JP4964527B2 - Driving method of image display device - Google Patents

Description

  The present invention relates to a method for driving an image display apparatus.

  2. Description of the Related Art Conventionally, there has been proposed an image display device using a current light emitting 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 (hereinafter referred to as “TFT”) formed of amorphous silicon, polycrystalline silicon, or the like, or an organic light emitting diode (Organic Light Emitting Diode): (Hereinafter referred to as “OLED”) constitutes each pixel, and the luminance of each pixel is controlled by setting an appropriate current value for each pixel.

  For example, in an active matrix image display device having a plurality of pixels in which a light emitting element and a driving transistor such as a TFT are arranged in series, the light flows through the light emitting element due to variations in threshold voltage of the driving transistor provided in each pixel. The current value changes and uneven brightness occurs. As a method for improving this phenomenon, for example, a threshold voltage of a driving transistor is detected in advance, and a current flowing through a light emitting element is controlled based on the detected threshold voltage (for example, Non-Patent Document 1), A specific circuit configuration (for example, Non-Patent Document 2) and the like are disclosed.

R. M.M. A. Dawson, et al. (1998). Design of an Improved Pixel for a Polysilicon Active-Matrix Organic LED Display. SID98 Digest, pp. 11-14. S. Ono et al. (2003). Pixel Circuit for a-Si AM-OLED. Proceedings of IDW '03, pp. 255-258.

  However, in the method disclosed in the above non-patent document, when a temperature change due to a change in the environment in which the image display device is used or a heat generation of the drive unit occurs, the display image is caused by the temperature change. There has been a problem that the brightness of the image fluctuates.

  On the other hand, using such a temperature change as a parameter, data (gamma data) representing the relationship of the write voltage with respect to the gradation is stored in advance, and the luminance fluctuation of the display image caused by the temperature change is adjusted based on the gamma data. It is also possible to do.

  However, in such a method, it is necessary to have the gamma data in the measurement temperature unit (for example, in increments of 1 ° C.), and there is a problem that the data to be held becomes enormous and the brightness adjustment becomes complicated.

  The present invention has been made in view of the above, and an object of the present invention is to provide a driving method of an image display device that can easily realize improvement in luminance fluctuation of a display image caused by a temperature change. To do.

In order to solve the above-described problems and achieve the object, a driving method of an image display device according to the present invention includes a light emitting element, a first terminal, a second terminal, and energization between the first terminal and the second terminal. A control terminal for controlling a state, the first terminal is electrically connected to the light emitting element, a driver element for controlling light emission of the light emitting element, and one end side of the control terminal of the driver element is electrically connected wherein a plurality of pixel circuits, a temperature measuring device for measuring the environmental temperature around the plurality of pixel circuits, a method for driving an image display device provided with an image signal including a capacitor which is connected Supplying a correction signal based on the measurement result of the temperature measuring element to the capacitive element after being supplied to the capacitive element; and the light emitting element based on the image signal and the correction signal supplied to the capacitive element. Departure Characterized in that it comprises a step of, the.

The image display apparatus driving method according to the next invention includes a light emitting element, a first terminal, a second terminal, and a control terminal for controlling the energization state between the first terminal and the second terminal. And a plurality of driver elements that are electrically connected to the light emitting element to control light emission of the light emitting element, and a capacitor element having one end side electrically connected to the control terminal of the driver element. of a pixel circuit, a method of driving an image display device provided with a temperature measuring device, the measuring the environmental temperature around the plurality of pixel circuits, before supplying an image signal to the capacitance element, the temperature Supplying a correction signal based on the measurement result of the measurement element to the capacitive element, and causing the light emitting element to emit light based on the image signal and the correction signal supplied to the capacitive element. And butterflies.

  The image display apparatus driving method according to the next invention is characterized in that, in the above invention, the value of the correction signal varies according to the measured temperature measured by the temperature measuring element.

  In the image display device driving method according to the next invention, in the above invention, the image signal and the correction signal are supplied from the other end of the capacitive element, and the correction signal is measured by the temperature measuring element. When the measured temperature is lower than the reference temperature, the potential on the other end of the capacitive element is increased, and when the measured temperature measured by the temperature measuring element is higher than the reference temperature, The potential at the other end is lowered.

  In the image display device driving method according to the next invention, in the above invention, the image signal and the correction signal are supplied from the other end of the capacitive element, and the correction signal is measured by the temperature measuring element. When the measured temperature is lower than the reference temperature, the potential on the other end of the capacitive element is lowered, and when the measured temperature measured by the temperature measuring element is higher than the reference temperature, The potential at the other end is raised.

  The image display apparatus driving method according to the next invention is characterized in that, in the above invention, the value of the correction signal does not depend on the value of the image signal.

  According to the driving method of the image display device according to the present invention, the luminance adjustment of the light emitting element is performed by supplying the pixel circuit with a correction signal corresponding to the luminance variation of the display image caused by the temperature change separately from the image signal. Therefore, the luminance adjustment can be improved in common for all gradations. As a result, it is possible to easily improve the light emission luminance fluctuation caused by the temperature characteristics.

  DESCRIPTION OF EMBODIMENTS Preferred embodiments according to a driving method of an image display device of the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited by embodiment shown below.

(Embodiment 1)
FIG. 1 is a diagram illustrating a schematic configuration of an image display device applied to a display unit such as a portable information terminal, and illustrates a schematic arrangement of main parts of the image display device.

  The image display device shown in FIG. 1 includes a light emitting unit 1 (display unit) composed of a plurality of pixels arranged in a matrix, an element substrate 2 composed of glass or the like, and glass or the like as a composition, and the light emitting unit 1 is disposed between the element substrate 2 and the sealing substrate 3 so as to cover the surface of the element substrate 2 so as to cover the surface of the element substrate 2. And a sealing material 4 that is a sealing material for joining (adhering) the substrate 3.

  The element substrate 2 has an organic EL element (normally, there are RGB three-color organic EL elements) in each pixel constituting the light emitting unit 1 on the upper surface thereof. Further, on the upper surface of the element substrate 2, in a region other than the light emitting unit 1, a drive IC 5 for driving the organic EL element and data relating to temperature-luminance characteristics of the organic EL element constituting the light emitting unit 1 (hereinafter referred to as “light emitting unit 1”) And a storage unit 6 which is, for example, an EEPROM, which stores and holds “temperature / luminance characteristic data”).

  Further, a temperature sensor 8 such as a thermistor is provided in the periphery of the element substrate 2 (or on the element substrate 2). The temperature sensor 8 detects the temperature (environment temperature) in the current use environment and transmits the environment temperature to the drive IC 5. The drive IC 5 determines a correction signal based on the environmental temperature transmitted from the temperature sensor 8 and the temperature / luminance characteristic data stored and held in the storage unit 6, and supplies the correction signal to the pixel circuit to The light emission luminance of the EL element is adjusted.

FIG. 2 is a diagram showing an example of the temperature characteristics related to the light emission luminance of the organic EL element, and plots the change in the light emission luminance (vertical axis) of the organic EL element with respect to the change in the environmental temperature (horizontal axis) against white display. It is what. As shown in the figure, it can be understood that a luminance change of about ² to 3 cd / m ² per 1 ° C. occurs.

3A and 3B are diagrams illustrating the concept of the driving method of the image display apparatus according to the present invention on a graph corresponding to FIG. In each of these drawings, the vertical axis represents the emission luminance of the organic EL element, and the horizontal axis represents the environmental temperature. In FIGS. 3A and 3B, the reference luminance K1 indicated by a bold line indicates a target light emission luminance level. In this example, the reference luminance K1 is set to the luminance level (about 140 cd / m ² ) of the organic EL element at room temperature (25 ° C.).

  Here, FIG. 3A shows a concept of control when the measured temperature is lower than the reference temperature. As shown in the figure, when the measured temperature measured by the temperature sensor 8 is lower than the reference temperature, control is performed to increase the light emission luminance of the organic EL element. Further, the amount of increase in light emission luminance is controlled so as to decrease as the difference between the measured temperature and the reference temperature decreases.

  FIG. 3-2 shows the concept of control when the measured temperature is higher than the reference temperature. As shown in the figure, when the temperature measured by the temperature sensor 8 is higher than the reference temperature, control is performed to reduce the light emission luminance of the organic EL element. Further, the amount of decrease in light emission luminance is controlled to decrease as the difference between the measured temperature and the reference temperature decreases.

  FIG. 4 is a diagram illustrating a configuration of a pixel circuit (one pixel) provided in the light emitting unit of the image display apparatus illustrated in FIG. 1, for example. The pixel circuits shown in the figure are arranged in a matrix, and each pixel circuit includes an organic light emitting element OLED which is one of organic EL elements, a driving transistor Td, a threshold voltage detecting transistor Ts, and a threshold voltage (Vth). And a capacitor Cs that holds an image signal potential.

  In FIG. 4, a drive transistor Td is a driver element for controlling the amount of current flowing through the organic light emitting element OLED in accordance with 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, or a beryllium complex, and light emitted by recombination of holes and electrons injected into the light-emitting layer. It has the function to produce.

  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 are for supplying a voltage to the organic EL element OLED and the driving transistor Td, and the supply voltage can be varied. 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.

  Next, the operation of the pixel circuit shown in FIG. 4 will be described with reference to FIGS. Here, FIG. 5 is a sequence diagram for explaining the operation of the pixel circuit shown in FIG. 4, and is performed under the control of the drive IC 5 shown in FIG. 6 to 11 show a Cs reset period (FIG. 6), a preparation period (FIG. 7), a Vth detection period (FIG. 8), a writing period (FIG. 9), which are the six periods divided in FIG. It is a figure for demonstrating the operation | movement of each area of a Coled reset period (FIG. 10) and a light emission period (FIG. 11). 6 to 11, Coled connected in parallel to the organic light emitting element OLED is an element capacity inherently possessed by the organic light emitting element OLED.

(Cs reset period)
The operation during the Cs reset period will be described with reference to FIGS. 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, as shown in FIG. 5, the threshold voltage detection transistor Ts is turned on and the drive transistor Td is turned off, and the first power supply line 11 → the organic light emitting element OLED → the threshold voltage detection transistor Ts → the capacitor Cs. When a current flows and the capacitor Cs is 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.

  Here, when the potentials of the gate (point A) of the drive transistor Td and the drain (point B) of the drive transistor Td are Va and Vb, Va and Vb immediately after the start of the Cs reset period and at the end of the Cs reset period are It can be expressed as follows. The voltage across the organic light emitting element OLED is Voled.

-Immediately after the start of the Cs reset period
Va = VDD + Coled / (Coled + Cs) × Vdata
Vb = VDD-Voled
... (1)
・ At the end of Cs reset period
Va = Vb = VDD
... (2)

  An actual transistor generally has a parasitic capacitance between the gate and the source and between the gate and the drain. The potentials of the gate (point A) and the drain (point B) of the driving transistor Td are the parasitic potentials. Slightly affected by capacity. However, in explaining the driving method of the image display apparatus according to the present invention, the influence of these parasitic capacitances can be ignored. Therefore, in the above formula and the formulas shown below, formulas that do not include the parasitic capacitance present in the transistor are presented.

(Preparation period)
The operation during the preparation period will be described with reference to FIGS. In the preparation period, the first power supply line 11 is at a negative potential (−VE), the second power supply line 12 is at a zero potential (GND), the scanning line 13 is at a low potential (VgL), and the image signal line 14 is at a high potential (VgH). Is done. As a result, as shown in FIG. 7, the threshold voltage detection transistor Ts is turned off and the drive transistor Td is turned on, and a current flows through the path of the second power supply line 12 → the drive transistor Td → the element capacitance Coled, and the element capacitance Coled. The charge is accumulated in the. The reason for accumulating charge in the element capacitance Coled during this preparation period is that the element capacitance Coled is set to the drain and drain of the drive transistor Td 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 sources.

  Similar to the Cs reset period, Va and Vb immediately after the start and end of the preparation period can be expressed as follows.

-Immediately after the start of the preparation period
Va = VDD + VdH
Vb = -VE
... (3)
・ At the end of the preparation period
Va = VDD + VdH
Vb = GND
... (4)

(Vth detection period)
Next, the operation during the Vth detection period will be described with reference to FIGS. 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). On the other hand, the image signal line 14 is maintained at a high potential (VdH), and the second power supply line 12 is maintained at a zero potential (GND). Thereby, as shown in FIG. 8, 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 element capacitor Coled are discharged, and the capacitor Cs → the threshold voltage detecting transistor Ts → the driving transistor Td → the second power supply line 12 and the element capacitor Coled → the driving transistor Td → the second power supply line. A current flows through the path 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.

  Further, Va and Vb immediately after the start of the Vth detection period and at the end thereof are as follows.

-Immediately after the start of the Vth detection period
Va = VDD + VdH
Vb = GND
... (5)
・ At the end of the Vth detection period
Va = Vb = Vth
(6)

(Writing period)
Further, the operation in the writing period will be described with reference to FIGS. In the writing period, the gate potential of the driving transistor Td is changed to a desired potential by reflecting the image signal potential (−Vdata) in 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 has 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 has a predetermined period in the writing period. In FIG. 2, the potential is high (VgH).

  As a result, as shown in FIG. 9, the threshold voltage detection transistor Ts is turned on, the electric charge accumulated in the element capacitance Coled is discharged, and the current flows along the path of element capacitance Coled → threshold voltage detection transistor Ts → capacitance Cs. Flowing. That is, the charge accumulated in the element capacitor Coled 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.

  Further, Va and Vb immediately after the start and end of the writing period are as follows.

-Immediately after the start of the writing period
Va = Vth-Vdata
Vb = Vth
... (7)
・ At the end of the writing period
Va = Vb = Vth + Coled / (Coled + Cs) × Vdata
(8)

  Note that since the capacitor Cs and the element capacitor Coled are connected in series during the writing period, the amount of decrease in the potential (that is, the point A) of one end of the capacitor Cs (the end connected to the gate of the drive transistor Td) is It does not become the potential drop amount Vdata of the signal line 14 but is affected by the capacitance ratio between the capacitance Cs and the element capacitance Coled as shown in the above equation.

(Coled reset period)
The operation during the Coled reset period will be described with reference to FIGS. 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, as shown in FIG. 10, the threshold voltage detection transistor Ts is turned off and the drive transistor Td is turned on, and a current flows through a path of the organic light emitting element OLED → the drive transistor Td → the second power supply line 12 to The electric charge remaining in Coled is 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.

  Further, Va and Vb immediately after the start of the Coled reset period and at the end thereof are as follows.

-Immediately after the start of the Coled reset period
Va = Vb = Vth + Coled / (Coled + Cs) × Vdata
... (9)
-At the end of the Coled reset period
Va = Vth + Coled / (Coled + Cs) × Vdata
Vb = -VE
(10)

  In the Coled reset period, since the potential of the first power supply line 11 rises by Vdata while the point A and the point B are not electrically connected, only Va rises by Vdata, and Vb becomes conduction of the drive transistor Td. Thus, the potential becomes the same as that of the second power supply line 12.

(Light emission period)
Finally, the operation in the light emission period will be described with reference to FIGS. 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, as shown in FIG. 11, 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. The current flows through the path of the driving transistor Td → the second power supply line 12, and the organic light emitting element OLED emits light.

Further, Va and Vb in the light emission period are as follows.
-Immediately after the start of the light emission period and at the end
Va = Vth + Coled / (Coled + Cs) × Vdata
Vb = VDD-Voled
... (11)

  The general operation of the pixel circuit shown in FIG. 4 is as described above. Next, a control method according to the first embodiment of the present invention will be described. Here, FIG. 12 is a sequence diagram when the control method according to the first embodiment of the present invention is applied to the pixel circuit shown in FIG.

  12 is different from the sequence shown in FIG. 5 in that a temperature compensation period is provided between the writing period and the Coled reset period. When a temperature compensation period is provided after the writing period, if the environmental temperature is higher than a reference temperature (for example, 25 ° C., which is normal temperature), the potential of the image signal line 14 needs to be lowered in order to reduce the light emission luminance of the organic EL element. . Therefore, the value of ΔV takes a positive value, and the value of ΔV increases as the difference between the environmental temperature and the reference temperature increases.

  On the other hand, when the environmental temperature is lower than a reference temperature (for example, 25 ° C. which is normal temperature), it is necessary to increase the potential of the image signal line 14 in order to increase the light emission luminance of the organic EL element. Therefore, the value of ΔV takes a negative value, and the value of ΔV decreases as the difference between the environmental temperature and the reference temperature increases (the absolute value of ΔV increases). In the present embodiment, it is assumed that the environmental temperature is higher than the reference temperature. In this temperature compensation period, as shown in FIG. 12, the potential of the image signal line 14 is set to ΔV in order to reduce the light emission luminance of the organic EL element. Control is performed to descend by (ΔV> 0). Note that the operation for the temperature compensation period enables compensation for reducing the light emission luminance.

  Next, an operation based on the control sequence of the first embodiment will be described. The operation from the Cs reset period to the writing period is the same as described above, and the description thereof is omitted.

(Temperature compensation period)
First, the state immediately before shifting to the temperature compensation period coincides with the state at the end of the writing period shown in FIG. The potential at point A (Va) and the potential at point B (Vb) at this time are as shown in the above equation (8) as shown below.

-Potential at the end of the writing period
Va = Vb = Vth + Coled / (Coled + Cs) × Vdata
... (8) (repost)

  On the other hand, in the temperature compensation period, as shown in FIG. 12, a potential of VdH−ΔV is applied to the image signal line 14. ΔV corresponds to the correction signal potential. On the other hand, the potential of the scanning line is VgL, and the threshold voltage detection transistor Ts is kept off. Accordingly, the potential at point A (Va1) and the potential at point B (Vb1) immediately after the start of the temperature compensation period are expressed by the following equations.

・ Potential immediately after start of temperature compensation period
Va1 = Va-ΔV = Vth + Coled / (Coled + Cs) × Vdata-ΔV
Vb1 = Vth + Coled / (Coled + Cs) × Vdata
(12)
These potentials are maintained even at the end of the temperature compensation period. That is, it is represented by the same formula as the above formula (12).
-Potential at the end of the temperature compensation period
Va1 = Va-ΔV = Vth + Coled / (Coled + Cs) × Vdata-ΔV
Vb1 = Vth + Coled / (Coled + Cs) × Vdata
... (13)

  Note that the value of ΔV varies depending on the environmental temperature measured by the temperature sensor 8. A plurality of such ΔV values are stored in advance in the storage unit 6, and an appropriate ΔV value is determined by the drive IC 5 based on the environmental temperature measured by the temperature sensor 8 and the temperature / luminance data stored in the storage unit 6. Selected. The selected ΔV is supplied to the image signal line 14 at a predetermined timing. Since the correction signal employs a value that does not depend on the gradation of the organic EL element, the data necessary for determining the correction signal is well prevented from becoming complicated.

(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−ΔV). Therefore, the potential at the point A (Va1) and the potential at the point B (Vb1) immediately after the start of the Coled reset period and at the end thereof are expressed by the following equations.

-Immediately after the start of the Coled reset period
Va1 = Vth + Coled / (Coled + Cs) × Vdata-ΔV
Vb1 = Vth + Coled / (Coled + Cs) × Vdata
... (14)
-At the end of the Coled reset period
Va1 = Vth + Coled / (Coled + Cs) × Vdata-ΔV
Vb1 = -VE
... (15)

(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−ΔV). Therefore, the potential at point A (Va1) and the potential at point B (Vb1) during the light emission period are expressed by the following equations.

-Immediately after the start of the light emission period and at the end
Va1 = Vth + Coled / (Coled + Cs) × Vdata-ΔV
Vb1 = VDD-Voled
... (16)

  Here, in the case of controlling based on the potential at point A (the gate of the driving transistor Td) (see the above equation (11)) in the light emission period when controlling based on the sequence shown in FIG. 5 and the sequence shown in FIG. The potential at point A in the light emission period (see equation (16) above) is compared. First, when the deviation δV1 between Va1 shown in the equation (16) and Va shown in the equation (11) is calculated, the following equation is obtained.

δV1 = Va1-Va
= [Vth + Coled / (Coled + Cs) × Vdata-ΔV]
-[Vth + Coled / (Coled + Cs) × Vdata]
= -ΔV
... (17)

  The meaning indicated by δV1 can be explained as follows. In other words, in the sequence shown in FIG. 12, a temperature compensation period is provided in which the potential of the image signal line 14 is lowered by ΔV (ΔV> 0) between the writing period and the Coled reset period, and the potential is extended until the light emission period. Control to maintain. As a result, the potential applied to the gate of the drive transistor Td can be lowered in the light emission period, and the light emission luminance in the light emission period can be reduced. As is apparent from the above description, this sequence does not depend on the value of the image signal potential Vdata, so that it is not necessary to have correction data for each gradation, and light emission luminance can be easily adjusted. be able to.

  By the way, as understood from the sequence of FIG. 12 and the pixel circuit of FIG. 10, the scanning line 13 is maintained at a low potential (VgL) from the temperature compensation period to the Coled reset period. Continues off. For this reason, there is no escape field of the charge of the capacitor Cs that determines the potential at the point A, so the potential of the image signal line 14 in the Coled reset period does not need to be (VdH−ΔV). That is, the potential of the image signal line 14 in the Coled reset period is arbitrary.

  It should be noted that when the potential drop amount ΔV of the image signal line 14 in the temperature compensation period is relatively large and the applied potential (VdH−ΔV) in the temperature compensation period is maintained in the Coled reset period, the element capacitance Coled is obtained. There is a concern that the discharge of the accumulated charge will be insufficient. In such a case, as in the conventional sequence shown in FIG. 5, the potential of the image signal line 14 is returned to, for example, VdH in the Coled reset period, while the potential of the image signal line 14 is again set in the light emission period. It is preferable to perform control such that the voltage is lowered by ΔV.

(Embodiment 2)
Next, a control method according to the second embodiment of the present invention will be described. FIG. 13 is a sequence diagram when the control method according to the second embodiment of the present invention is applied to the pixel circuit shown in FIG.

  The sequence shown in FIG. 13 provides a temperature compensation period in which the potential of the image signal line 14 is increased by | ΔV | (ΔV <0) between the writing period and the Coled reset period, and the potential is increased until the light emission period. It is characterized in that it is controlled to maintain. Others are the same as or equivalent to the sequence according to the first embodiment shown in FIG. 12, and detailed description thereof is omitted.

  In the present embodiment, the environmental temperature is lower than the reference temperature. Therefore, in order to increase the light emission luminance of the organic EL element, control is performed to increase the potential of the image signal line 14 by ΔV during the temperature compensation period. That is, the value of ΔV in the second embodiment is a negative value. As a result, the potential applied to the gate of the drive transistor Td can be increased in the light emission period, and the light emission luminance in the light emission period can be increased. Further, since this sequence is not affected by the value of the image signal potential Vdata as in the case of the first embodiment, it is not necessary to have correction data for the image signal potential, and the adjustment of the light emission luminance is simplified. It can be carried out. The point that the potential of the image signal line 14 is arbitrary in the Coled reset period is the same as that in the first embodiment.

(Embodiment 3)
Next, a control method according to the third embodiment of the present invention will be described. FIG. 14 is a sequence diagram when the control method according to the third embodiment of the present invention is applied to the pixel circuit shown in FIG.

  14 is different from the sequence according to the first embodiment shown in FIG. 12 in that the temperature compensation period is provided before the write period. Specifically, the temperature compensation period is provided between the Vth detection period and the writing period. Thus, when the temperature compensation period is provided before the writing period, unlike the first and second embodiments, if the environmental temperature is higher than the reference temperature (for example, 25 ° C. which is normal temperature), the light emission luminance of the organic EL element is lowered. The potential of the image signal line 14 is increased. On the other hand, when the environmental temperature is lower than a reference temperature (for example, 25 ° C. which is normal temperature), the potential of the image signal line 14 is lowered in order to increase the light emission luminance of the organic EL element. In the present embodiment, it is assumed that the environmental temperature is lower than the reference temperature. In this temperature compensation period, as shown in FIG. 14, the potential of the image signal line 14 is set to ΔV in order to increase the light emission luminance of the organic EL element. Control is performed to descend by (ΔV> 0). The operation during this temperature compensation period enables compensation to increase the light emission luminance.

  Next, an operation based on the control sequence of the third embodiment will be described. The operation from the Cs reset period to the Vth detection period is the same as that in the conventional sequence, and the description thereof is omitted.

(Temperature compensation period)
First, the state at the end of the temperature compensation period, that is, the state at the end of the Vth detection period coincides with the state at the end of the Vth detection period shown in FIG. Therefore, the potential at the end of the temperature compensation period is equal to the potential at the end of the Vth detection period. At this time, the potential at the point A (Va2) and the potential at the point B (Vb2) are as shown in the above equation (6) as shown below.

-Potential at the end of the temperature compensation period (potential at the end of the Vth detection period)
Va2 = Vb2 = Vth
... (18)

  On the other hand, in the temperature compensation period, as shown in FIG. 14, a potential of VdH−ΔV (ΔV is a correction signal) is applied to the image signal line 14. On the other hand, the potential of the scanning line is VgH, and the threshold voltage detection transistor Ts is kept on. Vth detection is already started when the temperature compensation period starts, but when the potential at point A (Va2) and the potential at point B (Vb2) immediately after the start of the temperature compensation period are set, Va2 and Vb2 are more than Vth + ΔV. If the correction signal potential is not applied to the image signal line 14, the value of Vgs becomes smaller than Vth and Vth cannot be detected correctly. It is necessary to satisfy the condition of the following formula.

・ Potential immediately after start of temperature compensation period
Va2 = Vb2 ≧ Vth + ΔV
... (19)

(Writing period)
In the writing period, the zero potential (GND) of the first power supply line 11 and the zero potential (GND) of the second power supply line 12 are maintained. On the other hand, 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 period within the writing period. In FIG. 2, the potential is high (VgH).

  As a result, the potential at point A (Va2) and the potential at point B (Vb2) immediately after the start and end of the writing period are expressed by the following equations.

・ Potential immediately after start of writing period
Va2 = Vth- (Vdata-ΔV) = Vth-Vdata + ΔV
Vb2 = Vth
... (20)
・ At the end of the writing period
Va2 = Vb2 = Vth + Coled / (Coled + Cs) × Vdata + Cs / (Coled + Cs) × ΔV
... (21)

  Note that, at the start of the writing period, the potential difference (Vb2−Va2) between the point B and the point A is Vth− (Vth−Vdata + ΔV) = Vdata−ΔV, and this potential difference is applied at the time of writing. It is necessary to pay attention to this point.

(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). Therefore, the potential at point A (Va2) and the potential at point B (Vb2) immediately after the start of the Coled reset period and at the end thereof are expressed by the following equations.

-Immediately after the start of the Coled reset period
Va2 = Vb2 = Vth + Coled / (Coled + Cs) × Vdata + Cs / (Coled + Cs) × ΔV
... (22)
-At the end of the Coled reset period
Va2 = Vth + Coled / (Coled + Cs) × Vdata + Cs / (Coled + Cs) × ΔV
Vb2 = -VE
... (23)

(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−ΔV). Therefore, the potential at point A (Va2) and the potential at point B (Vb2) during the light emission period are expressed by the following equations.

-Immediately after the start of the light emission period and at the end
Va2 = Vth + Coled / (Coled + Cs) × Vdata + Cs / (Coled + Cs) × ΔV
Vb2 = VDD-Voled
... (24)

  Here, in the case of controlling based on the potential at the point A (the gate of the driving transistor Td) (see the above formula (11)) in the light emission period in the case of controlling based on the sequence shown in FIG. 5 and the sequence shown in FIG. The potential at point A during the light emission period (see equation (24) above) is compared. First, when a deviation δV2 between Va2 expressed by equation (24) and Va expressed by equation (11) is calculated, the following equation is obtained.

δV2 = Va2-Va
= [Vth + Coled / (Coled + Cs) × Vdata + Cs / (Coled + Cs) × ΔV]
-[Vth + Coled / (Coled + Cs) × Vdata]
= Cs / (Coled + Cs) × ΔV
... (25)

  The meaning indicated by δV2 can be explained as follows. That is, in the sequence shown in FIG. 14, a temperature compensation period in which the potential of the image signal line 14 is lowered by −ΔV from the normal potential (VdH) is provided between the Vth detection period and the writing period. As a result, during the light emission period, the potential applied to the gate of the drive transistor Td can be substantially increased by the potential amount represented by the equation (25), and the light emission luminance during the light emission period can be increased. As is apparent from the above description, the correction signal does not depend on the value of the image signal potential Vdata, so that it is not necessary to have correction data for each gradation, and the adjustment of the light emission luminance can be easily performed. It can be carried out.

(Embodiment 4)
Next, a control method according to the fourth embodiment of the present invention will be described. FIG. 15 is a sequence diagram when the control method according to the fourth embodiment of the present invention is applied to the pixel circuit shown in FIG.

  In the present embodiment, assuming that the environmental temperature is higher than the reference temperature, the potential of the image signal line 14 is set to | ΔV | (ΔV <0) between the Vth detection period and the writing period, as shown in FIG. ) Is characterized in that a temperature compensation period is provided to raise the temperature by only. Others are the same as or equivalent to the sequence according to the third embodiment shown in FIG. 14, and a detailed description thereof is omitted.

  As described above, in the sequence according to the present embodiment, the control of increasing the potential of the image signal line 14 by | ΔV | is performed in the temperature compensation period, so that the voltage is applied to the gate of the drive transistor Td in the light emission period. The potential to be emitted can be substantially lowered, and the light emission luminance during the light emission period can be reduced. Further, as in the case of the third embodiment, this sequence does not depend on the value of the image signal potential Vdata, so that it is not necessary to have correction data for the image signal potential, and the adjustment of the light emission luminance is simplified. It can be carried out.

  In the above description, the case where the control sequence as shown in FIGS. 12 to 15 is applied to the pixel circuit having the configuration shown in FIG. 4 has been described. However, the present invention is naturally applicable to other than the pixel circuit shown in FIG. It can be applied to.

  For example, the pixel circuit shown in FIG. 4 is configured as a pixel circuit having a function of detecting a threshold voltage, but the present invention can also be applied to a case where the pixel circuit has no function of detecting a threshold voltage.

  In the pixel circuit shown in FIG. 4, the case where the number of transistors including the driving transistor is two has been described as an example. However, the present invention is also applied to the case where the number of transistors is three, four, or more. Can be applied.

  The important point is that the circuit configuration is such that the gate potential of the drive transistor Td can be varied by supplying a correction signal to the pixel circuit.

  Next, actual measurement results will be described.

FIG. 16 is a diagram illustrating a measurement result of luminance change when a temperature compensation period is provided after the writing period. FIG. 17 is a diagram illustrating the measurement result of the luminance change when the temperature compensation period is provided before the writing period. 16 and 17, the vertical axis represents the white light emission luminance of the light emitting element, and the horizontal axis represents the potential of the correction signal (ΔV) supplied to the image signal line during the temperature compensation period. The white light emission luminance of the light emitting element indicates the luminance of white light composed of light from the red light emitting element (R), the green light emitting element (G), and the blue light emitting element (B). Note that the value on the vertical axis represents the luminance value when the white light emission luminance of the light emitting element when ΔV = 0V is 1. In FIG. 16, the white light emission luminance of the light emitting element when ΔV = 0V is 110 cd / m ² , and in FIG. 17, the white light emission luminance of the light emitting element when ΔV = 0V is 250 cd / m ² . In both cases shown in FIGS. 16 and 17, the value of VdH is 10 V common to RGB, and the value of Vdata is 10 V for R, 7.5 V for G, and 8.9 V for B. As shown in FIGS. 16 and 17, it can be understood that the light emission luminance can be varied almost linearly by raising and lowering the potential of ΔV.

  Next, the superiority of the driving method according to the first to fourth embodiments described above is compared with the driving method that changes the potential of the image signal line at the time of writing. Here, FIG. 18-1 is a diagram showing the writing potential for the gradation when the environmental temperature is 25 ° C., and FIG. 18-2 is a diagram showing the writing potential for the gradation when the environmental temperature is 40 ° C. It is. 18A and 18B, the vertical axis represents the potential of the image signal line in the writing period, and the horizontal axis represents the gradation.

  As is apparent from a comparison between the case where the environmental temperature is 25 ° C. and the case where the environmental temperature is 40 ° C., the writing voltage with respect to the gradation varies considerably depending on the environmental temperature. Therefore, in order to control the brightness of the image display device with a certain degree of accuracy, the environmental temperature must be measured in fine steps (for example, in increments of 1 ° C.). In this case, for example, even with one correction curve shown in FIG. 18A, it is necessary to hold the value of the writing potential for each gradation and further hold the data every 1 ° C. These correction data alone are a huge amount of data.

  On the other hand, in the driving methods according to the first to fourth embodiments, the amount of change that increases or decreases the potential of the image signal line is common to all the gradations, so that the amount of data to be retained can be reduced. An effect is obtained.

  As described above, the driving method of the image display device according to the present invention is useful as an invention that can greatly contribute to the improvement of the temperature characteristics of the light emission luminance in the pixel circuit.

It is a figure which shows schematic structure of the image display apparatus applied to display parts, such as a portable information terminal. It is a figure which shows an example of the temperature characteristic concerning the light emission luminance of an organic EL element. It is a figure which shows the concept (measurement temperature <reference temperature) of the drive method of the image display apparatus concerning this invention. It is a figure which shows the concept (measurement temperature> reference temperature) of the drive method of the image display apparatus concerning this invention. It is a figure which shows the structure of the pixel circuit (1 pixel) provided in the light emission part of the image display apparatus shown in FIG. FIG. 5 is a sequence diagram for explaining a general operation of the pixel circuit shown in FIG. 4. It is a figure explaining the operation | movement in the Cs reset period of the sequence shown in FIG. It is a figure explaining the operation | movement in the preparation period of the sequence shown in FIG. It is a figure explaining the operation | movement in the Vth detection period of the sequence shown in FIG. It is a figure explaining the operation | movement in the write-in period of the sequence shown in FIG. It is a figure explaining the operation | movement in the Coled reset period of the sequence shown in FIG. It is a figure explaining the operation | movement in the light emission period of the sequence shown in FIG. FIG. 5 is a sequence diagram when the control method according to the first exemplary embodiment of the present invention is applied to the pixel circuit shown in FIG. 4. FIG. 5 is a sequence diagram when the control method according to the second exemplary embodiment of the present invention is applied to the pixel circuit shown in FIG. 4. FIG. 5 is a sequence diagram when the control method according to the third exemplary embodiment of the present invention is applied to the pixel circuit shown in FIG. 4. FIG. 5 is a sequence diagram when the control method according to the fourth embodiment of the present invention is applied to the pixel circuit shown in FIG. 4. It is a figure which shows the measurement result of the luminance change at the time of providing the temperature compensation period after the writing period. It is a figure which shows the measurement result of the brightness | luminance change when the temperature maintenance compensation period is provided before the writing period. It is a figure which shows the write-in potential with respect to the gradation in case environmental temperature is 25 degreeC. It is a figure which shows the write-in potential with respect to the gradation in case environmental temperature is 40 degreeC.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light emission part 2 Element substrate 3 Sealing substrate 4 Sealing material 5 Drive IC
6 Storage Unit 8 Temperature Sensor 11 First Power Line 12 Second Power Line 13 Scanning Line 14 Image Signal Line OLED Organic Light-Emitting Element Coled Element Capacitance Cs Capacity Td Drive Transistor Ts Threshold Voltage Detection Transistor

Claims (6)

A light emitting element, a first terminal, a second terminal, and a control terminal for controlling an energization state between the first terminal and the second terminal, the first terminal being electrically connected to the light emitting element is, the driver device for controlling light emission of the light emitting element, and a plurality of pixel circuits one end to said control terminal of said driver element has a capacitive element electrically connected, the environmental temperature around the plurality of pixel circuits A temperature measuring element for measuring, and a method for driving an image display device comprising:
Supplying a correction signal based on a measurement result of the temperature measuring element to the capacitive element after supplying an image signal to the capacitive element;
Causing the light emitting element to emit light based on the image signal and the correction signal supplied to the capacitive element;
A method for driving an image display device, comprising: A light emitting element, a first terminal, a second terminal, and a control terminal for controlling an energization state between the first terminal and the second terminal, the first terminal being electrically connected to the light emitting element is, the driver device for controlling light emission of the light emitting element, and a plurality of pixel circuits one end to said control terminal of said driver element has a capacitive element electrically connected, the environmental temperature around the plurality of pixel circuits A temperature measuring element for measuring, and a method for driving an image display device comprising :
Before supplying an image signal to the capacitive element, supplying a correction signal based on the measurement result of the temperature measuring element to the capacitive element;
Causing the light emitting element to emit light based on the image signal and the correction signal supplied to the capacitive element;
A method for driving an image display device, comprising:   3. The image display device driving method according to claim 1, wherein a value of the correction signal varies according to a measured temperature measured by the temperature measuring element. 4. The image signal and the correction signal are supplied from the other end side of the capacitive element,
When the measured temperature measured by the temperature measuring element is lower than the reference temperature, the correction signal increases the potential on the other end side of the capacitive element, and the measured temperature measured by the temperature measuring element is the reference temperature. 2. The method of driving an image display device according to claim 1, wherein the potential on the other end side of the capacitive element is lowered when the capacitance is higher than the upper limit. The image signal and the correction signal are supplied from the other end side of the capacitive element,
When the measured temperature measured by the temperature measuring element is lower than a reference temperature, the correction signal drops the potential on the other end side of the capacitive element, and the measured temperature measured by the temperature measuring element is the reference temperature. 3. The method of driving an image display device according to claim 2, wherein the potential on the other end side of the capacitive element is increased when the capacitance is higher than the upper limit.   The method of driving an image display device according to claim 1, wherein the value of the correction signal does not depend on the value of the image signal.

Images