Display device and organic light emitting device
Provided is an OLED display device preventing an occurrence of a crosstalk using a simple structure. A display device includes: a display unit that includes a plurality of pixel circuits each including an organic light emitting element; a control unit that applies electric potential to the pixel circuits for a first period, and that controls emission luminance of the organic light emitting elements for a second period after the first period; and an application unit that applies a voltage of less than or equal to a threshold voltage of the organic light emitting element before a start of the second period in which the organic light emitting element has internal capacitance to maintain an electric potential difference between the anode electrode and the cathode electrode for a vertical scanning period in which a displayed image to be refreshed when the control unit controls the organic light emitting element not to emit light.
1. A display device comprising:
a display unit that includes a plurality of pixel circuits each including both an organic light emitting element including a light emitting layer that emits light by a current flowing between an anode electrode and a cathode electrode and a control element controlling the current;
a control unit that applies electric potential according to an image signal to the pixel circuits for a first period, and that controls emission luminance of the organic light emitting elements based on the electric potential by means of the control elements for a second period after the first period; and
an application unit that applies a voltage of less than or equal to a threshold voltage of the organic light emitting element to the anode electrode before a start of the second period,
wherein the organic light emitting element has internal capacitance to maintain an electric potential difference between the anode electrode, the electric potential of which is applied by the application unit, and the cathode electrode at a voltage of less than or equal to the threshold voltage, for a vertical scanning period in which a displayed image to be refreshed when the control unit controls the organic light emitting element not to emit light.
2. The display device according to claim 1 , wherein the application unit applies electric potential that is less than electric potential of the cathode electrode to the anode electrode.
3. The display device according to claim 1 , wherein the application unit applies the electric potential to the anode electrode for a period before the first period.
4. The display device according to claim 1 , further comprising a common layer that is disposed to be common to a plurality of organic light emitting elements,
wherein the cathode electrode, the light emitting layer, the common layer, and the anode electrode are laminated,
wherein the common layer injects holes supplied through the anode electrode to the light emitting layer,
wherein the cathode electrode is disposed to be common to a plurality of organic light emitting elements,
wherein the anode electrode is connected to the control element, and
wherein the organic light emitting elements are arranged in a matrix pattern at a predetermined interval.
5. The display device according to claim 4 , wherein the internal capacitance of the organic light emitting element is larger than a value acquired by dividing the period in which the display unit displays one screen by a resistance value of the common layer between the organic light emitting element and one organic light emitting element adjacent to the organic light emitting element.
6. The display device according to claim 4 , wherein the internal capacitance of the organic light emitting element is larger than a value acquired by dividing the period in which the display unit displays one screen by a combined resistance value acquired by combining resistance values of the common layer between the organic light emitting element and a plurality of organic light emitting elements adjacent to the organic light emitting element.
7. The display device according to claim 1 ,
wherein the display unit has a rectangular shape, and
wherein the application unit, after signals controlling luminance are input to a group of organic light emitting elements along a scanning line from the control unit, before signals controlling luminance are input to a group of organic light emitting elements along a next scanning line from the control unit, applies electric potential to the anode electrodes of the group of organic light emitting elements along the next scanning line.
8. The display device according to claim 5 ,
wherein a shape of the organic light emitting element has at least four sides, and
wherein an arrangement of the organic light emitting elements, a thickness of the common layer, and the internal capacitance satisfy Equation (1),
ρ
×
D
×
C
o
l
e
d
T
×
W
>
F
r
(
1
)
Here, ρ is resistivity of the common layer,
T is a thickness of the common layer between a first organic light emitting element and a second organic light emitting element adjacent to the first organic light emitting element,
D is a distance between the first organic light emitting element and the second organic light emitting element,
W is a length of a portion in which a first side of the first organic light emitting element that faces the second organic light emitting element and a second side of the second organic light emitting element that faces the first side face each other,
Coled is internal capacitance of the first organic light emitting element,
Fr is a vertical scanning period in which the displayed image to be refreshed.
9. The display device according to claim 5 ,
wherein a shape of the organic light emitting element has at least four sides, and
wherein an arrangement of the organic light emitting elements, a thickness of the common layer, and the internal capacitance satisfy Equation (2),
min
(
ρ
n
×
D
n
T
n
×
W
n
)
×
C
o
l
e
d
>
F
r
(
2
)
Here, n is an integer of one to four,
ρn is resistivity of the common layer between a first organic light emitting element and an n-th organic light emitting element adjacent to the first organic light emitting element at the n-th side of the first organic light emitting element,
Tn is a thickness of the common layer between the first organic light emitting element and the n-th organic light emitting element,
Dn is a distance between the n-th side of the first organic light emitting element and the n-th organic light emitting element,
Wn is a length of a portion in which the n-th side of the first organic light emitting element and a side of the n-th organic light emitting element that faces the n-th side face each other,
Coled is internal capacitance of the first organic light emitting element,
Fr is a vertical scanning period in which the displayed image to be refreshed.
10. The display device according to claim 5 ,
wherein a shape of the organic light emitting element has at least four sides, and
wherein an arrangement of the organic light emitting elements, a thickness of the common layer, and the internal capacitance satisfy Equation (3),
1
∑
n
=
1
4
1
(
ρ
n
×
D
n
T
n
×
W
n
)
×
C
o
l
e
d
>
F
r
(
3
)
Here, ρn is resistivity of the common layer between the first organic light emitting element and the n-th organic light emitting element adjacent to the first organic light emitting element at the n-th side of the first organic light emitting element,
Tn is a thickness of the common layer between the first organic light emitting element and the n-th organic light emitting element,
Dn is a distance between the n-th side of the first organic light emitting element and the n-th organic light emitting element,
Wn is a length of a portion in which the n-th side of the first organic light emitting element and a side of the n-th organic light emitting element that faces the n-th side face each other,
Coled is internal capacitance of the organic light emitting element,
Fr is a vertical scanning period in which the displayed image to be refreshed.
11. The display device according to claim 5 ,
wherein the display unit includes organic light emitting elements arranged in a matrix pattern,
wherein a shape of the organic light emitting element is a rectangle, and
wherein an arrangement of the organic light emitting elements, a thickness of the common layer, and the internal capacitance satisfy Equation (4),
1
∑
n
=
1
2
1
(
ρ
n
×
D
n
T
n
×
W
n
)
×
C
o
l
e
d
>
F
r
(
4
)
ρn is resistivity of the common layer between a first organic light emitting element and an n-th organic light emitting element adjacent to the first organic light emitting element at an n-th long side of the first organic light emitting element,
Tn is a thickness of the common layer between the first organic light emitting element and the n-th organic light emitting element,
Dn is a distance between the n-th long side of the first organic light emitting element and the n-th organic light emitting element,
Wn is a length of a portion in which the n-th long side of the first organic light emitting element and a side of the n-th organic light emitting element that faces the n-th long side face each other,
Coled is internal capacitance of the first organic light emitting element,
Fr is a vertical scanning period in which the displayed image to be refreshed.
12. The display device according to claim 1 ,
wherein the display unit has a rectangular shape,
wherein the control unit controls luminance of the organic light emitting element for each scanning line along one side of the display unit,
wherein the control unit includes:
a first switching unit that switches the scanning line; and
a second switching unit that connects the organic light emitting element and the application unit together for a period in which the control unit does not input a signal to the organic light emitting element in synchronization with the first switching unit.
13. The display device according to claim 12 ,
wherein the first switching unit blocks a connection between the organic light emitting element and the control unit for a period in which the organic light emitting element and the application unit are connected together and for a predetermined time after the connection is blocked, and
wherein the second switching unit blocks a connection between the organic light emitting element and the application unit for a period in which the organic light emitting element and the control unit are connected together and for a predetermined period after the connection is blocked.
14. The display device according to claim 1 ,
wherein the display unit includes a plurality of pixels arranged in a matrix pattern,
wherein each of the pixels includes the organic light emitting elements of three colors,
wherein the control unit controls the luminance of the organic light emitting elements for each scanning line along the matrix, and
wherein the control unit includes:
a distributor that distributes and inputs the signal to the organic light emitting elements included in the each of the pixels;
a first switching unit that switches the scanning line; and
a second switching unit that connects the organic light emitting element and the application unit together for a period in which the distributor does not input a signal to the organic light emitting element in synchronization with the first switching unit.
15. The display device according to claim 14 ,
wherein the first switching unit blocks a connection between the organic light emitting element and the distributor for a period in which the organic light emitting element and the application unit are connected together and for a predetermined period after the connection is blocked, and
wherein the second switching unit blocks a connection between the organic light emitting element and the application unit for a period in which the organic light emitting element and the distributor are connected together and for a predetermined period after the connection is blocked.
16. The display device according to claim 1 , wherein the application unit has a function of an external compensation circuit compensating a signal used for controlling the luminance of the organic light emitting element from the outside.