JP2008032729A - Electro-optical device and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electro-optical device and electronic apparatus for accurately measuring light quantity of ambient light from minute signal current. <P>SOLUTION: In photodiode 310 of the device, its cathode is connected to high potential side power supply VH, while its anode connected to capacitor 320 via a node Q. Another end of the capacitor 320 is connected to ground GND, further switching element 330 which turns on/off at the period of reset signal RESET is provided in parallel with this capacitor. A NAND circuit 340 calculates invert of AND between potential of node Q and reference signal REF and then outputs the calculation result as pulse signal 300a via inverters 350, 360 and 370. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a light detection circuit capable of detecting illuminance, a control method thereof, an electro-optical panel, an electro-optical device, and an electronic apparatus.

  In a transmissive or anti-transmissive liquid crystal device, a backlight is provided on the back of the liquid crystal panel. Light from the backlight is modulated by the liquid crystal panel. A plurality of pixels are formed in a matrix on the liquid crystal panel, and an image is displayed by adjusting the transmittance for each pixel. In such a liquid crystal device, the power consumption of the backlight is large. Therefore, a photodetection circuit may be provided to reduce power consumption of the liquid crystal device, and the intensity of the backlight may be adjusted according to the magnitude of the ambient light (for example, Patent Document 1 and Patent Document 2). Furthermore, it is known that a light detection circuit is formed on a glass substrate of a liquid crystal device for the purpose of reducing parts (Patent Document 3).

  In a photodetection circuit, in general, a current in a reverse voltage state of a photodiode must be extracted to the outside as some signal. However, since the space for disposing the photodiode in the liquid crystal device is limited, the signal current becomes minute. Therefore, it is preferable to convert the voltage to the outside and extract it as a voltage value. A method of detecting a potential difference due to a signal current by providing an appropriate resistor is conceivable as a voltage value.

JP-A-5-265401 (Claims 1 and 2) JP-A-6-11713 (Claim 1 and FIG. 1) Japanese Unexamined Patent Publication No. 2000-131137

However, since the signal current of the photodiode is very small, it is necessary to provide a resistor having a large value in order to convert it as a sufficient voltage value. Since the wiring group on the glass substrate of the liquid crystal device is basically a material having a low resistance, it is difficult to provide an appropriate resistor.
The present invention has been made in view of such circumstances, and an object of the present invention is to provide a light detection circuit capable of accurately measuring the amount of ambient light from a minute signal current, an electro-optical device using the same, and a control thereof. It is to provide a method and an electronic apparatus.

In order to solve the above-described problems, a photodetection circuit according to the present invention includes a photodiode having a cathode connected to a high-potential-side power supply and an anode connected to a connection point, A capacitance element provided between the switching element and a switching element provided between the connection point and the low-potential side power source and turned on and off at a predetermined cycle, and taking out a voltage signal at the connection point as an output signal; It is characterized by.
According to the present invention, since the photodiode is in a reverse voltage state, a current corresponding to the amount of incident light is generated. Further, since both ends of the capacitive element are short-circuited at a predetermined period by the switching element, the voltage signal at the connection point is a signal indicating illuminance. Since the output current of the photodiode is very small, it is necessary to use a resistor having a large resistance value in order to generate a voltage signal using the resistor, which increases the circuit area. On the other hand, when a capacitive element is used, an element with a small low capacitance value sufficient for charging a minute current is sufficient. Therefore, the circuit scale can be greatly reduced. In addition, since the high-resistance resistor acts as an antenna, noise may be mixed in. However, since the photodetection circuit of the present invention uses a capacitive element, the illuminance can be accurately detected with a large noise margin.

The above-described photodetection circuit preferably includes a voltage frequency conversion circuit that converts the voltage signal into a frequency signal, and outputs the frequency signal as the output signal instead of the voltage signal. In this case, since the frequency signal is output from the photodetection circuit, the noise margin is improved and the signal is easily handled.
More specifically, the voltage frequency conversion circuit includes a logic circuit that calculates a logical product of the voltage signal and a reference signal having a cycle shorter than the ON / OFF cycle of the switching element and outputs a binarized signal. And the binarized signal is output as the frequency signal. According to this configuration, since the binarized signal that is a frequency signal can be output by the logic circuit, the configuration can be simplified.
In addition, the photodetection circuit includes a counting unit that counts the binarized signal and outputs a count data signal indicating a count result per unit time, and outputs the count data signal as the output signal. preferable. In this case, it can be output as a digital signal.

  Next, an electro-optical panel according to the present invention is provided with the above-described photodetection circuit, a plurality of data lines, and a plurality of scanning lines, each corresponding to the intersection of the data lines and the scanning data. A pixel circuit including an electro-optical element whose optical characteristics change due to an effect, and a drive circuit that outputs a signal to at least one of the plurality of data lines and the plurality of scanning lines to drive the electro-optical element Prepare. According to the present invention, since the light detection circuit is incorporated in the electro-optical panel, it is possible to reduce the size of the apparatus using the electro-optical panel.

  Next, an electro-optical device according to the present invention includes the above-described electro-optical panel, a light source that emits light from one surface of the electro-optical panel to the other surface, and a light amount of the light source in the light detection circuit. And a dimming circuit that adjusts based on the output signal, wherein the electro-optic element is a liquid crystal element whose transmittance changes in accordance with an applied voltage. According to the present invention, since the light amount of the light source can be adjusted according to the ambient illuminance detected by the light detection circuit, for example, the light emission luminance of the light source is increased in a bright place, while the light emission luminance of the light source is increased in a dark place. Can be lowered. As a result, an easy-to-view screen can be displayed and power consumption can be reduced.

  Further, as another aspect of the electro-optical device according to the present invention, the electro-optical panel described above and an image processing circuit that outputs an image signal whose level is adjusted based on the output signal of the light detection circuit, The electro-optical element includes a light emitting element that emits light with a luminance corresponding to a driving current, and the driving circuit controls the driving current based on the image signal output from the image processing circuit. . According to the present invention, since the level of the image signal is adjusted according to the environmental illuminance detected by the light detection circuit, the luminance of the light emitting element is increased over the entire screen in a bright place, while the luminance of the light emitting element is increased in a dark place. The entire screen can be lowered. As a result, an easy-to-view screen can be displayed and power consumption can be reduced. The light emitting elements include OLED elements and inorganic light emitting diode elements.

  Further, as another aspect of the electro-optical device according to the present invention, the electro-optical panel includes the above-described electro-optical panel, and a power supply circuit that outputs a power supply voltage whose level is adjusted based on the output signal of the light detection circuit, The drive circuit outputs a data signal corresponding to the gradation to be displayed on the data line, the electro-optical element is composed of a light emitting element that emits light with a luminance corresponding to a drive current, and the pixel circuit is configured to emit the light emitting element. And a driving transistor for supplying the driving current, wherein the driving transistor supplies the light emitting element with the driving current having a magnitude based on the power supply voltage and the data signal. According to the present invention, since the power supply voltage is adjusted according to the ambient illuminance detected by the light detection circuit, the luminance of the light emitting element is increased on the entire screen in a bright place, while the luminance of the light emitting element is increased on the entire screen in a dark place. Can be lowered. As a result, an easy-to-view screen can be displayed and power consumption can be reduced.

  Next, an electro-optical device according to the present invention is provided with a plurality of data lines, a plurality of scanning lines, each corresponding to the intersection of the data lines and the scanning data, and having an optical characteristic by an electrical action. A pixel circuit including a changing electro-optic element, a control circuit that generates a plurality of control signals, a drive signal is generated based on the plurality of control signals, and the drive signal is transmitted to the plurality of data lines and the plurality of scans. A drive circuit for outputting to at least one of the lines; a photodiode having a cathode connected to a high-potential-side power supply; an anode connected to a connection point; and a capacitor provided between the connection point and the low-potential-side power supply A light detection circuit that includes an element, a switching element that is provided between the connection point and the low-potential-side power supply and that is turned on / off based on a first signal, and that extracts a voltage signal from the connection point; Said first signal Characterized by being combined with any of the plurality of control signals. According to the present invention, since a special configuration for generating the first signal is not necessary, the configuration can be simplified, and the cost of the electro-optical device can be reduced. Furthermore, when the electro-optical panel is provided with data lines, scanning lines, pixel circuits, driving circuits, and light detection circuits, it is possible to reduce the number of input terminals of the electro-optical panel and cope with a narrow pitch. Become.

  Next, an electro-optical device according to the present invention is provided with a plurality of data lines, a plurality of scanning lines, each corresponding to the intersection of the data lines and the scanning data, and having an optical characteristic by an electrical action. A pixel circuit including a changing electro-optic element, a control circuit that generates a plurality of control signals, a drive signal is generated based on the plurality of control signals, and the drive signal is transmitted to the plurality of data lines and the plurality of scans. A drive circuit for outputting to at least one of the lines; a photodiode having a cathode connected to a high-potential-side power supply; an anode connected to a connection point; and a capacitor provided between the connection point and the low-potential-side power supply A logical product of an element, a switching element that is provided between the connection point and the low-potential-side power supply and is turned on / off based on the first signal, and a second signal having a shorter period than the first signal is calculated. Output a binary signal That includes a light detection circuit and a logic circuit, characterized in that said first signal and said second signal is also used as one of the plurality of control signals. According to the present invention, since a special configuration for generating the first signal and the second signal is not required, the configuration can be simplified, and the cost of the electro-optical device can be reduced. Furthermore, when the electro-optical panel is provided with data lines, scanning lines, pixel circuits, driving circuits, and light detection circuits, it is possible to reduce the number of input terminals of the electro-optical panel and cope with a narrow pitch. Become.

Next, an electronic apparatus according to the present invention preferably includes the above-described electro-optical device. Examples of the electronic device include a personal computer, a cellular phone, and an information portable terminal.
Next, a method for controlling a photodetection circuit according to the present invention is provided between a photodiode having a cathode connected to a high potential side power supply and an anode connected to a connection point, and the connection point and the low potential side power supply. A method of controlling a photodetection circuit comprising a capacitive element, wherein both ends of the capacitive element are short-circuited at a predetermined cycle, and a logic between a reference signal having a cycle shorter than the predetermined cycle and a voltage signal at the connection point The product is calculated to generate a binarized signal, and the binarized signal is output as an illuminance signal indicating illuminance. According to the present invention, when the photodiode generates a current corresponding to the amount of incident light, the capacitor element is charged, and the potential at the connection point increases. The potential at the connection point is reset at a predetermined cycle. The binarized signal obtained by calculating the logical product of the reference signal and the voltage signal at the connection point has a number of pulses corresponding to the illuminance per unit time. Accordingly, the illuminance can be converted into a frequency and output.

<First Embodiment>
The electro-optical device according to the first embodiment of the present invention uses liquid crystal as an electro-optical material. The electro-optical device 1 includes a liquid crystal panel AA (an example of an electro-optical panel) as a main part. The liquid crystal panel AA is bonded to an element substrate on which a thin film transistor (hereinafter referred to as “TFT”) is formed as a switching element and a counter substrate with the electrode formation surfaces facing each other and maintaining a certain gap. However, liquid crystal is sandwiched between the gaps.

  FIG. 1 is a block diagram showing the overall configuration of the electro-optical device 1 according to the first embodiment. The electro-optical device 1 includes a liquid crystal panel AA, a light control circuit 500, a backlight 600, a signal generation circuit 700, a control circuit 800, and an image processing circuit 900. The liquid crystal panel AA is a transmissive type, but may be a transflective type. The signal generation circuit 700 generates a reset signal RESET and a reference signal REF. These signals are used in the optical sensor circuit 300. The liquid crystal panel AA includes an image display area A, a scanning line driving circuit 100, a data line driving circuit 200, an optical sensor circuit 300, and a counting circuit 400 on the element substrate. The control circuit 800 generates an X transfer start pulse DX and an X clock signal XCK and supplies them to the data line driving circuit 200, and also generates a Y transfer start pulse DY and a Y clock signal YCK and supplies them to the scanning line driving circuit 100. To do. In the image display area A, a plurality of pixel circuits P1 are formed in a matrix, and the transmittance can be controlled for each pixel circuit P1. Light from the backlight 600 is emitted through the pixel circuit P1. Thereby, gradation display by light modulation becomes possible. The dimming circuit 500 adjusts so that the backlight 600 emits light with the luminance according to the illuminance data 400a. The illuminance data 400a is data indicating the illuminance of the environment.

  By the way, the visibility of the display image depends on the brightness of the environment. For example, under natural daylight, it is necessary to set the light emission luminance of the backlight 600 high and display a bright screen. On the other hand, in a dark environment at night, a clear image can be displayed even if the light emission activation of the backlight 600 is not as high as during the day. Therefore, it is desirable to adjust the light emission luminance of the backlight 600 according to the illuminance of the ambient light. The optical sensor circuit 300 and the counting circuit 400 provided in the liquid crystal panel AA are used for measuring the illuminance of ambient light.

  FIG. 2 shows a circuit diagram of the optical sensor circuit 300. As shown in this figure, the photodiode 310 and the capacitor 320 are connected in series between the high potential side power source VH and the ground GND (low potential side power source). The photodiode 310 is composed of, for example, a PIN diode and is reverse-biased. The photodiode 310 can be formed if there is a process for forming a semiconductor region, a process for forming an N-type region, and a process for forming a P-type region, so that the pixel circuit P1 / scanning line driving circuit / data line driving circuit is configured. It is formed on the element substrate by the same process as the TFT. The photodiode 310 outputs a current IL corresponding to the illuminance of the ambient light. One end of the switching element 330 is connected to the node Q, which is a connection point between the photodiode 310 and the capacitor 320, and the other end is connected to the ground GND. Charge is accumulated in capacitor 320 due to current IL and the potential of node Q rises. However, when switching element 330 is turned on, the accumulated charge is discharged and the potential of node Q becomes the ground level.

  The switching element 330 is constituted by a TFT, and is turned on when a reset signal REST supplied to its gate is active (high level), and is turned off when the reset signal REST is inactive (low level. Node Q is The reference signal REF is supplied to one input terminal of the NAND circuit 340, and the other input terminal is supplied with a reference signal REF whose cycle is shorter than that of the reset signal RESET. The pulse signal 300a is output through the inverters 350, 360, and 370.

  FIG. 3 shows a timing chart of the optical sensor circuit 300. In this example, the value of the current IL output from the photodiode 310 at low illuminance is i1, and the value of the current IL output from the photodiode 310 at high illuminance is i2. When the reset signal RESET becomes active during the period from time t1 to time t2, the switching element 330 is turned on, and both ends of the capacitor 320 are short-circuited. As a result, the potential of the node Q becomes the ground level. When time t2 is reached, switching element 330 is turned off and charging of capacitor 320 is started. For this reason, the potential of the node Q rises from time t2. In this case, since the capacitor 320 is charged with a constant current, the waveform of the potential change at the node Q is a straight line. The slope of the potential waveform increases as the current value increases. In this example, since i1> i2, the rise time Ta is shorter than the rise time Tb.

  The NAND circuit 340 functions as a logic circuit that calculates the logical product of the potential of the node Q and the reference signal REF. Therefore, when the current IL value is i1, the pulse signal 300a is output during the period from time ta to time t3, and when the current IL value is i2, the pulse signal 300a is output during the period from time tb to time t3. A pulse signal 300a is output. Here, when the number of pulse signals 300a generated in the period from time t2 to time t3 is compared, the number is 8 when the current value is i1, and is 3 when the current value is i2. As described above, the current value i1 is a value of the current IL obtained when the ambient illuminance is high and the current value i2 is low. Therefore, the frequency of the pulse signal 300a is an indicator of the illuminance of the environment, and the higher the illuminance, the higher the frequency. In other words, the optical sensor circuit 300 outputs the pulse signal 300a indicating the illuminance of the environment as a frequency signal. Although simply expressed in FIG. 3, the pulse signal 300 a is actually output when the potential of the node Q reaches the operating point of the NAND circuit 340.

The value of the current output from the photoelectric conversion element such as the photodiode 310 is extremely small. A resistor may be used to convert a current into a voltage, but a resistor having a large resistance value needs to be formed in order to extract a voltage signal from a minute current. Such an area occupied by the resistor is large, which causes a problem in layout. Furthermore, there is a possibility that noise acts due to the resistor acting as an antenna, and it is not easy to accurately detect the illuminance. According to the present embodiment, since the current IL is integrated and converted into a voltage signal using the capacitor 320, the illuminance can be accurately detected with a small occupied area. Further, since the reference signal REF is supplied from the outside and the illuminance is detected in the form of frequency, the noise margin is improved and the handling of the signal becomes easy. The pulse signal 300a obtained in this way is supplied to the counting circuit 400 shown in FIG.
FIG. 4 shows a configuration example of the counting circuit 400. The counting circuit 400 includes, for example, a counter circuit 410 whose count value is reset by a reset signal RESET, and a latch circuit 420 that latches count data indicating the count result of the counter circuit 410 with the reset signal RESET. The output data of the latch circuit 420 is output to the dimming circuit 500 as illuminance data 400a.

Next, the image display area A will be described. In the image display region A, as shown in FIG. 5, m (m is a natural number of 2 or more) scanning lines 2 are formed in parallel along the X direction, while n (n is (Natural number of 2 or more) number of data lines 3 are arranged in parallel along the Y direction. In the vicinity of the intersection of the scanning line 2 and the data line 3, the gate of the TFT 50 is connected to the scanning line 2, while the source of the TFT 50 is connected to the data line 3 and the drain of the TFT 50 is connected to the pixel electrode 6. Connected. Each pixel includes a pixel electrode 6, a counter electrode (described later) formed on the counter substrate, and a liquid crystal sandwiched between the two electrodes. As a result, the pixels are arranged in a matrix corresponding to each intersection of the scanning line 2 and the data line 3.
Further, scanning signals Y1, Y2,..., Ym are applied in a pulse-sequential manner to each scanning line 2 to which the gate of the TFT 50 is connected. Therefore, when a scanning signal is supplied to a certain scanning line 2, the TFT 50 connected to the scanning line is turned on, so that the data signals X1, X2,..., Xn supplied from the data line 3 at a predetermined timing are After being written in order to the corresponding pixels, they are held for a predetermined period.

Since the orientation and order of liquid crystal molecules change according to the voltage level applied to each pixel, gradation display by light modulation becomes possible. For example, the amount of light passing through the liquid crystal is limited as the applied voltage increases in the normally white mode, whereas the amount of light that passes through the liquid crystal is reduced as the applied voltage increases in the normally black mode. As a whole, light having contrast according to the image signal is emitted for each pixel. For this reason, a predetermined display becomes possible.
In order to prevent the held image signal from leaking, a storage capacitor 51 is added in parallel with a liquid crystal capacitor formed between the pixel electrode 6 and the counter electrode. For example, the voltage of the pixel electrode 6 is held by the storage capacitor 51 for a time that is three orders of magnitude longer than the time when the source voltage is applied, so that the holding characteristics are improved, so that a high contrast ratio is realized.

  FIG. 6 shows a timing chart of the scanning line driving circuit 100 and the data line driving circuit 200. The scanning line driving circuit 100 sequentially shifts the Y transfer start pulse DY of one frame (1F) period according to the Y clock signal YCK to generate the scanning signals Y1, Y2,. The scanning signals Y1 to Ym are sequentially activated in each horizontal scanning period (1H). The data line driving circuit 200 transfers the X transfer start pulse DX of the horizontal scanning period according to the X clock signal XCK, and internally generates the sampling signals S1, S2,. The data line driving circuit 200 samples the image signal VID using the sampling signals S1, S2,..., Sn to generate data signals X1, X2,.

  As described above, in the present embodiment, since the light emission luminance of the backlight 600 is adjusted using the light detection circuit 300, the brightness of the screen can be controlled in accordance with the environmental illuminance, and the consumption of the electro-optical device 1 can be controlled. Electric power can be reduced. In addition, since the optical sensor circuit 300 and the counting circuit 400 are formed on the liquid crystal panel AA using elements such as TFTs, the electro-optical device 1 can be greatly reduced in size. Furthermore, the light detection circuit 300 can accurately detect the illuminance because the current IL of the photodiode 310 is charged by the capacitor 320 and the signal corresponding to the illuminance of the environment is extracted. In addition, since the final output signal of the optical sensor circuit 300 is given as the pulse signal 300a, the illuminance data 400a can be easily obtained by measuring the number of pulses per unit time.

<2. Second Embodiment>
Next, an electro-optical device 1 according to a second embodiment of the invention will be described. The electro-optical device 1 according to the second embodiment is the same as that of the first embodiment except that the Y transfer start pulse DY is used instead of the reset signal RESET and the Y clock signal YCK is used instead of the reference signal REF. The configuration is the same as that of the optical device 1.
FIG. 7 shows a configuration of the electro-optical device 1 according to the second embodiment. As shown in this figure, in the electro-optical device 1 of this embodiment, the signal generation circuit 700 is omitted. This is because the reset signal RESET is also used as the Y transfer start pulse DY, and the reference signal REF is also used as the Y clock signal YCK. Note that the X transfer start pulse DX may be used instead of the reset signal RESET, and the X clock signal XCK may be used instead of the reference signal REF. That is, various signals for driving the pixel circuit P1 may be used as the reset signal RESET and the reference signal REF.

  However, since the frequency of the Y clock signal YCK is lower than that of the X clock signal XCK, the Y transfer start pulse DY and the Y clock signal YCK are used in place of the reset signal RESET and the reference signal REF from the viewpoint of reducing power consumption. preferable. In addition, since the change in environmental illuminance is sufficiently longer than one frame period, which is the period of the Y transfer start pulse DY, even if the Y transfer start pulse DY and the Y clock signal YCK are used, the change in environmental illuminance follows. Thus, the light emission luminance of the backlight 600 can be adjusted.

  As described above, in the present embodiment, since various signals for driving the pixel circuit P1 are also used as the reset signal RESET and the reference signal REF, it is necessary to generate a special signal in order to operate the optical sensor circuit 300. Disappear. As a result, the signal generation circuit 600 can be omitted to simplify the configuration. Further, since it is not necessary to provide an input terminal for supplying the reset signal RESET and the reference signal REF to the liquid crystal panel AA, it is possible to cope with a narrow pitch of the input terminals.

<3. Third Embodiment>
Next, an electro-optical device 1 according to a third embodiment of the invention will be described. The electro-optical device 1 according to the third embodiment is the second embodiment shown in FIG. 7 except that the pixel circuit P2 is used instead of the pixel circuit P1 and the image processing circuit 910 is used instead of the image processing circuit 900. The configuration is the same as that of the electro-optical device 1 according to the embodiment.
FIG. 8 shows the configuration of the electro-optical device 1 according to the third embodiment. The pixel circuit P2 includes a light emitting element as an electro-optical element. Specifically, an organic light emitting diode element (hereinafter referred to as an OLED element) is included. An OLED (Organic Light Emitting Diode) element is a current-driven light-emitting element that itself emits light, unlike a liquid crystal element that changes the amount of transmitted light. The power supply circuit 950 supplies a power supply Vdd for driving the OLED element to each pixel circuit P2.

  Further, the illuminance data 400a output from the counting circuit 400a is supplied to the image processing circuit 910. The image processing circuit 910 controls the level of the image signal VID according to the illuminance data 400a. Specifically, the image processing circuit 910 increases the level of the image signal VID as the illuminance of the environment increases. Conversely, when the ambient illuminance decreases, the level of the image signal VID is decreased. When the level of the image signal VID is decreased, the levels of the data signals X1 to Xn are also decreased, and the light emission luminance of the OLED element is decreased. Since the OLED element emits light with a luminance corresponding to the driving current, it is possible to control the brightness of the entire screen according to the environmental illuminance. This makes it possible to increase the brightness of the entire screen under natural daylight and display an easy-to-view image even in a bright environment, while reducing the overall screen brightness in a dark environment at night to reduce power consumption. It becomes possible.

  FIG. 8 shows a circuit diagram of the pixel circuit P2. The pixel circuit P2 shown in the figure is located in the i (i is a natural number satisfying 1 ≦ i ≦ m) row j (j is a natural number satisfying 1 ≦ j ≦ n) column. Then, the scanning signal Yi is supplied via the scanning line 2, and the data signal Xj is supplied as the voltage signal Vdata via the data line 3. The pixel circuit P2 includes two TFTs 401 and 402, a capacitor element 410, and an OLED element 420. Among these, the source electrode of the p-channel TFT 401 is connected to the power supply line L, and the drain electrode thereof is connected to the anode of the OLED element 420. In addition, a capacitor element 410 is provided between the source electrode and the gate electrode of the TFT 401. The gate electrode of the TFT 402 is connected to the scanning line 101, its source electrode is connected to the data line 103, and its drain electrode is connected to the gate electrode of the TFT 401.

  In such a configuration, when the scanning signal Yi becomes H level, the n-channel TFT 402 is turned on, so that the voltage at the connection point Z becomes equal to the voltage Vdata. At this time, a charge corresponding to Vdd−Vdata is accumulated in the capacitor 410. Next, when the scanning signal Yi becomes L level, the TFT 402 is turned off. Since the input impedance at the gate electrode of the TFT 401 is extremely high, the charge accumulation state in the capacitor 410 does not change. The voltage between the gate and source of the TFT 401 is held at the voltage (Vdd−Vdata) when the voltage Vdata is applied. Since the driving current Ioled flowing through the OLED element 420 is determined by the gate-source voltage of the TFT 401, the driving current Ioled corresponding to the voltage Vdata flows.

  In this embodiment, the Y transfer start pulse DY and the Y clock signal YCK are used instead of the reset signal RESET and the reference signal REF as in the second embodiment. However, as in the first embodiment, a signal generation circuit is used. 700 may be provided, from which the reset signal RESET and the reference signal REF may be supplied to the optical sensor circuit 300.

<4. Fourth Embodiment>
FIG. 10 shows the configuration of the electro-optical device 1 according to the fourth embodiment of the invention. The electro-optical device 1 according to the fourth embodiment is configured in the same manner as the electro-optical device 1 according to the third embodiment shown in FIG. 8 except that a power circuit 960 is used instead of the power circuit 950. In the electro-optical device 1, the illuminance data 400 a output from the counting circuit 400 is supplied to the power supply circuit 960. As described above, the current Ioled flowing through the OLED element 420 is determined by “Vdd−Vdata”. Therefore, by adjusting the power supply voltage Vdd according to the illuminance data 400a, it becomes possible to control the luminance of the entire screen according to the environmental illuminance. Specifically, control is performed so that the power supply voltage Vdd increases as the ambient illuminance increases. This makes it possible to increase the brightness of the entire screen under daylight and to display an image that is easy to see even in a bright environment, while lowering the brightness of the entire screen in a dark environment at night. Electric power can be reduced.

<5. Modification>
The present invention is not limited to the above-described embodiments, and for example, various modifications described below are possible.
(1) Although the liquid crystal element and the OLED element are taken up as an example of the electro-optical element in the above-described embodiment, the present invention is also applied to an electro-optical device using other electro-optical elements. An electro-optical element is an element whose optical characteristics such as transmittance and luminance change when an electric signal (current signal or voltage signal) is supplied. For example, an electrophoretic display using a display panel using a light emitting element such as an inorganic EL (ElectroLuminescent) or a light emitting polymer or a microcapsule containing a colored liquid and white particles dispersed in the liquid as an electro-optical material Panels, twist ball display panels using twist balls painted in different colors for areas of different polarity as electro-optical materials, toner display panels using black toner as electro-optical materials, or high pressure such as helium or neon The present invention can be applied to various electro-optical devices such as a plasma display panel using a gas as an electro-optical material as in the above embodiment.
(2) The pixel circuit P2 of the third embodiment and the fourth embodiment described above is a voltage drive type that inputs a voltage signal as a data signal, but is a current drive type that inputs a current signal as a data signal. Of course, it is also good.

(3) In each of the embodiments described above, the optical sensor circuit 300 outputs the pulse signal 300a. However, the potential of the node Q may be output as a voltage signal. The effective value of this voltage signal is a value corresponding to the illuminance. Therefore, the light control circuit 500 may control the light emission luminance of the backlight 600 based on the voltage signal. The image processing circuit 910 may adjust the level of the image signal VID based on the voltage signal. Further, the power supply circuit 960 may adjust the power supply voltage Vdd based on the voltage signal.
In addition, in each of the above-described embodiments, the photodetection circuit that detects the illuminance of the environment may be considered to include not only the photosensor circuit 300 but also the counting circuit 400.

<6. Electronic equipment>
Next, an electronic apparatus to which the electro-optical device 1 according to the above-described embodiments and modifications is applied will be described. FIG. 11 shows the configuration of a mobile personal computer to which the electro-optical device 1 is applied. The personal computer 2000 includes the electro-optical device 1 as a display unit and a main body 2010. The main body 2010 is provided with a power switch 2001 and a keyboard 2002.
FIG. 12 shows a configuration of a mobile phone to which the electro-optical device 1 is applied. A cellular phone 3000 includes a plurality of operation buttons 3001, scroll buttons 3002, and the electro-optical device 1 as a display unit. By operating the scroll button 3002, the screen displayed on the electro-optical device 1 is scrolled.
FIG. 13 shows a configuration of a portable information terminal (PDA: Personal Digital Assistants) to which the electro-optical device 1 is applied. The information portable terminal 4000 includes a plurality of operation buttons 4001, a power switch 4002, and the electro-optical device 1 as a display unit. When the power switch 4002 is operated, various types of information such as an address book and a schedule book are displayed on the electro-optical device 1.
The electronic apparatus to which the electro-optical device 1 is applied includes, in addition to those shown in FIGS. 11 to 13, a digital still camera, a liquid crystal television, a viewfinder type, a monitor direct view type video tape recorder, a car navigation device, a pager, Examples include electronic notebooks, calculators, word processors, workstations, videophones, POS terminals, and devices equipped with touch panels. The electro-optical device 1 described above can be applied as a display unit of these various electronic devices.

1 is a block diagram illustrating an overall configuration of an electro-optical device 1 according to a first embodiment of the present invention. It is a block diagram which shows the structural example of the optical sensor circuit 300 of the apparatus. It is a timing chart which shows operation | movement of the circuit. It is a block diagram which shows the structural example of the counting circuit 400 of the same apparatus. It is a circuit diagram which shows the structural example of the image display area A of the same apparatus. 3 is a timing chart showing operations of a scanning line driving circuit 100 and a data line driving circuit 200 of the same device. FIG. 6 is a block diagram illustrating an overall configuration of an electro-optical device 1 according to a second embodiment of the invention. FIG. 6 is a block diagram illustrating an overall configuration of an electro-optical device 1 according to a third embodiment of the invention. It is a circuit diagram of pixel circuit P2 used for the device. FIG. 6 is a block diagram illustrating an overall configuration of an electro-optical device 1 according to a fourth embodiment of the invention. 2 is a perspective view illustrating a configuration of a personal computer as an example of an electronic apparatus to which the electro-optical device 1 is applied. FIG. 2 is a perspective view illustrating a configuration of a mobile phone as an example of an electronic apparatus to which the electro-optical device 1 is applied. FIG. 3 is a perspective view showing a configuration of a portable information terminal as an example of an electronic apparatus to which the electro-optical device 1 is applied. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Electro-optical device, 2 ... Scan line, 3 ... Data line, 100 ... Scan line drive circuit, 200 ... Data line drive circuit, 300 ... Photosensor circuit, 310 ... Photodiode, 320 ... Capacitor, 330 ... Switching element, 340 ... NAND circuit, P1, P2 ... pixel circuit, 400 ... counting circuit.

Claims (12)

A photodiode having a cathode connected to a high-potential side power supply and an anode connected to a connection point;
A capacitive element provided between the connection point and the low-potential-side power source;
A switching element provided between the connection point and the low-potential-side power supply, and turned on and off at a predetermined cycle;
Taking out the voltage signal at the connection point as an output signal,
An optical detection circuit characterized by that. A voltage frequency conversion circuit for converting the voltage signal into a frequency signal;
Outputting the frequency signal as the output signal instead of the voltage signal;
The photodetection circuit according to claim 1. The voltage frequency conversion circuit includes a logic circuit that calculates a logical product of the voltage signal and a reference signal having a cycle shorter than the ON / OFF cycle of the switching element and outputs a binary signal.
Outputting the binarized signal as the frequency signal;
The photodetection circuit according to claim 2. Counting means for counting the binarized signal and outputting a counting data signal indicating a counting result per unit time;
The photodetection circuit according to claim 3, wherein the count data signal is output as the output signal. Photodetection circuit according to any one of claims 1 to 4,
Multiple data lines,
A plurality of scan lines;
A pixel circuit including an electro-optical element, each of which is provided corresponding to an intersection of the data line and the scanning data, and whose optical characteristics are changed by an electrical action;
A driving circuit for driving the electro-optic element by outputting a signal to at least one of the plurality of data lines and the plurality of scanning lines;
An electro-optical panel comprising: The electro-optical panel according to claim 5,
A light source that emits light from one surface of the electro-optical panel to the other surface;
A light control circuit for adjusting the light amount of the light source based on the output signal of the light detection circuit,
The electro-optical element is a liquid crystal element whose transmittance changes according to an applied voltage.
An electro-optical device. The electro-optical panel according to claim 5,
An image processing circuit that outputs an image signal whose level is adjusted based on the output signal of the photodetection circuit;
The electro-optic element comprises a light emitting element that emits light with a luminance corresponding to a driving current
The drive circuit controls the drive current based on the image signal output from the image processing circuit;
An electro-optical device. The electro-optical panel according to claim 5,
A power supply circuit that outputs a power supply voltage adjusted in level based on the output signal of the photodetection circuit;
The drive circuit outputs a data signal corresponding to a gradation to be displayed on the data line,
The electro-optic element comprises a light emitting element that emits light with a luminance corresponding to a driving current,
The pixel circuit includes a driving transistor that supplies the driving current to the light emitting element,
The drive transistor supplies the light emitting element with the drive current having a magnitude based on the power supply voltage and the data signal.
An electro-optical device. Multiple data lines,
A plurality of scan lines;
A pixel circuit including an electro-optical element, each of which is provided corresponding to an intersection of the data line and the scanning data, and whose optical characteristics are changed by an electrical action;
A control circuit for generating a plurality of control signals;
A drive circuit that generates a drive signal based on the plurality of control signals and outputs the drive signal to at least one of the plurality of data lines and the plurality of scanning lines;
A photodiode having a cathode connected to a high-potential-side power supply and an anode connected to a connection point; a capacitive element provided between the connection point and the low-potential-side power supply; the connection point and the low-potential-side power supply; And a switching element that is turned on / off based on a first signal, and includes a photodetector circuit that extracts a voltage signal from the connection point,
An electro-optical device, wherein the first signal is also used as one of the plurality of control signals. Multiple data lines,
A plurality of scan lines;
A pixel circuit including an electro-optical element, each of which is provided corresponding to an intersection of the data line and the scanning data, and whose optical characteristics are changed by an electrical action;
A control circuit for generating a plurality of control signals;
A drive circuit that generates a drive signal based on the plurality of control signals and outputs the drive signal to at least one of the plurality of data lines and the plurality of scanning lines;
A photodiode having a cathode connected to a high-potential-side power supply and an anode connected to a connection point; a capacitive element provided between the connection point and the low-potential-side power supply; the connection point and the low-potential-side power supply; And a logic circuit that calculates a logical product of a switching element that is turned on / off based on a first signal and a second signal having a shorter cycle than the first signal and outputs a binarized signal. Comprising a photodetection circuit having
An electro-optical device, wherein the first signal and the second signal are combined with any one of the plurality of control signals.   An electronic apparatus comprising the electro-optical device according to claim 5. A method for controlling a photodetection circuit comprising a photodiode having a cathode connected to a high-potential side power supply and an anode connected to a connection point, and a capacitive element provided between the connection point and the low-potential side power supply. There,
Short-circuit both ends of the capacitive element at a predetermined period,
Calculating a logical product of a reference signal having a period shorter than the predetermined period and a voltage signal at the connection point to generate a binarized signal;
Outputting the binarized signal as an illuminance signal indicating illuminance;
And a method of controlling the photodetection circuit.

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