SYSTEM AND METHOD FOR CALIBRATING DISPLAY DEVICE USING TRANSFER FUNCTIONS

• US 20130135272A1
• Filed: 02/06/2012
• Published: 05/30/2013
• Est. Priority Date: 11/25/2011
• Status: Active Grant

• Current Assignee: Jumi Lim
• Original Assignee: Taebo Jung
• Inventors: Park, Jaeyeol
• Granted Patent: US 8,711,136 B2
• Time in Patent Office: Days
• US Class Current: 345/211
• CPC Class Codes: G09G 2310/027 Details of drivers for data electrodes, the drivers handling digital grey scale data, e.g. use of D/A converters
• CPC Class Codes: G09G 2320/0276 for the purpose of adaptation to the characteristics of a display device, i.e. gamma correction
• CPC Class Codes: G09G 2320/041 Temperature compensation
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2320/0693 Calibration of display systems
• CPC Class Codes: G09G 2330/028 Generation of voltages supplied to electrode drivers in a matrix display other than LCD
• CPC Class Codes: G09G 2360/145 the light originating from the display screen
• CPC Class Codes: G09G 3/006 Electronic inspection or testing of displays and display drivers, e.g. of LED or LCD displays testing individual LED's G01R31/2635; testing lamps G01R31/44; testing of optical features of LCD displays G02F1/1309
• 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

The present invention provides a voltage transfer function, a luminance transfer function, and a transfer factors (for example, efficiency, critical point, and slope) between these two functions, derives the correlation (based on the condition change in all cases) between an input grayscale voltage and output luminance, and calibrates the input grayscale voltage by a difference between measurement luminance and target luminance using the transfer functions. Therefore, the present invention can respond to change in conditions for all cases, and increase the accuracy, easiness, and generalization of calibration compared to the existing calibration scheme that relies on the lookup table by checking the actual measurement data and readjusting the transfer factors in each calibration stage. Moreover, the present invention can further increase the manufacturing yield by an average of 35% than the existing yield, significantly saving the manufacturing cost.

Claims

1. A calibration system of a display device using transfer functions, the calibration system comprising:

a display panel;

a data driving IC configured to generate a grayscale voltage which is applied to the display panel, according to a predetermined gamma register value;

a transfer function processing unit configured to apply a measurement luminance value, a voltage condition, and the predetermined gamma register value to a transfer function algorithm to calculate a plurality of changed second transfer factors, and calculate an auto register for changing the gamma register value by a difference between the first and second transfer factors, wherein the transfer function processing unit comprises;

a voltage transfer function for calculating a voltage condition for change of luminance;

a luminance transfer function for calculating a luminance value based on change of a voltage; and

the transfer function algorithm comprising a plurality of first transfer factors corresponding to a correlation between the voltage transfer function and the luminance transfer function, as a logic circuit, and the measurement luminance value is obtained by applying a test pattern having a specific grayscale voltage value to the display panel;

a driving board configured to comprise a default code memory storing a default code comprising a default register which is used to calculate the auto register, a target code memory storing a target code comprising a target register which is used to calculate the default register, and a voltage generator generating a driving voltage necessary for driving the display panel and the data driving IC;

a luminance measurer configured to measure luminance of the display panel according to application of the test pattern; and

a control center configured to receive an initial driving condition of the data driving IC, and apply a work command signal for sequentially performing calibrations and luminance measurement data to the transfer function processing unit, the luminance measurement data being supplied from the luminance measurer.

2. The calibration system of claim 1, wherein the transfer function processing unit is mounted on one of the data driving IC and the driving board.

3. The calibration system of claim 1, wherein,

the luminance transfer function is divided into a high luminance transfer function corresponding to a high luminance period and a low luminance transfer function corresponding to a low luminance period and used,

critical luminance in the high luminance period is selected as a luminance level enabling obtainment of a stable low luminance value among measurement luminance, and

critical luminance in the low luminance period is selected as target critical luminance which is decided in setting the critical luminance, or selected as estimation critical luminance using the high luminance transfer function.

4. The calibration system of claim 1, wherein,

the transfer function processing unit separately calculates the second transfer factors under a voltage condition and luminance condition of a corresponding calibration stage whenever a plurality of calibration stages are performed, and calculates a difference between the first transfer factors and the second transfer factors, the first transfer factors being set in a calibration stage immediately before the corresponding calibration stage, and

each of the first and second transfer factors comprises:

an efficiency proportion factor which is defined as a value transferring energy change between an input voltage and output luminance;

a critical point proportion factor which is defined as a threshold voltage condition where an OLED of the display panel is actually driven when the input voltage is applied; and

a slope factor which is a slope value comprised in the voltage transfer function and the luminance transfer function, and defined as a voltage change amount and a luminance change amount in each of a plurality of grayscale levels.

5. The calibration system of claim 1, wherein,

in a target calibration stage, the transfer function processing unit applies a target luminance value and an arbitrary grayscale voltage value to the transfer function algorithm to calculate a plurality of target calibration transfer factors, matches a slope factor of the voltage transfer function with a slope factor of the luminance transfer function to calculate the target register through a transfer function operation using the target calibration transfer factors, and updates a predetermined initial code of an initial code with the target register,

in a zero calibration stage succeeding the target calibration stage, the transfer function processing unit calculates a plurality of zero calibration transfer factors based on a measurement luminance value which is obtained by applying a grayscale voltage value based on the target register to the display panel, applies the zero calibration transfer factors and the target luminance value to the transfer function algorithm to calculate the default register for changing the gamma register value by a difference between the target calibration transfer factors and the zero calibration transfer factors, and updates the target register with the default register, and

in an auto calibration stage succeeding the zero calibration stage, the transfer function processing unit calculates a plurality of auto calibration transfer factors based on a measurement luminance value which is obtained by applying the specific grayscale voltage value based on the default register to the display panel, applies the auto calibration transfer factors and the target luminance value to the transfer function algorithm to calculate the auto register for changing the gamma register value by a difference between the zero calibration transfer factors and the auto calibration transfer factors, and stores the calculated auto register in an auto/aging register MTP memory of the data driving IC.

6. The calibration system of claim 5, wherein the data driving IC further comprises:

a reference source current value MTP memory configured to store a luminance-current ratio value which is obtained in the zero calibration stage, the luminance-current ratio value being determined based on a current value which flows in a supply line for a high-level cell driving voltage of the display panel in target luminance between grayscale levels; and

a source current detection unit configured to sense a source current value due to the decrease in service life.

7. The calibration system of claim 6, wherein in an aging calibration stage succeeding the auto calibration stage, the transfer function processing unit calculates a luminance value corresponding to the source current value due to the decrease in the service life, calculates a plurality of aging calibration transfer factors based on the luminance value, applies the aging calibration transfer factors and the target luminance value to the transfer function algorithm to calculate an aging register for adjusting a cell driving voltage of the display panel by a difference between the auto calibration transfer factors and the aging calibration transfer factors, and stores the calculated aging register in the auto/aging register MTP memory of the data driving IC.

8. The calibration system of claim 5, wherein,

the data driving IC further comprises:

a temperature detection unit configured to store a temperature sensing value immediately after a time when the display panel operates normally in response to application of a driving voltage, as a normal operation temperature reference value, and compare the normal operation temperature reference value with a temperature sensing value to sense change of a temperature at certain intervals within a normal operation period, the temperature sensing value being obtained at certain intervals; and

a light leakage current detection unit configured to store a light leakage current sensing value immediately after a time when the display panel operates normally, as a normal operation light current reference value, and compare the normal operation light current reference value with a light current sensing value to sense change of a light leakage current at certain intervals within the normal operation period, the light current sensing value being obtained at certain intervals, and

the transfer function processing unit adjusts an input level of a low-level gamma source voltage for generating the grayscale voltage according to the change of the temperature, and adjusts an input level of a high-level gamma source voltage for generating the grayscale voltage according to the change of the light leakage current.

9. The calibration system of claim 1, wherein the data driving IC further comprises a grayscale voltage generation circuit configured to generate the grayscale voltage, the grayscale voltage generation circuit comprising:

a DY1 adjustment unit configured to comprise a first dynamic resistor connected to an input terminal for a high-level gamma source voltage and a first dynamic register, and adjust an input level of the high-level gamma source voltage in response to change of a resistance value of the first dynamic resistor based on the first dynamic register;

a DY2 adjustment unit configured to comprise a second dynamic resistor connected to an input terminal for a low-level gamma source voltage and a second dynamic register, and adjust an input level of the low-level gamma source voltage in response to change of a resistance value of the second dynamic resistor based on the second dynamic register;

an offset adjustment unit connected adjacently to the DY1 adjustment unit, and configured to adjust an offset of the voltage transfer function and an offset of the luminance transfer function;

a gain adjustment unit connected adjacently to the DY2 adjustment unit, and configured to adjust a gain of the voltage transfer function and a gain of the luminance transfer function; and

the gamma voltage adjustment unit configured to comprise a plurality of slope variable resistors and gamma registers connected between the offset adjustment and the gain adjustment unit, and adjust a slope of the voltage transfer function and a slope of the luminance transfer function in response to change of resistance values of the slope variable resistors based on the gamma registers.

10. The calibration system of claim 6, wherein,

the transfer function processing unit performs white balance calibration in consideration of IR drop in the target calibration stage, the zero calibration stage, the auto calibration stage, and the aging calibration stage, and

the IR drop comprises static IR drop due to a line resistor, and dynamic IR drop due to an amount of changed display data.

11. The calibration system of claim 10, wherein,

the static IR drop is measured in a white data state indicating a maximum drop amount, and reflected in adjusting a gamma register value by the transfer function processing unit, and

the dynamic IR drop is calculated on the basis of an analysis result on a change amount difference of input data, and reflected in compensating for the input data in real time.

12. The calibration system of claim 11, wherein the data driving IC further comprises an IR drop compensation unit configured to calibrate the dynamic IR drop, the IR drop compensation unit comprising:

a grayscale detector configured to analyze input digital image data, detect a grayscale level causing crosstalk based on the number of grayscale levels and a luminance difference between grayscale levels in each of a plurality of horizontal lines or vertical lines, and calculate a dynamic IR drop amount based on an amount of data having a grayscale level causing the crosstalk; and

a data compensator configured to generate a voltage amount with compensation data, and add the compensation data to the input digital image data, the voltage amount being correspond to a luminance difference which is compensated for based on the calculated dynamic IR drop amount.

13. The calibration system of claim 10, further comprising a plurality of gate driving ICs,

wherein,

the display panel is divided into a plurality of driving areas and driven according to the data driving IC and the gate driving ICs, and

white balance calibration based on the IR drop is separately performed for each of the driving areas.

14. A calibration method of a display device using transfer functions, the calibration method comprising:

executing an algorithm which is a transfer function comprising a voltage transfer function and a luminance transfer function, for calibrating change of output luminance to a desired value through calibration of an input voltage;

performing a target calibration stage of applying a target luminance value and an arbitrary grayscale voltage value to the transfer function to calculate a plurality of target calibration transfer factors, and matching a slope factor of the voltage transfer function with a slope factor of the luminance transfer function to calculate a target register through a transfer function operation using the target calibration transfer factors;

performing a zero calibration stage of applying a measurement luminance value, which is obtained by applying a grayscale voltage value based on the target register to the display panel, to the transfer function to calculate a plurality of zero calibration transfer factors, and applying the zero calibration transfer factors and the target luminance value to the transfer function to calculate a default register for compensating for a difference between the target calibration transfer factors and the zero calibration transfer factors with a gamma voltage; and

performing an auto calibration stage of applying a measurement luminance value, which is obtained by applying a grayscale voltage value based on the default register to the display panel, to the transfer function to calculate a plurality of auto calibration transfer factors, and applying the auto calibration transfer factors and the target luminance value to the transfer function to calculate a default register for compensating for a difference between the zero calibration transfer factors and the auto calibration transfer factors with a gamma voltage.

15. The calibration method of claim 14, wherein,

the voltage transfer function and the luminance transfer function is correlated to each other through a slope factor matching operation in the target calibration stage,

a plurality of transfer factors are separately calculated under a voltage condition and luminance condition of a corresponding calibration stage whenever each of the calibration stages is performed, and

each of the transfer factors comprises:

an efficiency proportion factor which is defined as a value transferring energy change between an input voltage and output luminance;

a critical point proportion factor which is defined as a threshold voltage condition where an OLED of the display panel is actually driven when the input voltage is applied; and

a slope factor which is a slope value comprised in the voltage transfer function and the luminance transfer function, and defined as a voltage change amount and a luminance change amount in each of a plurality of grayscale levels.

16. The calibration method of claim 14, further comprising:

performing an aging calibration stage of calculating a relative amount of current decreased due to the reduction in service life on the basis of a current amount reference value which flows in a cell driving voltage supply line of the display panel and has been secured in the zero calibration stage, and calculating an aging register for adjusting a cell driving voltage on the basis of the calculated amount of current; and

performing an environment calibration stage comprising temperature calibration and light leakage current calibration to compensate for a normal driving condition which is changed by an ambient temperature and a light leakage current.

17. The calibration method of claim 14, wherein,

the luminance transfer function is divided into a high luminance transfer function corresponding to a high luminance period and a low luminance transfer function corresponding to a low luminance period and used,

critical luminance in the high luminance period is selected as a luminance level enabling obtainment of a stable low luminance value among measurement luminance, and

critical luminance in the low luminance period is selected as target critical luminance which is decided in setting the critical luminance, or selected as estimation critical luminance using the high luminance transfer function.

18. The calibration method of claim 16, wherein,

white balance calibration is performed based on IR drop in the target calibration stage, the zero calibration stage, the auto calibration stage, and the aging calibration stage,

the IR drop comprises static IR drop due to a line resistor, and dynamic IR drop due to an amount of changed display data,

the static IR drop is measured in a white data state indicating a maximum drop amount, and reflected in adjusting a gamma register value, and

the dynamic IR drop is calculated on the basis of an analysis result on a change amount difference of input data, and reflected in compensating for the input data in real time.

19. The calibration method of claim 16, wherein the auto calibration stage comprises:

downloading a default code comprising the default register, displaying a grayscale level corresponding to maximum luminance of each of RGBW data, a grayscale level corresponding to slope luminance of at least one of the RGBW data, and a grayscale level corresponding to critical point luminance of at least one of the RGBW data on the display panel, and measuring luminance;

applying a measurement luminance value of each of the RGB data to the transfer function to calculate a plurality of primary auto calibration transfer factors due to IR drop, based on the default register;

applying a measurement luminance value of the W data and the primary auto calibration transfer factors to the transfer function to calibrate RGB luminance which is changed due to the IR drop;

applying the default register and a luminance value, for which the IR drop has been calibrated, to the transfer function to calculate a plurality of secondary auto calibration transfer factors;

calculating a voltage difference to be calculated through a transfer function operation using the secondary auto calibration transfer factors and the luminance value for which the IR drop has been calibrated; and

updating the default register with the auto register.

20. The calibration method of claim 16, wherein,

the target calibration stage, the zero calibration stage, and the auto calibration stage are performed before completion of a product, and

the aging calibration stage and the environment calibration stage are performed after a complete product has been produced.