JP4934976B2 - Display device and driving method of display device - Google Patents

Description

The present invention relates to a display device suitable for application to, for example, an organic EL (electro-luminescence) display and a display device driving method , and more particularly to a display technology capable of receiving light in parallel with light emission.

  Conventionally, when a touch panel that can be operated by touching a display screen of a display device such as a television receiver is configured, a touch panel separate from the display device is stacked on the display screen. . On the other hand, in recent years, there has been proposed an apparatus in which the screen of the display device functions as a touch panel as it is without providing a separate touch panel.

  For example, it has been proposed to store light in a light emitting element constituting an organic EL display and read out the charge so that not only light emission for display but also light reception can be performed. 11 and 12 illustrate the principle of this configuration.

  FIG. 11 shows one pixel when an image is displayed. When a positive voltage is applied from the gate line 3 to the gate electrode 1g of the TFT transistor 1 and turned on, as shown by the solid line arrow, according to the voltage applied by the source line 2, alpha moss silicon or A current flows through the active semiconductor layer (channel) made of polysilicon from the source electrode 1s to the drain electrode 1d.

  The anode electrode 4 a of the EL element 4 is connected to the drain electrode 1 d of the TFT transistor 1, and the cathode electrode 4 c of the EL element 4 is connected to the counter electrode 5. Here, when the current supplied from the drain electrode 1d of the TFT transistor 1 flows between the EL elements 4, the EL element 4 which is an electroluminescent element emits light according to the current.

  The light thus emitted is emitted to the outside of the display device 1, and one pixel of the image is displayed. In FIG. 11, for convenience of explanation, light is emitted from the EL element 4 in the right direction in the figure as indicated by a white arrow, but in actuality, either the anode electrode 4 a or the cathode electrode 4 c is used. Is constituted by a transparent electrode, and the light emitted from the EL element 4 through the transparent electrode is emitted to the outside.

  On the other hand, when a reverse voltage is applied from the gate line 3 to the gate electrode 1g of the TFT transistor 1 and the gate is turned off, even if a voltage is applied by the source line 2, a current is passed through the active semiconductor layer. Does not flow, and as a result, no current flows through the EL element 4 so that no light emission occurs. In this state, as shown by the white arrow in FIG. 12, when light is irradiated from the outside, the direction from the drain electrode 1d to the source electrode 1s is small due to the photoconductivity of the active semiconductor layer of the TFT transistor 1. Leak current (off current) occurs. Similarly, the EL element 4 generates a current in the reverse direction without emitting light when irradiated with light in a state where a voltage in the reverse direction is applied.

  By reading out the current generated in this way to the outside, it is detected that the pixel in FIG. 12 has been irradiated with light from the outside, that is, light reception can be detected. By alternately performing light emission and light reception, it is possible to simultaneously receive light while emitting light. FIG. 11 and FIG. 12 are diagrams for explaining the principle, and signal lines for reading out received light signals are omitted.

Patent Literature 1 discloses a display device that performs such light emission and light reception in parallel.
Japanese Patent Laying-Open No. 2004-127272 (FIG. 5)

  In the case of an apparatus that performs this type of light emission and light reception simultaneously, as can be seen from the light reception principle of FIG. 12, the current generated by the photoelectric effect at the time of light reception is a very weak current and must be detected with high sensitivity. It could not be said that sufficient detection could be performed with the conventional technology. In particular, when it is assumed that moving image display and light reception are performed simultaneously by light emission, a short light reception period is set in one field period such as 1/60 seconds, and a sufficient light reception period cannot be secured. As a result, it is difficult to accumulate sufficient charges in each pixel, and it is difficult to improve detection sensitivity.

  The present invention has been made in view of this point, and an object of the present invention is to detect a received light signal with high sensitivity when light emission and light reception are performed simultaneously in parallel.

The present invention uses an element capable of switching between light emission and light reception according to an applied voltage, and corresponds to display luminance when driving a display device in which a light emission period and a light reception period are alternately set . A light emission process for applying a light emission voltage to the element, a reverse bias application process for applying a reverse bias voltage to the element, and a read process for reading a signal accumulated in the element after a predetermined period of time has elapsed since the reverse bias application process was completed Is to do .

  By doing so, the charge accumulated in the period following the application of the reverse bias voltage can be read out with the reverse bias voltage applied during the light receiving period and the voltage of the light emitting element being low. Thus, it is read as a signal that is easy to detect the difference in the amount of received light.

  According to the present invention, with the reverse bias voltage applied during the light receiving period, the charge accumulated in the light emitting element is read during the period following the application of the reverse bias voltage in a state where the voltage of the light emitting element is low. Therefore, it is read out as a signal that is easy to detect the difference in the amount of received light. Therefore, since the light emission period is set alternately, the light reception sensitivity can be improved even when the light reception period is limited to a very short period.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

  In this example, the present invention is applied to a display device configured as an organic EL display, and each light emitting element constituting the organic EL display is also used as a light receiving element to emit light (display) and receive light (read). And can be performed simultaneously.

  FIG. 1 is a block diagram illustrating a configuration example of the display device 1 of the present example. The display device 1 includes a control unit 15 and controls the overall operation of the display device 1 based on a control program stored in a ROM (Read Only Memory) (not shown), for example, for a program of a predetermined channel. Display processing corresponding to a user's instruction from the input unit 16 such as a remote controller is executed, such as displaying a video, accessing a predetermined site and displaying a screen of the site.

  Based on the control by the control unit 15, the signal processing unit 12 acquires a broadcast signal of a predetermined channel from the television broadcast waves received by the antenna 11, and controls the program data broadcast on the channel to the control unit 15 is output. The communication unit 13 communicates with various devices via a network such as the Internet by wire or wireless, and outputs the acquired data to the control unit 15.

  The storage unit 14 includes, for example, a hard disk and stores various data such as data transferred from an external information processing terminal, program data of a television broadcast program, and data acquired by the communication unit 13. Further, data detected by light reception described later may be stored.

  The image signal generation unit 17 generates an image signal for displaying an image corresponding to the data supplied from the control unit 15 and the like, and outputs the generated image signal to the controller 18 that controls the driving of the display unit 30. .

  In addition, when the image data read by the reading processing unit 22 is supplied, the image signal generation unit 17 of this example superimposes the read image on the image supplied from the control unit 15 side. It is also possible to generate a signal or an image signal based only on the read image and output it to the display controller 18 for display.

  The display unit 30 has a plurality of pixels arranged in a matrix. The display controller 18 is arranged in each pixel of the display unit 30 to control the voltage applied to the gate electrode of the TFT transistor, and in conjunction with the driving of the gate driver 19, the TFT transistor The driving of the source driver 19 for controlling the voltage between the source electrode and the drain electrode is controlled. The TFT transistor is a display control switch, and display data is also supplied for each pixel via the TFT transistor. Each line driven by the source driver 19 corresponds to a display data signal line to be described later.

  In this example, a read line driver 24 for reading signals accumulated in each pixel is prepared during the light receiving period, and the read line driver 24 performs processing for reading signals from each pixel. Further, in this example, a reverse bias voltage driver 25 is prepared, and a reverse bias signal is applied during a light-receiving signal readout period of each pixel. Details of these light receiving periods will be described later.

  The detection unit 23 detects the electric charge read during the light receiving period of each image and detects a signal obtained by receiving the light. The detection processing timing in the detection unit 23 is set from the controller 18. The detected signal is supplied to the read processing unit 22 to generate read image data corresponding to the amount of light received by each pixel, and the read image data is supplied to the data processing unit 21.

  FIG. 2 is a diagram illustrating a configuration of each pixel of the display unit 30. In FIG. 2, switch means such as a transistor is shown as a switch. Referring to the configuration of FIG. 2, the display data signal line 32 to which display data is supplied is connected to one end of the switch SW1 via a correction circuit 33 prepared for each pixel. The correction circuit 33 is a circuit that corrects nonuniformity in characteristics such as a transistor constituting the switch SW1. The other end of the switch SW1 is connected to the light emitting element 31 of the EL display. In this example, the light emitting element 31 is shown as a light emitting diode, and the anode of the light emitting diode 31 is connected to the other end of the switch SW1. The cathode of the light emitting diode 31 is connected to the cathode electrode of the display unit 30. The cathode electrode voltage V_cathode is set to 0 V, for example. The light emitting diode 31 has a parasitic capacitance C_e1. This is the configuration for causing the light emitting element 31 to emit light. When the switch SW1 is turned on, a voltage corresponding to the light emission luminance is applied to the anode of the light emitting diode 31, and the light emitting element 31 emits light. When turned off, the light emission stops.

  Next, a pixel configuration in which the light emitting element 31 shown in FIG. 2 is used as a light receiving element will be described. The anode of the light emitting diode 31 is connected to the reception data signal line 35 via the switch SW2, and the reception data A signal obtained on the signal line 35 is detected by the detection unit 23 shown in FIG. The on / off of the switch SW2 is controlled by the read signal line 34. The read signal line 34 is a line driven by the read line driver 24 shown in FIG.

  In this example, one end of the switch SW3 is connected between the anode of the light emitting diode 31 and the switch SW2, and the other end of the switch SW3 is connected to the reset electrode of the display unit 30. ON / OFF of the switch SW3 is controlled by the reverse bias voltage driver 25 shown in FIG. In this example, the potential V_reset of the reset electrode is set to a relatively large potential (for example, -8 V) on the negative side. The switch SW3 connected in this manner is configured to be turned on immediately before the light reception signal is read by turning on the switch SW2.

  Next, the control state of the switch of each pixel shown in FIG. 2 will be described with reference to FIG. In this example, a light receiving period is set in the middle of one field period while displaying an image with a period of one field (here 1/60 second). The light receiving period is very short compared to one field period. For each field period, the horizontal line in which the light receiving period is set is changed in order, and the light receiving period is set in all the horizontal lines in order. It is. That is, for example, when the state at a certain timing of the display screen 30a is shown in FIG. 4, one or more specific horizontal lines in one screen are set as a reading area (light receiving period), and the remaining horizontal lines emit light. It is set as an area. The horizontal line of the reading area changes from the top to the bottom of the screen over a plurality of field periods, for example. During the period of the reading area, the corresponding line does not emit light, but for those who are viewing this screen 30a, it seems to emit light continuously due to the afterimage effect of the eyes, and the reading area ( I do not know that there is a light reception period).

  Here, as indicated by a broken line in FIG. 4, for example, when the display screen 30a is touched with the finger f or the finger f is brought close to the screen, this is detected by reading the light receiving period. By performing such processing, for example, when a relatively bright image is displayed on the display screen 30a, light (display image light) emitted from the upper and lower lines of the reading area is reflected by the finger f. By detecting the amount of reflected light during the light receiving period, the position touched by the finger f (or the approached position) can be specified.

  Returning to the description of FIG. 3, FIG. 3 shows the state of one field period, and the states of the switches shown in FIGS. 3A, 3B, and 3C are in the high level state. The low level state is off. As shown in FIG. 3A, the switch SW1 is turned on only during the light emission period, and the light receiving period is turned off, which coincides with the light emission period shown in FIG. Note that the off period at the end of one field period is a so-called blanking period. During the light emission period, the switch SW2 and the switch SW3 are in an off state. Then, in the light receiving period (reading period) in one field period shown in FIG. 3D, the switch SW2 and the switch SW3 are turned on. When the reading period starts, first, the switch SW3 is turned on for a short time, and the switch SW2 is turned on after a predetermined time α has elapsed. The time difference α at which the switch SW3 and the switch SW2 are turned on is, for example, about 30 μsec.

  FIG. 5 is an enlarged view showing the states of the three switches SW1 to SW3 during the readout period, and also shows changes in the anode voltage waveform of the light emitting element 31. As shown in FIG. 5, in the light emission period in which the switch SW1 is on, the anode voltage corresponds to the light emission luminance. The anode voltage during this light emission period is higher than the cathode voltage V_cathode. For example, in the example of FIG. 5, when the cathode voltage V_cathode is set to 0V, the anode voltage Va is set to a relatively high voltage of about 10V, and the light is emitted relatively brightly.

  In this state, when the switch SW1 is turned off and a readout period in which light emission stops is started, the switch SW3 is turned on, and the potential Vb is obtained by applying a reverse bias to the anode voltage until the reset voltage V_reset. In the example of FIG. 5, the reset voltage V_reset (anode voltage Vb) is −8V.

  The state where the reverse bias is applied to the anode voltage Vb is instantaneous, and the reverse bias voltage is charged and held in the parasitic capacitance C_e1. If light is received by the light emitting element 31 in this state, the anode voltage Vc is obtained so that the accumulated charge can be read according to the amount of received light. In a state where the anode voltage Vc is reached, the switch SW2 is turned on, and the charge accumulated corresponding to the amount of received light is read as a current value.

  FIG. 6 is a diagram showing, for reference, changes in the anode voltage when the reverse bias voltage applied during the readout period is substantially equal to the cathode voltage V_cathode. As shown in FIG. 6, when the reverse bias voltage is equal to the cathode voltage V_cathode, the anode voltage Vc ′ is slightly higher than the cathode voltage V_cathode, and only a current change in the vicinity of the voltage 0V occurs. The current change according to the amount of received light is very small. On the other hand, in the case of this example, the reverse bias voltage is set to a voltage that is significantly lower than the cathode voltage V_cathode, so that a current change corresponding to the amount of received light appears relatively large.

  FIG. 7 shows an example of voltage-current characteristics of the light-emitting element 31 composed of an organic EL display. As shown by currents A and B, the light emitting element increases current when forward bias is applied. On the other hand, in the region where the voltage is 0 V or less, the value of the flowing current changes depending on the presence or absence of light to be received. That is, the current D when the light is applied has a basic characteristic that a large amount of current flows compared to the current C when the light is not applied. The fact that a large amount of current flows means that the amount of charge generated by the photoelectric phenomenon is large. That is, the slope of the current D line changes corresponding to the amount of light received by the element. The lower the voltage, the greater the change in current value (the difference from the current C when no light is applied). The detection unit 23 shown in FIG. 1 detects this change in current value as the amount of received light.

  Therefore, as in this example, the reverse bias voltage is set to a voltage that is significantly lower than the cathode voltage V_cathode, and then the signal received by the element is detected. However, the light receiving sensitivity can be improved, and a state where the display screen is touched or an object close to the screen can be favorably detected as a read image.

  Note that a signal read from the switch SW2 in FIG. 2 to the reception data signal line 35 may be amplified by an amplifier circuit. That is, for example, as shown in FIG. 8, an amplification circuit 36 is connected between the switch SW2 and the reception data signal line 35, and the signal amplified by the amplification circuit 36 is connected to the reception data signal line 35. You may make it detect with a detection part. In this case, for example, when a circuit having a high input impedance, for example, a voltage amplifier circuit such as a source follower, is provided as the amplifier circuit 36, the charge accumulated in the light emitting element (light receiving element) cannot be removed. Electric charges can be used efficiently. In addition, in the case of a circuit having a low input impedance of the amplifier circuit, for example, a current amplifier circuit such as a current mirror, the charge accumulated in the anode is amplified by flowing instantaneously, so that the waveform after amplification becomes a pulse shape and is detected. However, it is required to capture that moment.

  In addition to the parasitic capacitance C_e1 of the light emitting element (light receiving element), an additional capacitor may be added in parallel with the light emitting element to increase the amount of charge that can be accumulated during light reception. That is, for example, as shown in FIG. 9, a capacitor Ca may be connected in parallel with the light emitting element 31, and charge storage at the time of light reception may be performed by the parasitic capacitance C_e <b> 1 of the light emitting element 31 and the capacitor Ca.

  In the examples described so far, the present invention is applied to a display device configured as an organic EL display. However, the present invention can also be applied to a case where a display element and a light receiving element are separate. That is, for example, as shown in FIG. 10, a pixel electrode 53 is connected to the intersection of the display data signal line 51 and the pixel write selection line 52 via the switch SW4, and the display data is applied to the pixel electrode 53. The display is configured. Independent of the pixel electrode 53, a light receiving element (PIN diode) 54 is provided at a position adjacent to the pixel electrode 53. A capacitor Cb is connected to the light receiving element 54 in parallel. The cathode side of the light receiving element 54 is set to a cathode voltage V_cathode such as 0V. The anode side of the light receiving element 54 is connected to the reception data signal line 56 via the switch SW2, and a reset voltage V_reset, which is a reverse bias voltage lower than the cathode voltage V_cathode, is applied via the switch SW3. The configuration. The switch SW2 is controlled by a signal supplied from the read line selection line 55. As the control timing of each switch SW2, SW3, SW4, the switch SW4 is controlled at the same timing as the timing of the switch SW1 in the example of FIG. 2 described above, and the switches SW2, SW3 are set to the same timing. Thus, the charge received by the light receiving element 54 can be read. An example of a display device in which the pixel electrode 53 and the light receiving element 54 are individually arranged is a liquid crystal display panel (a photosensor built-in type liquid crystal display panel).

It is a block diagram which shows the structural example of the display apparatus by one embodiment of this invention. It is a block diagram which shows the example of a connection of the light emitting element by one embodiment of this invention. It is a timing diagram showing an example of a light emission period and a reading period according to an embodiment of the present invention. It is explanatory drawing which shows the example of the light emission area | region and light reception area | region in 1 screen by one embodiment of this invention. It is a timing diagram which shows the detail of the reading period by one embodiment of this invention. It is a timing chart showing an example when the reverse bias voltage in the reading period is not lowered. It is a characteristic view which shows the example of the voltage-current characteristic of the light emitting element by one embodiment of this invention. It is a block diagram which shows the example of a connection of the light emitting element by other embodiment of this invention. It is a block diagram which shows the example of a connection of the light emitting element by further another embodiment of this invention. It is a block diagram which shows the example of a connection at the time of dividing the light emitting element and light receiving element by other embodiment of this invention. It is explanatory drawing which shows the example of a light emission state. It is explanatory drawing which shows the example of a light reception state.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 12 ... Signal processing part, 15 ... Control part, 17 ... Image signal generation part, 18 ... Controller, 19 ... Source driver, 20 ... Gate driver, 21 ... Data processing part, 22 ... Reading processing part, 23 ... Detection part, 24 ... Read line driver 25 ... Reverse bias voltage driver 30 ... Display unit 30a ... Display screen 31 ... Light emitting element 32 ... Display data signal line 33 ... Correction circuit 34 ... Read line selection line 35 ... Reception data Signal line 36 ... Amplifier circuit 51 ... Display data signal line 52 ... Read line selection line 53 ... Pixel electrode 54 ... Light emitting element 55 ... Read line selection line 56 ... Reception data signal line SW1, SW2, SW3, SW4 ... switch

Claims (13)

Equipped with an element that can switch between light emission and light reception according to the applied voltage,
In the light emission period, applying a light emitting voltage corresponding to the display luminance in the device,
In the light receiving period, a reverse bias voltage is applied to the element, and a signal accumulated in the element is read out after a predetermined period from the end of the application of the reverse bias .
Display device. The light emitting period and the light receiving period are set alternately.
The display device according to claim 1. The element includes
A first switch for applying the light emission voltage to the element during the light emission period;
A second switch for applying the reverse bias voltage to the element in the light receiving period;
A third switch for reading the signal in the light receiving period is connected;
In the light receiving period, after the second switch is turned on and a reverse bias voltage is applied to the element, the second switch is turned off,
A predetermined time after the second switch is turned off, the third switch is turned on and the signal is read out;
The display device according to claim 1. A plurality of the elements are arranged in a matrix,
In the middle of the light emission period of one frame, the different light reception periods are set for each element, and a signal is read by the third switch.
The display device according to claim 3 . A first state in which the light emitting voltage is applied to the element;
In the second state in which the reverse bias voltage is applied to the element,
The voltage applied between the cathode and anode of the element is set so that the positive and negative of the voltage are reversed.
The display device according to any one of claims 1 to 4. The display device according to any one of claims 1 to 5 , wherein a capacitor for storing received light charges is connected in parallel with the element. In a display device having a plurality of pixels arranged in a matrix and in which light emission periods and light reception periods are alternately set,
Each pixel is
An element capable of switching between light emission and light reception according to an applied voltage;
A first switch for applying a light emission voltage corresponding to display luminance to the element during a light emission period;
A second switch for applying a reverse bias voltage to the element during a light receiving period;
A third switch that reads a signal accumulated in the element after a predetermined period of time after a reverse bias voltage is applied by the second switch;
In the light emission period, the first switch is turned on, and the second switch and the third switch are turned off, whereby the light emission voltage is applied to the element,
The light receiving period is
A first period in which a reverse bias voltage is applied to the element by turning on the second switch and turning off the first switch and the third switch;
A second period in which any of the switches is turned off after the first period;
After the second period, the third switch is turned on, and the first switch and the second switch are turned off, so that the signal accumulated in the element is read out. Set to be
Display device. In a driving method of a display device having an element capable of switching between light emission and light reception according to an applied voltage,
A light emission process for applying a light emission voltage corresponding to the display brightness to the element;
A reverse bias application process for applying a reverse bias voltage to the element;
A read process is performed to read a signal accumulated in the element after a lapse of a predetermined period from the end of the reverse bias application process.
A driving method of a display device. The display device driving method according to claim 8, wherein the light emitting period and the light receiving period are alternately set. The element includes
A first switch for applying the light emission voltage to the element during the light emission period;
A second switch for applying the reverse bias voltage to the element in the light receiving period;
In a configuration in which a third switch for reading out the signal in the light receiving period is connected,
In the light receiving period, after the second switch is turned on and a reverse bias voltage is applied to the element, the second switch is turned off,
A predetermined time after the second switch is turned off, the third switch is turned on and the signal is read out;
The method for driving a display device according to claim 8. A plurality of the elements are arranged in a matrix,
In the middle of the light emission period of one frame, the different light reception periods are set for each element, and a signal is read by the third switch.
The method for driving a display device according to claim 10 . A first state in which the light emitting voltage is applied to the element;
In the second state in which the reverse bias voltage is applied to the element,
The voltage applied between the cathode and anode of the element is set so that the positive and negative of the voltage are reversed.
The method for driving a display device according to claim 8. In parallel with the element, a capacitor for storing received light charges is connected.
The method for driving a display device according to any one of claims 8 to 12.

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