JP2002072920A - Display device - Google Patents

Abstract

(57) [Problem] To provide a display device that can maintain a sufficient level of display quality under various environments with different ambient light intensities and has low power consumption. A display panel capable of displaying at least ambient light, a photosensor for detecting the intensity of ambient light incident on the display panel from an observer, and illumination for display on the display panel. Lighting device 3 that emits light
0, and a control circuit 40 connected to the photo sensor and the lighting device. The control circuit 40 adjusts the intensity of the emitted light from the lighting device 30 based on a predetermined relationship that the intensity of the ambient light is lower and the intensity of the illumination light is lower as the intensity of the ambient light is higher, according to the intensity of the ambient light detected by the photosensor 20. Control.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device, and more particularly, to a display device using at least ambient light, such as a reflective liquid crystal display device, a transflective liquid crystal display device and a transflective liquid crystal display device. Display device.

[0002]

2. Description of the Related Art In recent years, display devices such as various electric devices and automobiles have been reduced in size, weight and power consumption. As a display element having these features, a liquid crystal display device (hereinafter, referred to as “LCD”) is used for various purposes.

An LCD is a transmissive LCD that performs display using illumination light radiated from a backlight, and a reflective LC that performs display using ambient light (including sunlight and indoor illumination light).
D. Some reflective LCDs include a front light for displaying in an environment where ambient light is weak. In recent years, transflective LCDs have recently been developed.
(See, for example, JP-A-11-101992) and a transflective LCD (for example, see JP-A-2000-19501) and a display mode (transmission mode) using illumination light from a backlight and surroundings. There has been proposed an LCD capable of displaying both in a display mode using light (reflection mode).

The display quality (viewability of an image) of a display device such as the above-described LCD is not limited to the reflection type, but is affected by ambient light. Therefore, attempts have been made to optimize display quality according to the intensity of ambient light.

For example, some transmission type LCDs have a function of increasing the intensity of light emitted from the backlight when the ambient light is strong, and decreasing the intensity of light emitted from the backlight when the ambient light is weak. . Also, an LCD that automatically adjusts the intensity of the emitted light of the backlight according to the intensity of the ambient light has been proposed (for example, Japanese Patent Laid-Open No. 6-332).
385). Further, even if the control conditions (voltage value and duty ratio) are constant, the emitted light intensity may change depending on the ambient temperature and the lighting time. An illumination device has been proposed in which the intensity of emitted light is stabilized by performing detection and feedback control using the method (for example, JP-A-5-127602).

On the other hand, for the purpose of reducing the power consumption of an information processing device having a reflective LCD, an information processing device having a function of automatically turning on / off a front light according to the intensity of ambient light has been proposed. (JP-A-11-344)
958).

[0007]

However, the transmission type L disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 6-332385.
In a transmissive display device represented by a CD, illumination by a backlight is indispensable, and the intensity of light emitted from the backlight increases when the surroundings are bright, so that power consumption is particularly increased. On the other hand, Japanese Unexamined Patent Publication No.
The reflection type LCD disclosed in Japanese Patent Application Laid-Open No. H11-133205 turns on the front light only when the surroundings are dark, so that the power consumption is low. However, since the front light is only controlled to be turned on / off, a high-quality display corresponding to the degree of surrounding brightness is provided. Cannot be provided.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a display device which can maintain a sufficient level of display quality under various environments with different ambient light intensities and consumes low power. Is to provide.

[0009]

A display device according to the present invention includes a display panel capable of displaying at least ambient light, and a photosensor for detecting the intensity of ambient light incident on the display panel from an observer side. An illumination device that emits illumination light for display on the display panel, and a control circuit connected to the photosensor and the illumination device, wherein the control circuit includes an ambient light detected by the photosensor. The intensity of the ambient light is higher, the intensity of the illumination light is lower based on a predetermined relationship that the intensity of the illumination light is lower based on a predetermined relationship. Objective is achieved.

[0010] The display panel may be a reflective liquid crystal panel, and the lighting device may be a front light. Alternatively, the display panel may be a transflective liquid crystal panel, and the lighting device may be a backlight.

[0011] A further photosensor for detecting the intensity of the light emitted from the backlight is provided, and the control circuit is configured to detect the intensity of the ambient light detected by the photosensor. It is preferable to control the intensity of the emitted light of the lighting device so that the intensity of the emitted light becomes a predetermined value.

In the case where the display panel is an active matrix type display panel including a switching element formed on a substrate, it is preferable that the photo sensor is formed on the substrate. Wiring connecting the cathode and the anode of the photosensor is formed on the substrate, and the control circuit controls the intensity of emitted light of the lighting device based on a value of a current flowing through the wiring. Is preferred.

[0013] An illumination system according to the present invention includes a photosensor for detecting the intensity of ambient light, an illumination device for emitting illumination light, and a control circuit connected to the photosensor and the illumination device. The control circuit is responsive to the intensity of the ambient light detected by the photosensor, based on a predetermined relationship that the intensity of the illumination light is lower as the intensity of the ambient light is higher, based on a predetermined relationship, , Whereby the object is achieved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure and operation of a display device according to an embodiment of the present invention will be described below. In the following example, a display device having an active matrix type liquid crystal display panel having a TFT (thin film transistor) for each picture element is illustrated, but the present invention is not limited to this, and display can be performed using ambient light. It can be widely applied to known display devices.

FIG. 1 schematically shows an LCD 100 according to an embodiment of the present invention.

The LCD 100 has an active matrix type liquid crystal display panel 10, a photo sensor 20, an illuminating device 30, and a control circuit 40.

Active matrix type liquid crystal display panel 1
Reference numeral 0 denotes a display panel capable of performing display using at least ambient light, and specifically, may be a known display panel used for a reflective LCD, a transflective LCD, or a transflective LCD. . The dual-use LCD has, for each picture element, a transmissive area for performing display in the transmissive mode and a reflective area for performing display in the reflective mode. Typically, the picture element electrode has a transparent electrode and a reflective electrode, the transmissive area is defined by the transparent electrode, and the reflective area is defined by the reflective electrode (see the above-mentioned JP-A-11-101992). Transflective LCD
Has a semi-transmissive film (half mirror) that transmits part of incident light and reflects part of the light (see JP-A-2000-1).
No. 9501).

The display panel 10 can perform display using at least ambient light, that is, in a reflection mode.
The reflective display panel performs display using ambient light and irradiation light emitted from the front light. The dual-use display panel and the transflective display panel perform display in a reflection mode using ambient light reflected by the reflective electrode and the transflective film, respectively, and are illuminated by a backlight that transmits through the transparent electrode and the transflective film. Display in the transmission mode is performed using light.

The photo sensor 20 is provided for detecting the intensity of ambient light entering the display panel 10 from the observer side. The photo sensor 20 is, for example, a photodiode.

As illustrated, in the configuration using the active matrix type display panel 10, the switching elements (for example, a glass substrate) on which the switching elements (here, TFTs) of the active matrix type display panel 10 are formed are provided with the switching elements. Can be formed using the same process as the process of forming the photo sensor 20. This eliminates the need to mount the photosensor 20 on the display panel later and to provide wiring for wiring, thereby reducing power consumption. In addition to the reduction, it is possible to suppress an increase in cost. Further, in the case where a photodiode is used as the photosensor 20, it is preferable to form a wiring functioning as a load (resistance) on the same substrate in order to convert a photoelectromotive force generated in the photodiode into a current.

The illuminating device 30 is, for example, a backlight or a front light, and each is composed of, for example, a fluorescent tube. The lighting device 30 is appropriately selected according to the type of the display panel 10.

The control circuit 40 is connected to the photosensor 20 and the illumination device 30. According to the intensity of the ambient light detected by the photosensor 20, the intensity of the illumination light is lower as the intensity of the ambient light is higher. The intensity of light emitted from the lighting device 30 is controlled based on a predetermined relationship. That is,
When the ambient light is strong, a sufficient display quality can be obtained even when the illumination light emitted from the illumination device 30 is weak, so that the control circuit 40 lowers the intensity of the emitted light from the illumination device 30. On the other hand, when the ambient light is weak, the control circuit 40 increases the intensity of light emitted from the lighting device 30 so that sufficient display quality can be obtained. As described above, by controlling the lighting device 30, in a variety of environments with different ambient light intensities, sufficient display quality is maintained, and power consumption is suppressed by eliminating unnecessary illumination light irradiation.

The relationship between the intensity of ambient light and the intensity of illumination light is
It is determined in advance based on the type and use of the display panel 10 and the like. This predetermined relationship is stored in a memory (not shown) of the control circuit 40 or the like.

The control of the lighting device 30 is performed, for example, as follows.

The photo sensor 20 outputs a first intensity signal ALS1 to the control circuit 40 according to the detected ambient light intensity. On the other hand, a predetermined output voltage Vout generated by the control circuit 40 is applied to the lighting device 30, and emits illumination light. When the intensity of the ambient light changes, the first intensity signal ALS1
Changes, the control circuit 40 generates an output voltage Vout corresponding to the changed value of the first intensity signal ALS1, and outputs the output voltage Vout to the lighting device 30. At this time, the first intensity signal ALS1
The relationship between and the output voltage Vout corresponding thereto is predetermined as described above, and is stored in a memory (not shown) of the control circuit 40 or the like. The control circuit 40 generates an output voltage Vout corresponding to a predetermined relationship and a value of the first intensity signal ALS1, for example, using an arithmetic circuit. Instead of using a calculation, a look-up table (LUT) indicating the relationship between the first intensity signal ALS1 and the corresponding output voltage Vout may be used.

The above control method realizes simple and sufficient control when the output voltage Vout input to the lighting device 30 and the emission light intensity of the lighting device 30 have a good correspondence (one-to-one correspondence). it can. However, the intensity of the emitted light from the illumination device 30 using the fluorescent tube changes under the influence of the surrounding temperature and the lighting time. That is, the same output voltage V
Even if out is input, the same output light intensity is not always obtained. In such a case, as shown in FIG.
A photo sensor 50 for detecting the intensity of the emitted light from the illumination device 30 and outputting a second intensity signal ALS2 corresponding to the detected intensity of the emitted light to the control circuit 40 is further provided.
S1, the second intensity signal ALS2, and the current output voltage Vo
It is preferable to generate a new output voltage Vout based on the output voltage Vout.

Referring to FIGS. 3A and 3B,
Dual-use LCD 300A and 300 of Embodiment of the Present Invention
The configuration and operation of B will be described.

The dual-purpose LCD 300A shown in FIG.
Has a dual-purpose liquid crystal display panel 10a, a photodiode 20a, a backlight 30a, and a control circuit 40a.

The dual-purpose liquid crystal display panel 10a of the dual-purpose LCD 300A has a reflection area (reflection electrode) for each picture element.
And a known active matrix type liquid crystal display panel having a transparent region (transparent electrode) (for example, see Japanese Patent Application Laid-Open No. H11-101992). Dual-use LCD300
A can perform display in the reflection mode using ambient light incident from the observer side, and can perform display in the transmission mode using illumination light from the backlight 30a. Of course, in an environment where the surroundings are bright, display can be performed only in the reflection mode without using the backlight 30a. The ratio of the area between the reflection area and the transmission area is determined by
It is set appropriately depending on the use of A.

The photodiode 20a is, for example, as shown in FIG.
As shown in (a), the TFT of the dual-purpose liquid crystal panel 10a is used.
The light receiving surface of the photodiode 20a, which is formed on the substrate 12, is naturally directed to the observer side (upper side in the drawing), like the reflective electrode (not shown) formed on the TFT substrate 12.

As shown in FIG. 4B, a photodiode 20a is composed of a lower electrode (for example, an Al layer) 22 / semiconductor laminated structure (for example, Si) 24 formed on a glass substrate 12a of the TFT substrate 12 in this order. / Upper layer electrode (for example, I
TO) 28. The semiconductor laminated structure 24 has a structure in which an n-type or p-type semiconductor layer 23 / intrinsic semiconductor layer 25 / n-type semiconductor layer 27 is laminated in this order. The photodiode 20a has a TFT on a glass substrate 12a.
Can be formed in a known manner in parallel with the process of forming the. A wiring functioning as a load 22 connected to the anode and the cathode of the photodiode 20a is also formed on the TFT substrate 12, and is formed by, for example, a process of forming a gate wiring and a source wiring (not shown).

The control circuit 40a includes an arithmetic circuit 42 and a PW
It has an M voltage generation circuit 44 and an inverter 46. The arithmetic circuit 42 includes, for example, a setting control signal CTL generated in response to a user input and the photodiode 20a.
Intensity signal AL indicating the intensity of ambient light output from
S1 and generates a control signal ICS based on a predetermined relationship. The relationship between the control signal ICS and the first intensity signal depends on the specifications of the dual-purpose LCD 300A,
An appropriate irradiation light intensity corresponding to the ambient light intensity is set, and this relationship is stored in a memory (not shown) in the arithmetic circuit 42, for example. Note that the setting control signal C
TL is an external signal for adjusting the relationship between the control signal ICS and the first intensity signal. Depending on the configuration of the arithmetic circuit, the setting control signal CTL can be omitted.

The PWM voltage generating circuit 44 includes a control signal IC
S is received, converted into a predetermined voltage by pulse width modulation of the standard voltage according to the control signal ICS, and output to the inverter 46. The inverter 46 converts the voltage received from the PWM voltage generation circuit 44 and outputs the converted voltage to the backlight 30a. In this way, the intensity of the emitted light from the backlight 30a is controlled to an appropriate intensity according to the intensity of the ambient light.

For example, as shown in FIG. 5A, the arithmetic circuit 42 includes an operational amplifier OP1 and a resistor R connected in parallel between the negative-phase input terminal and the output terminal of the operational amplifier OP1.
1 and a capacitor C1 connected in parallel with the resistor R1. The photodiode 20a generates a photovoltaic power corresponding to (typically proportional to) the intensity of ambient light,
A photocurrent IL flowing through the load 22 is generated. This photocurrent I
L is introduced into the opposite-phase input terminal of the operational amplifier OP1, and −I
The control voltage ISC represented by L × R1 is output to the PWM voltage generation circuit 44. The control voltage ISC is inversely proportional to the photocurrent IL.

The PWM voltage generating circuit 44 is provided, for example, in FIG.
As shown in (b), two operational amplifiers OPa and Oa
Pb and four resistors Ra, Rb, Rc and Rd. The resistor Ra is connected to the negative-phase input terminal of the operational amplifier OPb, and the resistor Rb is connected in parallel between the negative-phase input terminal and the output terminal of the operational amplifier OPb. The output terminal of the operational amplifier OPb is connected to the negative-phase input terminal of the operational amplifier OPa via the resistor Rc, the output terminal of the arithmetic circuit 42 is connected to the positive-phase input terminal of the operational amplifier OPa, and the control signal ICS Is supplied. Further, a resistor Rd is connected in parallel between the opposite-phase input terminal and the output terminal of the operational amplifier OPa.

The standard voltage Va is applied to the opposite-phase input terminal of the operational amplifier OPb via the resistor Ra.
b is − (Rb / Ra) · Va, and the voltage Vc at the output of the operational amplifier OPa is ｛(Rb
・ Rd / Ra ・ Rc) ・ Va + ICS (ICS = -I
L × R1). In this way, the PWM voltage generation circuit 44 outputs the voltage Vc that decreases as the photocurrent increases.

FIG. 6 shows an example of the relationship between the ambient light intensity and the appropriate irradiation light intensity in the dual-use LCD 300A. As shown in FIG. 6, when the intensity of the ambient light is low, the control circuit 40a of the dual-purpose LCD 300A increases the intensity of the light emitted from the backlight 30a to make a large contribution to the display in the transmission mode. Is high, the intensity of the light emitted from the backlight 30a is controlled so that the intensity of the light emitted from the backlight 30a is reduced and the contribution of the display in the reflection mode is increased. By performing the feedback control according to the ambient light intensity in this manner, excellent display quality can be displayed in an environment with different ambient light intensity, and unnecessary power is not emitted, thereby reducing power consumption. it can.

In the illustrated example, one photodiode 30a is used. However, a plurality of photodiodes may be provided in consideration of the distribution of the ambient light intensity. Also,
The relationship that forms the basis of the feedback control is not limited to the relationship in which the illumination light intensity decreases linearly above a certain ambient light intensity as shown in FIG. Various relationships can be set, such as a relationship where the strength decreases.

When the output voltage Vout input to the backlight 30a and the intensity of the emitted light from the backlight 30a have a good correspondence (one-to-one correspondence), simple and sufficient control can be performed by the above-described method. realizable. However, the emitted light intensity of the backlight 30a using the fluorescent tube changes under the influence of the surrounding temperature and the lighting time. That is, even if the same output voltage Vout is input, the same output light intensity is not always obtained. In such a case, as in a dual-purpose LCD 300B shown in FIG. 3B, the output light intensity of the backlight 30a is detected, and the second intensity signal ALS2 corresponding to the detected output light intensity is sent to the control circuit 40b.
It is preferable to further provide a photodiode 50a that outputs the image data to the pixel. The photodiode 50a outputs the second intensity signal ALS2 to the arithmetic circuit 42 of the control circuit 40b, and the arithmetic circuit 42 generates the second intensity signal ALS1 based on the first intensity signal ALS1, the second intensity signal ALS2, and the current control signal ICS. Thus, a new control signal ICS is generated. As described above, the display quality can be further improved by performing control using the photodiode 50a that monitors the intensity of the emitted light from the backlight 30a.

Next, the configuration and operation of the reflective LCD 400 according to the embodiment of the present invention will be described with reference to FIG.

The reflection type LCD 400 shown in FIG. 7 has a reflection type liquid crystal display panel 10b and a photodiode 20b.
, A front light 30b, and a control circuit 40b.

The reflective liquid crystal display panel 10b of the reflective LCD 400 is a known active matrix liquid crystal display panel having a reflective electrode for each picture element. The reflection type LCD 400 includes: an ambient light incident from an observer side;
The display in the reflection mode can be performed using the illumination light from the front light 30b. Of course, in an environment where the surroundings are bright, the display can be performed using only the ambient light without using the front light 30b.

In the reflection type LCD 400, similarly to the above-mentioned dual-use type LCD 300A, as shown in FIG.
When the intensity of the ambient light is low, the intensity of the light emitted from the backlight 30b is increased. When the intensity of the ambient light is strong, the intensity of the light emitted from the backlight 30b is decreased, so that good display quality can be maintained and power consumption is reduced. it can. As the control circuit 40b of the reflective LCD 400, a control circuit having substantially the same configuration and operating in the same manner as the control circuit 40a of the dual-purpose LCD 300A is used. Further, similarly to the dual-purpose LCD 300B, a photodiode that directly monitors the intensity of the emitted light of the front light 30b may be further provided, and a control circuit having substantially the same configuration and operating in the same manner as the control circuit 40b may be used.

Further, in place of the dual-purpose liquid crystal display panels 10a and 10b in the dual-purpose LCDs 300A and 300B shown in FIGS. 195
No. 01), it is possible to obtain a transflective LCD having the same effects as those of the dual-purpose LCDs 300A and 300B.

[0045]

The display device according to the present invention reduces the intensity of light emitted from the illuminating device when the intensity of ambient light is high, and increases the intensity of light emitted from the illuminating device when the intensity of ambient light is low. The display panel is irradiated with illumination light of a necessary intensity according to the brightness. Therefore, according to the present invention, a display device which can maintain a sufficient level of display quality under various environments with different ambient light intensities and consumes low power is provided.

Further, in a configuration using an active matrix type display panel, a photo sensor for detecting the intensity of ambient light is formed on a substrate on which the switching elements of the active matrix type display panel are formed, thereby reducing power consumption. The rise and the rise in cost can be suppressed. The present invention exerts the most excellent effects when applied to a transmission-reflection type active matrix type LCD.

[Brief description of the drawings]

FIG. 1 is a view schematically showing an LCD 100 according to an embodiment of the present invention.

FIG. 2 is a diagram schematically showing another LCD 200 according to an embodiment of the present invention.

FIGS. 3A and 3B are diagrams schematically showing dual-use LCDs 300A and 300B according to an embodiment of the present invention.

FIG. 4A is a diagram schematically illustrating a photodiode formed on a dual-purpose liquid crystal panel, and FIG. 4B is a diagram schematically illustrating a cross section of the photodiode.

FIG. 5A is a block diagram schematically illustrating an example of an arithmetic circuit, and FIG. 5B is a block diagram schematically illustrating an example of a PWM voltage generation circuit.

FIG. 6 is a graph showing an example of a relationship between ambient light intensity and illumination light intensity used for controlling the illumination device of the LCD according to the embodiment of the present invention.

FIG. 7 is a diagram schematically showing a reflective LCD 400 according to an embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 10 display panel 10a dual-use liquid crystal display panel 10b reflective liquid crystal display panel 20, 50 photosensor 20a, 20b, 50a photodiode 22 photodiode load (wiring) 30 lighting device 30a backlight 30b front light 40 control circuit 42 arithmetic circuit 44 PWM voltage generating circuit 46 Inverter 100, 200 Display device 300A, 300B Dual-use LCD 400 Reflective LCD

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) G09G 3/36 G02F 1/1335 530 F term (reference) 2H091 FA42Z FA45Z FA45Z GA13 LA18 2H093 NC28 NC34 NC42 NC49 NC50 NC55 NC56 ND05 ND09 ND39 NE06 5C006 AF69 BB11 BB28 BF25 BF38 EA01 FA21 FA47 5C080 AA10 BB05 DD04 DD26 JJ02 JJ03 JJ05 5G435 AA01 AA04 AA16 BB12 BB15 BB16 EE22 EE25 EE30

Claims (6)

[Claims] 1. A display panel capable of displaying at least ambient light, a photosensor for detecting the intensity of ambient light incident on the display panel from an observer side, and illumination light for display on the display panel. And a control circuit connected to the photosensor and the lighting device, wherein the control circuit controls the intensity of the ambient light in accordance with the intensity of the ambient light detected by the photosensor. A display device that controls the intensity of the emitted light of the illumination device based on a predetermined relationship that the intensity of the illumination light is lower as the intensity is higher. 2. The display panel according to claim 1, wherein the display panel is a reflective liquid crystal panel, and the lighting device is a front light.
The display device according to claim 1. 3. The display device according to claim 1, wherein the display panel is a transflective liquid crystal panel, and the lighting device is a backlight. 4. A backlight device, further comprising: a photo sensor for detecting an intensity of light emitted from the backlight, wherein the control circuit detects the intensity of the ambient light detected by the photo sensor, and the control circuit detects the intensity of the ambient light detected by the photo sensor. In order for the light intensity of the light to be a predetermined value,
The display device according to claim 3, wherein the display device controls an output light intensity of the illumination device. 5. The display panel according to claim 1, wherein the display panel is an active matrix type display panel including a switching element formed on a substrate, and the photosensor is formed on the substrate. The display device according to claim 1. 6. A wiring connecting the cathode and the anode of the photosensor is formed on the substrate, and the control circuit controls the intensity of the emitted light of the lighting device based on a value of a current flowing through the wiring. The display device according to claim 5, which performs the following.