US 8,558,764 B2Granted

Light emitting device and method of driving the same

AssigneeSemiconductor Energy Laboratory Co., Ltd.

InventorJun Koyama

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Abstract

A method of driving a display device capable of obtaining a luminance of constant level irrespective of temperature change is provided. A change in luminance of an EL element due to temperature change is prevented by controlling the luminance of the EL element with current instead of voltage. Specifically, a TFT for controlling the amount of current flowing into the EL element is operated in a saturation range. Then a current value IDS of the TFT is hardly changed by VDS but is determined solely by VGS. Accordingly, the amount of current flowing in the EL element is kept constant by setting VGS to such a value as to make the current value IDS constant. The luminance of the EL element is substantially in proportion to the amount of current flowing through the EL element, and a change in luminance of the EL element upon temperature change can thus be prevented.

Claims18

Dependent claims

A method of driving a light emitting device comprising:

a first TFT,
a second TFT,
a third TFT,
a fourth TFT,
a capacitor, and
an EL element,
wherein a gate of the first TFT is directly connected to a first line,
wherein a gate of the second TFT is directly connected to the first line,
wherein one of a source and a drain of the third TFT is directly connected to one of a source and a drain of the first TFT,
wherein one of a source and a drain of the fourth TFT is directly connected to the one of the source and the drain of the third TFT,
wherein a gate of the fourth TFT is directly connected to a second line,
wherein the other of the source and the drain of the first TFT is directly connected to a third line,
wherein one of a source and a drain of the second TFT is directly connected to the one of the source and the drain of the third TFT,
wherein the other of the source and the drain of the second TFT is directly connected to a first electrode of the capacitor,
wherein a gate of the third TFT is directly connected to the first electrode of the capacitor,
wherein the other of the source and the drain of the third TFT is directly connected to a second electrode of the capacitor,
wherein the other of the source and the drain of the third TFT is directly connected to a fourth line, and
wherein the other of the source and the drain of the fourth TFT is directly connected to the EL element,
the method comprising the steps of:
selecting the first line such that the first TFT and the second TFT are in ON state;
and
selecting the second line such that the fourth TFT is in ON state,
wherein the second line is selected multiple times in one frame period.

20 more elements

A method of driving a light emitting device comprising:

a first TFT,
a second TFT,
a third TFT,
a fourth TFT,
a capacitor, and
an EL element,
wherein a gate of the first TFT is electrically connected to a first line,
wherein a gate of the second TFT is electrically connected to the first line,
wherein one of a source and a drain of the third TFT is directly connected to one of a source and a drain of the first TFT,
wherein one of a source and a drain of the fourth TFT is directly connected to the one of the source and the drain of the third TFT,
wherein a gate of the fourth TFT is electrically connected to a second line,
wherein the other of the source and the drain of the first TFT is electrically connected to a third line,
wherein one of a source and a drain of the second TFT is electrically connected to the one of the source and the drain of the third TFT,
wherein the other of the source and the drain of the second TFT is electrically connected to a first electrode of the capacitor,
wherein a gate of the third TFT is electrically connected to the first electrode of the capacitor,
wherein the other of the source and the drain of the third TFT is electrically connected to a second electrode of the capacitor,
wherein the other of the source and the drain of the third TFT is electrically connected to a fourth line, and
wherein the other of the source and the drain of the fourth TFT is electrically connected to the EL element,
the method comprising the steps of:
selecting the first line such that the first TFT and the second TFT are in ON state;
and
selecting the second line such that the fourth TFT is in ON state,
wherein the second line is selected multiple times in one frame period.

20 more elements

Dependencies are inferred from the claim text.

Facts

Application: 11/762,848Filed 14 Jun 2007 · continuation
Priority: JP 2000-32354324 Oct 2000
Published: US 2007/0236427 A111 Oct 2007
Granted: 15 Oct 2013
Term ends: Not estimatedThe source records don’t support an estimate.

Classification11 codes

G09G 3/3233
Using an active matrix: with pixel circuitry controlling the current through the light-emitting element
G09G 3/325
The current through the light-emitting element being set using a data current provided by the data driver, e.g. by using a two-transistor…
G09G 3/3266
Organic, e.g. using organic light-emitting diodes [OLED]: details of drivers for scan electrodes
G09G 3/3283
Details of drivers for data electrodes: in which the data driver supplies a variable data current for setting the current through, or the voltage…

Family

Application09/983,479Parent of this continuation · filed 24 Oct 2001
US 2007/0236427 A1Pre-grant publication · published 11 Oct 2007
US 2002/0047581 A1Published application
US 7,277,070 B2Related patent
US 8,558,764 B2This patent

From the US filing history. Foreign family members aren’t listed.