JP4978453B2 - Sensing device, display device, and electronic device - Google Patents

Description

  The present invention relates to a sensing device, a display device, and an electronic device that detect a change in capacitance.

A display device having a sensing circuit that detects a change in capacitance is known. For example, the technique described in Patent Document 1 incorporates a sensing circuit in a liquid crystal display device. In this sensing circuit, a reference capacitor and a capacitance detection element are connected in series, the connection point is connected to the gate of the amplification transistor, and a detection current corresponding to the gate potential is passed through the amplification transistor. Then, a change in capacitance of the capacitance element is taken out as a change in detection current. When external light is incident on the transistors constituting the sensing circuit, a leakage current is generated. When this leakage current occurs, the change in capacitance cannot be measured accurately. For this reason, a light-shielding film is provided on the upper part of the transistor constituting the sensing circuit to prevent outside light from entering.
JP 2007-48275 A

Incidentally, the illuminance of the display device is preferably adjusted according to the brightness of the environment. For example, in the daytime outdoors, the surroundings are bright, so that high illuminance is required to make the screen easy to see. On the other hand, at night, sufficient contrast can be obtained even at low illuminance. In order to execute such control, it is necessary to provide a sensor for measuring the illuminance of outside light in the display device. When a sensor is provided in a conventional display device, the sensor is disposed outside or around the panel. In such a case, there is a problem that the area outside the screen (the so-called frame) becomes large and the cost increases.
The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a sensing device that detects a change in capacitance to have a function of detecting external light.

  In order to solve this problem, a sensing device according to the present invention includes a light-shielding film that shields external light, a part of which is located under the light-shielding film, and a circuit layer in which a unit circuit is formed, The unit circuit has a first transistor (for example, 41 shown in FIG. 3) that has a power source line electrically connected to one electrode and outputs a detection current corresponding to the gate potential from the other electrode, and a first control line. A second transistor that controls a conduction state or a non-conduction state in response to a reset signal supplied to the gate via the first and supplies a first potential to the gate of the first transistor in the conduction state (for example, in FIG. 42), a reference capacitor in which the gate of the first transistor is electrically connected to one terminal and a second potential is supplied to the other terminal, and the gate of the first transistor is electrically connected to one terminal. Connected Provided between the capacitance detection element to which the third potential is supplied to the other terminal and the other electrode of the first transistor and the detection line, and is supplied to the gate through the second control line. A third transistor (for example, 43 shown in FIG. 2) that is turned on in response to a selection signal, and at least one of the first transistor and the second transistor blocks outside light by the light blocking film. It is characterized by being formed in a region that is not.

According to the present invention, at least one of the first transistor and the second transistor is formed in a region where external light is not shielded by the light shielding film. For this reason, the electric charge charged in the reference capacitance and the capacitance detection element flows out due to the generation of the leakage current. As a result, the gate potential of the amplification transistor changes, so that a detection current having a magnitude corresponding to the illuminance of external light can be taken out via the detection line.
Here, it is preferable that the first potential is supplied to the power supply line, and the second transistor is provided between the power supply line and the gate of the one transistor. In this case, since the first potential is supplied via the power supply line in order to reset the gate potential of the first transistor, it is not necessary to prepare a special power supply for resetting, and the number of wirings for supplying the first potential is reduced. Can be reduced.
Preferably, the second potential is the potential of the reset signal, and the other terminal of the reference capacitor is electrically connected to the first control line. In this case, since one terminal of the reference capacitor is connected to the first control line and performs a sensing operation by a reset signal, it is not necessary to provide a dedicated power source for the reference capacitor, and the number of wirings for supplying the reference capacitor is further reduced. be able to. Therefore, the configuration of the sensing circuit can be greatly simplified.
Further, the third potential is preferably a fixed potential. In this case, since the fixed potential is supplied to the other terminal of the capacitive element, the gate potential of the first transistor does not fluctuate in a predetermined cycle. In addition, since it is not necessary to perform sensing in synchronization with the image display cycle of the display device, sensing can be performed as necessary, or sensing can be performed with a longer cycle. As a result, power consumption can be reduced.

In the sensing device described above, it is preferable that the reference capacitance is a parasitic capacitance generated between a gate and a source of the second transistor. In this case, since it is not necessary to build a reference capacitor as an element, the configuration of the sensing circuit can be further simplified.
The first to third transistors are formed by the same process, and include a semiconductor layer, a gate oxide film, and a gate wiring. The reference capacitor uses the semiconductor layer as one electrode, and the gate wiring Is preferably used as the other electrode. In this case, a reference capacitor is formed, but since it can be formed by the same process as the first to third transistors, the manufacturing cost can be reduced.
Furthermore, in the sensing device described above, it is preferable that a plurality of the unit circuits are formed in a matrix in the circuit layer, and the detection current is extracted from each of the plurality of unit circuits. In this case, the sensing device can be applied to capture a two-dimensional image such as a scanner.

  Next, a display device according to the present invention includes a pixel electrode, a counter electrode, a plurality of pixel circuits having a dielectric sandwiched between the pixel electrode and the counter electrode, the sensing device described above, and the sensing Based on each detected current output from the device, the illuminance of the external light incident on each unit circuit is divided by a predetermined width, and the illuminance corresponding to the most frequent classification is output as the illuminance of external light. It has the control means to do. According to the present invention, even if a change in capacitance is detected in any of the plurality of unit circuits, the mode value is obtained, so that the illuminance of external light can be detected.

  Here, the capacitance detection element includes a first electrode formed simultaneously with the pixel electrode, a second electrode formed simultaneously with the counter electrode, and a gap between the first electrode and the second electrode. It is preferable to include the sandwiched dielectric. According to the present invention, when the distance (gap length) between the first electrode and the second electrode changes, the capacitance value of the capacitance detection element changes, so that it can be detected when touched by a person. it can.

Furthermore, in the above-described display device, the dielectric is a liquid crystal, and includes a backlight and a dimming unit that adjusts the brightness of the backlight according to the illuminance of external light output from the control unit. Is preferred. According to the present invention, since the brightness of the backlight is adjusted according to the detected illuminance of outside light, the brightness of the screen can be automatically adjusted according to the environment. In addition, since a special ambient light sensor is unnecessary, the display device can be reduced in size and the cost is not increased.
Next, an electronic apparatus according to the present invention preferably includes the display device described above. Such electronic devices include personal computers, mobile phones, portable information terminals, touch panels, and the like.

<1. Embodiment>
FIG. 1 is a block diagram illustrating a configuration of a liquid crystal display device (one aspect of a display device) according to an embodiment of the present invention. The liquid crystal display device 500 includes a display area A. In the display area A, a plurality of scanning lines 30, a plurality of data lines 31, and a plurality of pixel circuits P are arranged corresponding to the intersections thereof. The pixel circuit P includes a transistor 33, a pixel electrode 34, a counter electrode 36 to which a common potential Vcom is supplied, and a liquid crystal 35 sandwiched between the pixel electrode 34 and the counter electrode 36. The transistor 33 is constituted by a TFT (Thin Film Transistor), the gate thereof is connected to the scanning line 30, the drain is connected to the data line 31, and the source is connected to the pixel electrode 34.

Although details will be described later, the sensing circuit 40 is provided at a rate of one for each of the four pixel circuits P. The plurality of sensing circuits 40 are driven based on various signals supplied from the drive circuit 300, and supply changes in capacitance to the drive circuit 300 as detection currents (not shown). The drive circuit 300 converts the detection current into a voltage and supplies it to the control circuit 310 as a detection signal D. The detection signal D indicates the change in capacitance and the illuminance of external light in each sensing circuit 40. Based on the detection signal D, the control circuit 310 generates instruction data Da indicating the area where the display area A is pressed and illuminance data Db indicating the illuminance of the environment. Processing for generating the illuminance data Db will be described later.
The dimming circuit 320 adjusts the brightness of the backlight 330 based on the illuminance data Db. Specifically, the illuminance of the backlight 330 is increased when the illuminance indicated by the illuminance data Db is large, and the illuminance of the backlight 330 is decreased when the illuminance indicated by the illuminance data Db is small. Thereby, it is possible to reduce power consumption while ensuring contrast.

  The Y driver 100 generates a scanning signal for sequentially selecting the plurality of scanning lines 30 and supplies it to each pixel circuit P. The scanning signal is a pulse having a width corresponding to one horizontal scanning period (1H) from the first timing of one vertical scanning period (1F), and is supplied to the scanning line 30 in the first row. Thereafter, this pulse is sequentially shifted and supplied to each scanning line 30 as a scanning signal. On the other hand, the X driver 200 supplies a data signal having a magnitude corresponding to the gradation to be displayed to each of the pixel circuits P located on the selected scanning line 30.

  FIG. 2 shows an arrangement relationship of the black matrix BM, the pixel circuit P, and the sensing circuit 40. The black matrix BM functions as a light shielding film that shields external light. In this example, the black matrix BM is provided between the pixel circuits P. The sensing circuit 40 and the black matrix BM can be combined and understood as a sensing device. In this sensing device, a part of the sensing circuit 40 is located under the black matrix BM, and the other part is not located under the black matrix BM, and external light is incident thereon.

FIG. 3 shows a circuit diagram of the sensing circuit 40. The sensing circuit 40 includes an amplification transistor 41, a reset transistor 42, and a selection transistor 43. These transistors are composed of TFTs similarly to the transistor 33 of the pixel circuit P described above, and may be formed by the same process, for example.
A reset signal RES is supplied to the gate of the reset transistor 42 via the first control line 10. The drain of the reset transistor 42 is connected to the power supply line 20, and the source thereof is connected to the gate of the amplification transistor 41. The voltage VRH is supplied to the power line 20. Here, the reset transistor 42 is not positioned under the black matrix BM, and is disposed so that external light is incident thereon. In general, when light is incident on a transistor, a leakage current is generated when the transistor is off. The magnitude of the leakage current increases as the amount of incident light increases.

The drain of the amplification transistor 41 is connected to the power supply line 20, and the source thereof is connected to the drain of the selection transistor 43. The source of the selection transistor 43 is connected to the detection line 21, and the selection signal SEL is supplied to the gate of the selection transistor 43 via the second control line 11.
A reference capacitance element 44 is provided between the gate of the amplification transistor 41 and the first control line 10. Furthermore, one terminal of the capacitance detection element 45 is connected to the gate of the amplification transistor 41, and a fixed potential Vx is supplied to the other terminal. In this example, the amplification transistor 41 and the selection transistor 43 are arranged so as to be positioned under the black matrix BM.

Next, the operation of the sensing circuit 40 will be described with reference to FIGS. The sensing circuit 40 operates with the reset period Tres, the sensing period Tsen, and the readout period Tout as one unit.
First, in the reset period Tres, the level of the reset signal RES becomes VD, and the reset transistor 41 is turned on. At this time, the selection signal SEL is at a low level, and the selection transistor 43 is turned off. Then, as shown in FIG. 4, the potential of the gate of the amplification transistor 41 is reset to the power supply potential VRH.

  Next, in the sensing period Tsen following the reset period Tres, the level of the reset signal RES changes from VD to GND (= 0V). Then, as shown in FIG. 6, the reset transistor 42 is turned off. Since the first control line 10 is connected to one electrode of the reference capacitor element 44, the reference capacitor element 44 functions as a coupling capacitor, and the gate potential of the amplification transistor 41 changes when the level of the reset signal RES changes. .

Here, if the capacitance value of the reference capacitance element 44 is Cr, the capacitance value of the capacitance detection element 45 is Cs, and the potential change of the first control line 10 is ΔVgate (= VD), the gate potential of the amplification transistor 41 The change ΔV is given by the following equation (1). However, the parasitic capacitance is ignored.
ΔV = ΔVgate * Cr / (Cr + Cs) (1)
From equation (1), if the capacitance value Cs of the capacitance detection element 45 is large, the change ΔV due to capacitive coupling is small, and conversely, if the capacitance value Cs is small, the change ΔV is large. Therefore, the capacitance change of the capacitance detection element 45 can be reflected in the gate potential.

Next, in the reading period Tout, the selection signal SEL changes from the low level to the high level. Then, as shown in FIG. 7, the selection transistor 43 is turned on. As a result, a detection current Idet corresponding to the gate potential of the amplification transistor 41 flows through the detection line 21.
In order to ensure that the selection transistor 43 is turned on in the readout period Tout, it is preferable to precharge the potential of the detection line 21 to the precharge potential Vpre prior to the readout period Tout. In this example, as shown in FIG. 4, the reset period Tres and the sensing period Tsen are set as a precharge period Tpre, and the precharge potential Vpre is supplied to the detection line 21 during the period.

  Here, the change of the electrostatic capacitance by the electrostatic capacitance detection element 45 will be described with reference to FIG. As shown in FIG. 8, the capacitance detecting element 45 is configured by sandwiching a liquid crystal 35 between a first electrode 45a and a second electrode 45b. In a state where a human finger is not touched, the first electrode 45a and the second electrode 45b are parallel as shown in FIG. 5A, but when the liquid crystal display device 500 is pressed with the finger, the second electrode 45b is bent. The distance between the first electrode 45a and the second electrode 45b is shortened. For this reason, when a person presses the liquid crystal display device 500 with a finger, the capacitance value Cs of the capacitance detection element 45 increases. In this way, a change in capacitance is detected.

Further, as described above, since the reset transistor 42 is arranged so that external light is incident, the gate potential of the amplifying transistor 41 is changed by the leak current even if the person does not press the liquid crystal display device 500 with a finger. FIG. 9 shows the relationship between the output voltage (the level of the detection signal D) and the illuminance. As can be seen from the figure, the level of the detection signal D increases as the illuminance increases.
However, since the detection signal D also reflects a change in capacitance due to touch, it is necessary to distinguish this from the influence of external light. Therefore, the control circuit 310 executes the illuminance detection process shown in FIG.

  First, the control circuit 310 AD-converts the detection signal D for one screen, takes it as detection data, and stores it in the memory (S1). Next, the control circuit 310 reads the detection data stored in the memory and generates a histogram (S2). The histogram divides the data value of the detection data by a predetermined width and shows the frequency for each division. Next, the control circuit 310 specifies the center value of the classification with the highest frequency in the histogram as the mode value (S3). Furthermore, the control circuit 310 converts the mode value into illuminance and generates illuminance data Db.

  For example, it is assumed that a person presses down the region Q1 with a finger as shown in FIG. In this case, the size of the detection data is divided into a region Q1 that is affected by the finger pressing, a region Q2 that becomes a shadow of the finger and the illuminance of the external light is low, and a region Q3 that the external light is sufficiently incident. It is done. Since the touch operation is performed on a part of the display area A, the illuminance of the environment is obtained by the area Q3 having the largest area. By creating a histogram and obtaining the mode value, the illuminance of outside light in the region Q3 can be obtained. In this example, the histogram is created, but the mode value may be generated from the detection data itself without creating the histogram.

  In the embodiment described above, the illuminance of external light is detected using the leakage current of the reset transistor 42. However, the illuminance of external light may be detected using the leakage current of the amplification transistor 41. Further, external light may be detected using the leakage currents of both the reset transistor 42 and the amplification transistor 41. In other words, at least one of the reset transistor 42 and the amplification transistor 41 may be arranged so that external light is incident on the black matrix BM without being positioned below the black matrix BM.

  Further, the reference capacitor element 44 of this example is configured by using a semiconductor layer 47 as one electrode, using a gate wiring 48 as the other electrode, and sandwiching a gate oxide film 49 therebetween. The semiconductor layer 47, the gate wiring 48, and the gate oxide film 49 are formed by the same process as the other transistors 41 and 42. Therefore, a special process is not required for forming the reference capacitor element 44, and the manufacturing cost can be reduced.

Incidentally, the reference capacitance element 44 may be provided between the first control line 10 and the gate of the amplification transistor 41. Parasitic capacitance resulting from the structure is attached between the gate and drain of the reset transistor 42 and between the gate and source. Therefore, the parasitic capacitance of the reset transistor 42 may be used as the reference capacitance element 44 as in the sensing circuit 40A shown in FIG. In this case, as shown in FIG. 3, the reference capacitance element 44 does not need to be built in, so that the structure can be further simplified.
In the above-described embodiment, the drive circuit 300 is provided to drive the sensing circuit 40. However, if it is allowed to execute sensing in synchronization with the image display, the selection to be supplied to the sensing circuit 40 is selected. The signal SEL and the reset signal RES may be generated by the Y driver 201.
Furthermore, a sensing circuit 40B shown in FIG. 13 may be used in place of the sensing circuit 40 described above. This sensing circuit 40B is different from the sensing circuit 40 in the following points.
First, in the sensing circuit 40, one electrode of the reset transistor 42 is electrically connected to the power supply line 20, but in the sensing circuit 40B, it is not connected to the power supply line 20 and other wiring (see FIG. The first potential VRS is supplied through (not shown).
Second, in the sensing circuit 40, one electrode of the reset transistor 42 is electrically connected to the power supply line 20. However, in the sensing circuit 40B, one terminal of the reference capacitance element 44 is connected to the gate of the amplification transistor 41. Although the other terminal is connected to the first control line 10 in the sensing circuit 40B, the other terminal is not connected to the first control line 10 and is connected via another wiring (not shown). Thus, the second potential VRC is supplied.
Third, in the sensing circuit 40, the fixed potential Vx is supplied to the other terminal of the capacitance detection element 45. In the sensing circuit 40B, the third potential is applied to the other terminal of the capacitance detection element 45. Va is supplied.
The first to third potentials are generated by the peripheral circuit. For example, a variable output regulator or a DA converter can be used. If the potential is allowed to vary in this way, the degree of freedom of the sensing operation can be improved.
Further, the common potential Vcom may be used as the third potential Va. The third potential Va needs to be fixed during the sensing operation. However, even if the common potential Vcom is changed by AC driving, the third potential Va may be set so that the timing for inverting the polarity does not occur during the sensing operation.

<2. Application example>
Next, electronic equipment using the liquid crystal display device according to the present invention will be described. FIG. 13 is a perspective view showing the configuration of a mobile personal computer employing the liquid crystal display device 500 as a display unit. The personal computer 2000 includes a liquid crystal display device 500 as a display unit and a main body unit 2010. The main body 2010 is provided with a power switch 2001 and a keyboard 2002. Menu buttons 2020, 2030, and 2040 are displayed on the liquid crystal display device 500. Various programs can be assigned to these menu buttons. For example, an e-mail can be assigned to the menu button 2020, a browser can be assigned to the menu button 2030, and drawing software can be assigned to the menu button 2040. Even if the user does not operate the keyboard 2002, the user can activate desired software simply by touching the menu button.

  FIG. 14 shows a configuration of a mobile phone to which the liquid crystal display device 500 according to the embodiment is applied. A cellular phone 3000 includes a plurality of operation buttons 3001, scroll buttons 3002, and a liquid crystal display device 500 as a display unit. By operating the scroll button 3002, the screen displayed on the liquid crystal display device 500 is scrolled. Menu buttons 3010 and 3020 are displayed on the liquid crystal display device 500. For example, when the user touches the menu button 3010, the phone book is displayed, and when the user touches the menu button 3020, the telephone number of the mobile phone is displayed.

  FIG. 15 shows a configuration of a personal digital assistant (PDA) to which the liquid crystal display device 500 according to the embodiment is applied. The information portable terminal 4000 includes a plurality of operation buttons 4001, a power switch 4002, and a liquid crystal display device 500 as a display unit. When the power switch 4002 is operated, menu buttons 4010 and 4020 are displayed. When the menu button 4010 is pressed, the address book is displayed, and when the menu button 4020 is pressed, the schedule book is displayed.

  Note that electronic devices to which the electro-optical device according to the present invention is applied include those shown in FIGS. 13 to 15, ticket issuing devices for issuing various tickets, digital still cameras, televisions, video cameras, and car navigation devices. Electronic notebook, electronic paper, calculator, word processor, workstation, videophone, scanner, copying machine, video player, equipment equipped with a touch panel, and the like.

  The sensing circuit 40 described above is formed on the same plane on which the pixel circuit P in the display area A is formed. Good. Further, instead of the liquid crystal display device 500, a display device using an organic light emitting diode may be used. In addition, the liquid crystal is an example of a dielectric, and silicon nitride may be used as the dielectric.

It is a block diagram which shows the structure of the liquid crystal display device which concerns on embodiment of this invention. It is a top view which shows the arrangement | positioning relationship of a black matrix, a pixel circuit, and a sensing circuit. It is a circuit diagram which shows the structure of a sensing circuit. It is a timing chart which shows operation | movement of a sensing circuit. It is explanatory drawing which shows operation | movement of the sensing circuit in a reset period. It is explanatory drawing which shows operation | movement of the sensing circuit in a sensing period. It is explanatory drawing which shows operation | movement of the sensing circuit in a read-out period. It is sectional drawing which shows the structure of an electrostatic capacitance detection element. It is a graph which shows the relationship between an output voltage and illumination intensity. It is a flowchart which shows the content of an illumination intensity detection process. It is a schematic diagram at the time of touching a screen with a human finger. It is a circuit diagram which shows the other structural example of a sensing circuit. It is a circuit diagram which shows the other structural example of a sensing circuit. It is a perspective view which shows the specific form of the electronic device which concerns on this invention. It is a perspective view which shows the specific form of the electronic device which concerns on this invention. It is a perspective view which shows the specific form of the electronic device which concerns on this invention.

Explanation of symbols

500: Liquid crystal display, A: Display area, 40: Sensing circuit, 41: Amplification transistor, 42: Reset transistor, 43: Selection transistor, 44: Reference capacitance element, 45: Capacitance Detection element, RES ... reset signal, SEL ... selection signal, 10 ... first control line, 11 ... second control line, 20 ... power line, 21 ... detection line, Tres ... reset period, Tsen ... Sensing period, Tout ... Reading period, Tpre ... Precharge period.

Claims (10)

A light shielding film for shielding external light;
A part of which is located under the light-shielding film, and a circuit layer in which a plurality of unit circuits formed in a matrix are formed;
Control means;
With
Each of the plurality of unit circuits is
A first transistor that has a power line electrically connected to one electrode and outputs a detection current corresponding to the gate potential from the other electrode;
A second transistor for controlling a conduction state or a non-conduction state in response to a reset signal supplied to the gate via the first control line, and supplying a first potential to the gate of the first transistor in the conduction state;
A reference capacitor in which a gate of the first transistor is electrically connected to one terminal and a second potential is supplied to the other terminal;
A capacitance detecting element in which a gate of the first transistor is electrically connected to one terminal and a third potential is supplied to the other terminal;
A third transistor provided between the other electrode of the first transistor and the detection line and turned on in response to a selection signal supplied to the gate via the second control line;
At least one of the first transistor and the second transistor is formed in a region where external light is not shielded by the light shielding film ,
The control means divides the data value of the detection data based on each detection current output from each of the plurality of unit circuits by a predetermined width, and sets the mode value corresponding to the most frequent classification among the frequencies for each classification. A sensing device that generates illuminance data based on the data .   2. The sensing device according to claim 1, wherein the first potential is supplied to the power supply line, and the second transistor is provided between the power supply line and a gate of the one transistor.   3. The sensing device according to claim 1, wherein the second potential is a potential of the reset signal, and the other terminal of the reference capacitor is electrically connected to the first control line.   The sensing device according to any one of claims 1 to 3, wherein the third potential is a fixed potential.   5. The sensing device according to claim 1, wherein the reference capacitance is a parasitic capacitance generated between a gate and a source of the second transistor. The first to third transistors are formed by the same process, and include a semiconductor layer, a gate oxide film, and a gate wiring.
The reference capacitor uses the semiconductor layer as one electrode and the gate wiring as the other electrode.
The sensing device according to any one of claims 1 to 5, wherein: A plurality of pixel circuits having a pixel electrode, a counter electrode, and a dielectric sandwiched between the pixel electrode and the counter electrode;
A sensing device according to any one of claims 1 to 6 ,
A display device characterized by that. The capacitance detection element is sandwiched between a first electrode formed simultaneously with the pixel electrode, a second electrode formed simultaneously with the counter electrode, and the first electrode and the second electrode. The display device according to claim 7 , comprising the dielectric. The dielectric is a liquid crystal;
With backlight,
Dimming means for adjusting the brightness of the backlight according to the illuminance of external light output from the control means,
The display device according to claim 7 or 8, characterized in that. An electronic apparatus comprising the display device according to any one of claims 7 to 9.

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