JPH04254820A - Liquid crystal display - Google Patents

Abstract

PURPOSE:To adjust the quantity of back light in optimum corresponding to the quantity of external light by providing a means of adjusting the quantity of back light in inverse proportion to the quantity of external light detected by a light receiving element. CONSTITUTION:External light which illuminates the surface of a display area 21a also has illumination to a photo diode 26 in a non-display area, where the quantity of light is converted into detection signals levelled corresponding to the quantity of light. The detection signals are amplified to a desired level by an amplifier 35 and then input to a comparator 36, where it is converted into error signals corresponding to an error to reference voltage from a reference power supply 37 and then input to a back light power supply 38 and a control circuit 34. The back light power supply 38 generates a burst pulse that the ratio of duty varies in inverse proportion to the level of error signals from the comparator 3, to apply to back light 39 as power voltage.

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, and more particularly to a liquid crystal display device equipped with a backlight for illuminating a liquid crystal panel.

[0002] Transmissive liquid crystal panels can provide a bright display by providing a light source (that is, a backlight) behind them. is often used. When such a liquid crystal display device with a backlight is used as a display device for a portable personal computer, for example, the lower the power consumption of the backlight, the smaller and lighter the battery power source for the backlight, and the smaller and lighter the entire device. It is desirable to reduce the power consumption of the backlight because it allows for weight reduction.

0003

2. Description of the Related Art FIG. 8 shows a configuration diagram of an example of a conventional liquid crystal display device. In the figure, reference numeral 1 denotes a transmissive liquid crystal panel, in which a plurality of liquid crystal display elements serving as pixels are regularly arranged, for example, in each of the X and Y directions. Further, 2 is a scan driver, and 3 is a data driver, which drive each liquid crystal display element in the X direction (line direction) and Y direction, respectively. A control circuit 4 controls the scan driver 2 and data driver 3, respectively, and selects each liquid crystal display element of the liquid crystal panel 1 to display a desired image.

A backlight 5 is provided behind the liquid crystal panel 1 and illuminates the back surface of the liquid crystal panel 1. 6
A backlight power source supplies power voltage to the backlight 5, and is usually composed of a battery. The amount of light (brightness) emitted from the backlight can be adjusted by varying the variable resistor 7. The amount of light emitted from the backlight 5 is made smaller as the external light irradiated onto the surface of the liquid crystal panel 1 becomes brighter. This is because if the outside light is bright, the display on the liquid crystal panel 1 can be seen clearly even if the light from the backlight 5 is dark.

[0005]

However, in conventional liquid crystal display devices, the amount of light from the backlight 5 is adjusted by manually operating the variable resistor 7 at the user's discretion. Backlight for brightness 5
The light intensity adjustment of the backlight 5 may become vague, and the light intensity of the backlight 5 may be increased more than necessary even though the outside light is bright.

In this case, the power consumption of the backlight power source 6 is roughly proportional to the amount of light from the backlight 5, so if the light from the backlight 5 is brighter than necessary, the power consumption increases, and the life of the backlight power source 6 is shortened. The problem is that it becomes shorter.

[0007] The present invention has been made in view of the above points.
It is an object of the present invention to provide a liquid crystal display device that can optimally adjust the amount of light of a backlight according to the amount of external light.

[0008]

[Means for Solving the Problems] FIG. 1 shows a diagram of the basic configuration of the present invention. The present invention performs display on a liquid crystal panel 11 in which a plurality of liquid crystal display elements are regularly arranged as pixels,
In addition, in a liquid crystal display device configured to irradiate light from behind the liquid crystal panel with a backlight 12, the liquid crystal panel 11
A light receiving element 13 for detecting external light provided outside the display area of
and a light amount adjusting means 14. The light amount adjusting means 14 controls the power source of the backlight 12 based on the detection signal of the light receiving element 13, and adjusts the light amount of the backlight 12 in substantially inverse proportion to the amount of external light detected by the light receiving element 13.

[0009]

In the present invention, the amount of light emitted from the backlight 12 is adjusted by the light amount adjusting means 14 so that it is approximately inversely proportional to the amount of external light detected by the light receiving element 13 for detecting external light. Therefore, the present invention can optimally and automatically adjust the amount of light emitted from the backlight 12 according to the amount of external light.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 is a block diagram of an embodiment of the present invention, and FIG. 3 is a structural diagram of an embodiment of the present invention. In both figures, the same constituent parts are given the same reference numerals, and the same constituent parts as in FIG. In the front view of FIG. 3(A), reference numeral 21 denotes an active matrix drive type liquid crystal panel, which includes a display area 21a and a non-display area 21 on its outer periphery.
In the display area 21a, display is performed using liquid crystal display elements arranged in a matrix.

As shown in the side view of FIG. 3B, this liquid crystal panel 21 has thin film transistors (TFTs) and display electrodes, which will be described later, formed on a glass substrate 22, and a spacer 23 between a spacer 23 and an upper glass 24. A liquid crystal display element 25 is provided in the sealed space.

[0012] Furthermore, as shown in FIGS. 3(A) and 3(B),
For example, at the upper center of the non-display area 21b on the glass substrate 22, an external light detection photodiode 26 corresponding to the external light detection light receiving element 13 is formed. Further, a light shield 27 having an elongated hole 27a bored in the center is formed in the upper glass 24 at a position in front of the diode 26. Further, a light shield 28 is formed on the glass substrate 22 at a position opposite to the photodiode 26.

Thereby, the light shield 27 blocks external light from unnecessary directions, and only the external light from the front of the upper glass 24 passes through the elongated hole 27a and the upper glass 24, respectively, and enters the light receiving surface of the photodiode 26. be able to. Further, although light from the backlight (not shown) is incident on the back surface of the glass substrate 22, the circuit breaker 28 can prevent the light from the backlight from going around and being incident on the photodiode 22. .

Next, the embodiment shown in FIG. 2 will be explained. Display area 2 of active matrix drive type liquid crystal panel 21
In 1a, a plurality of liquid crystal display elements are formed as pixels in a direction perpendicular to the line direction, and a TFT is provided as a switching transistor for each liquid crystal display element. 30 in FIG. 2 is an arbitrary display pixel (liquid crystal display element) among a plurality of liquid crystal display elements arranged in a matrix;
31 is a TFT whose source is connected corresponding to this liquid crystal display element 30.

Among the TFT 31 and other TFTs (not shown), TFTs arranged in the same line direction (row direction)
Each gate is commonly connected to the scan driver 32,
Further, the drains of the TFTs arranged in the same column direction are commonly connected to the data driver 33. 34 is a control circuit, which includes a scan driver 32 and a data driver 3;
3 respectively.

As a result, the TFTs on one line from the scanned driver 32 are turned on at the same time, and the TFTs on one line that are turned on are sequentially switched from top to bottom. On the other hand, the data driver 33 outputs display data. As a result, display data is written to the liquid crystal display element connected to the turned-on TFT, and an image of the desired data is displayed in the display area 21a.

Further, 39 is a backlight, for example, an electroluminescence (EL) or a cold cathode fluorescent lamp (CCFL).
), which corresponds to the backlight. Here, the backlight 39 is composed of a CCFL, and is driven by a power supply voltage having a burst-like pulse waveform as shown in FIG. 4 generated by the backlight power supply 38.
It is assumed that the display area 21a is arranged so as to uniformly illuminate at least the entire rear surface of the display area 21a. The amount of light emitted from the backlight 39 increases in proportion to the duty ratio a/(a+b) of the pulse waveform in FIG.

The backlight power supply 38 constitutes the light amount adjustment means 14 together with the comparator 36 and the reference power supply 37, and is configured to output a burst-like pulse waveform whose duty ratio changes according to the signal from the comparator 36. has been done.

Next, the operation of this embodiment will be explained. The external light that illuminates the surface of the display area 21a is the non-display area 21b.
The light is also irradiated onto the photodiode 26, where the amount of light is converted into a detection signal with a level corresponding to the amount of light. After this detection signal is amplified to the required level by the amplifier 35,
The signal is input to the comparator 36 , where it is converted into an error signal according to the difference from the reference voltage from the reference power source 37 , and then input to the backlight power source 38 and the control circuit 34 .

The backlight power supply 38 generates a burst pulse whose duty ratio changes in inverse proportion to the error signal level from the comparator 36, and applies it to the backlight 39 as a power supply voltage. Therefore, as the amount of external light increases, the output duty ratio of the backlight power supply 38 is controlled to be smaller, and as a result, the amount of light emitted from the backlight 39 becomes smaller. Therefore, according to this embodiment, even when the outside light is bright, the backlight 39 can always emit the optimum minimum amount of light, and the power consumption of the backlight power supply 38 can be saved compared to the conventional method. can do.

Further, in this embodiment, the output error signal of the comparator 36 is input to the control circuit 34, and the level of the display data of the data driver 33 is changed in approximately inverse proportion to the level of the error signal. Therefore, it is possible to automatically adjust the contrast so that the brighter the outside light, the lower the contrast of the displayed image.

Furthermore, in this embodiment, by varying the reference voltage of the reference voltage source 37, the amount of light emitted from the backlight 39 and the contrast of the displayed image can be adjusted as desired.

Next, another embodiment of the present invention will be described. FIG. 5 is a structural diagram of another embodiment of the present invention, and FIG. 6 is a diagram showing the main part configuration of another embodiment of the present invention. As shown in the front view of FIG. 5A and the side view of FIG. It is perforated. Each of the light guiding holes 43 is arranged in a one-to-one correspondence in front of a photosensor 44 provided on the liquid crystal panel 41.

As shown in FIG. 5C, each of the photosensors 44 has a first photodiode 441 and a second photodiode 442 on light receiving surfaces 441a and 442a, respectively.
This is a configuration in which they are combined so that they face in opposite directions. 1st
The light receiving surface 441a of the second photodiode 441 receives external light incident through the light guide hole 43, while the light receiving surface 442a of the second photodiode 442 receives light from the backlight. 44 is arranged on the liquid crystal panel 41.

The basic structure of the liquid crystal panel 41 is the same as that of the liquid crystal panel 21 shown in FIG. 3, in which two glass substrates face each other with a liquid crystal display element interposed therebetween. Unlike the structure, a photosensor 44 is formed on the same surface of the glass substrate on the backlight side where the TFTs are formed, as shown in FIG. 5(C).

The detection signal obtained by photoelectrically converting the external light with the external light photodiode 441 is sent to the amplifier 5 in FIG.
1 to the comparator 36 shown in FIG. (BL) photodiode 442 photoelectrically converts backlight light, and amplifier 52
The detection signal is amplified and level-converted.

When the operator closes the light guiding hole 43 with his/her hand, external light is not incident on the external light photodiode 441, so the detection signal at that time changes significantly compared to the detection signal when external light is received. . On the other hand, the BL photodiode 44
The level of the detection signal from 2 does not change significantly since the light from the backlight is not blocked. Therefore, since the detection voltage from the comparator 53 changes greatly between when external light is received and when external light is blocked, this detection voltage determines whether the external light is blocked (whether the light guide hole 43 is closed) or not. can be detected.

The circuit of FIG.
Since the external light photodiodes 441 of the plurality of photosensors are provided in correspondence with each other, each of the external light photodiodes 441 of the plurality of photosensors can be used as an external input key. For example, by displaying a number as shown in the display area 21a of FIG. 5 and covering the light guide hole 43 above the display of "1" with your hand, the same effect as when operating the number key "1" can be performed. It can be configured to provide external input. Next, a method of manufacturing the photodiode 26 and photosensor 44 formed in the non-display area 21b will be described. The photodiode 26 and photosensor 44 described above may be manufactured separately from the elements of the display area 21a, but in this embodiment, considering that the TFT can also be used as a phototransistor, the TFT is manufactured in the procedure shown in FIG.
At the same time as each TFT such as T31 in the display area 21a, TFTs are formed in the non-display area 21b and used as the photodiode 26 and the photosensor 44.

In FIG. 7, first, gate electrodes of TFTs are formed in each of the display area 21a and non-display area 21b on the glass substrate (step 71), and then a known film forming process (
Step 72), self-alignment process (Step 73)
After that, the source and drain electrodes of the TFT are formed (step 74). Subsequently, element isolation is performed to electrically insulate adjacent TFTs (step 75).
), forming an interlayer insulating film for multilayer wiring (step 76),
Furthermore, a drain bus connected to the data driver is formed (step 77).

Among the TFTs manufactured by such a known manufacturing process, only the TFT in the display area 21a is
A rectangular planar display electrode constituting a pixel is formed for each TFT and connected to the source electrode of the corresponding TFT (step 78). Finally, terminal electrodes for connecting the liquid crystal panel to the scan driver and data driver are exposed by etching or the like (step 79). In this way, among the TFTs formed simultaneously in the display area 21a and the non-display area 21b, the TFs formed in the non-display area
T is used as the photodiode 26 or photosensor 44.

It should be noted that the present invention is not limited to the above-described embodiments; for example, a backlight whose amount of light changes depending on the voltage level from the backlight power source may be used.

[0032]

As described above, according to the present invention, the amount of light emitted from the backlight can be optimally and automatically adjusted according to the amount of outside light. This prevents the amount of light emitted from the backlight from increasing more than necessary in a bright place, thereby preventing unnecessary power consumption compared to conventional methods, extending the life of the backlight power supply, and reducing the amount of light emitted from outside light. If the detection light-receiving element is configured to detect whether or not external light is incident on the detection light-receiving element, the external light-detecting light-receiving element can also be used as an input device that closely monitors screen information without any external parts, and can also be used as an input device that closely monitors screen information. By simultaneously manufacturing the detection light-receiving element and the switching transistor of the liquid crystal panel in the same process, the manufacturing process can be simplified.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle configuration of the present invention.

FIG. 2 is a configuration diagram of an embodiment of the present invention.

FIG. 3 is a structural diagram of an embodiment of the present invention.

FIG. 4 is a diagram showing an example of a backlight power supply voltage waveform.

FIG. 5 is a structural diagram of another embodiment of the present invention.

FIG. 6 is a configuration diagram of main parts of another embodiment of the present invention.

FIG. 7 is a manufacturing explanatory diagram of the main part of the present invention.

FIG. 8 is a configuration diagram of a conventional example.

[Explanation of symbols]

11 Liquid crystal panel 12, 39 Backlight 13 External light detection photodiode 14 Light amount adjustment means 21 Active matrix drive type liquid crystal panel 21
a Display area 21b Non-display area 31 Thin film transistor (TFT) 36 Comparator 44 Photo sensor

Claims (4)

[Claims] 1. Display is performed on a liquid crystal panel (11) in which a plurality of liquid crystal display elements are regularly arranged as pixels, and the liquid crystal panel (11) is illuminated by a backlight (12).
In a liquid crystal display device configured to irradiate light from behind (1), a light receiving element (13) for detecting external light provided outside the display area of the liquid crystal panel (11);
), the power source of the backlight (12) is controlled based on the detection signal of the backlight (12), and the light amount of the backlight (12) is adjusted in approximately inverse proportion to the amount of external light detected by the light receiving element (13). 1. A liquid crystal display device comprising a light amount adjusting means (14). 2. The light amount adjusting means (14) includes a backlight power source (38) that causes the backlight (12) to emit light in an amount corresponding to a duty ratio of a pulse input to the backlight (12). , the light receiving element (13
) and a reference signal, and variably controls the duty ratio of the output pulse of the backlight power source (38) according to the comparison result. The liquid crystal display device according to claim 1. 3. A backlight light receiving element (442) for receiving light from the backlight (12);
The detection signals of both the backlight light receiving element (442) and the external light detecting light receiving element (13,441) are compared in level, and external light is incident on the external light detecting light receiving element (13,441). 2. The liquid crystal display device according to claim 1, further comprising detection means (51 to 53) for detecting the presence or absence of. 4. The liquid crystal panel (11) includes switching transistors (11) corresponding to a plurality of liquid crystal display elements, respectively.
31), and the external light detection light receiving element (13) is a transistor formed outside the display area in the same manufacturing process as the switching transistor (31). The liquid crystal display device according to claim 1, characterized in that: