Circuit and method for driving an array of light emitting pixels

• US 20070080908A1
• Filed: 09/23/2004
• Published: 04/12/2007
• Est. Priority Date: 09/23/2003
• Status: Active Grant

• Current Assignee: IGNIS Innovation Incorporated
• Original Assignee: IGNIS Innovation Incorporated
• Inventors: Servati, Peyman, Nathan, Arokia, Jafarabadiashtiani, Shahin, Vygranenko, Yuriy
• Granted Patent: US 7,978,187 B2
• Time in Patent Office: Days
• US Class Current: 345/77
• CPC Class Codes: G09G 2300/0417 Special arrangements specific to the use of low carrier mobility technology
• CPC Class Codes: G09G 2300/0809 Several active elements per pixel in active matrix panels
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2320/0646 Modulation of illumination source brightness and image signal correlated to each other
• CPC Class Codes: G09G 3/3241 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 current mirror
• 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
• CPC Class Codes: G09G 3/3266 Details of drivers for scan electrodes
• CPC Class Codes: G09G 3/3283 in which the data driver supplies a variable data current for setting the current through, or the voltage across, the light-emitting elements
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/60 Circuit arrangements for operating LEDs comprising organic material, e.g. for operating organic light-emitting diodes [OLED] or polymer light-emitting diodes [PLED]
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A technique for driving a column of pixels that include light emitting elements is presented. The technique incorporates feedback data provided from feedback data sources connected to the data line and to feedback line of the array, pixel driving circuit with feedback path. The technique can also include block of the reference elements for input signal corrections.

Claims

1. A pixel circuit for use in a display, the display comprising a plurality of pixels with each pixel having a select line, a signal line, a feedback line, the pixel circuit comprising:

a light emitting element;

a drive part for providing a drive current to the light emitting element, the drive part having a storage capacitor and a switch use transistor having a gate terminal connected to the select line, and a first terminal connected to the signal line, and a second terminal; and

an on-pixel feedback element for generating a feedback voltage representing a drive current provided to the light emitting element, the feedback signal being provided to the feedback line.

2. The pixel circuit according to claim 1, wherein the feedback element is a feedback circuit.

3. The pixel circuit according to claim 1, wherein the drive part further comprises a drive use transistor having a gate terminal connected to the second terminal of the switch use transistor, a first terminal connected to the light emitting element and a second terminal.

4. The pixel circuit according to claim 2, wherein the feedback circuit comprises:

a resistor connected between the second terminal of said drive use transistor and a potential providing the feedback voltage at a level proportional to the drive current; and

a feedback transistor having a gate connected to the select line, a first terminal connected to the second terminal of the drive use transistor and a second terminal connected to the feedback line.

5. The pixel circuit according to claim 1, wherein the drive part further comprises a first transistor having a gate terminal, a first terminal and a second terminal, and a second drive use transistor having a gate terminal, a first terminal and a second terminal, the first transistor and the second drive use trasistor arranged to form a current mirror structure, the gate terminals connected to the second terminal of the switch use transistor, the first terminal of the first transistor and the first terminal of the second drive use transistor connected to a power supply node, the second terminal of the second drive use transistor connected to the light emitting element.

6. The pixel circuit according to claim 3, wherein the feedback circuit further comprises a resistor connected between the second terminal of the first transistor and a potential to provide the feedback signal in form of voltage level proportional to the current level of drive current and a feedback transistor connected between the second terminal of the first transistor and the feedback line and having a gate connected to the select line.

7. The pixel circuit according to claim 1, wherein the drive part further comprises a first transistor having a gate terminal, a first terminal and a second terminal and a second drive use transistor having a gate terminal, a first terminal and a second terminal, the first transistor and the second drive us transistor being arranged to form a current mirror structure, the gate terminals being connected to the second terminal of the switch use transistor, the second terminal of the first transistor being connected to said feedback line, the first terminal of the second drive use transistor is connected to said light emitting element, the second terminal of the drive use transistor is connected to ground.

8. The pixel circuit according to claim 5, wherein the feedback element is a feedback circuit having a conductive path between the second terminal of the first transistor and the feedback line providing the feedback signal in form of a current level proportional to the drive current and a feedback transistor connected between the first terminal of the first transistor and the power supply node and having a gate terminal connected to the select line.

9. The pixel circuit according to claim 3, wherein said feedback element is a feedback circuit having a diode connected between the second terminal of said drive use transistor and a predetermined potential to provide the feedback signal in form of voltage level or current level and said feedback switch is an insulating gate type field effect transistor connected between the second terminal of said drive use transistor and said feedback line and having a gate connected to said select line.

10. The pixel circuit according to claim 3, further comprising a feedback transistor connected between the second terminal of the drive use transistor and the feedback line and having a gate connected to the first select line and the feedback circuit further comprises a switch transistor having a gate terminal connected to the second select line, a first terminal connected to the second terminal of the drive use transistor, a second terminal connected to a ground potential to provide the feedback signal in form of current to level equal to the drive current.

11. The pixel circuit according to claim 1, wherein said light emitting element is an organic light emitting diode.

12. The pixel circuits according to claim 5, wherein the transistors are insulating gate type field effect transistors that comprise n-channel and p-channel type transistors.

13. A pixel circuit for use in a display, the display comprising a plurality of pixels with each pixel having a first select line, a second select line, a signal line, a feedback line, the pixel circuit comprising:

a light emitting element;

a drive part for providing a drive current to the light emitting element, the drive part comprising;

a storage capacitor;

a switch use transistor having a gate terminal connected to the first select line, a first terminal connected to the signal line and a second terminal;

a drive use transistor having a gate terminal connected to the second terminal of the switch use transistor, a first terminal and a second terminal connected to the light emitting element; and

an on-pixel feedback circuit for generating a feedback voltage representing a drive current provided to the light emitting element, the feedback circuit comprising;

a resistor connected between the second terminal of said drive use transistor and a potential; and

a feedback transistor having a gate connected to the second select line, a first terminal connected to the first terminal of the drive use transistor and a second terminal connected to the feedback line.

14. The pixel circuit according to claim 13 wherein the switch use and drive use transistors are n-type, and the feedback transistor is p-type.

15. The pixel circuit according to claim 13 wherein the switch use and drive use transistors are p-type, and the feedback transistor is n-type.

19. The display device claimed in claim 13, wherein said feedback circuit includes a resistor to provide the feedback signal in form of a voltage level proportional to the drive current, and said reference circuit includes a reference resistor made from the same material as said resistor.

20. The display device claimed in claim 13, wherein said reference circuit includes a photo-sensor optically coupled to a reference light emitting element for brightness control, and said display column control circuit includes a compensating part to compare a generated photocurrent level with an input current level and to adjust a current through said reference light emitting element to achieve a desired brightness level.

16. A pixel circuit for use in a display, the display comprising a plurality of pixels with each pixel having a select line, a signal line, a feedback line, the pixel circuit comprising:

a light emitting element;

a drive part for providing a drive current to the light emitting element, the drive part comprising;

a storage capacitor;

a switch use transistor having a gate terminal connected to the select line,

a first terminal connected to the signal line and a second terminal;

a drive use transistor having a gate terminal connected to the second terminal of the switch use transistor, a first terminal and a second terminal connected to the light emitting element; and

an on-pixel feedback circuit for generating a feedback voltage representing a drive current provided to the light emitting element, the feedback circuit comprising;

a resistor connected between the second terminal of said drive use transistor and a potential; and

a feedback transistor having a gate connected to the select line, a first terminal connected to the first terminal of the drive use transistor and a second terminal connected to the feedback line.

17. The pixel circuit according to claim 16 wherein the switch use transistor, drive use transistor and the feedback transistor are p-type.

18. A display device, comprising:

a select line;

a signal line to which a voltage signal in accordance with both brightness and feedback information is supplied;

a feedback line to which a feedback voltage signal in accordance with current level of drive current is supplied;

a plurality of pixels forming an array of pixels, each pixel of the plurality formed on a substrate at an intersecting portion of said scanning line and said signal and feedback lines, each pixel comprising;

a light emitting element;

a current driving circuit having a storage capacitor and a switch use transistor; and

a feedback circuit to provide feedback signals representing a current output of said current driving circuit;

a display column control circuit for receiving input signals, adjusting the input signals using a reference circuit formed on the substrate at each column, and modifying the input signals in response to the feedback signals from pixels in the column to produce a desired brightness level of said light emitting element in a selected pixel; and

a selecting line drive circuit for successively activating selecting lines.

21. A method of driving a plurality of light emitting elements arranged in a column at a desired brightness, comprising the steps of:

selecting one pixel of a plurality of pixels in the column;

establishing the desired brightness of a reference light emitting element by adjusting a reference current flowing through the light emitting element in response to a photocurrent from a photo-sensor that is optically coupled with the reference light emitting element;

converting the reference current into a corresponding voltage level;

transmitting the voltage level to the selected pixel;

converting the voltage level into a drive current and generating a feedback signal representing a drive current level;

adjusting the voltage level in response to the feedback signal from the selected pixel to establish a drive current substantially equal to the reference current;

storing the adjusted voltage level; and

driving the light emitting element with the drive current in accordance with the adjusted voltage level to produce the desired brightness level in the pixel.