JP5106010B2 - Image display device, current measuring method in image display device, and driving method of electronic device - Google Patents

Description

  The present invention relates to an image display device including a light emitting element, a current measurement method in the image display device, and a method for driving an electronic apparatus having the image display device.

  Conventionally, there has been proposed an image display device using an organic EL (Electroluminescence) element having a function of generating light by recombination of holes and electrons injected into a light emitting layer.

  In this type of image display device, for example, a thin film transistor (TFT) formed of amorphous silicon, polycrystalline silicon, or the like, an organic light emitting diode (OLED) that is one of organic EL elements, and the like. Each pixel is configured, and each pixel is arranged in a matrix. Then, by setting an appropriate current value for each pixel, the luminance of each pixel is controlled, and a desired image is displayed.

  For example, in an active matrix type image display device having a plurality of pixels in which a current-driven light-emitting element such as an OLED and a drive transistor such as a TFT that controls a current flowing in the OLED are arranged in series, each pixel is provided with each pixel. Due to variations in the threshold voltage of the driving transistor, the value of the current flowing through the light emitting element changes, resulting in luminance unevenness. As a technique for improving this phenomenon, for example, a method of detecting a threshold voltage of a driving transistor in advance and controlling a current flowing through a light emitting element based on the detected threshold voltage is disclosed (for example, Non-Patent Document 1). .

  In addition to the variation in threshold voltage of the driving transistor, it is known that the OLED also varies with time and with time. For this reason, even when the same voltage is applied to the drive transistor, the current density flowing through the OLED and the light emission luminance of the OLED change. For this reason, it is necessary to periodically detect the current flowing through the OLED and to correct the emission luminance of the OLED using information on the detected current that is periodically detected.

  Patent Document 1 listed below discloses a current detection circuit provided for each image signal line that supplies image data to each pixel as a control device and control method that can correct a change in luminance due to variations or deterioration of organic EL elements. Is used to detect a current flowing through a lighted organic EL element and control the next lighting time in accordance with the detected current value.

JP 2000-187467 A S. Ono, et al. (2003). Pixel Circuit for a-Si AM-OLED. Proceedings of IDW '03, pp. 255-258.

  However, in the technique disclosed in Patent Document 1, a detection circuit for detecting a current flowing through a lighting organic EL element is arranged for each column for driving the organic EL elements arranged in a matrix. In addition to providing the corresponding anode drive circuits, it is necessary to newly provide control lines for controlling each of these detection circuits, which increases the size of the pixel circuit and increases the cost. There was a point.

  The present invention has been made in view of the above, and an object of the present invention is to provide an image display device that can easily and inexpensively realize a pixel circuit having a function of current measurement.

  In order to solve the above-described problems and achieve the object, an image display device according to the present invention includes a plurality of pixel circuits each having a light emitting element and a driving element for driving the light emitting element, and a power source for each pixel circuit. An image display unit including a power supply line that supplies a voltage in common, a current detection circuit that is connected to the power supply line and detects a current flowing through each pixel circuit, and a current value detected by the current detection circuit A storage unit that stores data and a drive control unit that controls timing of operating the current detection circuit are provided.

  In the image display device according to the next invention, in the above invention, the plurality of pixel circuits are arranged in a matrix, and the power supply line is commonly connected to a pixel circuit group arranged in a row direction. In addition, the power lines commonly connected to the pixel circuit group are commonly connected to a common terminal, and the current detection circuit is connected to the common terminal.

  Further, in the image display device according to the next invention, in the above invention, the light emitting element is an organic light emitting diode, the power supply line is a first power supply line connected to an anode side of the organic light emitting diode, and the A second power supply line connected to the cathode side of the organic light emitting diode is included, and the current detection circuit is electrically connected to the second power supply line.

  Further, in the image display device according to the next invention, in the above invention, the light emitting element is an organic light emitting diode, the power supply line is a first power supply line connected to an anode side of the organic light emitting diode, and the It includes a second power supply line connected to the cathode side of the organic light emitting diode, and the current detection circuit is electrically connected to the first power supply line.

  In the image display device according to the next invention, in the above invention, when the image display mode has an image display mode for displaying an image and a current measurement mode for measuring a current flowing through the pixel circuit, the current detection circuit It is configured to operate in the measurement mode.

  The image display device according to the next invention is characterized in that, in the above invention, the current detection circuit includes a resistance element, a switching element connected in parallel to the resistance element, and an operational amplifier. .

  The image display apparatus according to the next invention is characterized in that, in the above invention, each of the pixel circuits further includes a threshold voltage detection element for controlling detection of a threshold voltage in the drive element.

  The current measuring method in the image display device according to the next invention is a current measuring method in the image display device, each having a light emitting element and a driving element for driving the light emitting element, and arranged in a matrix. An image including a plurality of pixel circuits, a power supply line that supplies a power supply voltage to each pixel circuit in common, and a current detection circuit that is connected to the power supply line and detects a current flowing through each pixel circuit. A step of preparing a display unit, a step of applying an image data potential corresponding to the light emission luminance of the light emitting element for each pixel circuit group arranged in a row direction, and a pixel circuit constituting each pixel circuit group The step of sequentially selecting and causing the light emitting element of the pixel circuit to emit light and the step of measuring the current flowing through the light emitting element by the current detection circuit are included.

  In the electronic device driving method according to the next invention, a first step of inputting power-off information to the image display device, and a current flowing through each pixel circuit is measured after the power-off information is input. A second step; and a third step in which the power of the image display device is turned off after the end of the second step.

  In the electronic device driving method according to the next invention, a first step of inputting power-on information to the image display device, and a current flowing through each pixel circuit is measured after the power-on information is input. A second step; and a third step in which the power of the image display device is turned on after completion of the second step.

  According to a second aspect of the present invention, there is provided a method for driving an electronic device, the first step of setting the display screen of the image display unit in a standby state, and the second step of measuring a current flowing through each pixel circuit during the standby state. It is characterized by having.

  According to the present invention, since the current flowing through each pixel circuit is detected by the current detection circuit connected to the power supply line that commonly supplies the power supply voltage to each pixel circuit, the current measurement function is provided. The effect that the pixel circuit can be realized simply and inexpensively is obtained.

  Hereinafter, an image display device according to a preferred embodiment of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the following embodiments. In this embodiment, an organic light-emitting element is described as an example. However, it goes without saying that the present invention can be applied to light-emitting elements other than organic light-emitting elements, for example, LEDs and inorganic EL elements.

<Schematic configuration of image display device>
FIG. 1 is a diagram showing a configuration of an image display apparatus according to a preferred embodiment of the present invention. In FIG. 1, a display panel (image display unit) 5 of the image display device is provided with control lines and image signal lines 14 including a first power line 11, a second power line 12, and a scanning line 13. In addition, a current detection circuit 24 which is a detection circuit for detecting a current flowing through each pixel is provided. Of each control line, the first power supply line 11 and the scanning line 13 are connected to a line driver (Y driver) 20 provided in the display panel 5. On the other hand, the second power supply line 12 is connected to a line driver (Y driver) 20 via a current detection circuit 24. Note that a power line dedicated driver for controlling the first power line 11 and the second power line 12 may be separately provided, and the first power line and the second power line may be connected to the power line dedicated driver. .

  The current detection circuit 24 may be provided for each of the plurality of second power supply lines 12, but one detection circuit may be disposed on the previous wiring bundled with the plurality of second power supply lines 12. From the viewpoint of miniaturization of the image display device, it is preferable to arrange it as such.

  On the other hand, the image signal line 14 is arranged along a direction (substantially orthogonal direction) different from the control line, and is connected to a data driver (X driver) 22 provided on the display panel 5. Although not shown in FIG. 1, the display panel 5 includes a plurality of pixels (pixel circuits) in which organic light emitting diodes (organic light emitting elements) are arranged in a matrix. Each control line and image signal line 14 are connected to the pixel.

  In addition, a timing controller 1, a frame buffer 2, a current measurement control unit 3, and a detected current storage unit 4 are provided outside the display panel 5.

  The timing controller 1 can be configured by using, for example, a driving IC or the like that includes an arithmetic circuit or the like. The timing controller 1 displays the timing at which the image data stored in the frame buffer 2 is supplied to the X driver 22 and the image data The timing for supplying the control signal for performing the control to the Y driver 20 is controlled.

  The current measurement control unit 3 is a drive control unit in the present invention. The current measurement control unit 3 is a control unit that operates in an operation mode (hereinafter, this operation mode is defined as “current measurement mode”) in response to a current measurement instruction from a host device (not shown). In the measurement mode, the output of the X driver 22 is changed to data corresponding to the current measurement mode, and switching control of operation / non-operation (connection / non-connection to the current detection element) of the current detection circuit 24 is performed.

  The detected current storage unit 4 corresponds to the storage unit in the present invention. The detected current storage unit 4 stores and holds the data measured by the current detection circuit 24. The configuration of FIG. 1 is configured to provide a current measurement control unit 3 outside the timing controller 1 from the viewpoint of adding a new current measurement function to the function of the conventional image display device. You may make it provide the function of the electric current measurement control part 3 inside.

  The Y driver 20 can be configured using, for example, a driving IC that includes a switching element and the like, and controls the timing and magnitude of the voltage applied to each control line based on the control of the timing controller 1.

  The X driver 22 can be configured using, for example, a driving IC or the like that includes an arithmetic circuit or the like, and based on the control of the timing controller 1 and the current measurement control unit 3, a potential (hereinafter referred to as “image” Data timing) and the timing of supplying the generated image data potential to the image signal line 14 is controlled. In the display panel 5 of FIG. 1, the layout of the figure regarding each control line, the image signal line 14, the Y driver 20, and the X driver 22 is an example, and is not limited to these layouts. .

<Configuration of pixel circuit>
FIG. 2 is a diagram showing a configuration of a pixel circuit (one pixel) provided in the display panel 5 shown in FIG. 1, for example. In addition, the same code | symbol is attached | subjected and shown to the component same as FIG.

  The pixel circuits shown in the figure are arranged in a matrix on the display panel 5, and each pixel circuit includes an organic light emitting element OLED which is one of organic EL elements, a drive transistor Td, a threshold voltage detecting transistor Ts, and The capacitor Cs is configured to hold a threshold voltage (Vth) and an image signal potential.

  In FIG. 2, the drive transistor Td is a driver element for controlling the amount of current flowing through the organic light emitting element OLED according to the potential difference applied between the gate electrode and the source electrode. In addition, when the threshold voltage detection transistor Ts is turned on, the gate electrode and the drain electrode of the drive transistor Td are electrically connected to each other so that a current flows from the gate electrode of the drive transistor Td toward the drain electrode. And the potential difference between the gate electrode and the source electrode of the driving transistor Td is brought closer to the threshold voltage Vth of the driving transistor Td, and as a result, the potential difference between the gate electrode and the source electrode of the driving transistor Td is brought closer to the threshold voltage Vth or the threshold value It has a function of setting the voltage Vth (hereinafter referred to as “Vth detection function”).

  The organic light emitting element OLED is an element having a characteristic that current flows when a potential difference (anode-cathode voltage) equal to or higher than a threshold voltage is generated at both ends, and light is emitted. As a specific structure and function, the organic light emitting device OLED includes an anode layer and a cathode layer formed of Al, Cu, ITO (Indium Tin Oxide), and the like, and phthalocyanine and tris aluminum between the anode layer and the cathode layer. A light emitting layer formed of an organic material such as a complex, a benzoquinolinolato, a beryllium complex, and the like, and light is emitted by recombination of holes and electrons injected into the light emitting layer. Has the resulting function.

  The drive transistor Td and the threshold voltage detection transistor Ts are, for example, thin film transistors. In each drawing referred to below, the channel (N-type or P-type) of each thin film transistor may be either N-type or P-type, but in this embodiment, N-type is used. And

  The first power supply line 11 and the second power supply line 12 apply a predetermined potential (variable potential) corresponding to each of these operation periods to the organic EL element OLED and the drive transistor Td. The scanning line 13 supplies a signal for controlling the threshold voltage detection transistor Ts. The image signal line 14 supplies an image signal corresponding to the light emission luminance of the organic light emitting element OLED to the capacitor Cs.

<Configuration of pixel circuit group>
FIG. 3 is a diagram illustrating a configuration of a pixel circuit group including a plurality of pixel circuits and a current detection circuit 24 connected to the pixel circuit group in the image display apparatus in FIG. Here, the pixel circuit group refers to a series of pixel circuits arranged in the same row direction (horizontal direction in FIG. 3) or a series of pixel circuits arranged in the same column direction (vertical direction in FIG. 3). Say. In FIG. 3, the control lines of the first power supply line 11 and the second power supply line 12 are commonly connected to a pixel circuit group including a series of pixel circuits arranged in the row direction. The second power supply lines 12 in each row are connected in common to a common terminal 15, and a current detection circuit 24 is connected to the common terminal 15. Here, the second power supply line 12 of each row is commonly connected to the common terminal. However, the first power supply line 11 is connected to the common terminal and current measurement is performed for each pixel circuit. It is also possible. On the other hand, the scanning lines 13 are connected in common to the pixel circuit groups (for example, k rows and (k + 1) rows) arranged in the row direction, and the image signal lines 14 are arranged in the pixel circuit groups (for example, n columns, ( n + 1) columns) are commonly connected. That is, the scanning line 13 is provided for each row, and the image signal line 14 is provided for each column.

<Configuration of current detection circuit>
The current detection circuit 24 is an FET 31 that is a switching element, a resistance element 32 that is a current detection element, and a current detection unit, and includes an operational amplifier 33 that converts the current detected by the resistance element 32 into a voltage value and outputs the voltage value. Yes. The control signal from the timing controller 1 is input to the gate of the FET 31, and the output of the operational amplifier 33, that is, the detected value of the current flowing through each pixel circuit is output to the detected current storage unit 4.

<Operation of current detection circuit>
In FIG. 3, when the current detection mode is selected, a control signal for turning off the FET 31 is output from the timing controller 1 through the current measurement control unit 3. At this time, since the current flowing through the second power supply line 12 flows through the resistance element 32, the current flowing through the pixel circuit is detected by detecting the voltage across the resistance element 32 having a high resistance (for example, 100 kΩ). . When the current detection mode is not selected (hereinafter referred to as “image display mode”), a control signal for making the FET 31 conductive is output from the timing controller 1, and the current flowing through the pixel circuit does not flow through the resistance element 32. Therefore, the current flows through the FET 31 having a low resistance (for example, 0.2Ω). Therefore, the influence of the voltage drop caused by providing the current detection circuit 24 can be almost ignored.

<Operation of Pixel Circuit—Image Display Mode>
Next, the operation of the pixel circuit shown in FIG. 2 in the image display mode will be described with reference to FIGS. Here, FIG. 4 is a sequence diagram for explaining the operation in the image display mode. In the pixel circuit shown in FIG. 2, as shown in FIG. 4, after six periods of Cs reset period, Vth detection preparation period), Vth detection period, data writing period, Coled reset period, and light emission period. Operate. Here, Coled is an element capacity inherently possessed by the organic light emitting element OLED.

(Cs reset period)
In the Cs reset period, the first power supply line 11 has a high potential (VDD), the second power supply line 12 has a high potential (VDD), the scanning line 13 has a high potential (VgH), and the image signal line 14 has a zero potential (GND). Is done. As a result, the threshold voltage detection transistor Ts is turned on and the drive transistor Td is turned off, and a current flows through the path of the first power supply line 11 → the organic light emitting element OLED → the threshold voltage detection transistor Ts → the capacitance Cs, and the capacitance Cs becomes smaller. By being charged, the charge of the capacitor Cs is reset. The reason why the capacitor Cs is charged in this Cs reset period is to reset the image signal potential of one frame before written in the capacitor Cs.

(Vth detection preparation period)
In the Vth detection preparation period, the first power supply line 11 has a negative potential (−VE), the second power supply line 12 has a zero potential (GND), the scanning line 13 has a low potential (VgL), and the image signal line 14 has a high potential (VgH). ). As a result, the threshold voltage detection transistor Ts is turned off and the drive transistor Td is turned on, a current flows through the path of the second power supply line 12 → the drive transistor Td → the organic light emitting element OLED, and the element capacitance Coled included in the organic light emitting element OLED. The charge is accumulated in the. The reason why charges are accumulated in the organic light emitting element OLED in this Vth detection preparation period is that the organic light emitting element OLED is driven when the gate-source voltage of the drive transistor Td is brought close to the threshold voltage in the Vth detection period described later. This is to act as a supply source of current flowing between the drain and source of the transistor Td.

(Vth detection period)
In the Vth detection period, the first power supply line 11 is set to zero potential (GND) and the scanning line 13 is set to high potential (VgH), while the image signal line 14 is set to high potential (VdH) and the second power supply line 12 is set to It is maintained at zero potential (GND). As a result, the threshold voltage detection transistor Ts is turned on, and the gate and drain of the drive transistor Td are connected.

  Further, the charges accumulated in the capacitor Cs and the organic light emitting element OLED are discharged, and the capacitor Cs → the threshold voltage detecting transistor Ts → the driving transistor Td → the second power supply line 12 and the organic light emitting element OLED → the driving transistor Td → second. Current flows through both paths of the power line 12. When the gate-source voltage Vgs of the drive transistor Td reaches the threshold voltage Vth, the drive transistor Td is turned off, and as a result, the threshold voltage Vth of the drive transistor Td is detected.

(Data writing period)
In the data writing period, the gate potential of the driving transistor Td is changed to a desired potential by reflecting the image signal potential (−Vdata) on the capacitor Cs. More specifically, the first power supply line 11 is maintained at zero potential (GND), and the second power supply line 12 is maintained at zero potential (GND). The image signal line 14 is set to a potential (VdH−Vdata) obtained by subtracting the image signal potential (Vdata) from the applied potential (VdH) during the Vth detection period, and the scanning line 13 is set to a predetermined value in the data writing period. In the period, a high potential (VgH) is set.

  As a result, the threshold voltage detection transistor Ts is turned on, the charge accumulated in the element capacitance Coled is discharged, and a current flows through the path of the organic light emitting element OLED → the threshold voltage detection transistor Ts → the capacitance Cs. That is, the charge accumulated in the organic light emitting element OLED moves to the capacitor Cs. As a result, a predetermined charge determined based on the image signal potential (Vdata) is accumulated in the capacitor Cs.

  Note that, during the data writing period, the capacitor Cs and the organic light emitting element OLED are connected in series. Therefore, the amount of decrease in the potential of one end of the capacitor Cs (the end connected to the gate of the drive transistor Td) is the image signal line 14. Is not affected by the capacitance ratio between the capacitor Cs and the organic light emitting element OLED as shown in the above equation.

(Coled reset period)
In the Coled reset period, the first power supply line 11 is set to a negative potential (−VE), and the second power supply line 12 is also set to a negative potential (−VE). On the other hand, the scanning line 13 is maintained at a low potential (VgL) and the image signal line 14 is maintained at a high potential (VdH). At this time, the threshold voltage detection transistor Ts is turned off and the driving transistor Td is turned on, and a current flows through the path of the organic light emitting element OLED → the driving transistor Td → the second power supply line 12, and the charge remaining in the organic light emitting element OLED Discharged. The reason for discharging the charge of the element capacitor Coled during this Coled reset period is to avoid the influence on the light emission by the remaining charge of the element capacitor Coled.

(Light emission period)
In the light emission period, the first power supply line 11 is set to a high potential (VDD), and the second power supply line 12 is set to a zero high potential (GND). On the other hand, the scanning line 13 is maintained at a low potential (VgL) and the image signal line 14 is maintained at a high potential (VdH). Accordingly, the driving transistor Td is kept on and the threshold voltage detection transistor Ts is kept off, and a forward bias voltage is applied to the organic light emitting element OLED. Therefore, the organic light emitting element OLED → the driving transistor Td → the second power source. A current flows through the path of the line 12, and the organic light emitting element OLED emits light.

<Operation of pixel circuit-current detection mode>
Next, the operation in the current detection mode will be described with reference to FIG. 2, FIG. 3, and FIG. Here, FIG. 5 is a sequence diagram for explaining the operation in the current detection mode. As a sequence for the pixel circuits other than the first column, the pixels in the second to fourth columns connected to the same scanning line 13. A sequence for the circuit (only the image signal line 14) is also shown.

  In FIG. 5, the operation from the Cs reset period to the Coled reset period is the same as the operation in the image display mode, and thus the description thereof is omitted here. In the data writing period, white data is written in the pixel circuit group in the row where the pixel whose current is to be measured exists, and black data is written in the pixel circuit group in the other row.

On the other hand, in the light emission period, first, only the potential of the pixel circuit in the first column (hereinafter referred to as “pixel 1”, and the same applies to the pixels in the second column and thereafter) is set to VdH. That is, the potential of the pixel 1 is maintained at the high potential (VdH) that is the potential during the Coled reset period, while the potentials of the pixels 2 to 4 are set to zero potential (GND). As a result, only the gate-source voltage Vgs of the drive transistor Td in the pixel to be measured (pixel 1) in the first column exceeds the threshold voltage Vth, and the gate-source voltage Vgs of the drive transistor Td in the other pixels. Is below the threshold voltage Vth. More precisely, when measuring the current of the pixel 1, a plurality of pixel circuits are divided into the following four types of pixel circuit groups (i) to (iv) according to the magnitude of the voltage Vgs applied between the gate and source of the drive transistor Td. ).
(I) Pixel to be measured in the first column (pixel 1): A potential for causing the organic light emitting element OLED to emit light is written to the capacitor Cs in the pixel 1, and the potential of the image signal line 14 in the light emission period is VdH. It is said. As a result, the gate-source voltage Vgs of the drive transistor Td of the pixel 1 becomes higher than the threshold voltage Vth.
(Ii) Pixel circuit group other than the first column in the same row as the pixel 1: A potential necessary for causing the organic light emitting element OLED to emit light is written in the capacitance Cs of each pixel circuit in the pixel circuit group. Since the potential of the image signal line 14 in the light emission period is set to VdL (GND), the gate-source voltage Vgs of the drive transistor Td becomes lower than the threshold voltage Vth.
(Iii) Pixel circuit group other than the first row in the same column as the pixel 1: Since a potential at which the organic light emitting element OLED does not emit light is written in the capacitance Cs of each pixel circuit in this pixel circuit group, the organic light emitting element OLED does not emit light. .
(Iv) Pixel circuit group other than the above (i) to (iii): A potential at which the organic light emitting element OLED does not emit light is written in the capacitance Cs of each pixel circuit in the pixel circuit group, and the image signal line 14 in the light emission period. Is set to VdL (GND), the gate-source voltage Vgs of the drive transistor Td becomes lower than the threshold voltage Vth.

  By controlling as described above, only the drive transistor Td connected to the pixel 1 is turned on, and the other drive transistors Td are turned off. Therefore, the current flowing through the current detection circuit 24 is only the current flowing through the pixel 1, and the current flowing through the pixel 1 is detected.

  Next, only the potential of the pixel 2 is set to VdH, and the potentials of the other pixels (pixel 1, pixel 3, pixel 4...) Are set to zero potential (GND). As a result, only the gate-source voltage Vgs of the drive transistor Td in the pixel to be measured (pixel 2) in the second column becomes equal to or higher than the threshold voltage Vth, and the gate-source voltage Vgs of the drive transistor Td in the other pixels. Is below the threshold voltage Vth. Also in this case, similarly to the pixel 1 described above, a plurality of pixel circuits can be divided into four types of pixel circuit groups depending on the magnitude of the voltage Vgs applied between the gate and source of the drive transistor Td.

  Thereby, only the drive transistor Td connected to the pixel 2 is turned on, and the other drive transistors Td are turned off. Therefore, the current flowing through the current detection circuit 24 is only the current flowing through the pixel 2, and the current flowing through the pixel 2 is detected. Thereafter, the drive transistors Td connected to the respective pixels are sequentially turned on in the order of the pixel 3, the pixel 4,..., And the current flowing through each pixel is sequentially measured.

<Current measurement for all pixels of image display device>
Next, the current measurement for all the pixels of the image display device will be described by taking as an example a QVGA (Quarter Video Graphics Array) color image display device (320 × 240 × 3 (RGB) = 230,400 pixels).

  FIG. 6 is a diagram illustrating the concept of pixel positions in a QVGA image display device. In FIG. 6, i and j are variables representing the column position and row position of the pixel position, respectively, and in the case of a QVGA color image, the range i can take is “0 to 719” (240 × 3 = 720). The range that j can take is “0 to 320”.

  FIG. 7 is a diagram illustrating an example of a program code for performing current measurement processing on all pixels. In FIG. 7, the value of variable j representing the row position of the pixel position is set (step S1). Next, the row number (LineCounter) that is the target of the data writing process is set, and, for example, the white level potential (High) is written to the pixel of the row number that is the target of the writing process, and is not the target of the writing process. A black level potential is set to the pixel of the row number (other than the pixel) (step S2).

  Next, the value of the variable m indicating the storage position of the memory (or register) that holds the current measurement value is set (step S3). Further, the column number of the pixel to emit light (column number at a specific row position: PixelCounter) is set, and the pixel at the PixelCounter position is set with, for example, a white level potential (High), and the other pixels are black. A level potential is set (step S5). Thereafter, a start pulse is output to the X driver (step S6), the current of the pixel is measured (step S7), and the next current measurement point (measurement target pixel) is designated (step S8). Each process of step S5 to step S8 is repeatedly executed for 720 pixels arranged in the row direction (step S4), and the measured current value is stored and held (step S4). The next row is designated by the row number increment process (step S9), and the above-described steps S2 to S8 are repeated by the number of row numbers, thereby executing current measurement for all the pixels of the image display device. (Step S1).

  The processing flow shown in FIG. 7 may be executed by either software processing or hardware processing. In the case of execution by hardware, an IC having functions such as a counter, a comparator, and a selector can be used.

<Processing time required for current measurement>
Next, the processing time required for current measurement will be described. The image display apparatus will be described by taking the QVGA color image display apparatus described above as an example. It is assumed that the display specifications of the image display device are as follows.
(1) 1 frame: 16.6 ms (60 Hz)
(2) Light emission period in one frame: 8.3 ms (corresponding to 1/2 frame)
(3) X driver clock frequency: 16.6 μs (corresponding to 1/1000 frame)
(4) Write time for one row: same as clock frequency of X driver

(Conventional technology)
First, the measurement time in the case of the prior art will be described. In the conventional technique, if one pixel can be measured in one frame (16.6 ms), the time required for current measurement of all pixels can be calculated as follows.
16.6 ms × 240 × 3 × 320 = 382.86S≈1.06 hours In other words, in the related art, a measurement time of about 1 hour is required for current measurement of all pixels.

(This embodiment)
Next, the measurement time when the measurement method according to this embodiment is applied will be described. First, the number of pixels that can be measured in one frame is
• 8.3 ms / 16.6 μs = 500 pixels.
Therefore, the time required for current measurement of all pixels can be calculated as follows.
・ (240 × 3 × 320/500) × 16.6 ms≈7.65 s
That is, with the measurement method according to the present embodiment, it is possible to perform current measurement for all pixels in about 8 seconds.

<Application to other pixel circuits>
FIG. 8 is a diagram illustrating a configuration example of a pixel circuit different from the pixel circuit of FIG. Unlike the pixel circuit shown in FIG. 2, the pixel circuit shown in FIG. 8 includes four transistors including the drive transistor Td, and one end of the capacitor Cs that is not connected to the gate of the drive transistor Td. A switching transistor T1 for connecting to the image signal line 44 at a predetermined timing and a switching transistor T2 for controlling the timing of connecting one end of the capacitor Cs to the power supply line 40 at a predetermined timing are provided. A Tth control line 41 different from the scanning line 43 for controlling the switching transistor T1 is provided. Note that since the pixel circuit shown in FIG. 8 is a known circuit, a detailed description of its configuration and operation is omitted.

  In the circuit of FIG. 8, as in the pixel circuit of FIG. 2, the light emission / non-light emission of the organic light emitting element OLED can be controlled while the potential of the image signal line 44 is maintained. Specifically, for example, white level potential (High) is written to the pixels in the same column by controlling the scanning lines 43 in the data writing period, and the merge lines 42 are sequentially controlled in the column direction in the light emitting period. If the driving transistors Td in the column direction are sequentially turned on, the current flowing through each pixel can be measured sequentially. Alternatively, for example, a white level potential (High) is written to the pixel group in the same column, and the potential of the power supply line 40 of the column in which the white level is written is sequentially controlled in the column direction during the light emission period. It is also possible to sequentially measure the current flowing through each pixel by sequentially emitting light from the organic light emitting element OLED.

<Electronic device driving method>
Next, a method for driving an electronic apparatus having the above-described image display device will be described. Note that the term “electronic device” as used herein naturally includes a mobile phone, a personal computer, a digital camera, a car navigation system, a PDA, a POS terminal, a measuring device, a copying machine, and the like.

Example 1
When current measurement is performed when the power of the image display device is turned off from on (1) First, assume a state in which the image display device is in an operating state and image display is being performed.
(2) Next, power-off information is input to the image display device, and the image display device enters the current measurement mode.
(3) Here, the above-described current measurement is performed.
(4) Then, the current measurement is completed, the power of the image display device is turned off, and the electronic device is in a non-operating state.

  As described above, if current measurement is performed within the period for turning off the power of the image display device, the user of the electronic device can use the electronic device without feeling uncomfortable.

(Example 2)
When current measurement is performed when the power source of the image display apparatus is turned on from OFF (1) First, it is assumed that the image display apparatus is in a non-operating state and the power source of the image display apparatus is off. Note that when the power is turned off, no voltage is supplied to the pixel circuit.
(2) Next, power ON information is input to the image display device, and the image display device is activated in the current measurement mode.
(3) Here, the current measurement is performed.
(4) Then, the current measurement is completed, and the electronic device is in a normal operating state.

  When the current measurement takes about 8 seconds as in the above-described embodiment, the user of the electronic device is somewhat waited, which may cause an irritating feeling to the user. Therefore, the current measurement may be performed step by step according to the current measurement required time. For example, current measurement for half of all pixels may be performed in one current measurement mode, and the remaining current measurement may be performed in the next current measurement mode. Note that the number of times of current measurement to be divided is not limited to two, and may be divided into three or more times.

  In addition, when the measurement data obtained by current measurement is instantly reflected in the next image display, when the current measurement is divided into a plurality of times as described above, the current measurement pixel and the current measurement are performed. It is expected that the luminance unevenness is visually recognized between the pixels that did not exist. In consideration of such a situation, for example, in the above-described embodiment, the current measurement is sequentially performed according to the arrangement order of the pixel circuits. However, the pixel circuit to be measured is skipped or randomly selected. Thus, it is possible to suppress the occurrence of uneven brightness.

  As described above, if current measurement is performed within the period for turning on the power of the image display device, the user of the electronic device can use the electronic device without feeling uncomfortable.

(Example 3)
When current measurement is performed during a period when the power of the image display device is ON but the display screen is in a standby state (1) First, the image display is started from the state where the first image is displayed by the image display device. Assume that the display screen of the device is in a standby state. Here, the standby state is, for example, when the image is not displayed on the display screen, when the screen saver is activated, when the image is displayed on the display screen, but with a lower brightness than the first image. When the display is performed, the image is displayed on the display screen, but the image cannot be seen from the outside (the image is hidden) (for example, in a folding mobile phone, the housing is When the screen is hidden by a frame by being folded).
(2) Next, the image display apparatus is instructed to shift to the current measurement mode, and the image display apparatus enters the current measurement mode.
(3) Here, the current measurement is performed.
(4) Then, the current measurement is finished, the standby state of the display screen is released, and the image display is performed on the image display device.

  As described above, if current measurement is performed during a period in which the display screen of the image display device is in a standby state, the user of the electronic device can use the electronic device without feeling uncomfortable.

  Even in the case of the third embodiment, the current measurement may be divided into a plurality of times as in the second embodiment, and the pixel circuit to be measured is skipped or randomly selected. It may be.

  In this embodiment, the pixel circuit having the threshold voltage detection transistor for detecting the threshold voltage of the driving transistor as shown in FIGS. 2 and 8 has been described. The present invention can also be applied to a pixel circuit that does not have a threshold voltage detection transistor.

  As described above, the image display device according to the present invention is useful as an invention that can easily and inexpensively realize a pixel circuit having a function of current measurement.

It is a figure which shows the structure of the image display apparatus concerning suitable embodiment of this invention. FIG. 2 is a diagram showing a configuration of a pixel circuit (one pixel) provided in the display panel shown in FIG. 1. FIG. 3 is a diagram illustrating a configuration of a pixel circuit group including a plurality of pixel circuits and a current detection circuit connected to the pixel circuit group in the image display device in FIG. 2. It is a sequence diagram for demonstrating operation | movement at the time of image display mode. It is a sequence diagram for demonstrating operation | movement at the time of electric current detection mode. It is a figure which shows the concept of the pixel position in the image display apparatus of QVGA. It is a figure which shows an example of the program code which performs the current measurement process with respect to all the pixels. It is a figure which shows the structural example of the pixel circuit different from FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Timing controller 2 Frame buffer 3 Current measurement control part 4 Detected current memory | storage part 5 Display panel 11 1st power supply line 12 2nd power supply line 13 Scanning line 14 Image signal line 15 Common terminal 20 Y driver 22 X driver 24 Current detection circuit 31 FET
32 resistance element 33 operational amplifier 40 power supply line 41 control line 42 merge line 43 scanning line 44 image signal line Cs capacity OLED organic light emitting element Td drive transistor T1, T2 switching transistor Ts, Tth threshold voltage detection transistor

Claims (9)

A plurality of pixel circuits each having a light emitting element and a driving element for driving the light emitting element, a power supply line for supplying a power supply voltage to each pixel circuit in common, and the power supply line are connected to each pixel circuit. An image display unit comprising a current detection circuit for detecting a flowing current;
A storage unit for storing and holding a current value detected by the current detection circuit;
A drive control unit for controlling timing for operating the current detection circuit;
With
The plurality of pixel circuits are arranged in a matrix,
The power supply line is connected in common to the pixel circuit group arranged in the row direction, and the power supply lines connected in common to the pixel circuit group are connected in common to a common terminal,
The current detection circuit is connected to the common terminal;
Each of the pixel circuits further includes a threshold voltage detection element that controls detection of a threshold voltage in the drive element,
In one frame, after each threshold voltage in the pixel circuit group arranged in the current measurement target row is detected by each threshold voltage detection element, the gate source of the drive element in each column in the current measurement target row An image display device, wherein each light emitting element is driven so that a voltage sequentially becomes equal to or higher than each threshold voltage, and a current flowing through each pixel circuit is detected .
The light emitting element is an organic light emitting diode,
The power line includes a first power line connected to an anode side of the organic light emitting diode and a second power line connected to a cathode side of the organic light emitting diode, and the current detection circuit includes the second power line. The image display device according to claim 1, wherein the image display device is electrically connected to the image display device.
The light emitting element is an organic light emitting diode,
The power line includes a first power line connected to the anode side of the organic light emitting diode and a second power line connected to the cathode side of the organic light emitting diode, and the current detection circuit includes the first power line. The image display device according to claim 1, wherein the image display device is electrically connected to the image display device.
When having an image display mode for displaying an image and a current measurement mode for measuring a current flowing through the pixel circuit,
The image display device according to claim 1, wherein the current detection circuit is configured to operate in the current measurement mode.
The image display apparatus according to claim 1, wherein the current detection circuit includes a resistance element, a switching element connected in parallel to the resistance element, and an operational amplifier.
A current measuring method in an image display device,
A plurality of pixel circuits each having a light emitting element , a driving element for driving the light emitting element , and a threshold voltage detecting element for controlling detection of a threshold voltage in the driving element, and arranged in a matrix; A power supply line that supplies a common power supply voltage, and a current detection circuit that is connected to the power supply line and detects a current flowing through each of the pixel circuits.
In one frame
Each threshold voltage detection element detecting each threshold voltage in a pixel circuit group arranged in a current measurement target row; and
Applying an image data potential according to the light emission luminance of the light emitting element for each pixel circuit group arranged in the row direction;
Sequentially selecting one pixel circuit constituting each pixel circuit group, and causing the light emitting element of the pixel circuit to emit light so that the gate-source voltage of the driving element sequentially becomes equal to or higher than each threshold voltage ;
Measuring the current flowing through the light emitting element with the current detection circuit;
A current measuring method in an image display device.
In the drive method of the electronic device which has an image display device according to claim 1,
A first step of inputting power-off information to the image display device;
A second step of measuring a current flowing through each pixel circuit after inputting the power-off information;
A third step in which the power of the image display device is turned off after completion of the second step;
A method for driving an electronic device, comprising:
In the drive method of the electronic device which has an image display device according to claim 1,
A first step of inputting power-on information to the image display device;
A second step of measuring a current flowing through each of the pixel circuits after inputting the power-on information;
A third step in which the power of the image display device is turned on after completion of the second step;
A method for driving an electronic device, comprising:
In the drive method of the electronic device which has an image display device according to claim 1,
A first step of setting the display screen of the image display unit to a standby state;
A second step of measuring a current flowing through each pixel circuit during the standby state;
A method for driving an electronic device, comprising:

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