Pixel circuit, display unit, and pixel circuit drive method

• US 20070057873A1
• Filed: 05/21/2004
• Published: 03/15/2007
• Est. Priority Date: 05/23/2003
• Status: Active Grant

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Yamamoto, Tetsuro, Uchino, Katsuhide, Yamashita, Junichi
• Granted Patent: US 8,149,185 B2
• Time in Patent Office: Days
• US Class Current: 345/76
• CPC Class Codes: G09G 2300/043 Compensation electrodes or other additional electrodes in matrix displays related to distortions or compensation signals, e.g. for modifying TFT threshold voltage in column driver
• 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 2300/0861 with additional control of the display period without amending the charge stored in a pixel memory, e.g. by means of additional select electrodes
• CPC Class Codes: G09G 2310/0256 with the purpose of reversing the voltage across a light emitting or modulating element within a pixel
• CPC Class Codes: G09G 2320/0233 Improving the luminance or brightness uniformity across the screen
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2320/045 Compensation of drifts in the characteristics of light emitting or modulating elements
• CPC Class Codes: G09G 3/30 using electroluminescent panels
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3258 with pixel circuitry controlling the voltage across the light-emitting element
• CPC Class Codes: G09G 3/3426 the different display panel areas being distributed in two dimensions, e.g. matrix
• CPC Class Codes: G09G 3/36 using liquid crystals
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence
• 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]

Abstract

A pixel circuit, display device, and method of driving a pixel circuit enabling source-follower output with no deterioration of luminance even with a change of the current-voltage characteristic of the light emitting element along with elapse, enabling a source-follower circuit of n-channel transistors, and able to use an n-channel transistor as an EL drive transistor while using current anode-cathode electrodes, wherein a source of a TFT 111 as a drive transistor is connected to an anode of a light emitting element 114, a drain is connected to a power source potential VCC, a capacitor C111 is connected between a gate and source of the TFT 111, and a source potential of the TFT 111 is connected to a fixed potential through a TFT 113 as a switching transistor.

Claims

1. A pixel circuit for driving an electro-optic element with a luminance changing according to a flowing current, comprising:

a data line through which a data signal in accordance with luminance information is supplied;

a first control line;

first and second nodes;

first and second reference potentials;

a drive transistor forming a current supply line between the first terminal and the second terminal and controlling a current flowing through said current supply line in accordance with the potential of a control terminal connected to said second node;

a pixel capacitance element connected between said first node and said second node;

a first switch connected between said data line and either of a first terminal or second terminal of said pixel capacitance element and controlled in conduction by said first control line; and

a first circuit for making a potential of said first node change to a fixed potential while said electro-optic element is not emitting light;

said current supply line of the drive transistor, said first node, and said electro-optic element being connected in series between said first reference potential and second reference potential.

2. A pixel circuit as set forth in claim 1, wherein:

said circuit further comprises a second control line;

said drive transistor is a field effect transistor with a source connected to said first node, a drain connected to said first reference potential or second reference potential, and a gate connected to said second node; and

said first circuit includes a second switch connected between said first node and fixed potential and is controlled in conduction by said second control line.

3. A pixel circuit as set forth in claim 2, wherein when said electro-optic element is driven,

as a first stage, said first switch is held in a non-conductive state by said first control line, said second switch is held in a conductive state by said second control line, and said first node is connected to a fixed potential;

as a second stage, said first switch is held in a conductive state by said first control line, data to be propagated over said data line is written in said pixel capacitance element, then said first switch is held in a non-conductive state; and

as a third stage, said second switch is held in a non-conductive state by said second control line.

4. A pixel circuit as set forth in claim 1, wherein:

said circuit further comprises a second control line;

said drive transistor is a field effect transistor with a drain connected to said first reference potential or second reference potential and a gate connected to said second node; and

said first circuit includes a second switch connected between a source of said field effect transistor and an electro-optic element and is controlled in conduction by said second control line.

5. A pixel circuit as set forth in claim 4, wherein when said electro-optic element is driven,

as a first stage, said first switch is held in a non-conductive state by said first control line, and said second switch is held in a non-conductive state by said second control line;

as a second stage, said first switch is held in a conductive state by said first control line, data to be propagated over said data line is written in said pixel capacitance element, then said first switch is held in a non-conductive state; and

as a third stage, said second switch is held in a conductive state by said second control line.

6. A pixel circuit as set forth in claim 1, wherein:

said circuit further comprises a second control line;

said drive transistor is a field effect transistor with a source connected to said first node, a drain connected to said first reference potential or second reference potential, and a gate connected to said second node; and

said first circuit includes a second switch connected between said first node and said electro-optic element and is controlled in conduction by said second control line.

7. A pixel circuit as set forth in claim 6, wherein when said electro-optic element is driven,

as a first stage, said first switch is held in a non-conductive state by said first control line, and said second switch is held in a non-conductive state by said second control line;

as a second stage, said first switch is held in a conductive state by said first control line, data to be propagated over said data line is written in said pixel capacitance element, then said first switch is held in a non-conductive state; and

as a third stage, said second switch is held in a conductive state by said second control line.

8. A pixel circuit as set forth in claim 1, further comprising a second circuit making said first node be held at a fixed potential when said first switch is held in a conductive state and writes data propagated through the data line.

9. A pixel circuit as set forth in claim 8, wherein:

said circuit further comprises second and third control lines and

a voltage supply;

said drive transistor is a field effect transistor with a drain connected to said first reference potential or second reference potential and a gate connected to said second node;

said first circuit includes a second switch connected between a source of said field effect transistor and said electro-optic element and is controlled in conduction by said second control line; and

said second circuit includes a third switch connected between said first node and said voltage source and is controlled in conduction by said third control line.

10. A pixel circuit as set forth in claim 9, wherein when said electro-optic element is driven,

as a first stage, said first switch is held in a non-conductive state by said first control line, said second switch is held in a non-conductive state by said second control line, and said third switch is held in a non-conductive state by said third control line;

as a second stage, said first switch is held in a conductive state by said first control line, said third switch is held in a conductive state by said third control line, said first node is held at a predetermined potential, and, in that state, data to be propagated over said data line is written in said pixel capacitance element, then said first switch is held in a non-conductive state by said first control line; and

as a third stage, said third switch is held in a non-conductive state by said third control line and said second switch is held in a conductive state by said second control line.

11. A pixel circuit as set forth in claim 8, wherein

said circuit further comprises second and third control lines and

a voltage source;

said drive transistor is a field effect transistor with a source connected to said first node, a drain connected to said first reference potential or second reference potential, and a gate connected to said second node;

said first circuit includes a second switch connected between said first node and said electro-optic element and is controlled in conduction by said second control line; and

said second circuit includes a third switch connected between said first node and said voltage source and is controlled in conduction by said third control line.

12. A pixel circuit as set forth in claim 11, wherein when said electro-optic element is driven,

as a first stage, said first switch is held in a non-conductive state by said first control line, said second switch is held in a non-conductive state by said second control line, and said third switch is held in a non-conductive state by said third control line;

as a second stage, said first switch is held in a conductive state by said first control line, said third switch is held in a conductive state by said third control line, said first node is held at a predetermined potential, and, in that state, data to be propagated over said data line is written in said pixel capacitance element, then said first switch is held in a non-conductive state by said first control line; and

as a third stage, said third switch is held in a non-conductive state by said third control line and said second switch is held in a conductive state by said second control line.

13. A pixel circuit as set forth in claim 1, further comprising a second circuit making said second node be held at a fixed potential when said first switch is held in a conductive state and writes data propagated through the data line.

14. A pixel circuit as set forth in claim 13, wherein said fixed potential is said first reference potential or second reference potential.

15. A pixel circuit as set forth in claim 13, wherein:

said circuit further comprises second, third, and fourth control lines;

said drive transistor is a field effect transistor with a source connected to said first node, a drain connected to said first reference potential or second reference potential, and a gate connected to said second node;

said first circuit includes a second switch connected between said first node and said electro-optic element and is controlled in conduction by said second control line and a third switch connected between a source of said field effect transistor and said first node and Is controlled in conduction by said third control line; and

said second circuit includes a fourth switch connected between said first node and said fixed potential and is controlled in conduction by said fourth control line.

16. A pixel circuit as set forth in claim 15, wherein when said electro-optic element is driven,

as a first stage, said first switch Is held In a non-conductive state by said first control line, said second switch is held in a non-conductive state by said second control line, said third switch is held in a non-conductive state by said third control line, and said fourth switch is held in a non-conductive state by said fourth control line;

as a second stage, said first switch is held in a conductive state by said first control line, said fourth switch is held in a conductive state by said fourth control line, said second node is held at a fixed potential, and, in that state, data to be propagated over said data line is written in said pixel capacitance element, then said first switch Is held in a non-conductive state by said first control line, and said fourth switch is held at a non-conductive state by said fourth control line; and

as a third stage, said second switch Is held in a conductive state by said second control line and said third switch is held in a conductive state by said third control line.

17. A display device comprising:

a plurality of pixel circuits arranged in a matrix;

a data line arranged for each column of said matrix array of pixel circuits and through which a data signal in accordance with luminance information is supplied;

a first control line arranged for each row of said matrix array of pixel circuits; and

first and second reference potentials;

each said pixel circuit further having;

an electro-optic element with a luminance changing according to a flowing current,

first and second nodes,

a drive transistor forming a current supply line between a first terminal and a second terminal and controlling a current flowing through said current supply line in accordance with the potential of a control terminal connected to said second node,

a pixel capacitance element connected between said first node and said second node,

a first switch connected between said data line and said second node and controlled in conduction by said first control line, and

a first circuit for making a potential of said first node change to a fixed potential while said electro-optic element is not emitting light,

said current supply line of the drive transistor, said first node, and said electro-optic element being connected in series between said first reference potential and second reference potential.

18. A display device as set forth in claim 17, further comprising a second circuit for making said first node be held at a predetermined potential when said first switch is held in the conductive state and writes data to be propagated through the data line.

19. A display device as set forth in claim 17, further comprising a second circuit for making said second node be held at a fixed potential when said first switch is held in the conductive state and writes data to be propagated through the data line.

20. A method of driving a pixel circuit having:

an electro-optic element with a luminance changing according to a flowing current,

a data line through which a data signal in accordance with luminance information is supplied;

first and second nodes;

first and second reference potentials;

a field effect transistor with a drain connected to said first reference potential or second reference potential, a source connected to said first node, and a gate connected to said second node;

a pixel capacitance element connected between said first node and said second node;

a first switch connected between said data line and either of a first terminal or a second terminal of said pixel capacitance element; and

a first circuit for making a potential of said first node change to a fixed potential;

said current supply line of the drive transistor, said first node, and said electro-optic element being connected in series between said first reference potential and second reference potential,

said method of driving a pixel circuit comprising steps of;

making a potential of said first node change to a fixed potential by said first circuit in the state with said first switch held at a non-conductive state,

holding said first switch at a conductive state, writing data propagated over said data line In said pixel capacitance element, then holding said first switch in the non-conductive, and

stopping the operation for making a potential of said first node of said first circuit change to a fixed potential.