JP2008158025A - Display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display device which can improve following capability in optical detection in a low-illuminance region. <P>SOLUTION: The display device includes an illumination unit which illuminates a display panel, an optical sensor which detects external light, an optical detecting unit having a capacitor which is charged with a predetermined reference voltage and has a drop of the charged voltage due to a leak current of the optical sensor, an optical sensor read unit which reads the charged voltage charged in the capacitor at a predetermined readout time after the starting point of charging to the capacitor, and a control unit which controls the illumination unit based upon the output value of the optical sensor read unit. Then a plurality of optical detecting units are provided and have starting points of charging to respective capacitors thereof made a predetermined time different, and the optical sensor read unit is so set that read times of the respective capacitors are equalized to one another. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a display device, and more particularly to a display device that can automatically control the brightness of a light source in accordance with the brightness of external light in a display device having a light source such as a backlight or a front light.

As a conventional display device, a TFT photosensor is provided on a substrate of a liquid crystal display panel, the ambient brightness is detected by detecting the light leakage current of the photosensor, and the backlight luminance is adjusted. (For example, refer to Patent Document 1).
In addition, in order to ensure highly accurate detection from low illuminance to high illuminance, there is known one provided with a plurality of light detection units having different spectral sensitivity characteristics (see, for example, Patent Document 2).
JP 2000-124484 A JP 2003-29239 A

By the way, a TFT light sensor has a so-called light leakage in which a slight dark current flows in the gate-off region when no light is applied, whereas a large leakage current flows according to the intensity (brightness) of the light when the light is applied. It has characteristics. And the TFT photosensor with such characteristics is
For example, it is used by being incorporated in a detection circuit as shown in FIG.
The sensing circuit, as shown in FIG. 14, the capacitor C is connected in parallel between the drain electrode D _L and the source electrode S _L of the TFT ambient light sensors, switches and the one terminal of the source electrode S _L and the capacitor C is connected to a reference voltage source via the element SW, further, the other terminal of the drain electrode D _L and the capacitor C of the TFT ambient light photosensor has a structure which is grounded.

The operation of the detection circuit, first, in advance by applying a constant reverse bias voltage (e.g. -10 V) to the gate electrode G _L of the TFT ambient light photosensor, and turns on the switch SW constant reference voltage Vs
(For example, + 2V) is applied to both ends of the capacitor C, and the switch element SW is turned off after a predetermined time. Thus, a source voltage that decreases with time, that is, a charging voltage, is obtained at both ends of the capacitor C according to the brightness around the TFT photosensor. Therefore, the brightness around the TFT photosensor can be detected by measuring the charging voltage across the capacitor C a predetermined time after the switch element SW is turned off.

However, in this detection circuit, the sensitivity of light detection depends on the brightness of the surroundings. FIGS. 15 and 16 show discharge curves (light leakage characteristics) during light irradiation showing the relationship between the charging voltage to the optical sensor and the readout time, that is, the detection time.
According to this light leakage characteristic, in a dark place, for example, a low illuminance region of 30 to 300 Lx,
As shown in FIG. 15, since the discharge amount of the capacitor is small, the difference in discharge voltage when a predetermined time elapses is extremely small, and it is extremely difficult to detect the voltage difference in this region. This problem can be improved by reducing the capacitor capacity and increasing the discharge speed. Then, the light leakage characteristics in a bright place, for example, a high illuminance region of 3000 to 10000 Lx are shown in FIG.
As shown in FIG. 3, the difference in discharge voltage at the time when the same time has passed as described above becomes extremely small, so that it becomes difficult to detect the voltage difference in this region.

Therefore, in such a detection circuit, the sensitivity in the dark place decreases when attempting to increase the sensitivity in the bright place, and conversely, the sensitivity in the bright place decreases when attempting to increase the sensitivity in the dark place. After all,
These are in a trade-off relationship, and the detection sensitivity is influenced by light and dark.
Therefore, from the relationship between ambient light and darkness and light leak, focusing on the phenomenon that the discharge speed due to light leak increases in the bright place, while the discharge speed due to light leak slows in the dark place. By changing the timing of reading detection, it is considered to perform light detection with high sensitivity without being influenced by light and dark.

However, in this case, the read detection timing in the low illuminance area is delayed with respect to the read detection timing in the high illuminance area, and light detection in the low illuminance area requires a certain amount of time. The followability of light detection when there is a change is poor.
Therefore, an object of the present invention is to provide a display device that can improve the follow-up performance of light detection in a low illuminance region.

In order to solve the above problem, a display device according to a first invention is a display device,
An illumination unit for illuminating the display panel;
A light detection unit having a light sensor for detecting outside light, and a capacitor that is charged with a predetermined reference voltage and that has a voltage that is charged down due to a leakage current of the light sensor;
An optical sensor reading unit that reads a charging voltage charged in the capacitor at a time when a predetermined reading time has elapsed from a charging start time to the capacitor;
A control unit for controlling the illumination unit based on an output value of the optical sensor reading unit;
With
A plurality of the light detection units are provided and the charging start time of each capacitor is different for each predetermined time,
The photosensor reading unit reads each charging voltage charged in each capacitor of the plurality of photodetecting units when an equal reading time elapses from the charging start time of each capacitor. .

This makes it possible to increase the number of detections within a certain period, in other words, to shorten the period of light detection, and to improve the followability to changes in the illuminance of external light, compared to the case where only one light detection unit is provided. Can be made. Therefore, for example, by providing a plurality of light detection units for detecting low illuminance having a relatively long reading time and shifting the charging timing of these light detection units by a predetermined time, the illuminance change of external light can be detected even in light detection in a low illuminance region. It is possible to appropriately control the illumination unit by improving the followability with respect to.

Further, according to a second aspect, in the first aspect, the number of the light detection units is N (N is an integer of 2 or more).
The charging start time of each of the plurality of light detection units is different by 1 / N period of one discharge period from the charging start time of the capacitor to the next charging start time. It is a feature.
Thereby, compared with the case where only one light detection part is provided, the frequency | count of detection within a fixed period can be doubled, and the period of light detection can be shortened to a half. Therefore, for example, by providing two light detection units for detecting low illuminance and shifting the charging timing of these two light detection units by 1/2 period of one discharge period, in the light detection in the low illuminance region, external light The followability with respect to the illuminance change can be reliably improved.

Further, in a third invention according to the first or second invention, the optical sensor reading unit sets the reading time to a time when a charging voltage read during light irradiation in a low illuminance region is equal to or lower than a dark reference value. It is characterized by that.
Thereby, a plurality of light detection units for detecting low illuminance can be provided, and in light detection in a low illuminance region, followability to changes in illuminance of external light can be improved.

In a fourth aspect based on the first or second aspect, the optical sensor reading unit calculates a charging voltage charged in the capacitor from a charging start time to the next charging start time to the capacitor. It is characterized by reading multiple times at different timings within one discharge period.
As a result, the light detection period in the low illuminance region can be shortened to improve the followability to the illuminance change of external light, and light detection in an arbitrary illuminance region can be performed.

Furthermore, in a fourth aspect based on the fourth aspect, the optical sensor reading unit, as the plurality of reading timings, is a timing at which a charging voltage read at the time of light irradiation at least in a low illuminance region is equal to or lower than a dark reference value. The charging voltage read at the time of light irradiation in a high illuminance region is set to a timing at which the charging reference value is equal to or higher than a bright reference value.
Thereby, it is possible to detect light with high sensitivity over a wide range from low illuminance to high illuminance.

According to a sixth invention, in the fourth or fifth invention, the optical sensor reading unit has a non-destructive reading unit that suppresses the influence of the charging voltage reading operation on the discharge characteristics of the capacitor. It is characterized by that.
Thus, as a non-destructive reading unit, for example, an amplifier having a high input impedance is provided between the light detection unit and the optical sensor reading unit so that almost no current flows from the optical sensor to the amplifier. The influence of the reading operation on the discharge curve of the capacitor can be reduced, and a highly accurate reading value can be obtained in a plurality of reading operations.

Further, according to a seventh invention, in any one of the first to sixth inventions, the photosensor reading unit includes a selection unit that selects an optimum voltage among the charging voltages read from the plurality of photodetecting units. And outputting based on the optimum voltage.
Accordingly, the illumination unit can be controlled based only on data for which accurate light detection can be performed, and more accurate control can be performed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of a liquid crystal display device 1 as a display device of the present embodiment.
Here, a transflective liquid crystal display device is illustrated as the liquid crystal display device 1. In addition, FIG.
It is sectional drawing cut | disconnected by X-X line.
As shown in FIGS. 1 and 2, the liquid crystal display device 1 is an active matrix substrate (hereinafter referred to as a TFT substrate) which is made of a transparent insulating material such as a glass substrate and has a thin film transistor (TFT) mounted on the surface thereof. ) 2 and a color filter substrate (hereinafter referred to as a CF substrate) 25 having a color filter or the like formed on the surface thereof, a liquid crystal layer 14 is formed. Among these, the TFT substrate 2 has a gate line 4 and a source line 5 formed in a matrix in the display area DA, and a pixel electrode 12 is formed in a portion surrounded by the gate line 4 and the source line 5.
And a TFT as a switching element connected to the pixel electrode 12 is formed at the intersection of the gate line 4 and the source line 5 (see FIGS. 3 and 4). Reference numeral LS denotes a light detection unit, which is provided at the outer peripheral edge in the display area DA as will be described later. These wires,
The TFT and the pixel electrode are schematically shown as the first structure 3 in FIG. 2, and a specific configuration is shown in FIGS. 3 and 4 and will be described later.

As shown in FIG. 1, the TFT substrate 2 is provided with a flexible wiring board FPC for connection to an image supply device (not shown) for driving the liquid crystal display device 1 on the short side portion, and through the flexible wiring board FPC. Data lines and control lines derived from the image supply device are connected to the driver IC. Then, signals such as a VCOM signal, a source signal, and a gate signal for driving the liquid crystal are generated in the driver IC and are respectively connected to the common line 1 on the TFT substrate 2.
1 is supplied to the source line 5 and the gate line 4.

A plurality of transfer electrodes 10 a to 10 d are provided at the four corners of the TFT substrate 2. These transfer electrodes 10a to 10d are directly connected to each other through a common line 11 or connected to each other in a driver IC. Each transfer electrode 10a-10d
Are electrically connected to a counter electrode 26 to be described later, and a counter electrode voltage output from the driver IC is applied to the counter electrode 26.

In the CF substrate 25, a color filter composed of a plurality of colors such as R (red), G (green), and B (blue) and a black matrix are formed on the surface of the glass substrate. This CF substrate 25 is made of T
The black matrix is disposed at a position corresponding to at least the gate line 4 and the source line 5 of the TFT substrate 2 while being opposed to the FT substrate 2, and a color filter is provided in a region partitioned by the black matrix. These color filters and the like are schematically shown as the second structure 27 in FIG. The CF substrate 25 is further provided with a counter electrode 26 made of a transparent electrode made of indium oxide, tin oxide or the like. The counter electrode 26 is formed over the entire display area DA. .

The sealing material 6 is applied around the display area DA of the TFT substrate 2 except for an injection port (not shown). Further, the contact material 10A for connecting both the substrates is made of, for example, conductive particles whose surfaces are plated with metal and a thermosetting resin. Then, the bonding of the TFT substrate 2 and the CF substrate 25 is performed according to the following procedure.
First, the TFT substrate 2 is set in the first dispenser device and the sealing material 6 is applied in a predetermined pattern, and then the TFT substrate 2 is set in the second dispenser device and the contact material 10 is applied.
A is applied on each of the transfer electrodes 10a to 10d. After that, the spacers 15 are uniformly distributed over the display area DA of the TFT substrate 2 and a temporary fixing adhesive is applied to the portion of the CF substrate 25 where the sealing material 6 and the contact material 10A come into contact. Thereafter, the TFT substrate 2 and the CF substrate 25 are bonded together, and the temporary fixing adhesive is cured to complete the temporary fixing. Then, when both the temporarily fixed substrates 2 and 25 are heat-treated, the thermosetting resin of the sealing material 6 and the contact material 10A is cured, and an empty liquid crystal display panel is completed. When the liquid crystal 14 is injected into the empty liquid crystal display panel from an injection port (not shown) and the injection port is closed with a sealing material, the transflective liquid crystal display device 1 is completed. Below the TFT substrate 2, a well-known light source (or illumination unit) (not shown),
A backlight or a sidelight having a light guide plate, a diffusion sheet and the like is disposed.

Next, a pixel configuration including a region surrounded by the gate line 4 and the source line 5 will be described with reference to FIGS. Here, FIG. 3 is a plan view of one pixel shown through the CF substrate of the liquid crystal display device, and FIG. 4 is a cross-sectional view taken along the line AA of FIG.
The TFT substrate 2 has a plurality of gate lines 4 made of a metal such as aluminum or molybdenum formed in parallel at substantially equal intervals on the display area DA. In addition, an auxiliary capacitance line 16 is formed in parallel with the gate line 4 at the approximate center between the adjacent gate lines 4, and a gate electrode G of the TFT extends from the gate line 4. Further, on the TFT substrate 2, a gate line 4 and an auxiliary capacitance line 1 are provided.
6 and a gate insulating film 17 made of silicon nitride, silicon oxide or the like is laminated so as to cover the gate electrode G.

A semiconductor layer 19 made of amorphous silicon, polycrystalline silicon, or the like is formed on the gate electrode G via a gate insulating film 17, and a metal such as aluminum or molybdenum is formed on the gate insulator 17. A plurality of source lines 5 are formed so as to be orthogonal to the gate lines 4, and the source electrode S of the TFT is extended from the source line 5, and the source electrode S is in contact with the semiconductor layer 19. Furthermore, a drain electrode D, which is formed of the same material as the source line 5 and the source electrode S and is formed at the same time, is provided on the gate insulating film 17, and the drain electrode D is also in contact with the semiconductor layer 19.

As described above, the TFT includes the gate electrode G, the gate insulating film 17, the semiconductor layer 19, the source electrode S, and the drain electrode D. This TFT is formed in each pixel.
In this configuration, the drain electrode D and the auxiliary capacitance line 16 form an auxiliary capacitance of each pixel. Further, a protective insulating film 18 made of, for example, an inorganic insulating material is laminated so as to cover the source line 5, the TFT, and the gate insulating film 17.
An interlayer film 20 made of an organic insulating film is laminated thereon. On the surface of the interlayer film 20, fine uneven portions are formed in the reflection portion R, and the transmission portion T is flat. In FIG. 4, the uneven portion of the interlayer film 20 in the reflection portion R is omitted.

A contact hole 13 is formed in the protective insulating film 18 and the interlayer film 20 at a position corresponding to the drain electrode D of the TFT. Further, in each pixel, a reflective electrode R ₀ made of, for example, aluminum metal is provided in the reflective portion R on the contact hole 13 and a part of the surface of the interlayer film 20, and the surface of the reflective electrode R ₀ and the transmissive portion are provided. A pixel electrode 12 made of, for example, ITO is formed on the surface of the interlayer 20 at T.

Next, the structure of the light detection unit LS will be described.
FIG. 5 is a cross-sectional view of an optical sensor and a switch element constituting the optical detection unit LS.
As shown in FIG. 5, the TFT photosensor and the switch element SW constituting the photodetecting unit LS are as follows.
Both are made of TFT and formed on the TFT substrate 2. That is, the TFT substrate 2 is
The gate electrode G _L of the TFT photosensor, one terminal C ₁ of the capacitor C, and the gate electrode G _S constituting one switch element SW are formed on the surface, and silicon nitride or silicon oxide is formed so as to cover these surfaces. A gate insulating film 17 made of, for example, is laminated.

Further, on the gate electrode G _S and on the TFT constituting the switching element SW of the gate electrode G _L of the TFT ambient light photosensor, and the like amorphous silicon and polycrystalline silicon through the respective gate insulating film 17 the semiconductor Layers 19 _L and 19 _S are formed.
Further, on the gate insulator 17, the source electrode S _L and the drain electrode D _{L of} the TFT photosensor made of a metal such as aluminum or molybdenum, and the TFT constituting one switch element SW
The source electrode S _S and the drain electrode D _S are provided in contact with the respective semiconductor layers 19 _L and 19 _S.

Among these, the source electrode S _L of the TFT photosensor and the drain electrode D _S of the TFT constituting the switch element SW are extended and connected to each other to form the other terminal C ₂ of the capacitor C. Further, a protective insulating film 18 made of, for example, an inorganic insulating material is laminated so as to cover the surface of the TFT photosensor, the capacitor C, and the switch element SW made of TFT, and the surface of the switch element SW made of TFT. Is covered with a black matrix 21 so as not to be affected by external light.

Further, on the opposite CF substrate 25 on which the light detection unit LS is disposed, as shown in FIG. 2, a counter electrode 26 is extended to a position facing the light detection unit LS. TFT light drain electrode D _L and the other terminal C ₂ of the ground terminal GR side of the capacitor C of the sensor arrangement is connected via a transfer electrode 10b to the counter electrode 26.
Light detecting section LS of this structure, as shown in FIG. 6, the capacitor C is connected in parallel between the drain electrode D _L and the source electrode S _L of the TFT ambient light photosensor, one of a source electrode S _L and the capacitor C and the terminal connected to the reference voltage source via a switch element SW, further, a configuration in which the other terminal of the drain electrode D _L and the capacitor C of the TFT ambient light sensor is connected to the counter electrode (VCOM).

With such a configuration, when the switch element SW is turned on every predetermined period, a predetermined reference voltage Vs (for example, +2 V) is applied to the capacitor C from the reference voltage source and charged.
By this charging, both ends of the capacitor C are charged with a potential difference between the reference voltage Vs and the counter electrode voltage VCOM. However, the gate electrode G _L is charged with the gate voltage GV having the opposite polarity, and thus the gate is turned off. When the switch element SW is turned off, the charging voltage is reduced by a leakage current generated by irradiating the TFT photosensor with light.

Then, after a predetermined reading time from the charging timing of the capacitor C, the capacitor C
The voltage charged in the battery is read (detected), and the backlight and the like can be controlled by this detection output.
Here, in the present embodiment, a plurality of light detection units LS having the same configuration as the light detection unit LS shown in FIG.
1 to LS3 are provided. In the following description, each light detection unit LS
A switch element (corresponding to SW in FIG. 6) provided in n (n = 1, 2, 3,...) is referred to as SWn, and a capacitor (corresponding to C in FIG. 6) is referred to as Cn.

FIG. 7 is a block diagram showing a detailed configuration of the backlight control circuit. In addition, FIG.
It is a timing chart at the time of low illumination intensity irradiation.
As shown in FIG. 7, the backlight control circuit includes two light detection units LS for detecting low illuminance.
A reading unit 3 that acquires a plurality of analog information obtained from 1 and LS2 and one light detection unit LS3 for detecting high illuminance, and selects and outputs an optimum value among these reading values
1 and a comparison unit 32 that compares an output value of the reading unit 31 with a predetermined reference value to be described later, and a B / L control unit 33 that controls the backlight 34 based on the result of the comparison unit 32. Yes.

The reading unit 31 turns on / off the switch elements SW1 to SW3 of the light detection units LS1 to LS3.
Off control is performed to charge the capacitors C1 to C3 of the light detection units LS1 to LS3.
At this time, as shown in FIG. 8, the charging timing of the light detection units LS1 and LS2 is shifted by a predetermined time (in this case, 1/2 of one discharge period (1F _L ) of the light detection units LS1 and LS2). Shall. Further, the charging timing of the light detection unit LS3 is equal to the charging timing of the light detection units LS1 and LS2, and its one discharge period (1F _H ) is half of one discharge period (1F _L ) of the light detection units LS1 and LS2. It has become. Here, one discharge period is a period from the start of charging the capacitor Cn to the next start of charging, and in the present embodiment, for example, _FL = 0.
05 [s], F _H = 0.025 [s].

Further, the reading unit 31 switches the switch SW _{LS in} FIG. 7 to alternately read the charging voltage charged in the capacitor C1 or C2 of the light detection unit LS1 or LS2 at every predetermined timing. At this timing, the charging voltage charged in the capacitor C3 of the light detection unit LS3 is read.
At this time, with respect to the light detection units LS1 and LS2, the charging voltage is read when a relatively long read time T _L (for example, 0.03 s) has elapsed from the start of charging, and the light detection unit LS.
3 is a relatively short reading time T _H (for example, 0.005 s) from the start of charging.
The charging voltage shall be read when elapses.

Of the plurality of reading values acquired in this way, a condition that is not less than an optimum value, for example, a first reference value (corresponding to a bright reference value) and not more than a second reference value (corresponding to a dark reference value) in a selection unit (not shown). A read value that satisfies the above is selected and output to the comparison unit 32. Here, the first reference value is set to 10% of the charging voltage, for example, and the second reference value is set to 90% of the charging voltage, for example.
The comparison unit 32 A / D converts the analog information input from the reading unit 31 into illuminance data, compares this with a predetermined illuminance threshold value, and outputs the result to the B / L control unit 33. Here, the illuminance threshold is set to such a value that it can be determined whether or not the illuminance of outside light is the illuminance at which the backlight 34 should be turned on (or turned off).

The B / L control unit 33 determines whether the backlight 34 should be turned on (or turned off) based on the comparison result in the comparison unit 32. Specifically, the illuminance data is smaller than the illuminance threshold (
If it is bright, the backlight 34 is turned off. If the illuminance data is larger (darker) than the illuminance threshold, it is determined that the backlight 34 should be turned on. Then, on / off control of the backlight 34 is performed based on the determination result.

In FIG. 7, the reading unit 31 corresponds to the optical sensor reading unit, and the comparison unit 32 and B / L
The control unit 33 corresponds to the control unit, and the backlight 34 corresponds to the illumination unit.
Next, the operation of the first embodiment of the present invention will be described.
Now, it is assumed that external light with low illuminance (for example, 100 Lx) is applied to the TFT optical sensor. At this time, at time t1 in FIG. 8, the reading unit 31 turns on the switch elements SW2 and SW3 of the light detection units LS2 and LS3, and charges the capacitors C2 and C3 of the light detection units LS2 and LS3 with the reference voltage Vs, respectively. . After that, the reading unit 31 switches the switch elements SW2 and SW3 to the off state, and the charging voltages charged in the capacitors C2 and C3 are the same due to the leakage current generated when the TFT light sensor is irradiated with the external light. Reduced by discharge characteristics.

At this time, assuming that the relationship between the charging voltage of each of the capacitors C1 to C3 and the reading time (detection time) is as shown in FIG. 9, the discharge characteristics when 100 Lx low-light external light is irradiated. Is a curve indicated by α in FIG.
Thereafter, the reading unit 31 reads the charging voltage of the capacitor C3 at a time t2 after the reading time T _H (for example, 0.005 s) has elapsed from the start of charging the capacitor C3. At this time, as indicated by α in FIG. 9, the light leakage current of the TFT photosensor is small and the voltage drop amount is extremely small. The charging voltage of the capacitor C3 is greater than the second reference value, greater than the first reference value and second
Since the condition below the reference value is not satisfied, the reading unit 31 does not adopt this read value as an output of light detection.

Then, a 1/2 discharge period (for example, 0. 0) from the start of charging of the capacitor C2 (time t2).
At time t3 after elapse of 025s), the reading unit 31 turns on the switch elements SW1 and SW3 of the light detection units LS1 and LS3, and charges the capacitors C1 and C3 of the light detection units LS1 and LS3 with the reference voltage Vs, respectively. Then, after that, the reading unit 31 switches the switch elements SW1 and SW3 to the off state, and the charging voltages charged in the capacitors C1 and C3 by the leakage current generated by irradiating the TFT light sensor with the external light are respectively described above. The discharge characteristics deteriorate. Further, the capacitor C2 continues to discharge.

Thereafter, the reading unit 31 reads the charging voltage of the capacitor C2 at time t4 after the reading time T _L (for example, 0.03 s) has elapsed since the charging of the capacitor C2 was opened (time t2). At this time, as indicated by α in FIG. 9, the charging voltage of the capacitor C2 is a value that satisfies the condition that is not less than the first reference value and not more than the second reference value. On the other hand, the charging voltage of the capacitor C3 read at the time t4 is not within the reference range. Therefore, the reading unit 31 adopts a reading value from the light detection unit LS2 within the reference range and outputs this to the comparison unit 32.

In the comparison unit 32, the analog information input from the reading unit 31 is A / D converted into illuminance data, and this is compared with the illuminance threshold value. Here, since the external light applied to the TFT optical sensor is low illuminance light, the B / L control unit determines that the illuminance data is larger than the illuminance threshold and the backlight 34 should be turned on. At 33, the backlight 34 is turned on.

Further, at time t5, the capacitors C2 and C3 of the light detection units LS2 and LS3 are charged with the reference voltage Vs, respectively, and then the capacitors C2 and C3 are caused by the leakage current generated when the TFT light sensor is irradiated with the external light. The charging voltage charged in the above decreases with the above-described discharge characteristics. Further, the capacitor C1 continues to discharge.
Thereafter, the reading unit 31 reads the charging voltage of the capacitor C1 at the time t6 after the elapse of the reading time _TL from the start of charging the capacitor C1 (time t3). At this time, the charging voltage of the capacitor C1 is within the reference range, while the charging voltage of the capacitor C3 is not within the reference value range. Therefore, the reading unit 31 adopts a reading value from the light detection unit LS1 within the reference range, and the backlight 34 is controlled to be turned on based on the reading value.

As described above, the two light detection units LS1 and LS2 for detecting the low illuminance are provided, and the timing of charging the capacitors C1 and C2 is shifted so that the light detection unit for detecting the low illuminance is 1
Compared to the case where only one is provided, the number of times of detection of low illuminance within a certain period can be increased (doubled). As a result, the light detection sampling period can be made equal between the light detection unit for detecting low illuminance and the light detection unit for detecting high illuminance.

On the other hand, assuming that outside light of medium to high illuminance (for example, 1000 Lx) is irradiated on the TFT optical sensor, the reading unit 31 switches the switch elements SW2 and SW3 of the light detection units LS2 and LS3 at time t11 in FIG. Is turned on, and the capacitors C of the light detection units LS2 and LS3
2 and C3 are charged with the reference voltage Vs, respectively. After that, the reading unit 31 switches the switch elements SW2 and SW3 to the off state, and the charging voltages charged in the capacitors C2 and C3 are the same due to the leakage current generated when the TFT light sensor is irradiated with the external light. Reduced by discharge characteristics.

At this time, the discharge characteristic when 1000 Lx medium to high illuminance external light is irradiated is β in FIG.
It becomes the curve shown in.
Thereafter, the reading unit 31 reads the charging voltage of the capacitor C1 and the capacitor C3 at time t12 after the elapse of the reading time T _H (for example, 0.005 s) from the start of charging the capacitor C3. At this time, as indicated by β in FIG. 9, the charging voltage of the capacitor C3 is within the reference range. At this time, the charging voltage of the capacitor C1 is equal to the reading time T _L (eg, 0.03 s from the start of charging). ) Since the charging voltage value after the lapse is smaller than the first reference value and not within the reference range, the reading unit 31 adopts the reading value from the light detection unit LS3 as the light detection output. This is output to the comparison unit 32.

In the comparison unit 32, the analog information input from the reading unit 31 is A / D converted into illuminance data, and this is compared with the illuminance threshold value. Here, since the external light applied to the TFT optical sensor is medium to high illuminance light, it is determined that the illuminance data is smaller than the illuminance threshold and the backlight 34 should be turned off. The controller 33 controls the backlight 34 to be turned off.

Thus, in the case of light detection in a high illuminance region, light detection is performed at a relatively early reading timing of the light detection unit LS3.
By the way, the timing of reading detection in the low illuminance region in order to provide one light detection unit for low illuminance detection and one light detection unit for high illuminance detection and perform high-sensitivity light detection without being influenced by light and darkness. Is delayed with respect to the timing of reading detection in the high illuminance area, a certain amount of time is required for light detection in the low illuminance area, so that the followability of light detection when there is an illuminance change in the low illuminance area is poor.

For example, when the liquid crystal display device is applied to a mobile phone, it is desirable to operate the optical sensor at a cycle of one frame period (generally about 60 Hz, 0.017 s) in the liquid crystal panel display of the mobile phone.
In the case of light detection in a high illuminance region (for example, 1000 Lx), the charging voltage value is compared within the above one frame period after the start of charging the capacitor of the light detection unit, as indicated by β in FIG. Since it falls to the reference range at an early stage, light detection can be performed in a short time and the followability is good.

However, in the case of light detection in a low illuminance region (for example, 30 Lx), the charge voltage value gradually decreases after the start of charging the capacitor of the light detection unit, as indicated by γ in FIG. , It takes a relatively long time for the charging voltage value to fall within the above reference range,
It is difficult to perform light detection at the timing of each frame period.
In contrast, in the present embodiment, the light detection period in the low illuminance area can be accelerated to the same period as the light detection period in the high illuminance area. It is possible to appropriately follow the light detection and follow the backlight control.

As described above, in the first embodiment, a plurality of light detection units are provided, the charging start time of each of the plurality of light detection units is shifted by a predetermined time, and the reading time for each capacitor of each light detection unit is shifted. As compared with the case where only one light detection unit is provided, the number of times of detection within a certain period can be increased, in other words, the period of light detection can be shortened,
The followability to the illuminance change of outside light can be improved.

Also, at this time, two photodetecting units are provided, and the charging start time of each photodetecting unit to each capacitor is shifted by one half of one discharge period, so that only one photodetecting unit is provided. As compared with, the number of detections within a certain period can be doubled and the light detection cycle can be reduced to half.
Furthermore, since the reading time of the plurality of light detection units is set to a time when the charging voltage read at the time of light irradiation in the low illuminance region is equal to or lower than the dark reference value, a plurality of light detection units for low illuminance detection are provided. In the light detection in the low illuminance region, it is possible to improve the followability to the illuminance change of the external light.

In addition to a plurality of light detection units for detecting low illuminance, a light detection unit for high illuminance detection, which has a relatively fast reading time, can be used to detect light over a wide range from low to high illuminance. It becomes. At this time, the light detection period in the low illuminance area can be accelerated to a period substantially equal to the light detection period in the high illuminance area. The sex can be made approximately equal.

Furthermore, the optical sensor reading unit selects the optimum voltage from among the charging voltages read from the plurality of light detection units, and performs output based on the optimum voltage, so that only data that can be accurately detected can be obtained. Based on this, the illumination unit can be controlled, and more accurate control can be performed.
In the first embodiment, the case where two light detection units for detecting low illuminance are described, but three or more light detection units may be provided. Thereby, since the period of light detection in a lower illuminance region can be shortened, the followability to the illuminance change can be further improved.

Next, a second embodiment of the present invention will be described.
In the second embodiment, a plurality of light detection units are provided, the charging timing of each light detection unit is shifted by a predetermined time, and the charge voltage is read a plurality of times within one discharge period in each light detection unit. is there.
FIG. 11 is a block diagram illustrating a detailed configuration of the backlight control circuit according to the second embodiment. FIG. 12 is a timing chart at the time of low illumination irradiation.

As shown in FIG. 11, the light detection units LS1 to LS3 in the first embodiment shown in FIG.
Instead of the two light detection units LS4 and Ls having the same configuration as the light detection unit LS shown in FIG.
S5 is provided, and the reading unit 31 is replaced with a reading unit 35 that reads a charge voltage value from the light detection units LS4 and LS5 at a predetermined timing, and an amplifier 36 having a high input impedance is provided in front of the reading unit 35. Since the configuration is the same as that shown in FIG.

The reading unit 35 performs on / off control of the switch elements SW4 and SW5 of the light detection units LS4 and LS5, and charges the capacitors C4 and C5 of the light detection units LS4 and LS5. At this time, the charging timing of the light detection units LS4 and LS5 is as shown in FIG.
It is assumed that there is a shift of a predetermined time (here, 1/2 of one discharge period (1F _L ) of the light detection units LS4 and LS5).

Further, the reading unit 35 performs switching of the switch SW _{LS in} FIG. 11 so that the charging voltage charged in the capacitor C4 or C5 of the light detection unit LS4 or LS5 at every predetermined timing is within one discharge period. Read twice.
Then, an optimum value, for example, a read value that satisfies the condition that is equal to or higher than the first reference value and equal to or lower than the second reference value is adopted from the plurality of read values acquired in this manner, and is output to the comparison unit 32.

In FIG. 11, the reading unit 35 and the amplifier 36 correspond to the optical sensor reading unit, and the amplifier 36 corresponds to the non-destructive reading unit.
Next, the operation of the second embodiment of the present invention will be described.
Now, it is assumed that external light with low illuminance (for example, 100 Lx) is applied to the TFT optical sensor. At this time, at time t21 in FIG. 12, the reading unit 35 turns on the switch element SW4 of the light detection unit LS4 and charges the capacitor C4 of the light detection unit LS4 with the reference voltage Vs. After that, the reading unit 35 switches the switch element SW4 to the OFF state, and the charging voltage charged in the capacitor C4 is lowered with a predetermined discharge characteristic due to the leakage current generated when the TFT light sensor is irradiated with the external light. To do.

At this time, assuming that the relationship between the charging voltages of the capacitors C4 and C5 and the reading time (detection time) is as shown in FIG. 9, the discharge characteristics when 100 Lx of low-light external light is irradiated are as follows. 9 is a curve indicated by α in FIG.
Thereafter, the reading unit 35 reads the charging voltage of the capacitor C4 at the time t22 after the reading time T _H (for example, 0.005 s) has elapsed since the start of charging the capacitor C4. At this time, as indicated by α in FIG. 9, the light leakage current of the TFT photosensor is small and the voltage drop amount is extremely small. Since the charging voltage of the capacitor C4 is larger than the second reference value and not within the reference range, the reading unit 35 does not adopt the read value as an output of light detection.

At time t23, the reading unit 35 turns on the switch element SW5 of the light detection unit LS5 and charges the capacitor C5 of the light detection unit LS5 with the reference voltage Vs. After that, the reading unit 35 switches the switch element SW5 to the OFF state, and the charging voltage charged in the capacitor C5 is reduced by the above-described discharge characteristics due to the leakage current generated when the TFT light sensor is irradiated with the external light. To do. Further, the capacitor C4 continues to discharge.

Thereafter, the reading unit 35 reads the charging voltage of the capacitor C4 at a time t24 after the reading time T _L (for example, 0.03 s) has elapsed from the start of charging the capacitor C4. At this time, as indicated by α in FIG. 9, since the charging voltage of the capacitor C4 is within the reference range, the reading unit 35 employs this read value as an output of light detection.
Since the external light applied to the TFT light sensor is light with low illuminance, and the illuminance data obtained based on the reading value adopted by the reading unit 35 is larger than the illuminance threshold, the comparison unit 3
2, it is determined that the backlight 34 should be turned on, and the B / L control unit 33 performs on-control of the backlight 34.

Thus, two detections are performed at different timings within one discharge period from the start of charging of the light detection unit LS4 to the capacitor C4 until the next charging is performed. At this time, an amplifier 36 having a high input impedance is provided in front of the reading unit 35 so that almost no current flows from the light detection unit LS4 to the amplifier 36. Therefore, the reading operation in the reading unit 35 is a discharge curve of the capacitor C4. Has little effect on Therefore, even if the reading operation is performed a plurality of times within one discharge period, it is possible to obtain a highly accurate reading value.

Then, the reading unit 35 at time t25 after the read time T _H elapses from the start of charging of the capacitor C5 at time t23, but reading the charge voltage of the capacitor C5, the charging voltage value at this time is not within the reference range Therefore, this reading value is not adopted as the output of light detection.
On the other hand, the charging voltage value of the capacitor C5 read at time t27 after the reading time _{TL has} elapsed from the start of charging of the capacitor C5 at time t23 is within the reference range. The reading value is adopted as the output of light detection.

As described above, in the light detection in the low illuminance region, the second reading value from each light detection unit is adopted as the light detection output. And the period of the light detection will be greatly shortened compared with the case where only one light detection part is provided, and the number of times of low illuminance detection within a certain period is increased in a pseudo manner (doubled). )be able to.
On the other hand, assuming that the TFT light sensor is irradiated with medium to high illuminance (for example, 1000 Lx), the reading unit 35 turns on the switch element SW4 of the light detection unit LS4 at time t31 in FIG. The capacitor C4 of the light detection unit LS4 is charged with the reference voltage Vs. After that, the reading unit 35 switches the switch element SW4 to the OFF state, and the charging voltage charged in the capacitor C4 is lowered with a predetermined discharge characteristic due to the leakage current generated when the TFT light sensor is irradiated with the external light. To do.

At this time, the discharge characteristic when 1000 Lx medium to high illuminance external light is irradiated is β in FIG.
It becomes the curve shown in.
Thereafter, the reading unit 35 reads the charging voltage of the capacitor C4 at time t32 after the reading time T _{H has} elapsed from the start of charging the capacitor C4. At this time, as indicated by β in FIG. 9, since the charging voltage of the capacitor C4 is within the reference range, the reading unit 35 employs this read value as an output of light detection.

The external light applied to the TFT optical sensor is light of medium to high illuminance, and the illuminance data obtained based on the reading value adopted by the reading unit 35 is smaller than the illuminance threshold. It is determined that the backlight 34 should be turned off, and the backlight 34 is turned off by the B / L control unit 33.
At time t33, the reading unit 35 turns on the switch element SW5 of the light detection unit LS5, and charges the capacitor C5 of the light detection unit LS5 with the reference voltage Vs. After that, the reading unit 35 switches the switch element SW5 to the OFF state, and the charging voltage charged in the capacitor C5 is reduced by the above-described discharge characteristics due to the leakage current generated when the TFT light sensor is irradiated with the external light. To do. Further, the capacitor C4 continues to discharge.

Thereafter, the reading unit 35 reads the charging voltage of the capacitor C4 at time t34 after the reading time _{TL has} elapsed from the start of charging the capacitor C4. At this time, as indicated by β in FIG. 9, the charging voltage of the capacitor C4 is substantially zero, and is smaller than the first reference value. Therefore, the reading unit 35 adopts this read value as an output of light detection. Never do.
Then, the reading unit 35 at time t35 after the read time T _H elapses from the start of charging to the capacitor C5 at time t33, reads the charging voltage of the capacitor C5, to adopt this reading as an output of the optical detection.

On the other hand, since the charging voltage value of the capacitor C5 read at time t37 after the elapse of the reading time _TL from the start of charging of the capacitor C5 at time t33 is substantially zero, the reading unit 35 is at the time t37. The reading value is not used as the light detection output.
Thus, in the light detection in the high illuminance region, the first reading value from each light detection unit is adopted as the output of the light detection.

That is, the first reading is for light detection in a high illuminance region with a fast discharge time, and the second reading is for light detection in a low illuminance region with a slow discharge time. In this way, light detection over a wide range from low illuminance to high illuminance is possible.
Thus, in the second embodiment, the charging voltage charged in each capacitor is set to 1
Since it is read multiple times at different timings within the discharge period, the light detection cycle in the low illuminance area can be shortened to improve the followability to changes in the illuminance of external light, and light detection in any illuminance area is possible It becomes.

In addition, as a plurality of reading timings within one discharge period, at least the charging voltage read during light irradiation in the low illuminance region is equal to or lower than the dark reference value, and the charging voltage read during light irradiation in the high illuminance region is the bright reference value. Since the above timing is set, it is possible to detect light with high sensitivity over a wide range from low illuminance to high illuminance.
In addition, since an amplifier with high input impedance is provided in front of the optical sensor reading unit,
Almost no current flows from the optical sensor to the amplifier to reduce the influence of the charging voltage reading operation on the discharge curve of the capacitor.
A highly accurate reading can be obtained.

In the second embodiment, the case where two light detection units are provided has been described. However, three or more light detection units may be provided. Thereby, since the period of light detection can be shortened, the followability to illuminance change can be improved over a wide range from low illuminance to high illuminance.
In the second embodiment, the case where the charge voltage is read twice in one discharge period has been described. However, the charge voltage can be read three times or more. Thereby, highly sensitive light detection can be performed over a wide range in the low illuminance to high illuminance region.

In each of the above embodiments, the backlight is turned on / off at a predetermined brightness.
Although the case of performing the off control has been described, it is also possible to change the brightness when the backlight is turned on and the brightness when the backlight is turned off (having hysteresis characteristics).
In each of the above embodiments, the case where the present invention is applied to a transflective liquid crystal display device has been described. However, the present invention can also be applied to a transmissive liquid crystal display device and a reflective liquid crystal display device. In this case, a transmissive liquid crystal display device can be obtained by omitting the reflective electrode R ₀ , and a reflective liquid crystal display device can be obtained by providing the reflective electrode over the entire lower part of the pixel electrode 12. In addition,
In the case of a reflective liquid crystal display device, a front light may be used instead of the backlight or side light.

Further, in each of the embodiments described above, the case where a TFT photosensor is applied as the photosensor has been described. However, any photo-electricity such as a well-known photodiode, phototransistor, photoTFT, photoSCR, photoconductor, photocell, or the like can be used. A conversion element can be applied.

1 is a plan view schematically showing a display panel seen through a color filter substrate of a liquid crystal display device according to an embodiment of the present invention. It is XX sectional drawing of FIG. It is a top view for 1 pixel, seeing through CF substrate of a liquid crystal display device. It is AA sectional drawing of FIG. It is sectional drawing of the photosensor and switch element on a TFT substrate. It is a circuit diagram of a photon detection part. It is a block diagram which shows the detailed structure of backlight control. It is a timing chart at the time of low illumination intensity irradiation. It is a curve figure which shows the discharge characteristic of light irradiation. It is a timing chart at the time of high illumination intensity irradiation. It is a block diagram which shows the detailed structure of the backlight control in 2nd Embodiment. It is a timing chart at the time of low illumination intensity irradiation. It is a timing chart at the time of high illumination intensity irradiation. It is a circuit diagram which shows the structure of the conventional detection circuit. It is a figure which shows a light leak characteristic. It is a figure which shows a light leak characteristic.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display device, 2 ... TFT substrate, 4 ... Gate line, 5 ... Source line, 11 ... Common line,
DESCRIPTION OF SYMBOLS 12 ... Pixel electrode, 25 ... CF board | substrate, 26 ... Counter electrode, 31, 35 ... Reading part, 32 ... Comparison part, 33 ... B / L control part, 35 ... Back light, LS1-LS5 ... Light detection part, SW1-
SW5: Switch element, C1 to C5: Capacitor, Vs: Reference voltage

Claims (7)

In the display device,
An illumination unit for illuminating the display panel;
A light detection unit having a light sensor for detecting outside light, and a capacitor that is charged with a predetermined reference voltage and that has a voltage that is charged down due to a leakage current of the light sensor;
An optical sensor reading unit that reads a charging voltage charged in the capacitor at a time when a predetermined reading time has elapsed from a charging start time to the capacitor;
A control unit for controlling the illumination unit based on an output value of the optical sensor reading unit;
With
A plurality of the light detection units are provided and the charging start time of each capacitor is different for each predetermined time,
The optical sensor reading unit reads each charging voltage charged in each capacitor of the plurality of light detecting units at a time when an equal reading time has elapsed from a charging start time of each capacitor. Display device. N light detection units (N is an integer of 2 or more) are provided, and the charging start time of each of the plurality of light detection units from the charging start time to the next charging start time to the capacitor The display device according to claim 1, wherein each of the discharge periods is different by 1 / N period. 3. The display according to claim 1, wherein the optical sensor reading unit sets the reading time to a time when a charging voltage read during light irradiation in a low illuminance region is equal to or lower than a dark reference value. apparatus. The optical sensor reading unit reads the charging voltage charged in the capacitor a plurality of times at different timings within one discharge period from the charging start time to the next charging start time of the capacitor. Item 3. The display device according to Item 1 or 2. The optical sensor reading unit, as the plurality of reading timing, at least a charging voltage read at the time of light irradiation in the low illuminance area is equal to or less than a dark reference value, and a charging voltage read at the time of light irradiation of the high illuminance area is a bright reference The display device according to claim 4, wherein a timing at which the value becomes equal to or greater than a value is set. The said optical sensor reading part has a nondestructive type reading part which suppresses the influence on the discharge characteristic of the said capacitor which the reading operation of the said charging voltage gives.
The display device described in 1. The said optical sensor reading part has a selection part which selects the optimal voltage among each charging voltage read from these light detection parts, and performs the output based on the said optimal voltage. The display device according to any one of the above.

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