Pixel circuit, display device, and driving method of pixel circuit

• US 20050007357A1
• Filed: 05/18/2004
• Published: 01/13/2005
• Est. Priority Date: 05/19/2003
• 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 7,236,149 B2
• Time in Patent Office: Days
• US Class Current: 345/204
• 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 2300/0852 being a dynamic memory with more than 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 2310/0262 The addressing of the pixel, in a display other than an active matrix LCD, involving the control of two or more scan electrodes or two or more data electrodes, e.g. pixel voltage dependent on signals of two data electrodes
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element

Abstract

A pixel circuit able to stably and correctly supply a current having a desired value to a light emitting diode of each pixel without being influenced by variation of a threshold value of an active element inside the pixel or variation of mobility and able to display a high quality image as a result of this, wherein a TFT as a fourth switch is turned on together with a TFT as a second switch at the time of an auto-zero operation, a reference current line is connected to a drive transistor of the pixel through a first node, and the variation of the threshold value Vth is corrected, whereby variation of the on current due to the mobility at the time of a white display can be suppressed and the uniformity with respect to variation in the mobility can be greatly enhanced, and a display device and a driving method of the pixel circuit.

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, second, and third nodes;

first and second reference potentials;

a reference current supplying means for supplying a predetermined reference current;

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

a first switch connected to said first node;

a second switch connected between said first node and said second node;

a third switch connected between said data line and said third node and controlled in conduction by said first control line;

a fourth switch connected between said first node and said reference current supplying means; and

a coupling capacitor connected between said second node and said third node, wherein the current supply line of said drive transistor, said first node, said first switch, and said electro-optic element are connected in series between said first reference potential and second reference potential.

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

the circuit further comprises second, third, and fourth control lines, and

said first switch is controlled in conduction by said second control line, said second switch is controlled in conduction by said third control line, and said fourth switch is controlled in conduction by said fourth control line.

3. A pixel circuit as set forth in claim 2, wherein said third control line and fourth control line are shared, and said second switch and fourth switch are controlled in conduction by one control line.

4. A pixel circuit as set forth in claim 1, wherein when said electro-optic element is driven,

as a first stage, said second switch and said fourth switch are made conductive for a predetermined time to electrically connect said first node and said second node, then the reference current is supplied to the first node, and

as a second stage, said second switch and said fourth switch are held in the non-conductive state after an elapse of the predetermined time, and

as a third stage, said third switch is made conductive by said first control line, said first switch is made conductive, and the data propagated through said data line is written into said third node, then said third switch is held in the non-conductive state and a current in accordance with said data signal is supplied to said electro-optic element.

5. A pixel circuit as set forth in claim 4, wherein the value of said reference current is set at a value corresponding to an intermediate color of the light emission of said electro-optic element.

6. A display device comprising:

a plurality of pixel circuits arranged in a matrix;

a data line laid for every column of the matrix array of said pixel circuits and supplied with a data signal in accordance with the luminance information;

a first control line laid for every row of the matrix array of said pixel circuit;

first and second reference potentials; and

a reference current supplying means for supplying a predetermined reference current, wherein

each pixel circuit has;

first, second, and third nodes,

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

a first switch connected to said first node,

a second switch connected between said first node and said second node,

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

a fourth switch connected between said first node and said reference current supplying means, and

a coupling capacitor connected between said second node and said third node, and

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

7. A display device as set forth in claim 6, wherein:

said reference current supplying means includes a reference current source and a reference current supply line laid for every column of the matrix array of said pixel circuits and supplied with the reference current from said reference current source, and

said fourth switch is connected between said first node and the reference current supply line.

8. A display device as set forth in claim 6, wherein:

said reference current supplying means includes a reference current source and a plurality of reference current supply lines laid for every column of the matrix array of said pixel circuits and supplied with the reference current from said reference current source, and

the plurality of pixel circuits of the same column are connected to different reference current supply lines via said fourth switch.

9. A display device as set forth in claim 7, wherein the device further comprises a reference voltage supplying means for selectively supplying a predetermined reference voltage to said reference current supply line.

10. A display device as set forth in claim 9, wherein said reference voltage supplying means further comprises a reference voltage source and a switch circuit selectively connecting said reference current source and said reference voltage source to said reference current supply line.

11. A display device as set forth in claim 7, wherein when said electro-optic element is driven,

as a first stage, said second switch and said fourth switch are made conductive for a predetermined time to electrically connect said first node and said second node, then the reference current is supplied to the first node,

as a second stage, said second switch and said fourth switch are held in the non-conductive state after an elapse of a horizontal scanning period, and

as a third stage, said third switch is made conductive by said first control line, said first switch is made conductive and the data propagated through said data line is written into said third node, then said third switch is held in the non-conductive state and a current in accordance with said data signal is supplied to said electro-optic element.

12. A display device as set forth in claim 11, wherein the value of said reference current is set to a value corresponding to an intermediate color of the light emission of said electro-optic element.

13. A display device as set forth in claim 8, wherein when said electro-optic element is driven,

as a first stage, said second switch and said fourth switch are made conductive for a predetermined time to electrically connect said first node and said second node, then the reference current is supplied to the first node,

as a second stage, said second switch and said fourth switch are held in the non-conductive state after an elapse of a time of a few times the horizontal scanning period, and

as a third stage, said third switch is made conductive by said first control line, said first switch is made conductive, and the data propagated through said data line is written into said third node, then said third switch is held in the non-conductive state and a current in accordance with said data signal is supplied to said electro-optic element.

14. A display device as set forth in claim 13, wherein the value of said reference current is set to a value corresponding to an intermediate color of the light emission of said electro-optic element.

15. A display device as set forth in claim 9, wherein, where said electro-optic element is driven,

as a first stage, said reference current supply line is precharged by the supply of the reference voltage by said reference voltage supplying means,

as a second stage, said second switch and said fourth switch are made conductive for a predetermined time to electrically connect said first node and said second node, then supply the reference current to the first node,

as a third stage, said second switch and said third switch are held in the non-conductive state by said third control line after an elapse of the horizontal scanning period, and

as a fourth stage, said third switch is made conductive by said first control line, said first switch is made conductive, and the data propagated through said data line is written into said third node, then said third switch is held in the non-conductive state and a current in accordance with said data signal is supplied to said electro-optic element.

16. A display device as set forth in claim 15, wherein the value of said reference current is set to a value corresponding to an intermediate color of the light emission of said electro-optic element.

17. A display device as set forth in claim 15, wherein the value of said reference voltage is set to an intermediate value of the variation of the threshold value of said drive transistor.

18. A display device comprising:

a plurality of pixel circuits arranged in a matrix;

a data line laid for every column of the matrix array of said pixel circuits and supplied with a data signal in accordance with luminance information;

a first control line laid for every row of the matrix array of said pixel circuits; and

first and second reference potentials, wherein

each pixel circuit has;

a reference current supplying means for supplying a predetermined reference current,

first, second, and third nodes,

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

a first switch connected to said first node,

a second switch connected between said first node and said second node,

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

a fourth switch connected between said first node and said reference current supplying means, and

a coupling capacitor connected between said second node and said third node, and

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

19. A driving method of a pixel circuit comprising:

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

a data line supplied with the data signal in accordance with luminance information,

first, second, and third nodes,

a reference current supplying means for supplying a predetermined reference current,

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

a first switch connected to said first node,

a second switch connected between said first node and said second node,

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

a fourth switch connected between said first node and said reference current supplying means, and

a coupling capacitor connected between said second node and said third node, and

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

making said second switch and said fourth switch conductive for a predetermined time to electrically connect said first node and said second node and supplying a reference current to the first node,

holding said second switch and said third switch in the non-conductive state after the elapse of a predetermined time,

making said third switch conductive,

making said first switch conductive, and writing data propagated through said data line into said third node, then holding said third switch in the non-conductive state and supplying current in accordance with said data signal to said electro-optic element.