Display apparatus, display driving apparatus and method for driving same

• US 20080074413A1
• Filed: 09/26/2007
• Published: 03/27/2008
• Est. Priority Date: 09/26/2006
• Status: Active Grant

• Current Assignee: Solas OLED Limited (Atlantic IP Services Limited)
• Original Assignee: Casio Computer Company Limited
• Inventors: Ogura, Jun
• Granted Patent: US 7,760,168 B2
• Time in Patent Office: Days
• US Class Current: 345/212
• 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 3/3233 with pixel circuitry controlling the current through the light-emitting element

Abstract

A light-emitting element capable of emitting light having a preferred gradation level depending on display data. During a precharge period, a data driver applies a precharge voltage to a capacitor via a data line. After the application of the precharge voltage, a voltage converter reads a first reference voltage Vref(t1) and a second reference voltage Vref(t2) to generate a compensation voltage based on a difference between the respective reference voltages. Based on the compensation voltage, a voltage calculator compensates an original gradation level voltage Vorg having a value in accordance with display data generated by a gradation level voltage generator. The voltage calculator generates a compensated gradation level voltage Vpix corresponding to a variation amount of an element characteristic for a transistor Tr13 for driving light emission to apply the compensated gradation level voltage Vpix to a data line Ld.

Claims

1. A display apparatus, comprising:

a light-emitting element for emitting light having a gradation level depending on supplied current;

a pixel driving circuit for supplying the current to the light-emitting element depending on a voltage applied via a data line;

a precharge voltage source for applying a predetermined precharge voltage to the pixel driving circuit via the data line;

a voltage reader for reading the voltage of the data line a plurality of times with different timings in a predetermined transient response period after the application of the precharge voltage by the precharge voltage source; and

a compensated gradation data signal generator for generating, based on a voltage difference among the voltages of the data line read at the different timings, a compensated gradation data signal having a voltage value corresponding to an element characteristic unique to the pixel driving circuit to apply the compensated gradation data signal to the pixel driving circuit.

2. The display apparatus according to claim 1, wherein:

the display apparatus includes an original gradation level voltage generator for generating an original gradation level voltage having a voltage value not depending on the element characteristic unique to the pixel driving circuit, and

the original gradation level voltage is for causing the light-emitting element to emit light having a desired brightness corresponding to the gradation level.

3. The display apparatus according to claim 2, wherein:

the compensated gradation data signal generator generates the compensated gradation data signal based on the original gradation level voltage, a first compensation voltage generated based on the difference voltage, and a second compensation voltage determined based on the element characteristic unique to the pixel driving circuit.

4. The display apparatus according to claim 3, wherein:

the compensated gradation data signal generator comprises a calculation circuit for calculating the original gradation level voltage, the first compensation voltage, and the second compensation voltage to generate the compensated gradation data signal.

5. The display apparatus according to claim 1, wherein:

the display apparatus includes a black gradation level voltage source for applying, to the pixel driving circuit, a black gradation level voltage for causing the light-emitting element to perform a black display, and a switch for connecting the black gradation level voltage source to the data line at a predetermined timing.

6. The display apparatus according to claim 1, wherein:

the display apparatus includes a connection path switching switch for connecting the data line to the voltage reader, the compensated gradation data signal generator, and the precharge voltage source respectively with a predetermined timing.

7. The display apparatus according to claim 6, wherein:

the voltage reader is structured to read a plurality of times, after the precharge voltage is applied to the pixel driving circuit and the connection path switching switch is switched to block application of the precharge voltage by the precharge voltage source to the data line, the voltage of the data line with different timings within the transient response period, and the transient response period is shorter than a time required for the voltage of the data line to converge to a converge voltage value unique to the pixel driving circuit.

8. The display apparatus according to claim 7, wherein:

the precharge voltage source applies, when the connection switching switch is used to connect the precharge voltage source to the data line, the precharge voltage, and the precharge voltage has a voltage value having a higher absolute value than an absolute value of the converge voltage value unique to the pixel driving circuit.

9. The display apparatus according to claim 6, wherein:

the display apparatus further includes a controller for performing, within a predetermined period;

(i) using the connection path switching switch to connect the precharge voltage source to the data line to apply the precharge voltage to the pixel driving circuit, (ii) using the connection path switching switch to connect the voltage reader to the data line to read, a plurality of times, the voltage of the data line corresponding to the element characteristic unique to the pixel driving circuit with different timings within the transient response period, and (iii) using the connection path switching switch to connect the compensated gradation data signal generator to the data line to apply the compensated gradation data signal to the pixel driving circuit.

10. The display apparatus according to claim 1, wherein:

the display apparatus includes;

a selection driver for applying a selection signal to the pixel driving circuit via a selection line to cause the pixel driving circuit to be in a selected state, and a display panel in which a plurality of display pixels are arranged in a matrix manner, each of the plurality of display pixels including a pair of one said light-emitting element and one said pixel driving circuit, and

wherein;

the plurality of display pixels are arranged in a row direction and a column direction,

the data line is connected to the pixel driving circuits of a plurality of display pixels arranged in the column direction, and

the selection line is connected to the pixel driving circuits of a plurality of display pixels arranged in the row direction.

11. The display apparatus according to claim 1, wherein:

the pixel driving circuit includes a driving transistor serially connected to the light-emitting element, and

a variation amount of the element characteristic unique to the pixel driving circuit is a variation amount of a threshold voltage of the driving transistor.

12. The display apparatus according to claim 1, wherein the pixel driving circuit includes:

a driving transistor serially connected to the light-emitting element;

a selection transistor connected between the driving transistor and the data line; and

a diode connection transistor for causing the driving transistor to be in a diode-connected state.

13. The display apparatus according to claim 12, wherein the pixel driving circuit is structured such that:

a first end of a current path of the driving transistor is connected with a power source voltage for which a potential is switched with a predetermined timing and a second end of the current path of the driving transistor is connected with a first end of the light-emitting element,

a first end of a current path of the selection transistor is connected with the second end of the current path of the driving transistor and a second end of the current path of the selection transistor is connected with the data line,

a first end of a current path of the diode connection transistor is connected with the power source voltage and a second end of the current path of the diode connection transistor is connected with a control terminal of the driving transistor,

control terminals of the selection transistor and the diode connection transistor are connected to the selection line, and

a second end of the light-emitting element is connected to a fixed reference voltage.

14. The display apparatus according to claim 11, wherein:

a voltage between a control terminal of the driving transistor and one terminal of a current path of the driving transistor is determined based on a sum of a first voltage component that does not depend on the element characteristic unique to the pixel driving circuit for causing the light-emitting element to emit light having a desired brightness corresponding the gradation level and a second voltage component that is at least 1.05 times a threshold voltage of the driving transistor.

15. The display apparatus according to claim 11, wherein:

a voltage retained between a control terminal of the driving transistor and one terminal of a current path of the driving transistor by the compensated gradation data signal that specifies a compensated gradation level is determined by a sum of a first voltage component that does not depend on the element characteristic unique to the pixel driving circuit for causing the light-emitting element to emit light having a desired brightness corresponding to the gradation level and a second voltage component that is higher than the threshold voltage of the driving transistor by a predetermined multiple.

16. The display apparatus according to claim 1, wherein the display apparatus includes:

a selection driver for applying a selection signal to the pixel driving circuit via a selection line to cause the pixel driving circuit to be in a selected state, and a display panel in which a plurality of display pixels are arranged in a matrix manner, each of the plurality of display pixels including a pair of one said light-emitting element and one said pixel driving circuit,

wherein the plurality of display pixels are arranged in a row direction and a column direction, the data line is connected to the pixel driving circuits of a plurality of the display pixels arranged in the column direction, and the selection line is connected to the pixel driving circuits of a plurality of the display pixels arranged in the row direction,

wherein the pixel driving circuit includes a driving transistor serially connected to the light-emitting element, a selection transistor connected between the driving transistor and the data line, and a diode connection transistor for causing the driving transistor to be in a diode-connected state, and a variation amount of the element characteristic unique to the pixel driving circuit is a variation amount of a threshold voltage of the driving transistor, and

wherein a driving current flowing in the light-emitting element via a current path of the driving transistor by the compensated gradation data signal and based on a voltage between a control terminal of the driving transistor and one terminal of the current path of the driving transistor is associated with an element size of the selection transistor and a voltage of the selection signal so that all gradation levels for causing the light-emitting element to emit light can cause a variation amount of a current value due to variation in the threshold voltage of the driving transistor that is within 2% of a maximum current value in an initial state under which the driving transistor has no variation in the threshold voltage.

17. The display apparatus according to claim 1, wherein:

the compensated gradation data signal generator generates, based on the voltage difference among the voltages of the data line read at the different timings and a voltage retained in the pixel driving circuit, the compensated gradation data signal having the voltage value corresponding to the element characteristic unique to the pixel driving circuit to apply the compensated gradation data signal to the pixel driving circuit.

18. A display apparatus, comprising:

a light-emitting element for emitting light having a gradation level depending on supplied current;

a pixel driving circuit for supplying the current to the light-emitting element depending on a voltage applied via a data line;

a precharge voltage source for applying a predetermined precharge voltage to the pixel driving circuit via the data line;

a voltage reader for reading the voltage of the data line a plurality of times with different timings in a predetermined transient response period after the application of the precharge voltage to the pixel driving circuit by the precharge voltage source; and

a compensated gradation data signal generator for generating, based on a voltage difference among the voltages of the data line read at the different timings and a voltage retained in the pixel driving circuit, a compensated gradation data signal having a voltage value corresponding to a voltage characteristic unique to the pixel driving circuit to apply the compensated gradation data signal to the pixel driving circuit.

19. The display apparatus according to claim 18, wherein:

the display apparatus includes an original gradation level voltage generator for generating an original gradation level voltage having a voltage value not depending on the voltage characteristic unique to the pixel driving circuit, and

the original gradation level voltage is for causing the light-emitting element to emit light having a desired brightness corresponding to the gradation level.

20. The display apparatus according to claim 19, wherein:

the compensated gradation data signal generator generates the compensated gradation data signal based on the original gradation level voltage and a compensation voltage generated based on the voltage difference and the voltage characteristic unique to the pixel driving circuit.

21. The display apparatus according to claim 20, wherein:

the compensated gradation data signal generator comprises a calculation circuit for calculating the original gradation level voltage and the compensation voltage to generate the compensated gradation data signal.

22. The display apparatus according to claim 18, wherein:

the pixel driving circuit includes a driving transistor serially connected to the light-emitting element, and

the voltage characteristic unique to the pixel driving circuit is based on a change in a voltage between a control terminal of the driving transistor and one terminal of a current path of the driving transistor.

23. A method for driving a display apparatus, comprising:

applying a predetermined precharge voltage to a pixel driving circuit via a data line;

reading a plurality of times the voltage of the data line with different timings in a predetermined transient response period after the application of the precharge voltage, the transient response period being shorter than a time during which the voltage of the data line converges to a converge voltage value unique to the pixel driving circuit;

generating, based on one of;

(i) a voltage difference among the voltages of the data line read at the different timings and (ii) the voltage difference among the voltages of the data line read at the different timings and a voltage retained in the pixel driving circuit, a compensated gradation data signal having a voltage value corresponding to an element characteristic unique to the pixel driving circuit;

applying the generated compensated gradation data signal to the pixel driving circuit; and

supplying current depending on a voltage applied via the data line from the pixel driving circuit to a light-emitting element.

24. A display driving apparatus, comprising:

a precharge voltage source for applying, via a data line, a predetermined precharge voltage to a pixel driving circuit connected to a light-emitting element;

a voltage reader for reading a plurality of times the voltage of the data line at different timings in a predetermined transient response period after the application of the precharge voltage by the precharge voltage source; and

a compensated gradation data signal generator for applying, based on one of;

(i) a voltage difference among the voltages of the data line read at the different timings and (ii) the voltage difference among the voltages of the data line read at the different timings and a voltage retained in the pixel driving circuit, a compensated gradation data signal having a voltage value corresponding to an element characteristic unique to the pixel driving circuit to apply the compensated gradation data signal to the pixel driving circuit.

25. A method for driving a display driving apparatus, comprising:

applying, via a data line, a predetermined precharge voltage to a pixel driving circuit connected to a light-emitting element;

reading a plurality of times the voltage of the data line with different timings in a predetermined transient response period after the application of the precharge voltage;

generating, based on one of;

(i) a voltage difference among the voltages of the data line read at the different timings and (ii) the voltage difference among the voltages of the data line read at the different timings and a voltage retained in the pixel driving circuit, a compensated gradation data signal having a voltage value corresponding to an element characteristic unique to the pixel driving circuit; and

applying the generated compensated gradation data signal to the pixel driving circuit.