Light emitting device display circuit and drive method thereof

• US 20060038762A1
• Filed: 08/20/2005
• Published: 02/23/2006
• Est. Priority Date: 08/21/2004
• Status: Active Grant

• Current Assignee: Chen-Jean Chou
• Original Assignee: Chen-Jean Chou
• Inventors: CHOU, CHEN-JEAN
• Granted Patent: US 7,053,875 B2
• Time in Patent Office: Days
• US Class Current: 345/92
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2300/0866 by means of changes in the pixel supply voltage
• CPC Class Codes: G09G 3/325 the data current flowing through the driving transistor during a setting phase, e.g. by using a switch for connecting the driving transistor to the data driver

Abstract

Multiple conducting channels in a display pixel, controlled by a single access electrode are provided in the present invention. Such pixel circuits operate to set a pixel data voltage by directing a data current to one of the conducting channels, while deliver a drive current to the light emitting device in a pixel via the other conducting channel. Current-controlled drive scheme, independent of threshold voltage, is achievable in the present invention without substantial increase in pixel complexity. Such merged pixel structures provide simplicity and greater flexibility in implementing current drive pixel structure.

Claims

1. A display comprising at least:

a data electrode for delivering input data;

a scan-power electrode;

said scan-power electrode delivering at least a first signal and a second signal in operating said display;

a reference voltage source;

a pixel disposed at the intersect of said scan-power electrode and said data electrode;

said pixel comprising;

a light emitting element;

said light emitting element emits light according to an electrical current supplied thereto;

a storage element for holding data information, having a first and a second ends;

a control circuit for regulating a drive current directed to said light emitting element according to said data information, and for controlling data input from said data electrode;

wherein said storage element is connected to said control circuit;

wherein said scan-power electrode controls data input to said pixel by carrying at least a first and a second signals;

wherein by carrying said first signal, said control circuit allows a data information to be received at said storage element from said data electrode;

wherein by carrying said second signal, said control circuit inhibits the influence from said data electrode on said storage element, and retains said data information held at said storage element;

Wherein said control circuit further comprises;

a first conducting channel for conducting electrical current between said data electrode and said reference voltage source via said control circuit;

a second conducting channel for directing an electrical current from said scan-power electrode to said reference voltage source via said control circuit and said light emitting element;

wherein said first conducting channel, when enabled, provides a first direct current path connecting said data electrode and said reference voltage source via said control circuit;

wherein said first conducting channel, when enabled, sets a voltage at said storage element corresponding to said data information;

wherein said second conducting channel, when enabled, provides a second direct current path connecting said scan-power electrode and said reference voltage source via said control circuit and said light emitting element;

wherein said second conducting channel, when enabled, directs a drive current to said light emitting element according to said data information in said storage element.

2. The display according to claim 1, wherein the enabling of said first conducting channel disables said second conducting channel, and wherein the disabling of said first conducting channel enables said second conducting channel.

3. The display according to claim 1, wherein said enabling and disabling of said conducting channels are controlled by said scan-power electrode.

4. The display according to claim 3, wherein said scan-power electrode carrying a first signal enables said first conducting channel and disable said second conducting channel;

wherein said scan-power electrode carrying a second signal voltage enables said second conducting channel and disables said first conducting channel;

wherein said first signal voltage and said signal voltage are different by at least a voltage difference between turning on and off of a transistor.

5. The display according to claim 1, wherein applying said first signal to said scan-power electrode enables said first conducting channel, thereby allowing a data current from said data electrode to said reference voltage source via said control circuit.

6. The display according to claim 5, wherein said applying said first signal to said scan-power electrode inhibits said second conducting channel.

7. The display according to claim 5, wherein said first conducting channel, when enabled, converts said data current to a data voltage at the two ends of said storage element;

wherein said conversion sets the voltage on said storage element according to said data current.

8. The display according to claim 7, wherein said first conducting channel comprises a first active element having a gate terminal, a second terminal and a third terminal;

wherein said first end of said storage element is connected to said gate;

wherein said active element converts said data current to a data voltage between said gate and said second terminal of said active element;

wherein said data voltage is provided for said storage element to store.

9. The display according to claim 5, wherein said control circuit further comprises a switching element for controlling the current in said second conducting channel;

said switching element having a gate, a second and a third terminal;

said control circuit converts said data current to a data voltage at the gate of said switching element.

10. The display according to claim 1, wherein applying said second signal to said scan-power electrode enables said second conducting channel, therein directing a current to said light emitting element via said scan-power electrode.

11. The display according to claim 10, wherein said applying said second signal to said scan-power electrode inhibits said first conducting channel.

12. The display according to claim 1, wherein said control circuit comprises a first active element in said second conducting channel, said first active element having a control gate, and a channel between a second and a third terminals;

wherein said first active element forms part of said second direct current path via said second and third terminals;

wherein said first active element regulates a drive current directed to said light emitting element through said second conducting channel, according to a data voltage held at said storage element;

wherein said first active element forms part of said first conducting channel via said second and third terminals of said first active element.

13. The display according to claim 1, wherein said control circuit comprises a first active element in said second conducting channel, said first active element having a control gate, and a channel between a second and a third terminals;

wherein said first active element forms part of said second direct current path via said second and third terminals;

wherein said first active element regulates a drive current directed to said light emitting element through said second conducting channel, according to a data voltage held at said storage element;

wherein said storage element is connected to said gate of said first active element;

wherein said control circuit converts a data current directed along said first conducting channel to a data voltage, and provides such data voltage at said storage element and at the control gate terminal of said first active element.

14. The display according to claim 1, wherein said control circuit comprises a drive transistor for regulating a drive current directed to said light emitting element, and wherein said first end of said storage element is connected to the gate of said drive transistor;

the voltage at the gate of said drive transistor is brought to the same voltage at the drain of said drive transistor by applying said first signal to said scan-power electrode.

15. The display according to claim 1, wherein said control circuit comprises a drive transistor for regulating a drive current directed to said light emitting element, and wherein said first end of said storage element is connected to the gate of said drive transistor;

the voltage at the gate of said drive transistor is brought to the same as the voltage of the scan-power electrode by applying said first signal to said scan-power electrode.

16. The display according to claim 1, wherein said control circuit comprises a drive transistor for regulating a drive current directed to said light emitting element, and wherein said first end of said storage element is connected to the gate of said drive transistor;

wherein said drive transistor further operates as a conversion transistor in a data input period during which said first signal is applied to said scan-power electrode;

wherein said conversion transistor converts a data current directed from said data electrode to said pixel during a data input period into a data voltage at the gate of said conversion transistor.

17. The display according to claim 1, wherein said second conducting channel, when enabled, provides entire drive current required for drive said light emitting element according to said data information.

18. The display according to claim 1, wherein said storage element is a capacitor;

said capacitor being one, or a combination of;

capacitor formed with an insulator between two conductive layers in parallel, parasitic capacitor in a transistor, inherent capacitor of a diode.

19. The display according to claim 1, wherein said storage element is a capacitor;

wherein said control circuit comprises;

a first transistor having a gate terminal, and a channel between a second terminal and a third terminal;

wherein said channel of said first transistor constitutes a part of both said first conducting channel and said second conducting channel;

a second transistor having a gate terminal, and a channel between a second terminal and a third terminal;

wherein said gate of said second transistor is connected to a scan-power electrode, and wherein said channel of said second transistor constitutes a part of said first conducting channel;

wherein said capacitor is connected to said gate of said first transistor.

20. The display according to claim 19 wherein said light emitting element is an organic light emitting device.

21. The display according to claim 19, wherein said control circuit further comprises a third transistor having a gate, a second terminal and a third terminal;

wherein said gate of said third transistor is connected to a scan-power electrode; and

wherein said second terminal of said third transistor is connected to said gate of said first transistor.

22. The display according to claim 21, wherein said first transistor controls a drive current directed to said light emitting element during a drive period when said second signal is applied to said scan-power electrode;

wherein said first transistor converts said data current to a data voltage between the gate and the source of said first transistor in a scanning period during which said first signal is applied to said scan-power electrode;

wherein all said transistors are n-channel transistors.

28. The display according to claim 1 further comprises a plurality of said data electrode, a plurality of scan-power electrode, a plurality of said pixel disposed at the intersects of the data electrodes and the scan-power electrodes;

a data driving circuit;

a scan-power driving circuit;

each said control circuit in each said pixels comprises, an active element for regulating said drive current, and an active element for controlling data input from said data electrodes;

wherein said data driving circuit comprises at least a number of output terminals matching the number of said data electrodes;

each output terminal being connected to a said data electrode;

wherein said scan-power driving circuit comprises at least a number of output terminals matching the number of said scan-power electrodes;

each said output terminals being connected to a said scan-power electrodes;

said data driving circuit delivering input data signals in the form of current levels at said output terminals to said data electrodes;

said scan-power driving circuit delivering a scanning voltage in an operating period to turn on the gates of active elements connected to said scan-power electrode to enable data input;

said scan-power driving circuit delivering a drive voltage in the other period of operating said display to turn off all selecting transistors connected to said scan-power electrode;

said drive voltage delivering drive current to the light emitting elements in all pixels connected to said scan-power electrode according to respective data information in said pixels;

wherein said scanning voltage and said drive voltage generated by said scan-power driving circuit differ by at least a voltage difference between turning on and off of a transistor.

23. A method for operating a display, said display comprising:

a data electrode for delivering input data;

a scan-power electrode;

said scan-power electrode delivering at least a first signal and a second signal in operating said display;

a reference voltage source;

a pixel disposed at the intersect of said scan-power electrode and said data electrode;

said pixel comprising;

a light emitting element;

said light emitting element emits light according to an electrical current supplied thereto;

a storage element for holding data information, having a first and a second ends;

a control circuit for regulating a current directed to said light emitting element according to said data information;

wherein said storage element is connected to said control circuit;

wherein said scan-power electrode controls data input to said pixel by carrying at least a first and a second signals;

wherein by carrying said first signal, said control circuit allows a data information to be received at said storage element from said data electrode;

wherein by carrying a second signal, said control circuit inhibits the influence from said data electrode on said storage element, and retains said data information held at said storage element;

wherein said method comprising the following steps;

applying a first signal to said scan-power electrode to select said pixel for data input in a data writing period;

same said first signal enabling a first conducting channel between said data electrode to said reference voltage source;

by enabling said conducting channel, a direct current path being provided to allow a data current to be conducted from said data electrode to said reference voltage source;

applying a second signal to said scan-power electrode to enable a second conducting channel between said scan-power electrode and said reference voltage source;

said first signal inhibiting said second conducting channel;

said second signal inhibiting said first conducting channel.

24. The method according to claim 23, wherein said first signal causes a data voltage to be generated at the two ends of said storage element.

25. The method according to claim 23, wherein said control circuit comprises a first transistor, wherein the drain to source channel of said first transistor is part of said first conducting channel;

wherein said applying said first signal to said scan-power electrode brought the gate of said first transistor to the same voltage as the drain of said first transistor.

26. The method according to claim 23, wherein said control circuit comprises a first transistor;

wherein the drain to source channel of said first transistor is part of said first conducting channel;

wherein said applying said first signal to said scan-power electrode brought the gate of said first transistor to the same voltage as that of said scan-power electrode.

27. The method according to claim 23, wherein each of said input data is delivered via said data electrode in the form of a current.