PIXEL DRIVE APPARATUS, LIGHT EMITTING APPARATUS, AND DRIVE CONTROL METHOD FOR THE LIGHT EMITTING APPARATUS

• US 20100328297A1
• Filed: 06/28/2010
• Published: 12/30/2010
• Est. Priority Date: 06/29/2009
• Status: Active Grant

• Current Assignee: Solas OLED Limited (Atlantic IP Services Limited)
• Original Assignee: Casio Computer Company Limited
• Inventors: SHIMODA, Satoru
• Granted Patent: US 8,384,629 B2
• Time in Patent Office: Days
• US Class Current: 345/212
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2300/0866 by means of changes in the pixel supply voltage
• CPC Class Codes: G09G 2310/0216 Interleaved control phases for different scan lines in the same sub-field, e.g. initialization, addressing and sustaining in plasma displays that are not simultaneous for all scan lines
• CPC Class Codes: G09G 2320/0285 using tables for spatial correction of display data
• CPC Class Codes: G09G 2320/0693 Calibration of display systems
• CPC Class Codes: G09G 2330/02 Details of power systems and of start or stop of display operation
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3291 in which the data driver supplies a variable data voltage for setting the current through, or the voltage across, the light-emitting elements

Abstract

An offset voltage generating circuit sets an offset voltage through binary search based on a voltage value of the initial voltage, and a voltage controlling circuit generates an output voltage which is a predetermined gradation voltage added with the offset voltage, and applies a voltage based on the output voltage to a control terminal of a drive transistor. A current comparison circuit applies a supply voltage from a power supply to the other end of current path of the drive transistor. The current comparison circuit compares the current value of a reference current corresponding to the gradation voltage with a current value of the current flowing in the current path of the drive transistor at this time. The offset voltage generating circuit acquires a specific offset voltage corresponding to variation of the characteristic of the drive transistor based on a result of comparison performed by the current comparison circuit.

Claims

1. A pixel drive apparatus for driving pixels each having a light emitting device and a drive transistor whose current path has one end connected to the light emitting device, the apparatus comprising:

a power supply configured to be connectable to an other end of the current path of the drive transistor and output a supply voltage;

an offset voltage generating circuit that generates an offset voltage;

a voltage controlling circuit that generates an output voltage which is a predetermined gradation voltage added with the offset voltage; and

a current comparison circuit that compares a current value of a reference current corresponding to the gradation voltage with a current value of the current flowing in the current path of the drive transistor when the supply voltage is applied to the other end of the current path of the drive transistor and a voltage based on the output voltage is applied to a control terminal of the drive transistor,

the offset voltage generating circuit setting a voltage value of the offset voltage through binary search based on a voltage value of an initial voltage, and acquiring a specific offset voltage corresponding to variation of a characteristic of the drive transistor based on a result of comparison performed by the current comparison circuit according to the offset voltage.

2. The pixel drive apparatus according to claim 1, wherein the current value of the reference current is set to a current value of a current flowing in the current path of the drive transistor when the drive transistor has an initial characteristic and a voltage based on the gradation voltage is applied to the control terminal of the drive transistor.

3. The pixel drive apparatus according to claim 1, wherein the offset voltage generating circuit generates the offset voltage based on a digital value of a predetermined number of bits,

generates, as the digital value, a first value set through the binary search, and a second value obtained by increasing or decreasing one bit from the first value,

repetitively performs re-setting of the voltage value of the offset voltage to a value changed through the binary search, and the comparison in the current comparison circuit according to the set offset voltage, until the current value of the reference current is judged to lie in a range of current values of two currents flowing in the current path of the drive transistor according to two offset voltages corresponding to the first value and the second value, and

acquires the offset voltage corresponding to the first value as the specific offset voltage when the current value of the reference current is judged to lie in the range.

4. The pixel drive apparatus according to claim 1, further including a gradation voltage generating circuit that generates and supplies the gradation voltage to the voltage controlling circuit.

5. The pixel drive apparatus according to claim 4, further including a storage circuit that stores a specific offset value corresponding to the specific offset voltage acquired by the offset voltage generating circuit.

6. The pixel drive apparatus according to claim 5, wherein the gradation voltage generating circuit generates the gradation voltage based on a display signal supplied externally,

the offset voltage generating circuit generates a specific offset voltage based on the specific offset value stored in the storage circuit, and

the voltage controlling circuit generates the output voltage which is the gradation voltage added with the offset voltage.

7. The pixel drive apparatus according to claim 1, wherein the current comparison circuit is provided between an output terminal of the power supply and the other end of the current path of the drive transistor.

8. The pixel drive apparatus according to claim 1, wherein the current comparison circuit is provided between an output terminal of the voltage controlling circuit and the one end of the current path of the drive transistor.

9. A light emitting apparatus comprising:

at least one pixel having a light emitting device and a drive transistor whose current path has one end connected to the light emitting device;

at least one signal line connected to the pixel;

a power supply configured to be connectable to an other end of the current path of the drive transistor and output a supply voltage;

at least one offset voltage generating circuit provided in association with the signal line to generate an offset voltage;

at least one voltage controlling circuit provided in association with the signal line to generate an output voltage which is a predetermined gradation voltage added with the offset voltage; and

at least one current comparison circuit that compares a current value of a reference current corresponding to the gradation voltage with a current value of the current flowing in the current path of the drive transistor when the supply voltage is applied to the other end of the current path of the drive transistor and a voltage based on the output voltage generated is applied to a control terminal of the drive transistor,

the offset voltage generating circuit setting a voltage value of the offset voltage through binary search based on a voltage value of an initial voltage, and acquiring a specific offset voltage corresponding to variation of a characteristic of the drive transistor based on a result of comparison performed by the current comparison circuit according to the offset voltage.

10. The light emitting apparatus according to claim 9, wherein the current value of the reference current is set to a current value of a current flowing in the current path of the drive transistor when the drive transistor has an initial characteristic and a voltage based on the gradation voltage is applied to the control terminal of the drive transistor.

11. The light emitting apparatus according to claim 9, wherein the offset voltage generating circuit generates the offset voltage based on a digital value of a predetermined number of bits,

generates, as the digital value, a first value set through the binary search, and a second value obtained by increasing or decreasing one bit from the first value,

repetitively performs re-setting of the voltage value of the offset voltage to a value changed through the binary search, and the comparison in the current comparison circuit according to the set offset voltage, until the current value of the reference current is judged to lie in a range of current values of two currents flowing in the current path of the drive transistor according to two offset voltages corresponding to the first value and the second value, and

acquires the offset voltage corresponding to the first value as the specific offset voltage when the current value of the reference current is judged to lie in the range.

12. The light emitting apparatus according to claim 9, further including at least one gradation voltage generating circuit provided in association with the signal line to generate and supply the gradation voltage to the voltage controlling circuit.

13. The light emitting apparatus according to claim 12, further including a storage circuit that stores a specific offset value corresponding to the specific offset voltage acquired by the offset voltage generating circuit.

14. The light emitting apparatus according to claim 13, wherein the gradation voltage generating circuit generates the gradation voltage based on a display signal supplied externally,

the offset voltage generating circuit generates a specific offset voltage based on the specific offset value stored in the storage circuit, and

the voltage controlling circuit generates the output voltage which is the gradation voltage added with the offset voltage.

15. The light emitting apparatus according to claim 9, wherein the current comparison circuit is provided between an output terminal of the power supply and one end of a power supply line connected to the other end of the current path of the drive transistor.

16. The light emitting apparatus according to claim 9, wherein one end of the signal line is electrically connected to the one end of the current path of the drive transistor, and

the current comparison circuit is provided between an output terminal of the voltage controlling circuit and an other end of the signal line.

17. The light emitting apparatus according to claim 9, wherein the light emitting device comprises an organic electroluminescent device.

18. A drive control method for a light emitting apparatus including at least one pixel having a light emitting device and a drive transistor whose current path has one end connected to the light emitting device, and at least one signal line connected to the pixel, the method comprising:

a gradation voltage generating step of generating a predetermined gradation voltage;

an offset voltage generating step of generating an offset voltage;

an output voltage generating step of generating an output voltage which is the gradation voltage added with the offset voltage;

an output voltage applying step of applying a voltage based on the output voltage to a control terminal of the drive transistor via the signal line;

a current comparison step of comparing a current value of a reference current corresponding to the gradation voltage with a current value of the current flowing in the current path of the drive transistor when a supply voltage is applied to the other end of the current path of the drive transistor and the voltage based on the output voltage is applied to the control terminal of the drive transistor; and

a specific offset voltage acquiring step of acquiring a specific offset voltage corresponding to variation of a characteristic of the drive transistor based on a result of comparison performed in the current comparison step,

the offset voltage generating step including a binary search step of setting a voltage value of the offset voltage through a binary search based on a voltage value of an initial voltage,

wherein in the specific offset voltage acquiring step including, the specific offset voltage corresponding to the variation of the characteristic of the drive transistor is acquired based on the result of comparison performed in the current comparison step according to the offset voltage set in the binary search step.

19. The drive control method according to claim 18, wherein the offset voltage in the offset voltage generating step is generated based on a digital value of a predetermined number of bits,

the specific offset voltage acquiring step includes:

a generation step of generating, as the digital value, a first value set through the binary search, and a second value obtained by increasing or decreasing one bit from the first value, a judgment step of judging whether or not the current value of the reference current lies in a range of current values of two currents flowing in the current path of the drive transistor according to two offset voltages corresponding to the first value and the second value, based on a result of the current comparison step;

a repetition step of repeating re-setting of the voltage value of the offset voltage to a value changed through the binary search step, and judgment performed according to the set offset voltage in the judgment step, until the current value of the reference current is judged to lie in the range in the judgment step; and

an offset voltage acquiring step of acquiring the offset voltage corresponding to the first value as the specific offset voltage when the current value of the reference current is judged to lie in the range in the judgment step.