this, and can be naturally applied to the liquid crystal panel which is in the non-transmissive state when not driven. .

[0029]

[Effect of device]

 As described above, according to the present invention, the drive voltage of the liquid crystal panel is controlled according to the difference between the amount of light transmitted through the transmissive portion of the liquid crystal panel and the amount of light transmitted through the non-transmissive portion thereof. It has features such that a constant contrast ratio can always be secured and the image quality of the liquid crystal display panel can be improved especially at low temperatures.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of the present invention.

FIG. 2 is a block diagram of a main part of an embodiment of the present invention.

FIG. 3 is a configuration diagram of a conventional example.

[Explanation of symbols]

 1 Liquid crystal panel 5 Display section 6 Transmission section 7 Non-transmission section 8, 9 Transmitted light detection section

Claims (1)

[Scope of utility model registration request] 1. A liquid crystal display device comprising a liquid crystal panel for displaying an image by applying a drive voltage to a position corresponding to a display image, wherein the liquid crystal panel is formed on the liquid crystal panel, and makes light transmissive regardless of the display image. A transmissive part that holds the non-transmissive part that is formed in the liquid crystal panel and that holds light in a non-transmissive state regardless of the display image, and irradiates the transmissive part with a certain amount of light, First transmitted light detecting means for detecting a transmitted amount; second transmitted light detecting means for irradiating the non-transmissive portion with a certain amount of light to detect the transmitted amount of light of the non-transmissive portion; According to the difference between the amount of transmitted light detected by the first transmitted light detecting means and the amount of transmitted light detected by the second transmitted light detection, the drive voltage is set to the transmission amount of the transmission part and the non-transmission part. Drive voltage control means for controlling the difference with the transmission amount to be constant. The liquid crystal display device comprising.