Electro-optical device and electronic apparatus

• US 20050225683A1
• Filed: 03/15/2005
• Published: 10/13/2005
• Est. Priority Date: 04/12/2004
• Status: Active Grant

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Nozawa, Toshiyuki
• Granted Patent: US 7,554,514 B2
• Time in Patent Office: Days
• US Class Current: 348/801
• 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 2300/0833 forming a linear amplifier or follower
• 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 2310/0251 Precharge or discharge of pixel before applying new pixel voltage
• 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 2360/148 the light being detected by light detection means within each pixel
• CPC Class Codes: G09G 3/2014 by modulation of the duration of a single pulse during which the logic level remains constant
• 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

Abstract

To ensure uniformity of display regardless of a characteristics difference and temporal deterioration of a light-emitting element. An optical feedback type pixel circuit having a photoelectric transducer therein comprises a capacitor C1 for storing as an electric charge an integral value of the photoelectric current output from the photoelectric transducer; a comparator for changing a level of an output voltage Vout at a timing when a first voltage set according to the electric charge stored in the capacitor C1 reaches a second voltage set according to data supplied through a data line X; and a transistor T2 electrically controlled according to the output voltage Vout from the comparator for making an organic EL element OLED emit light when the first voltage has not reached the second voltage and for making the organic EL element OLED stop emitting the light when the first voltage reaches the second voltage.

Claims

1. A pixel circuit comprising:

a light-emitting element for emitting light according to a driving current supplied through a predetermined path;

a photoelectric transducer for receiving the light emitted from the light-emitting element to output a photoelectric current according to the received light;

a first capacitor for storing as an electric charge the integral value of the photoelectric current output from the photoelectric transducer;

a comparator for changing a level of an output voltage at a timing when a first voltage set according to the electric charge stored in the first capacitor reaches a second voltage set according to data supplied through a data line; and

a first switching element electrically controlled according to the output voltage output from the comparator for making the light-emitting element emit the light when the first voltage has not reached the second voltage and for making the light-emitting element stop emitting the light when the first voltage reaches the second voltage.

2. The pixel circuit according to claim 1,

wherein the first switching element is provided in the middle of a path for supplying a driving current to the light-emitting element, to form the path of the driving current when the first voltage has not reached the second voltage and to cut off the path of the driving current when the first voltage reaches the second voltage.

3. The pixel circuit according to claim 1, further comprising:

a second capacitor for storing the data supplied through the data line; and

a driving transistor having its gate connected to the second capacitor for generating the driving current according to the data stored in the second capacitor.

4. The pixel circuit according to claim 3,

wherein the first switching element is provided in parallel with the second capacitor, to electrically separate a pair of electrodes of the second capacitor from each other when the first voltage has not reached the second voltage and to electrically connect the pair of electrodes of the second capacitor to each other when the first voltage reaches the second voltage.

5. The pixel circuit according to claim 1, further comprising:

a second switching element provided between a node to which the photoelectric transducer and the first capacitor are commonly connected and a voltage terminal supplied with a predetermined reset voltage, and for resetting the electric charge stored in the first capacitor using the reset voltage.

6. The pixel circuit according to claim 1, further comprising:

a source follower circuit provided between a node to which the photoelectric transducer and the first capacitor are commonly connected and an input node of the comparator.

7. An electro-optical device comprising:

a plurality of scanning lines;

a plurality of data lines;

a plurality of pixel circuits provided at intersections of the plurality of scanning lines and the plurality of data lines;

a scanning line driving circuit for sequentially selecting the plurality of scanning lines; and

a data line driving circuit operating in conjunction with the scanning line driving circuit for outputting a data voltage to the plurality of data lines,

wherein the pixel circuit is the pixel circuit according to claim 1.

8. An electronic apparatus having the electro-optical device according to claim 7.

9. A method of driving a pixel circuit comprising:

a first step of supplying a driving current to a light-emitting element through a predetermined path to make the light-emitting element emit light;

a second step of receiving the light emitted from the light-emitting element to output a photoelectric current according to the received light from a photoelectric transducer;

a third step of storing as an electric charge in a first capacitor the integral value of the photoelectric current output from the photoelectric transducer;

a fourth step of changing the level of an output voltage output from a comparator at a timing when a first voltage set according to the electric charge stored in the first capacitor reaches a second voltage set according to data supplied through a data line; and

a fifth step of electrically controlling a first switching element according to the output voltage output from the comparator, to make the light-emitting element emit the light when the first voltage has not reached the second voltage and to make the light-emitting element stop emitting the light when the first voltage reaches the second voltage.

10. The method of driving a pixel circuit according to claim 9,

wherein the first switching element is provided in the middle of a path for supplying a driving current to the light-emitting element, and

the fifth step comprises:

a step of forming the path of the driving current by turning on the first switching element when the first voltage has not reached the second voltage; and

a step of cutting off the path of the driving current by turning off the first switching element when the first voltage reaches the second voltage.

11. The method of driving a pixel circuit according to claim 9,

wherein the first step comprises:

a step of writing data supplied through the data line in a second capacitor;

a step of modulating the driving current according to the data stored in the second capacitor; and

a step of supplying the modulated driving current to the light-emitting element through a predetermined path to make the light-emitting element emit the light.

12. The method of driving a pixel circuit according to claim 11,

wherein the first switching element is provided in parallel with the second capacitor, and

the fifth step comprises:

a step of electrically separating a pair of electrodes of the second capacitor from each other by turning off the first switching element when the first voltage has not reached the second voltage; and

a step of electrically connecting the pair of electrodes of the second capacitor to each other by turning on the first switching element when the first voltage reaches the second voltage.