JP2007065004A - Illuminance detecting method, luminance control method, electro-optical device, and electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately detect external light, without having to perform adjustment operations. <P>SOLUTION: An electro-optical device is equipped with a display unit, a first sensor 2 which detects illuminance of reference light, a second sensor 4 which detects the illuminance of ambient light of the display unit, and a comparing means 5 of comparing the output of the first sensor and the output of the second sensor with each other, to find the illuminance of the external light relative to the illuminance of the reference light. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an illuminance detection method, a luminance control method, an electro-optical device, and an electronic apparatus suitable for a display device that controls display luminance.

  The liquid crystal panel is configured by sealing liquid crystal between two substrates such as a glass substrate and a quartz substrate. Each substrate is provided with an electrode, and an image signal is supplied to the electrode. The optical characteristics of the liquid crystal between the electrodes of each substrate change according to the image signal. That is, by applying a voltage based on the image signal to the liquid crystal between the electrodes of each substrate, the alignment of the liquid crystal molecules is changed. Thereby, the light transmittance in each pixel changes according to the image signal, and the image display according to the image signal is performed.

  In order to display with high brightness in such a liquid crystal panel, a backlight is generally provided on the back of the liquid crystal panel. As such a backlight, an apparatus for improving the uniformity of illumination using a light guide plate has been developed. By illuminating the display area of the liquid crystal panel with the backlight, the display on the display area can be observed with sufficient luminance.

  By the way, the visibility of the display on the liquid crystal panel changes according to the ambient brightness. For example, the brighter the ambient light, the easier it is to see the display when the illumination in the display area is brighter. Conversely, when the ambient light is sufficiently dark, it is not necessary to make the display area brighter than necessary.

Patent Document 1 discloses a technique for detecting ambient light and controlling the brightness of a backlight based on feedback information in order to provide an easy-to-see display regardless of ambient brightness.
JP 2003-78838 A

  By the way, in the apparatus of patent document 1, a discrete component is employ | adopted as an optical sensor which detects ambient light (external light). For this reason, it is necessary to mount an optical sensor on a flexible printed circuit board, resulting in an increase in man-hours and costs.

  Therefore, it is conceivable to form an optical sensor on a substrate constituting a display panel such as a liquid crystal panel. However, for example, when a light receiving element is formed on a liquid crystal panel manufactured by low-temperature polysilicon technology, the light detection current of the light receiving element is relatively small and it is difficult to obtain sufficient accuracy. In addition, there is a problem that adjustment of the optical sensor is required at the product shipment stage in order to improve the detection accuracy of the external light because the individual difference of the light receiving elements is large.

  This is a problem common to all display devices that detect external light and perform luminance control.

  The present invention uses the output of a sensor for detecting reference light and ambient light, and detects ambient light with high accuracy without performing adjustment work by obtaining a relatively accurate illuminance of ambient light. An object of the present invention is to provide an illuminance detection method, a luminance control method, an electro-optical device, and an electronic apparatus.

  The electro-optical device according to the present invention includes a display unit, a first sensor that detects illuminance of reference light, a second sensor that detects illuminance of external light around the display unit, and the first sensor. And a comparison means for comparing the output of the second sensor and the output of the second sensor to obtain the illuminance of external light relative to the illuminance of the reference light.

  According to such a configuration, the first sensor detects the illuminance of the reference light. The second sensor detects the illuminance of outside light. The characteristic of the first sensor can be grasped from the output of the first sensor that detects the known reference light. If the characteristics of the first sensor and the second sensor are approximated, the illuminance of the external light can be accurately obtained by comparing the illuminance of the external light with the illuminance of the reference light using the outputs of the first and second sensors. it can. Even if there is a relatively large individual difference between the first sensor and the second sensor, the illuminance of outside light can be accurately obtained.

  The electro-optical device according to the present invention further includes luminance control means for controlling display luminance in the display unit based on the illuminance of external light obtained by the comparison means.

  According to such a configuration, the luminance control unit controls the display luminance based on the output of the comparison unit. The illuminance of outside light is obtained with high accuracy by the comparison means, and display brightness can be controlled according to the outside light. Thereby, the visibility of a display can be improved. Further, the display luminance can be prevented from becoming unnecessarily high, and the power consumption can be reduced.

  Further, the reference light is light from an illumination device that illuminates the display unit.

  According to such a configuration, by using the known reference light of the illumination device that illuminates the display unit, the illuminance of the external light can be relatively obtained from the output of the second sensor, with a simple configuration. The illuminance of outside light can be detected with high accuracy.

  In addition, the reference light is light from a light emitting element constituting the display unit.

  According to such a configuration, the illuminance of external light can be relatively obtained from the output of the second sensor by using the known reference light of the light emitting element that constitutes the display unit, and with a simple configuration. The illuminance of outside light can be detected with high accuracy.

  Further, the comparison means obtains the illuminance of outside light relative to the illuminance of the reference light based on a ratio between the output of the first sensor and the output of the second sensor. .

  According to such a configuration, if the characteristics of the first sensor and the second sensor are approximate, the ratio between the output of the second sensor and the output of the first sensor is the external light and the reference light. Corresponds to the ratio of illuminance. Therefore, the illuminance of outside light can be accurately obtained from the ratio between the output of the second sensor and the output of the first sensor and the illuminance of the known reference light.

  Further, the comparison means obtains the illuminance of outside light relative to the illuminance of reference light based on a difference between the output of the first sensor and the output of the second sensor. .

  According to such a configuration, if the characteristics of the first sensor and the second sensor are approximate, the difference between the output of the second sensor and the output of the first sensor is the external light and the reference light. Corresponds to the difference in illuminance. Therefore, the illuminance of external light can be accurately obtained from the difference between the output of the second sensor and the output of the first sensor and the illuminance of the known reference light.

  Further, the first and second sensors are constituted by thin film diodes formed on a substrate.

  According to such a configuration, there may be a relatively large individual difference between the first sensor and the second sensor. Even in this case, by arranging the first sensor and the second sensor close to each other, the characteristics of the both can be approximated, and the output of the second sensor can be approximated using the output of the first sensor. The illuminance of light can be accurately obtained by comparing with the illuminance of reference light.

  The display unit includes a liquid crystal panel in which liquid crystal is sealed between first and second substrates, and the first and second sensors are thin film diodes formed on the first substrate. The reference light is configured to be light from a backlight that illuminates the liquid crystal panel.

  According to such a configuration, external light can be relatively detected from the output of the second sensor based on the backlight light of the liquid crystal panel, and the brightness of the backlight is controlled to an optimum brightness. be able to.

  Further, an electronic apparatus according to the present invention is characterized by using the electro-optical device.

  According to such a configuration, it is possible to accurately detect external light and control display luminance, thereby improving display visibility and reducing power consumption.

  Further, the illuminance detection method according to the present invention includes a procedure for detecting the illuminance of the reference light, a procedure for detecting the illuminance of external light around the display unit, and the detected illuminance of the reference light. A comparison procedure for comparing the illuminance of the external light with respect to the illuminance of the reference light by comparing with the illuminance of the external light is provided.

  According to such a configuration, the illuminance of the reference light and the illuminance of external light around the display unit are detected. The illuminance of the detected reference light is known, and the detection characteristics of the illuminance of the reference light can be grasped. If the detection characteristic of the illuminance of the external light and the detection characteristic of the illuminance of the reference light are similar, the illuminance of the external light detected using the detected illuminance of the reference light can be obtained relatively. In this way, the accurate illuminance of outside light can be obtained.

  Further, the luminance control method according to the present invention includes a procedure for detecting the illuminance of the reference light, a procedure for detecting the illuminance of the external light around the display unit, and the detected illuminance of the reference light. The display brightness is controlled based on the comparison procedure for comparing the illuminance of the external light to obtain the illuminance of the external light relative to the illuminance of the reference light and the illuminance of the external light obtained by the comparison procedure. And a luminance control procedure.

  According to such a configuration, in the luminance control procedure, the display luminance is controlled using the illuminance of outside light obtained in the comparison procedure. The illuminance of the external light obtained by the comparison procedure accurately indicates the illuminance of the external light, and the display luminance can be controlled according to the external light. Thereby, the visibility of display can be improved and power consumption can be reduced.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a circuit diagram showing an illuminance detection and luminance control circuit employed in the electro-optical device according to the first embodiment of the invention. FIG. 2 is an explanatory diagram showing an outline of a display device in which the electro-optical device according to the present embodiment is incorporated. FIG. 3 is a cross-sectional view showing a cross-sectional structure when a liquid crystal panel is employed as the electro-optical device 12 of FIG. FIG. 4 is an equivalent circuit diagram showing a specific configuration example of the backlight reference sensor 2 and the external light sensor 4 in FIG.

<First Embodiment>
In FIG. 2, the display device 11 includes an electro-optical device 12. When a liquid crystal panel is used as the electro-optical device 12, the electro-optical device 12 includes a display panel 21 and an illumination device 22. Note that a self-luminous display panel may be employed as the electro-optical device, and in this case, an illumination device is not necessary. FIG. 3 shows a configuration example when a liquid crystal panel is adopted as the display panel 21. Note that FIG. 3 shows an example of a small number of pixels in order to simplify the description, but the number of pixels is not particularly limited.

  The display panel 21 is configured by enclosing a liquid crystal 25 between an element substrate 23 and a counter substrate 24 that transmit light. The element substrate 23 and the counter substrate 24 arranged so as to face each other are bonded together by a sealing material 26.

  The display panel 21 has a display screen 13, and an effective display area 14 surrounded by a broken line in FIG. 2 is provided at the center of the display screen 13. The effective display area 14 includes, for example, a plurality of scanning lines (not shown) extending in the vertical direction and a plurality of data lines (not shown) extending in the horizontal direction. A pixel is formed corresponding to the intersection of the plurality of data lines.

  A reflective layer 27 and an overcoat layer 28 are laminated on the element substrate 23, and a pixel electrode (ITO) 29 constituting a pixel is disposed on the overcoat layer 28. A counter electrode (common electrode (ITO)) 30 is provided on the counter substrate 24 side. On the pixel electrode 29 of the element substrate 23, an alignment film (not shown) that has been subjected to a rubbing process is provided in contact with the liquid crystal 25. On the other hand, the counter substrate 24 is also provided with an alignment film (not shown) that is in contact with the liquid crystal 25 and has been subjected to a rubbing process. Each alignment film is made of a transparent organic film such as a polyimide film. A light shielding film 31 is formed on the counter substrate 24 along the data lines and the scanning lines.

  A polarizing plate 32 is provided on the observation surface side of the counter substrate 24, and a polarizing plate 33 is provided on the surface opposite to the element formation surface of the element substrate 23. The polarizing plates 32 and 33 are set to the polarization axis corresponding to the rubbing direction of the alignment film formed on the element substrate 23 and the counter substrate 24.

  In the display panel 21, an image signal is supplied to the data line, and a scanning signal is supplied to the scanning line. In this way, each pixel is driven based on the image signal, the light transmittance is changed, and image display is performed.

  The lighting device 22 emits light from below the element substrate 23 of the display panel 21. In the display panel 21, image display is performed by controlling the transmittance of the emitted light of the illumination device 22 in accordance with the image signal in the effective display area 14.

  The illuminating device 22 is provided with light emitting diodes (hereinafter referred to as LEDs) 35 which are a plurality of point light sources constituting a light source. A light guide plate 36 is provided on the side of the LED 35 and below the effective display area 14 of the display panel 21. The LED 35 is disposed on the side surface of the light guide plate 36 and can emit light into the light guide plate 36.

  The light guide plate 36 has a substantially plate shape, and is disposed so that one side surface (incident surface) thereof faces the output surface of the LED 35. The light guide plate 36 is formed of, for example, a transparent acrylic resin, and the three side surfaces other than the one side facing the LED 35 are made of a material having high reflection characteristics or scattering characteristics, for example, a reflection layer such as a white printing layer. Is formed. From one side surface of the light guide plate 36 facing the LED 35, light from the LED 35 enters and is guided into the light guide plate 36.

  In addition to the acrylic resin, the light guide plate 36 is made of a polycarbonate resin having transparency or translucency, various resins such as amorphous polyolefin resin, inorganic materials such as glass, or various composites thereof. Can be used.

  The light guide plate 36 reflects and scatters incident light by the bottom and side reflection layers, and emits light from the top surface. An optical sheet 37 including a diffusion sheet and a prism sheet is disposed on the upper surface of the light guide plate 36. The optical sheet 37 diffuses the light from the light guide plate 36 and emits the light upward. An effective display area 14 of the display panel 21 is disposed on the optical sheet 37. Thereby, the light from the optical sheet 37 enters the effective display area 14 of the display panel 21.

  A non-display area 15 is provided around the effective display area 14. In the non-display area 15, the light receiving element arrangement area 16 of the illuminance detection and luminance control circuit of FIG. 1 is provided. The light receiving element arrangement region 16 has a region that transmits light from the upper surface (observation surface) side of the counter substrate 24 into the substrate and a region that blocks transmission. That is, the light shielding film 3 is formed on the counter substrate 24 in a part of the light receiving element arrangement region 16, and outside light is prevented from entering the element substrate 23 side in the region where the light shielding film 3 is formed. It has become so.

  In the present embodiment, the backlight reference sensor 2 and the external light sensor 4 are provided in the light receiving element arrangement region 16. The backlight reference sensor 2 and the external light sensor 4 are formed on the element substrate 23 by a process of a so-called polysilicon type thin film transistor, a low temperature polysilicon type thin film transistor which is preferably manufactured at a temperature of about 600 ° C. or less. A light shielding film 3 is formed above the backlight reference sensor 2, and the light shielding film 3 prevents external light from the observation surface side of the counter substrate 24 from entering the backlight reference sensor 2. The backlight reference sensor 2 receives light from the illumination device 22 that passes through the element substrate 23. Further, external light from the observation surface side of the counter substrate 24 enters the external light sensor 4.

  In FIG. 1, the backlight 1 corresponds to the illumination device 22 of FIG. The backlight 1 can irradiate the display panel with backlight light.

  The backlight reference sensor 2 and the external light sensor 4 each output an output corresponding to incident light. The backlight reference sensor 2 is configured such that the outside light is blocked by the light shielding film 3 and the backlight light from the backlight 1 is incident. In addition, external light is incident on the external light sensor 4. Thus, the backlight reference sensor 2 outputs an output based on the illuminance of the backlight light, and the external light sensor 4 outputs an output based on the illuminance of the external light.

  In the present embodiment, the backlight 1 includes, for example, an LED, and can control the illuminance with relatively high accuracy. The backlight reference sensor 2 and the outside light sensor 4 are formed by a so-called low-temperature polysilicon type thin film transistor process at positions close to each other, and have substantially the same characteristics.

  In the present embodiment, these characteristics are used to detect external light with high accuracy. As will be described later, the known illuminance of the backlight light whose illuminance is controlled with high accuracy is detected by the backlight reference sensor 2, and the illuminance of the external light is relatively determined from the output of the external light sensor based on the detection result. Thus, the detection accuracy of outside light is improved.

  FIG. 4 shows an example of the backlight reference sensor 2 and the outside light sensor 4. FIG. 5 is a graph showing the relationship between incident light intensity and output. The light receiving elements of the backlight reference sensor 2 and the external light sensor 4 can be represented by an equivalent circuit of a parallel circuit of a diode D1 such as a PIN diode and a capacitor C1.

  A voltage from the power supply 41 is applied to the capacitor C1 via the switch. The terminal voltage of the capacitor C1 decreases due to the photogenerated charge generated in the diode D1 by the incidence of light. A voltage drop amount Vdrop indicated by an arrow in FIG. 5 is obtained as a sensor output via the amplifier 43 at the output terminal 44.

  Vdrop corresponding to the sensor output is expressed by the following equation (1).

Vdorp = V0 exp (-t / RC) (1)
Further, when detecting a voltage drop of the capacitor C1 by a change in the pulse time width, an output element having a threshold voltage is connected to the switch 42, and when the voltage of the capacitor C1 reaches the threshold, the output element A signal may be output. In this case, the output element can output a pulse signal having a time width inversely proportional to the intensity of light incident on the diode D1.

  As shown in FIG. 4, the backlight reference sensor 2 and the external light sensor 4 may have the same configuration or different configurations. In addition, the sensor output is described as using a voltage corresponding to incident light, but a current output corresponding to incident light may be used, or an output whose pulse width varies according to incident light is used. May be.

  In order to simplify the description, the backlight reference sensor 2 and the external light sensor 4 are applied to the output of the above expression (1) after performing conversion in which the output changes linearly according to the light intensity. The output will be described as output.

  That is, the backlight reference sensor 2 and the external light sensor 4 output sensor outputs in which the relationship between the light intensity and the output changes linearly as shown in FIG.

  Each sensor output from the backlight reference sensor 2 and the outside light sensor 4 is given to a comparator 5 as a comparison means. The comparator 5 compares the sensor outputs from the backlight reference sensor 2 and the external light sensor 4 and outputs the comparison result to a backlight controller 6 as a luminance control means.

  For example, the comparator 5 may output the ratio of the output of the backlight reference sensor 2 that has detected predetermined reference light and the output of the external light sensor 4 as a comparison result. Now, it is assumed that the sensor characteristics of the backlight reference sensor 2 and the outside light sensor 4 have linear characteristics that pass 0 as shown in FIG. Then, a reference light having a known predetermined brightness is generated in the backlight 1, and this reference light is detected by the backlight reference sensor 2. On the other hand, the external light sensor 4 detects external light. In this case, it is determined how many times the brightness of the outside light is higher than the brightness of the reference light according to how many times the sensor output of the sensor 4 for external light is the sensor output of the sensor 2 for backlight reference. Can do. As described above, if the brightness of the reference light is controlled with high accuracy and the characteristics of the backlight reference sensor 2 and the external light sensor 4 are linearly the same characteristic passing through 0, the brightness of the external light is increased. It can be detected with accuracy. Even when the sensor characteristics do not pass through 0, it is obvious that external light can be detected in the same manner as long as it is linear.

  Furthermore, in the present embodiment, the brightness of the external light can be reliably detected even when the sensor characteristics of the backlight reference sensor 2 and the external light sensor 4 are not linear. That is, in this case, the output of the backlight reference sensor 2 is obtained while changing the brightness of the backlight light (reference light), and the output characteristics between the brightness of the reference light and the output of the backlight reference sensor 2 are obtained. You should ask for. In this case, the comparator 5 includes a memory (not shown) and stores the output characteristics of the backlight reference sensor 2. The accurate brightness of the external light can be determined by comparing the output of the external light sensor 4 with the output characteristics of the backlight reference sensor 2 stored in the memory.

  The comparator 5 may output the ratio of the sensor outputs of the backlight reference sensor 2 and the external light sensor 4 as a comparison result as it is, and the absolute brightness of the external light can be determined based on the comparison between the sensor outputs. A signal indicating the brightness of the obtained external light may be obtained as a comparison result.

  The comparison result of the comparator 5 is given to the backlight controller 6. The backlight controller 6 generates a backlight control signal for controlling the brightness of the backlight 1 based on the comparison result of the comparator 5 and outputs the backlight control signal to the backlight 1.

  For example, when the comparison result indicates that the external light is relatively bright, the backlight controller 6 can also increase the brightness of the backlight 1 according to the brightness of the external light. Further, the backlight controller 6 may turn off the backlight 1 and use the display panel 21 as a reflection type when the external light is shown to be brighter than a predetermined threshold. The backlight 1 emits light with brightness based on the backlight control signal.

  Next, the operation of the embodiment configured as described above will be described with reference to FIGS. FIG. 7 is a flowchart showing an illuminance detection method and a luminance control method, and FIG. 8 is an explanatory diagram for explaining a backlight control method.

  The display device 11 controls the brightness of the illumination device 22 so that the illumination device 22 in the electro-optical device 12 emits light with an appropriate brightness according to ambient light (external light). That is, the illuminance detection and luminance control circuit in FIG. 1 controls the backlight controller 6 to emit reference light having a predetermined luminance to the backlight 1 (step S1). The backlight light enters the backlight reference sensor 2. The backlight reference sensor 2 detects the brightness of the backlight and outputs the detection result to the comparator 5 (step S2).

  On the other hand, external light incident from the observation surface side of the counter substrate 24 passes through the counter substrate 24 and enters the sensor 4 for external light. The external light sensor 4 detects the brightness of the external light and outputs the detection result to the comparator 5 (step S3). In step S4, the comparator 5 obtains the ratio between the sensor outputs from the backlight reference sensor 2 and the external light sensor 4 and outputs the ratio to the backlight controller 6 (step S5).

  For example, it is assumed that the illuminance by the backlight 1 is 10,000 lux as the reference light, and the output of the backlight reference sensor 2 by this backlight light is 5V. On the other hand, it is assumed that the output of the external light sensor 4 that has detected the external light is 6V. In this case, the comparator 5 outputs 6/5 = 1.2. That is, in this case, the brightness of the external light is 12,000 lux which is 1.2 times the reference light.

  The backlight controller 6 determines the brightness of the backlight 1 based on the comparison result from the comparator 5 (step S6), and outputs a backlight control signal for lighting the backlight 1 with the determined brightness. (Step S7).

  Note that the detection in steps S2 and S3 may be performed simultaneously.

  FIG. 8 shows an example of the brightness control of the backlight 1. The example of FIG. 8 shows the relationship between the comparison result of the comparator 5 and the brightness control. In the example of FIG. 8, when the comparison result is 1, it is divided into the case of 0-0.5, the case of 0.5-1, the case of 1-1.5, and the case of 1.5 or more. Defines the brightness of the backlight 1. For example, when the comparison result is 0.5-1, that is, when the external light is in the range of brightness of the reference light to ½ of the reference light, the backlight controller 6 determines the brightness of the backlight 1. To be the reference light. When the comparison result is 0-0.5, that is, when the external light is darker than half the brightness of the reference light, the backlight controller 6 sufficiently reduces the brightness of the backlight 1. When the comparison result is 1 to 1.5, that is, when the external light is within the range of the brightness of the reference light to 3/2 of the reference light, the backlight controller 6 sets the brightness of the backlight 1. Make it bright enough. When the comparison result is 1.5 or more, that is, when the external light is 1.5 times or more brighter than the reference light, the backlight controller 6 turns off the backlight 1. That is, in this case, the display panel 21 operates as a reflection type. The backlight 1 is turned on with brightness according to the backlight control signal (step S8).

Furthermore, it is preferable that the backlight controller 6 controls the brightness of the backlight light in consideration of the attenuation of the backlight light. Usually, in the liquid crystal panel, the brightness of the backlight is adjusted in consideration of the attenuation amount of a color filter, a polarizing plate, and the like. For example, the surface brightness of the backlight itself is usually 5000 to 10000 Cd / cm ² . Backlight is attenuated to a brightness of about 200 Cd / cm ² on the surface of the liquid crystal panel. However, the brightness of outdoor direct sunlight can be 10,000 Cd / cm ² . Therefore, in consideration of these values, when the ratio (or difference) between the brightness of the backlight and the outside light is reached, it is determined in advance how much brightness should be obtained. is there.

  Further, when detecting the time of the output pulse from the backlight reference sensor and the external light sensor, the output time τ1 of the external light sensor and the output time τ2 of the backlight reference sensor are used according to the relative intensity of both. What is necessary is just to obtain the time τ3. That is, 1 / τ3 = 1 / τ1-1 / τ2, and the backlight controller may determine the brightness of the backlight based on τ3.

  In the above embodiment, the backlight reference sensor and the ambient light sensor detect the illuminance by the same method, but different detection methods may be adopted. In addition, the detection timing of incident light by the backlight reference sensor and the external light sensor may be the same or different from each other. Although FIG. 7 shows an example in which the reference light from the backlight light is detected first, it is obvious that the external light may be detected first.

  As described above, in the present embodiment, the reference light whose brightness is controlled with high accuracy is generated, and the brightness of the reference light is detected by the backlight reference sensor. The brightness of external light is detected by an external light sensor having substantially the same characteristics as the backlight reference sensor. By comparing the sensor output of the backlight reference sensor and the sensor output of the outside light sensor, the illuminance of outside light is relatively obtained. Thereby, it is possible to detect the brightness of external light with high accuracy.

  Further, the brightness of the backlight light is controlled according to the brightness of the external light detected with high accuracy, and a display device with excellent visibility can be obtained. In addition, it is possible to prevent the backlight from becoming brighter than necessary, and power consumption can be reduced.

  Polycrystalline thin film sensors such as PIN diodes manufactured by so-called low-temperature polysilicon technology have individual variations in photosensitivity greater than those in bulk silicon. In order to use it as a sensor for detecting ambient light (external light), it has been necessary to calibrate the sensitivity. On the other hand, in the present embodiment, the sensor output for detecting the external light is automatically calibrated by using the output of the sensor for detecting the reference light. External light detection is possible.

  In the above-described embodiment, the example of controlling the brightness of the backlight according to the external light has been described. However, when a self-luminous display panel is used, the light emission is performed according to the detected external light. The display brightness of the body may be controlled. In this case, display light itself by self-light emission may be used as the reference light.

  Furthermore, not only the brightness control but also the γ value of the projected image and the picture itself may be controlled according to the external light. Further, it can be applied not only to video but also to control of audio and the like. For example, when it is detected that the external light has become darker than a predetermined brightness, it is possible to change the ringing tone of the mobile phone to the ringing tone for night.

<Second Embodiment>
FIG. 9 is a circuit diagram showing an equivalent circuit of the backlight reference sensor and the external light sensor employed in the second embodiment of the present invention. In FIG. 9, the same components as those of FIG.

  In the present embodiment, the backlight reference sensor and the external light sensor not only detect the backlight light and the external light but also exhibit the same operation as the comparator 5 in FIG. Therefore, in the present embodiment, a configuration in which the comparator 5 in FIG. 1 is omitted can be employed.

  A diode D11 corresponding to the backlight reference sensor and a diode D12 corresponding to the outside light sensor are connected in series between the power supply terminal 45 and the reference potential point. Also in the present embodiment, backlight light is incident on the diode D11 corresponding to the backlight reference sensor, and external light is incident on the diode D12 corresponding to the external light sensor.

  A capacitor C11 is provided between the connection point between the diodes D11 and D12 and the reference potential point. The connection point between the diodes D11 and D12 is connected to the output terminal 44 via the amplifier 43.

  In the embodiment configured as described above, the diode D11 generates a detection current corresponding to the backlight, and the diode D12 generates a detection current corresponding to the external light. Thus, a difference current between the detection current corresponding to the backlight and the detection current corresponding to the external light flows through the amplifier 43 connected to the connection point of the diodes D11 and D12. This difference current corresponds to the difference in brightness between the backlight and the outside light.

  In this case, since the characteristics of the diodes D11 and D12 are substantially the same, the difference between the detection currents accurately corresponds to the difference in brightness between the external light and the reference light.

  In this case, the brightness of the external light cannot be directly determined, but the brightness of the backlight 1 may be changed based on the brightness difference. Further, the brightness of the backlight 1 may be controlled to change depending on whether the external light is brighter or darker than the reference light.

  For example, when the output appearing at the output terminal 44 indicates that the external light is brighter than the reference light, the backlight controller 6 makes the backlight 1 brighter than the reference light. Further, the output of the output terminal 44 controls the backlight 1 based on whether the brightness of external light or the brightness of the backlight is bright. By sequentially changing the brightness of the backlight 1 based on the output of the output terminal 44, the brightness of the external light depends on the brightness of the backlight light when the brightness of the external light and the brightness of the backlight light are reversed. Can be judged. Thereafter, the brightness of the backlight 1 may be controlled based on the detected brightness of the external light.

  Thus, in the present embodiment, the comparator 5 can be omitted. It should be noted that the illuminance detection method and the luminance control method in the present embodiment can be applied to the configuration in the first embodiment when the comparator 5 obtains the difference.

<Third Embodiment>
FIGS. 10 and 11 relate to a third embodiment of the present invention, and FIG. 10 is a circuit diagram showing an illuminance detection and luminance control circuit employed in an electro-optical device according to the third embodiment. FIG. 11 is a cross-sectional view showing a cross-sectional structure when a liquid crystal panel is employed as the electro-optical device according to the third embodiment. In FIG. 10 and FIG. 11, the same components as those in FIG. 1 and FIG.

  This embodiment is different from the first embodiment in that the light shielding film 3 for preventing external light from entering the backlight reference sensor 2 is omitted.

  As shown in FIGS. 10 and 11, the backlight reference sensor can be disposed even in a place where the light shielding film 3 above the backlight reference sensor 2 cannot be added. For example, as shown in FIG. 11, the backlight reference sensor can be arranged even at a position where the backlight 1 is located below and where there is no counter substrate. In this case, not only backlight light but also external light is incident on the backlight reference sensor 2. Even in this case, when the backlight light is sufficiently brighter than the external light, the backlight reference sensor 2 can detect the illuminance of the backlight 1 almost accurately.

  Other configurations and operations are the same as those in the first embodiment. In the present embodiment, there is an advantage that the light shielding film 3 can be omitted and the configuration can be simplified.

  Further, in each of the above embodiments, an example in which two backlight reference sensors and an external light sensor are used has been described. However, these sensors are shared by one sensor, and the reference sensor and the external light sensor are used. It is also possible to detect the illuminance of the backlight and the outside light by shifting the detection timing and using it in a time-sharing manner.

<Fourth embodiment>
FIGS. 12 to 14 relate to a fourth embodiment of the present invention, and FIG. 12 is a circuit diagram showing an illuminance detection and luminance control circuit employed in an electro-optical device according to the fourth embodiment. FIG. 13 is a cross-sectional view showing a cross-sectional structure when a liquid crystal panel is employed as the electro-optical device according to the fourth embodiment. FIG. 14 is a graph for explaining the dark current characteristics with the substrate temperature on the horizontal axis and the sensor output (current) on the vertical axis. In FIG. 12 and FIG. 13, the same components as those in FIG. 1 and FIG.

  In the present embodiment, a dark current reference sensor 62 in which the incidence of external light and backlight light is blocked is provided, and a comparator 65 is provided for the backlight reference sensor 2, the external light sensor 4, and the dark current reference sensor. The second embodiment is different from the first embodiment in that 62 sensor outputs are compared and a comparison result is output.

  A dark current reference sensor 62 is provided at the end of the element substrate 23 of the display panel 61. A light shielding film 63 is formed on the counter substrate 24 above the dark current reference sensor 62, and the dark current reference sensor 62 is configured so that outside light and backlight light do not enter.

  The dark current reference sensor 62 detects a sensor output when the incident light is 0, that is, a dark current, and outputs a detection result to the comparator 65. The comparator 65 performs the same comparison as the comparator 5 of FIG. 1 and outputs an output indicating that a temperature error has occurred when the sensor output from the dark current reference sensor 62 reaches a predetermined value. It has become.

  The PIN diode constituting each sensor increases in thermal current as the temperature rises, and at a predetermined temperature or higher, the thermal current dominates and loses photosensitivity. FIG. 14 shows outputs (currents) of the backlight reference sensor 2, the external light sensor 4, and the dark current reference sensor 62 in a state where the backlight light and the external light are fixed. As shown in FIG. 14, when the substrate temperature reaches 80 ° C., it can be seen that the thermal current is dominant in the output of each sensor. Conversely, by detecting dark current, it can be determined that a temperature error has occurred in the sensor output.

The dark current reference sensor 62 detects dark current when the external light is blocked. The comparator 65 determines that a temperature error has occurred when the output current value of the dark current reference sensor 62 exceeds a predetermined value. For example, in the example of FIG. 14, if the substrate temperature exceeds the output of the sensor 62 at 80 ° C. (1 × 10 ⁻¹⁰ amperes), it is determined that a temperature error has occurred. When the comparator 65 determines that a temperature error has occurred, the comparator 65 outputs a predetermined fixed value as a comparison result. In other words, this case is equivalent to not performing the brightness determination of the outside light.

  Further, since the difference between the output of the backlight reference sensor 2 and the output of the dark current reference sensor 62 is extremely small at the high temperature, the comparator 65 generates a temperature error by comparing these sensor outputs with each other. May be detected.

  When an output indicating a temperature error is output from the comparator 65, the backlight controller 6 controls the brightness of the backlight 1 to be a predetermined fixed brightness. In a high temperature state of 80 ° C. or higher, it is considered that most devices such as mobile phones are not used by human beings displayed for a long time. Therefore, when a temperature error is detected, no particular problem arises even if the brightness of the backlight is set to a fixed value. Further, for example, “temperature error” may be displayed on the display screen by the comparator 65 outputting an output indicating the detection of the temperature error.

  Other configurations and operations are the same as those in the first embodiment. In the present embodiment, it is possible to prevent a problem in brightness control due to a temperature error.

<Fifth embodiment>
15 and 16 relate to a fifth embodiment of the present invention, and FIG. 15 is a circuit diagram showing an illuminance detection and luminance control circuit employed in an electro-optical device according to the fifth embodiment. FIG. 16 is a cross-sectional view showing a cross-sectional structure when a liquid crystal panel is employed as the electro-optical device according to the fifth embodiment. In FIG. 15 and FIG. 16, the same components as those in FIG. 10, FIG. 12, FIG. 11, and FIG.

  This embodiment is different from the fourth embodiment in that the light shielding film 3 for preventing external light from entering the backlight reference sensor 2 is omitted.

  As shown in FIGS. 15 and 16, in the display panel 67, the light shielding film 3 above the backlight reference sensor 2 is omitted. In this case, not only backlight light but also external light is incident on the backlight reference sensor 2. Even in this case, when the backlight light is sufficiently brighter than the external light, the backlight reference sensor 2 can detect the illuminance of the backlight 1 almost accurately.

  Other configurations and operations are the same as those in the fourth embodiment. In the present embodiment, two of the three sensors can be arranged in a place where the light shielding film 3 is not provided, and there is an advantage that the degree of freedom of design is widened.

<Sixth Embodiment>
FIG. 17 relates to a sixth embodiment of the present invention, and is a sectional view showing a sectional structure when an EL (electroluminescence) panel is adopted as an electro-optical device according to the sixth embodiment.

  A low-pitched polysilicon layer 73 is formed on the substrate 71. The substrate 71 and the substrate 72 are opposed to each other with the organic EL layer 74 interposed therebetween. The organic EL layer 74 constitutes R, G, and B pixels. A light shielding film 75 is formed on the substrate 72.

  In the present embodiment, the reference light reference sensor 76 is formed on the substrate 73 so as to be opposed to one or all of the R, G, and B pixels of the organic EL layer 74. ing. A light shielding film 77 is formed on the substrate 72 facing the reference light reference sensor 76. As a result, the reference light reference sensor 76 is prevented from entering external light and can detect the light emission intensity of each pixel of the organic EL layer 74.

  An external light sensor 78 is formed at the end of the substrate 71. The external light sensor 78 can detect external light.

  The electro-optical device configured as described above also includes an illuminance detection and luminance control circuit similar to that shown in FIG. That is, the organic EL layer 74 corresponds to the backlight 1, the reference light reference sensor 76 corresponds to the backlight reference sensor 2, the external light sensor 78 corresponds to the external light sensor 4, and the light shielding film 77 It corresponds to the light shielding film 3. The sensor outputs of the reference light reference sensor 76 and the external light sensor 78 are given to the comparator 5 and the light emission of the organic EL layer 74 is controlled based on the comparison result.

  In the embodiment configured as described above, the sensor output of the external light sensor 78 can be calibrated by detecting the light emission intensity of the organic EL layer 74 as the intensity of the reference light. In this way, it is possible to accurately detect outside light and control display luminance.

  Further, an electronic apparatus using the above electro-optical device is also included in the present invention. FIG. 18 is a perspective view showing an example of an electronic device, and shows the appearance of a mobile phone. As shown in FIG. 18, the above-described electro-optical device, for example, a liquid crystal display device, is used for the display unit 201 of the mobile phone 200 as an electronic device.

  In addition, as an electronic device, for example, a projection display device including a light source, a light valve that modulates light emitted from the light source, and an optical system for projecting light modulated by the light valve It is. In addition, other electronic devices include televisions, viewfinder type / monitor direct view type video tape recorders, car navigation devices, pagers, electronic notebooks, calculators, word processors, workstations, videophones, POS terminals, digital Examples include a still camera and a device equipped with a touch panel. Needless to say, the electro-optical device according to the present invention is applicable to these various electronic devices.

  The electro-optical device of the present invention is not limited to a passive matrix type liquid crystal display panel but an active matrix type liquid crystal panel (for example, a liquid crystal display panel including a TFT (thin film transistor) or a TFD (thin film diode) as a switching element). It is possible to apply to the same. In addition to liquid crystal display panels, electroluminescence devices, organic electroluminescence devices, plasma display devices, electrophoretic display devices, devices using electron emission (such as Field Emission Display and Surface-Conduction Electron-Emitter Display), DLP ( The present invention can be similarly applied to various electro-optical devices such as Digital Light Processing (aka DMD: Digital Micromirror Device).

FIG. 3 is a circuit diagram showing an illuminance detection and luminance control circuit employed in the electro-optical device according to the first embodiment of the invention. FIG. 3 is an explanatory diagram showing an overview of a display device in which the electro-optical device according to the present embodiment is incorporated. FIG. 3 is a cross-sectional view illustrating a cross-sectional structure when a liquid crystal panel is employed as the electro-optical device 12 of FIG. 2. FIG. 2 is an equivalent circuit diagram illustrating a specific configuration example of the backlight reference sensor 2 and the external light sensor 4 in FIG. 1. The graph which shows the relationship between incident light intensity and a sensor output. The graph for demonstrating the sensor output from which the relationship between light intensity and an output changes linearly. The flowchart which shows the detection method of an illumination intensity, and the control method of a brightness | luminance. Explanatory drawing for demonstrating the control method of a backlight. The circuit diagram which shows the equivalent circuit of the sensor for backlight references and the sensor for external light which are employ | adopted for the 2nd Embodiment of this invention. FIG. 10 is a circuit diagram illustrating an illuminance detection and luminance control circuit employed in an electro-optical device according to a third embodiment. FIG. 9 is a cross-sectional view illustrating a cross-sectional structure when a liquid crystal panel is employed as an electro-optical device according to a third embodiment. FIG. 10 is a circuit diagram showing an illuminance detection and luminance control circuit employed in an electro-optical device according to a fourth embodiment. FIG. 9 is a cross-sectional view illustrating a cross-sectional structure when a liquid crystal panel is employed as an electro-optical device according to a fourth embodiment. A graph for explaining dark current characteristics with the substrate temperature on the horizontal axis and the sensor output (current) on the vertical axis. FIG. 10 is a circuit diagram showing an illuminance detection and luminance control circuit employed in an electro-optical device according to a fifth embodiment. FIG. 10 is a cross-sectional view illustrating a cross-sectional structure when a liquid crystal panel is employed as an electro-optical device according to a fifth embodiment. Sectional drawing which shows sectional structure at the time of employ | adopting EL (electroluminescence) panel as an electro-optical apparatus which concerns on 6th Embodiment. The perspective view which shows the example of an electronic device.

Explanation of symbols

    DESCRIPTION OF SYMBOLS 1 ... Backlight, 2 ... Backlight reference sensor, 3 ... Light shielding film, 4 ... External light sensor, 5 ... Comparator, 6 ... Backlight controller.

Claims (11)

A display unit;
A first sensor for detecting the illuminance of the reference light;
A second sensor for detecting the illuminance of external light around the display unit;
An electro-optical device comprising: a comparison unit that compares the output of the first sensor and the output of the second sensor to obtain the illuminance of external light relative to the illuminance of reference light.   The electro-optical device according to claim 1, further comprising a luminance control unit that controls display luminance in the display unit based on the illuminance of external light obtained by the comparison unit.   The electro-optical device according to claim 1, wherein the reference light is light from an illumination device that illuminates the display unit.   The electro-optical device according to claim 1, wherein the reference light is light from a light emitting element that constitutes the display unit.   The comparison means obtains the illuminance of external light relative to the illuminance of reference light based on a ratio between the output of the first sensor and the output of the second sensor. The electro-optical device according to any one of 1 and 2.   The comparison means obtains the illuminance of external light relative to the illuminance of reference light based on the difference between the output of the first sensor and the output of the second sensor. The electro-optical device according to any one of 1 and 2.   The electro-optical device according to claim 1, wherein the first and second sensors are constituted by thin film diodes formed on a substrate. The display unit is configured by a liquid crystal panel in which liquid crystal is sealed between the first and second substrates,
The first and second sensors are constituted by thin film diodes formed on the first substrate,
The electro-optical device according to claim 1, wherein the reference light is light from a backlight that illuminates the liquid crystal panel.   An electronic apparatus using the electro-optical device according to claim 1. A procedure for detecting the illuminance of the reference light;
A procedure for detecting the illuminance of ambient light around the display unit;
A comparison procedure for comparing the detected illuminance of the reference light with the detected illuminance of the external light to obtain the illuminance of the external light relative to the illuminance of the reference light. Detection method. A procedure for detecting the illuminance of the reference light;
A procedure for detecting the illuminance of ambient light around the display unit;
A comparison procedure for comparing the detected illuminance of the reference light and the detected illuminance of the external light to determine the illuminance of the external light relative to the illuminance of the reference light,
A luminance control method comprising: a luminance control procedure for controlling display luminance based on the illuminance of the external light obtained by the comparison procedure.

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