Display device and method for controlling the same

1. A display device, comprising:

a luminescence element including a first electrode and a second electrode;

a first power line electrically connected to the first electrode;

a second power line electrically connected to the second electrode;

a capacitor including a third electrode and a fourth electrode, the capacitor holding a voltage;

a driving transistor between the first electrode and the first power line that causes the luminescence element to emit light by passing a current between the first power line and the second power line, the current corresponding to the voltage held by the capacitor;

a data line through which a signal voltage is supplied to one of the third electrode and the fourth electrode;

a data-line driver that supplies the signal voltage to the data line;

a first switch between the data line and the one of the third electrode and the fourth electrode for switchedly supplying the capacitor with the signal voltage;

a voltage detector connected to the data line for detecting a luminescence voltage applied to the luminescence element;

a second switch between the data line and the first electrode;

a controller that:

causes the capacitor to hold a first voltage corresponding to a first signal voltage supplied through the data line by switching on the first switch, the driving transistor to pass, between the first power line and the second power line, a first current corresponding to the first voltage held by the capacitor, and the voltage detector to detect a first luminescence voltage applied to the luminescence element via the data line by switching off the first switch, switching on the second switch, and making a connection between the data-line driver and the data line open while the luminescence element emits the light; and

causes the capacitor to hold a second voltage corresponding to a second signal voltage which is different in value from the first signal voltage and is supplied through the data line by switching on the first switch, the driving transistor to pass, between the first power line and the second power line, a second current corresponding to the second voltage held by the capacitor, and the voltage detector to detect a second luminescence voltage applied to the luminescence element via the data line by switching off the first switch and switching on the second switch while the luminescence element emits the light; and

a determiner that determines a first drain current and a second drain current of the driving transistor based on the first luminescence voltage and the second luminescence voltage detected by the voltage detector, respectively, and calculates a gain coefficient and a threshold voltage of the driving transistor based on the first luminescence voltage, the second luminescence voltage, the first drain current, and the second drain current.

2. The display device according to claim 1 , further comprising:

a memory that stores data corresponding to a voltage-current characteristic of the luminescence element,

wherein the determiner determines the first drain current of the driving transistor based on the first luminescence voltage detected by the voltage detector using the data corresponding to the voltage-current characteristic of the luminescence element.

3. The display device according to claim 2 ,

wherein the luminescence element, the capacitor, and the driving transistor are included in a pixel, and

the data corresponding to the voltage-current characteristic of the luminescence element is data on the voltage-current characteristic of the luminescence element included in the pixel.

4. The display device according to claim 2 , further comprising:

a plurality of pixels, each of which includes the luminescence element, the capacitor, and the driving transistor,

wherein the data corresponding to the voltage-current characteristic of the luminescence element is data on the voltage-current characteristic of the luminescence element which is representative of each luminescence element included in the plurality of pixels.

5. The display device according to claim 2 , further comprising:

a luminescent panel that includes a plurality of pixels and a plurality the data line, each of the plurality of pixels including the luminescence element, the capacitor, and the driving transistor, each of the plurality of the data line connected to one of the plurality of pixels,

wherein the voltage detector includes:

at least one voltage detector that detects the first luminescence voltage of the luminescence element of one of the plurality of pixels via a corresponding one of the plurality of the data line; and

a multiplexer that is connected to each of the plurality of the data line and the at least one voltage detector and causes the corresponding one of the plurality of the data line and the at least one voltage detector to electrically contact with each other,

wherein a number of the at least one voltage detector is less than a number of the plurality of the data line.

6. The display device according to claim 5 ,

wherein the multiplexer is formed on the luminescent panel.

7. The display device according to claim 1 ,

wherein the first electrode is an anode of the luminescence element, and

a voltage of the first power line is higher than a voltage of the second power line, to which a current flows from the first power line.

8. A method for controlling a display device, the display device comprising:

a luminescence element including a first electrode and a second electrode;

a first power line electrically connected to the first electrode;

a second power line electrically connected to the second electrode;

a capacitor including a third electrode and a fourth electrode, the capacitor holding a voltage;

a driving transistor between the first electrode and the first power line that causes the luminescence element to emit light by passing a current between the first power line and the second power line, the current corresponding to the voltage held by the capacitor;

a data line through which a signal voltage is supplied to one of the third electrode and the fourth electrode;

a data-line driver that supplies the signal voltage to the data line;

a first switch between the data line and the one of the third electrode and the fourth electrode for switchedly supplying the capacitor with the signal voltage;

a voltage detector connected to the data line for detecting a luminescence voltage applied to the luminescence element; and

a second switch between the data line and the first electrode,

the method comprising:

causing the capacitor to hold a first voltage corresponding to a first signal voltage supplied through the data line by switching on the first switch;

causing the driving transistor to pass, between the first power line and the second power line, a first current corresponding to the first voltage held by the capacitor;

causing the voltage detector to detect a first luminescence voltage applied to the luminescence element via the data line by switching off the first switch, switching on the second switch, and making a connection between the data-line driver and the data line open while the luminescence element emits the light;

causing the capacitor to hold a second voltage corresponding to a second signal voltage which is different in value from the first signal voltage and is supplied through the data line by switching on the first switch;

causing the driving transistor to pass, between the first power line and the second power line, a second current corresponding to the second voltage held by the capacitor;

causing the voltage detector to detect a second luminescence voltage applied to the luminescence element via the data line by switching off the first switch and switching on the second switch while the luminescence element emits the light;

determining a first drain current and a second drain current of the driving transistor based on the first luminescence voltage and the second luminescence voltage detected by the voltage detector, respectively; and

calculating a gain coefficient and a threshold voltage of the driving transistor based on the first luminescence voltage, the second luminescence voltage, the first drain current, and the second drain current.

9. The method according to claim 8 ,

wherein the display device further comprises a memory that stores data corresponding to a voltage-current characteristic of the luminescence element, and

the method further comprises determining the first drain current of the driving transistor based on the first luminescence voltage detected by the voltage detector using the data corresponding to the voltage-current characteristic of the luminescence element.

10. The method according to claim 9 ,

wherein the display device further comprises a memory that stores data corresponding to a voltage-current characteristic of the luminescence element, and

the method further comprises determining the first drain current and the second drain current based on the first luminescence voltage and the second luminescence voltage, respectively, using the data corresponding to the voltage-current characteristic of the luminescence element.

11. The method claim 9 , comprising

calculating the gain coefficient and the threshold voltage of the driving transistor using a relational expression

β

=

(

2

⁢

I

1

⁢

-

2

⁢

I

2

V

gs

⁢

⁢

1

-

V

gs

⁢

⁢

2

⁢

)

2

Vth

=

V

gs

⁢

⁢

2

×

2

⁢

I

1

-

V

gs

⁢

⁢

1

×

2

⁢

I

2

2

⁢

I

1

-

2

⁢

I

2

⁢

,

wherein:

Vgs 1 is a voltage obtained by subtracting, from the first signal voltage, a power supply voltage set for the first power line connected to one of the source and the drain of the driving transistor;

Vgs 2 is a voltage obtained by subtracting the power supply voltage from the second signal voltage:

I 1 is the first drain current;

I 2 is the second drain current;

β is a gain coefficient for a channel region, a capacity of an oxide film, and mobility of the driving transistor; and

Vth is the threshold voltage of the driving transistor.

12. A display device, comprising:

a luminescence element including a first electrode and a second electrode;

a first power line electrically connected to the first electrode;

a second power line electrically connected to the second electrode;

a capacitor including a third electrode and a fourth electrode, the capacitor holding a voltage;

a driving transistor between the first electrode and the first power line that causes the luminescence element to emit light by passing a current between the first power line and the second power line, the current corresponding to the voltage held by the capacitor;

a data line through which a signal voltage is supplied to one of the third electrode and the fourth electrode;

a data-line driver that supplies the signal voltage to the data line;

a first switch between the data line and the one of the third electrode and the fourth electrode for switchedly supplying the capacitor with the signal voltage;

a read line is separate from the data line and that reads a luminescence voltage applied to the luminescence element;

a voltage detector connected to the read line for detecting the luminescence voltage applied to the luminescence element;

a second switch between the read line and the first electrode;

a controller that:

causes the capacitor to hold a first voltage corresponding to a first signal voltage supplied through the data line by switching on the first switch, the driving transistor to pass, between the first power line and the second power line, a first current corresponding to the first voltage held by the capacitor, and the voltage detector to detect a first luminescence voltage applied to the luminescence element via the read line by switching off the first switch, switching on the second switch, and making a connection between the data-line driver and the data line open while the luminescence element emits the light; and

causes the capacitor to hold a second voltage corresponding to a second signal voltage which is different in value from the first signal voltage and is supplied through the data line by switching on the first switch, the driving transistor to pass, between the first power line and the second power line, a second current corresponding to the second voltage held by the capacitor, and the voltage detector to detect a second luminescence voltage applied to the luminescence element via the read line by switching off the first switch and switching on the second switch while the luminescence element emits the light; and

a determiner that determines a first drain current and a second drain current of the driving transistor based on the first luminescence voltage and the second luminescence voltage detected by the voltage detector respectively and calculates a gain coefficient and a threshold voltage of the driving transistor based on the first luminescence voltage, the second luminescence voltage, the first drain current, and the second drain current.