JP2004361727A - Display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display device capable of obtaining satisfactory visibility under a wide environmental condition. <P>SOLUTION: In the display device, an illumination part 140 illuminating a display part 110 driven based on a controlling signal for displaying an image is disposed in the rear of the display part 110 and a transmission/reflection part 130 whose optical characteristic can be switched to either of two states having degrees of transmission and reflection different from each other is inserted between the display part 110 and the illumination part 140. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a liquid crystal display device for displaying characters, images, and the like, and more particularly, to a technique for improving the visibility of a liquid crystal display.
[0002]
[Prior art]
At present, as a thin display device, a liquid crystal display device used for various products such as a TV receiver, a mobile phone, a wristwatch, and a personal computer includes an organic EL (Electro Luminescence) display and a plasma display panel in which a display unit emits light. Unlike the above, since the display unit itself does not emit light, it is necessary to illuminate the display unit.
[0003]
The liquid crystal display devices are roughly classified into three types, that is, a total transmission type, a reflection type, and a semi-transmission type, depending on the difference in the illumination system.
The transmissive liquid crystal display device is a method in which a light source on a back surface is turned on to illuminate a display unit provided with a color filter on a liquid crystal display element from behind. Particularly, in a dark external environment, display is easy to see. Has advantages. (For example, see Patent Document 1)
On the other hand, a reflection type liquid crystal display device reflects light from a light source placed on the front of the display unit or light from the outside (hereinafter, referred to as “external light”) once to a reflector on the rear surface of the display unit, and reflects the reflected light. This is a method of illuminating the display unit, and has an advantage that the display is easy to see especially in a bright external environment. (For example, see Patent Document 2)
The transflective liquid crystal display device is a transflective liquid crystal display device in which a translucent film called a so-called half mirror is inserted between a liquid crystal display element and a light source located on the back surface of the transflective liquid crystal display device. When the external environment is bright, illumination is performed by light reflected on the film, and when the external environment is dark, the total transmission type liquid crystal display device and the reflection type liquid crystal display device are an eclectic existence. However, the illumination is performed by the light of the light source, and has an advantage that the visibility is not significantly reduced even when the external environment is extremely bright or extremely dark. (For example, see Patent Document 3)
[0004]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2003-122260
[Patent Document 2]
JP 2001-305527 A
[Patent Document 3]
JP 2003-048291 A
[Problems to be solved by the invention]
However, in a liquid crystal display device mounted on a portable device used indoors and outdoors, such as a mobile phone and a wristwatch, the difference in brightness in the surrounding environment is remarkable, so that it is difficult to always make the display easily viewable.
For example, in a full-transmission type liquid crystal display device, in a very bright external environment such as outdoors on a sunny day, the illuminance of the external environment is higher than the illuminance of the display unit illuminated by the light source, and the display is visually recognized. There is a problem that the property is reduced.
[0008]
Further, in a reflective liquid crystal display device, the incident light passes back through a member such as a display portion, so that the optical path length is increased, and the light is easily diffused or reflected in a direction other than the intended direction. Further, since the reflectance of the reflector is not strictly 100%, the amount of light contributing to illumination is reduced, and there is a problem that the visibility of the liquid crystal display is reduced particularly in a dark external environment.
[0009]
Further, in a transflective liquid crystal display device, the ratio of external light and light from an internal light source used as illumination is lower than that of a transflective liquid crystal display device and a reflective liquid crystal display device. There is a problem that display visibility is poor.
Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a display device capable of obtaining good visibility under a wide range of environmental conditions.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a display device according to the present invention is provided with an illuminating unit for illuminating the first liquid crystal element on a back surface of the first liquid crystal element driven based on a control signal for displaying an image. A second liquid crystal element whose optical characteristics can be switched between two states having different degrees of transmission and reflection between the first liquid crystal element and the illumination unit. Features.
[0011]
Accordingly, when an image is displayed on the first liquid crystal element, the degree of transmission and reflection of the second liquid crystal element is switched, so that external light transmitted through the first liquid crystal element is reflected by the second liquid crystal element. It functions as both a display device and a transmission type display device that irradiates light from a lighting unit to the back surface of the first liquid crystal element.
In other words, an illumination method with high visibility can be selected according to the brightness of the external environment, so that good visibility is ensured under a wide range of environmental conditions.
[0012]
Further, the display device may further include an external environment having a predetermined brightness or higher such that the second liquid crystal element is in a reflection state for reflecting the received light under an external environment having a predetermined brightness or less. Below, the second liquid crystal element may include a control unit that controls the second liquid crystal element to be in a transmission state in which the received light is transmitted.
Thus, the display device functions as a reflective display device under bright environmental conditions, and functions as a transmissive display device under dark environmental conditions.
[0013]
That is, the display is performed using the illumination method most suitable for each environmental condition.
Further, the display device further includes a receiving unit for receiving a first or second instruction from an operator, and when the receiving unit receives the first instruction, the second liquid crystal element receives the received light. When the receiving unit receives the second instruction so as to reflect the light, the second liquid crystal element includes a control unit that controls the liquid crystal element to be in a transmission state that transmits the received light. Is also good.
[0014]
This allows the operator to select whether the display device functions as a reflective display device or as a transmissive display device.
Further, when the second liquid crystal element is in the reflection state, its reflection surface may be in a substantially mirror state.
Thereby, the ratio used for illuminating the external light passing through the first liquid crystal element increases, and more efficient illumination is performed.
[0015]
That is, the visibility when the present display device functions as a reflective display device is improved.
Further, the second liquid crystal element may be substantially transparent when in the transmission state.
Thereby, the ratio of the light emitted from the illumination unit used as the light for illuminating the first liquid crystal element increases, and more efficient illumination is performed.
[0016]
In addition, the display device further includes a detection unit that detects light and shade in the environment, and the control unit grasps the brightness of the external environment based on the detection result by the detection unit, and performs the control. You may do it.
Accordingly, the transmittance and the reflectance of the second liquid crystal element are changed according to the brightness of the environment, that is, the switching between the reflection type and the transmission type is performed.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
(Constitution)
FIG. 1 is a functional block diagram of a display device according to the embodiment of the present invention.
The display device 100 is, for example, a display device built in a portable device such as a mobile phone, and includes a display unit 110 that displays characters and images and an illumination unit 140 that illuminates the display unit 110 from behind. In addition, a transmission / reflection unit 130 whose optical characteristics can be switched between a transparent state and a mirror surface is inserted therein, and these three function units (hereinafter, referred to as “display function unit group 101”) are respectively provided. Is connected to the control unit 102. In addition, an operation unit 103 for receiving an external input, an external light illuminance detection unit 104 for detecting illuminance, and a timer unit 105 are connected to the control unit 102. Become.
[0018]
FIG. 2 is a schematic diagram of the display function unit group 101.
The display unit 110 is a liquid crystal element having a thickness of 4.0 mm, a width of 40 mm, and a height of 50 mm for displaying characters and images, and a polarizing plate 111 having a polarization direction in the Y-axis direction in the drawing as an uppermost layer. On the lower layer side, a color filter 112, a plate-shaped transparent electrode 113, an alignment plate 114 having the Y-axis direction as an alignment direction, a liquid crystal layer 115, an alignment / electrode plate 116, and an X-axis direction in the drawing as a polarization direction. The polarizing plate 117 is laminated in the Z-axis direction in the figure.
[0019]
As is generally known, the display unit 110 has two types of a liquid crystal display panel by active matrix driving using a switching element such as a TFT (Thin Film Transistor) and a liquid crystal display panel by multiplex driving. Yes, any of them can be selected and used.
The color filter 112 is a plate-shaped filter in which R (Red), G (Green), and B (Blue) minute filters are regularly arranged.
[0020]
The alignment / electrode plate 116 has a stripe-shaped transparent electrode 119 having a longitudinal direction in the X-axis direction and a stripe-shaped transparent electrode 119 having a longitudinal direction in the Y-axis direction on the lower surface of the alignment plate 118 having the X-axis direction as an alignment direction. The electrode 120 is formed.
The transmission / reflection unit 130 is a liquid crystal element having a thickness of 4.0 mm, a width of 40 mm, and a height of 50 mm having a function of being in a transparent state in a non-energized state and being in a mirror state in an energized state.
[0021]
Here, the transmission / reflection unit 130 transmits light from the illumination unit 140 when in the transparent state, and reflects external light passing through the display unit 110 when in the mirror state.
The technical contents related to the above functions are disclosed in, for example, JP-A-2001-318374.
More specifically, the transmission / reflection unit 130 has a polarizing plate 131 whose polarization direction is in the X-axis direction as the uppermost layer, and a plate-shaped transparent electrode 132 on the lower layer side, and an alignment in which the X-axis direction is the alignment direction. A plate 133, a liquid crystal layer 134, an alignment plate 135 having an alignment direction in the Y-axis direction, a plate-shaped transparent electrode 136, and a polarizing plate 137 having a polarization direction in the Y-axis direction are laminated in the Z-axis direction.
[0022]
Unlike the conventional liquid crystal element for display, the polarizing plate 137 transmits light polarized in the Y-axis direction, such as DBEF (trademark of 3M), and light polarized in the Y-axis direction. Is a member for specular reflection.
Here, the above-mentioned mirror state refers to a state where the reflectance is 38.4% to 38.6%, and the transparent state which is the state opposite to the mirror state refers to a state where the transmittance is 76% to 80%. Say.
[0023]
The illuminating unit 140 is formed by joining four white LEDs 142 that are turned on and off as the voltage applied from the control unit is turned on and off, at the end face of the light guide plate 141.
In FIG. 1, an operation unit 103 is, for example, an operation button of a mobile phone that receives an input from an operator, and is an external light illumination mode in which a liquid crystal display is illuminated by external light. A signal that specifies one of the internal illumination mode for illuminating the liquid crystal display and the automatic illumination mode for automatically selecting the method of illuminating the liquid crystal display depending on the brightness of the external environment, , "Mode signal") to the control unit 102.
[0024]
The external light detection unit 104 is a detection element that detects illuminance, and outputs a signal indicating the value of the detected illuminance (hereinafter, referred to as an “illuminance signal”) to the control unit 102.
The timer unit 105 is a clock for measuring time. The timer unit 105 initializes the count value to 0 based on an instruction from the control unit 102, and adds 1 to the current count value every 0.1 seconds. Perform a count up.
[0025]
Further, when the count value reaches 10, the timer unit 105 outputs a signal indicating that (hereinafter, referred to as a “notification signal”) to the control unit 102.
The control unit 102 includes a CPU, a readable and writable memory, and outputs a signal for displaying characters and images to the display unit 110 on the display unit 110, and outputs a signal coming from the operation unit 103 and an external light detection unit. It has a function of performing processing for improving visibility (hereinafter, referred to as “visibility improvement processing”) by switching the optical characteristics of the transmission / reflection unit 130 based on a signal coming from 104.
[0026]
Hereinafter, the visibility improvement processing will be described.
(Visibility improvement processing)
When a mode signal (digital signal) and an illuminance signal (digital signal) are output from the operation unit 103 and the external light detection unit 104, the control unit 102 stores these signals, that is, digital values, in the memory. Overwrites the signal-only storage area.
[0027]
Then, the control unit 102 periodically refers to the inside of the memory, and grasps the type of the mode indicated by the mode signal and the value of the illuminance indicated by the illuminance signal at the time of the reference.
If the mode signal acquired latest indicates the external light illumination mode, the control unit 102 supplies power to the display function unit group 101 so as to supply power to the transmission / reflection unit 130. The power supply unit is instructed to stop supplying power to the lighting unit 140.
[0028]
If the mode signal acquired latest indicates the internal illumination mode, the control unit 102 instructs the power supply unit to stop supplying power to the transmission / reflection unit 130. Is instructed to supply power to the lighting unit 140.
On the other hand, when the mode signal acquired latest indicates the automatic lighting mode, the control unit 102 transmits the above-described power to the power supply unit when the value of the illuminance indicated by the received illuminance signal is equal to or less than the threshold. An instruction is performed in the same manner as in the case of the internal lighting mode, and when the illuminance value indicated by the illuminance signal exceeds a threshold value, the power supply unit described above is compared with the case of the external lighting mode. Perform similar instructions.
[0029]
When the above-described visibility improvement processing is completed, the control unit 102 instructs the timer unit 105 to reset the count value to 0 and start the above-described count-up, and the notification signal is transmitted from the timer unit 105. Until the arrival, the mode signal and the illuminance signal are received, and the visibility improvement process is performed again with the reception of the notification signal.
(motion)
FIG. 3 is a flowchart showing the details of the visibility improvement processing performed to ensure good visibility in a wide range of environmental conditions in the display device 100.
[0030]
When the mode signal and the illuminance signal are output from the operation unit 103 and the external light detection unit 104, the control unit 102 overwrites these signals, that is, the digital values, in the dedicated storage area of the memory and saves them (step S101), the stored mode signal and illuminance signal are acquired with reference to the memory (step S102).
[0031]
Then, the control unit 102 determines whether or not the obtained mode signal is the automatic lighting mode (step S103), and when the obtained mode signal indicates the automatic lighting mode, the value of the illuminance indicated by the obtained illuminance signal Is determined to be less than or equal to the threshold value (step S104). If the value is less than or equal to the threshold value, as shown in FIG. The supply is stopped and the lighting unit 140 is supplied with power (step S105).
[0032]
On the other hand, when the illuminance value exceeds the threshold value, as shown in FIG. 5, the control unit 102 supplies power to the transmission / reflection unit 130 via a power supply unit (not shown) and The power supply to is stopped (step S106).
When it is determined in step S103 that the obtained mode signal does not indicate the automatic lighting mode, the control unit 102 further determines whether the obtained mode signal indicates the internal lighting mode. (Step S107) When the acquired mode signal indicates the internal illumination mode, the above-described step S105 of stopping power supply to the transmission / reflection unit 130 and performing power supply to the illumination unit 140 is performed.
[0033]
When the acquired mode signal does not indicate the internal illumination mode, that is, in the case of the external illumination mode, the control unit 102 causes the transmission / reflection unit 130 to perform power supply, and controls the illumination unit 140 to supply power. The above-described step S106 for stopping is executed. Subsequently, the control unit 102 instructs the timer unit 105 to start counting up after setting the count value to 0 (steps S108 to S109).
[0034]
As a result, the timer unit 105 increments the count value by one each time 0.1 second elapses.
Then, until the count value becomes 10 or more, the control unit 102 performs the same processing as the processing in step S101 described above, that is, the mode signal and the illuminance signal from the operation unit 103 and the external light detection unit 104, respectively. Is output, the digital values of these signals are overwritten and stored in the dedicated storage area of the memory (steps S110 to S111).
[0035]
When the above-mentioned count value becomes 10 or more, the control unit 102 ends the count-up (step S112), and executes the processing from step S102 and thereafter to step S112 again.
As described above, according to the present embodiment, in the liquid crystal display device, external light and a light source inside the device can be selectively used as a light source for illuminating the display unit according to the illuminance of the external environment. Good visibility is obtained under environmental conditions.
[0036]
In the present embodiment, the display unit 110 and the transmission / reflection unit 130 have different configurations. However, the liquid crystal display element may have a multi-layer structure to have a single configuration.
In that case, when the display unit 110 is illuminated using external light, the optical path length is shortened, and further, the distance between the color filter and the reflection surface is shortened, so that parallax is eliminated and visibility is further improved. There is a merit that it is improved.
[0037]
Further, in the present embodiment, the display device 100 is incorporated in a portable device such as a mobile phone, but this is merely an example, and the present invention is not limited to this. I do not care.
Although the display device 100 of the present embodiment has been described as a display device that performs color display, it may be a display device that performs monochrome display.
[0038]
In that case, since the color filter 112 of the display unit 110 becomes unnecessary, for example, the power supply to all the transparent electrodes 119 and all the transparent electrodes 120 of the display unit 110 is stopped to make the display unit 110 transparent. By applying a voltage between the transparent electrode 132 and the transparent electrode 136 of the transmission / reflection unit 130 to make the transmission / reflection unit 130 a mirror surface, the display device 100 can be used as a mirror.
[0039]
As described above, when the display device 100 is being used as a mirror, the control unit 102 may perform control to return to the normal standby state in accordance with an instruction from the user received by the operation unit 103. Also, the control unit 102 may perform control so as to display an incoming call such as displaying the telephone number of the caller when an incoming call is received.
[0040]
【The invention's effect】
As is apparent from the above description, the display device according to the present invention functions as a transmissive liquid crystal display device by illuminating the display unit with a built-in illumination unit, that is, a backlight, when the external environment is dark. When the environment is bright, the transmission / reflection part is mirror-finished to reflect external light and function as a reflection type liquid crystal display device. Good visibility is ensured.
[Brief description of the drawings]
FIG. 1 is a functional block diagram of a display device according to an embodiment of the present invention.
FIG. 2 is a schematic diagram of a display function unit group 101.
FIG. 3 is a flowchart illustrating details of a visibility improvement process.
FIG. 4 is a diagram showing a signal flow when the external environment is dark.
FIG. 5 is a diagram showing a signal flow when the external environment is bright.
[Explanation of symbols]
REFERENCE SIGNS LIST 100 display device 101 display function unit group 102 control unit 103 operation unit 104 external light illuminance detection unit 105 timer unit 110 display unit 111 polarizing plate 112 color filter 113 transparent electrode 114 alignment plate 115 liquid crystal layer 116 alignment / electrode plate 117 polarizing plate 118 alignment Plate 119 Transparent electrode 120 Transparent electrode 130 Reflector 131 Polarizer 132 Transparent electrode 133 Alignment plate 134 Liquid crystal layer 135 Alignment plate 136 Transparent electrode 137 Polarizer 140 Illumination unit 141 Light guide plate 142 White LED

Claims (6)

An illumination unit for illuminating the first liquid crystal element is provided on a back surface of the first liquid crystal element driven based on a control signal for displaying an image,
A second liquid crystal element is inserted between the first liquid crystal element and the illuminating section, the second liquid crystal element having optical characteristics that can be switched between two states having different degrees of transmission and reflection. Display device. The display device further comprises:
Under an external environment having a brightness equal to or higher than a predetermined brightness, the second liquid crystal device may be configured to be in a reflection state in which received light is reflected under an external environment having a brightness lower than a predetermined brightness. The display device according to claim 1, further comprising a control unit configured to control a transmission state of transmitting the received light. The display device further comprises:
A receiving unit for receiving the first or second instruction from the operator;
When the receiving unit receives the second instruction so that the second liquid crystal element is in a reflection state for reflecting the received light, the receiving unit receives the first instruction. 2. The display device according to claim 1, further comprising control means for controlling the two liquid crystal elements to be in a transmission state for transmitting the received light. 4. The display device according to claim 2, wherein when the second liquid crystal element is in the reflection state, a reflection surface thereof is in a substantially mirror state. 5. The display device according to claim 2, wherein the second liquid crystal element is in a substantially transparent state when in the transmission state. The display device further comprises:
Comprising a detecting means for detecting light and shade in the environment,
3. The display device according to claim 2, wherein the control unit recognizes brightness of an external environment based on a result of the detection by the detection unit and performs the control. 4.

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