ORGANIC LIGHT EMITTING DIODE DISPLAY DEVICE AND METHOD FOR SENSING CHARACTERISTIC PARAMETERS OF PIXEL DRIVING CIRCUITS

• US 20130162617A1
• Filed: 12/14/2012
• Published: 06/27/2013
• Est. Priority Date: 12/26/2011
• Status: Active Grant

• Current Assignee: LG Display Co., Ltd.
• Original Assignee: LG Display Co., Ltd.
• Inventors: KIM, Seung-Tae, LEE, Ji-Eun, YOON, Joong-Sun, KANG, Ji-Hyun
• Granted Patent: US 8,988,329 B2
• Time in Patent Office: Days
• US Class Current: 345/211
• 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 2320/0295 by monitoring each display pixel
• 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

Disclosed are an OLED display device and method for sensing characteristic parameters of pixel driving circuits. The display device includes a display panel including pixels each having a light emitting element and a pixel driving circuit for independently driving the light emitting element, and a characteristic parameter detecting unit for driving the pixel driving circuit of one of the plural pixels, which is a sensing pixel, sensing a voltage discharged in accordance with characteristics of a driving TFT in the pixel driving circuit of the sensing pixel, on a data line connected to the pixel driving circuit of the sensing pixel, among data lines connected to respective pixel driving circuits of the pixels, and detecting a threshold voltage (Vth) of the driving TFT and a deviation of a process characteristic parameter (k-parameter) of the driving TFT, using the measured voltage.

Claims

1. An organic light emitting diode (OLED) display device comprising:

a display panel comprising a plurality of pixels each having a light emitting element and a pixel driving circuit for independently driving the light emitting element; and

a characteristic parameter detecting unit for sensing characteristic parameters of the pixel driving circuit in each of the plural pixels, the characteristic parameter detecting unit driving the pixel driving circuit of one of the plurality of pixels, which is a sensing pixel, sensing a voltage discharged in accordance with characteristics of a driving thin film transistor (TFT) in the pixel driving circuit of the sensing pixel, on a data line connected to the pixel driving circuit of the sensing pixel, among data lines connected to respective pixel driving circuits of the pixels, and detecting a threshold voltage (Vth) of the driving TFT and a deviation of a process characteristic parameter (k-parameter) of the driving TFT, using the measured voltage.

2. The display device according to claim 1, wherein the characteristic parameter detecting unit comprises:

a data driver for driving the data line, sensing a voltage on the data line, and outputting the measured voltage; and

a timing controller for detecting the threshold voltage (Vth) and the k-parameter deviation, based on the measured voltage from the data driver, calculating an offset value to compensate the detected threshold voltage (Vth) and a gain value to compensate for the detected k-parameter deviation, storing the calculated offset value and the calculated gain value, compensating input data by use of the stored offset value and the stored gain value, and supplying the compensated input data to the data driver.

3. The display device according to claim 2, wherein the timing controller detects the threshold voltage (Vth) by calculating a difference voltage between the measured voltage from the data driver and a reference voltage supplied to the pixel driving circuit of the sensing pixel.

4. The display device according to claim 3, wherein the timing controller detects the k-parameter deviation by detecting a variation in the voltage discharged in accordance with the characteristics of the driving TFT in the sensing pixel, based on the measured voltage from the data driver, and calculating a ratio of the detected voltage variation in the sensing pixel to a predetermined or previously-detected voltage variation in a reference one of the pixels.

5. The display device according to claim 2, wherein the pixel driving circuit comprises:

the driving TFT, which drives the light emitting element;

a first switching TFT for supplying the voltage on the data line to a first node of the driving TFT in response to a first scan signal from a scan line;

a second switching TFT for supplying a reference voltage from a reference voltage line to a second node of the driving TFT in response to a second scan signal from the scan line; and

a storage capacitor for charging a voltage between the first node and the second node, and supplying the charged voltage as a driving voltage for the driving TFT.

6. The display device according to claim 5, wherein:

the data driver supplies a pre-charge voltage to the data line, measures the voltage on the data line at a time when the driving TFT is driven in a saturated state in accordance with discharge of the pre-charge voltage from the data line through driving of the first and second switching TFTs, and outputs the measured voltage; and

the timing controller detects the threshold voltage (Vth) by calculating a difference voltage between the measured voltage from the data driver and a reference voltage supplied to the pixel driving circuit of the sensing pixel.

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

in a programming period, the data driver supplies, to the data line, a sum of a data voltage compensated for the detected threshold voltage (Vth) and the reference voltage, and the driving TFT is driven in accordance with the driving of the first and second switching TFTs;

in a pre-charging period following the programming period, the data driver pre-charges the data line with the pre-charge voltage, and the first and second switching TFTs are turned off;

in a discharging period following the pre-charging period, the data driver is disconnected from the data line, and the pre-charge voltage on the data line is discharged through the first switching TFT and the driving TFT;

at a sensing time corresponding to the sensing time or each of the sensing times and following the discharging period, the first switching TFT is turned off, and the data driver measures the voltage on the data line, and outputs the measured voltage; and

the timing controller detects the k-parameter deviation by calculating a difference voltage between the pre-charge voltage and the voltage measured at the sensing time, to detect a voltage variation in the sensing pixel, and calculating a ratio of the voltage variation in the sensing pixel to a voltage variation in a reference one of the pixels.

8. The display device according to claim 5, wherein:

a first reference voltage is supplied to the reference voltage line, and the data driver supplies a pre-charge voltage to the data line, measures the voltage on the data line at a plurality of times when the driving TFT is driven in a saturated state in accordance with discharge of the pre-charge voltage from the data line through driving of the first and second switching TFTs, and outputs the measured voltages as first measured voltages;

a second reference voltage different from the first reference voltage is supplied to the reference voltage line, and the data driver supplies the pre-charge voltage to the data line, measures the voltage on the data line at the plurality of times when the driving TFT is driven in the saturated state in accordance with the discharge of the pre-charge voltage from the data line through the driving of the first and second switching TFTs, and outputs the measured voltages as second measured voltages; and

the timing controller detects the threshold voltage (Vth) by detecting a time when a difference voltage between corresponding ones of the first and second measured voltages output from the data driver is equal or similar to a difference voltage between the first and second reference voltages, and calculating a difference voltage between the first measured voltage measured at the detected time and the first reference voltage or a difference voltage between the second measured voltage measured at the detected time and the second reference voltage.

9. The display device according to claim 8, wherein:

in a programming period, the data driver supplies, to the data line, a sum of a data voltage compensated for the detected threshold voltage (Vth) and the reference voltage, and the driving TFT is driven in accordance with the driving of the first and second switching TFTs;

in a pre-charging period following the programming period, the data driver pre-charges the data line with the pre-charge voltage, and the first and second switching TFTs are turned off.

in a discharging period following the pre-charging period, the data driver is disconnected from the data line, and the pre-charge voltage on the data line is discharged through the first switching TFT and the driving TFT;

at a sensing time corresponding to the sensing time or each of the sensing times and following the discharging period, the first switching TFT is turned off, and the data driver measures the voltage on the data line, and outputs the measured voltage; and

the timing controller detects the k-parameter deviation by calculating a difference voltage between the pre-charge voltage and the voltage measured at the sensing time, to detect a voltage variation in the sensing pixel, and calculating a ratio of the voltage variation in the sensing pixel to a voltage variation in a reference one of the pixels.

10. The display device according to claim 2, wherein the data driver comprises:

a plurality of digital-analog converters (DACs) for converting input data into analog data voltages by channels, respectively;

a plurality of sampling/holder circuits respectively connected to the data lines by channels, each of the sampling/holder circuits sampling a voltage on a corresponding one of the data lines, and holding and outputting the sampled voltage as the measured voltage;

an analog-digital converter (ADC) for converting the measured voltage from each of the sampling/holder circuits into digital data, and outputting the digital data; and

a plurality of first switches connected between the DACs and the data lines by channels, respectively, to switch respective output voltages from the DACs.

11. The display device according to claim 10, wherein:

the data driver further comprises a multiplexer/scaler connected between the sampling/holder circuits and the ADC, the multiplexer/scaler selecting and scaling a plurality of measured voltages from the sampling/holder circuits by groups, and outputting the scaled voltages to the ADC, each group including at least one measured voltage; and

the ADC are equal, in number, to output channels of the multiplexer/scaler.

12. The display device according to claim 11, wherein the data driver further comprises second switches the pre-charge voltage to respective output channels of the DACs.

13. A method for sensing characteristic parameters of pixel driving circuits in an organic light emitting diode (OLED) display device including a plurality of pixels each including a light emitting element and a corresponding one of the pixel driving circuits to independently drive the light emitting element, comprising the steps of:

driving the pixel driving circuit of one of the plurality of pixels, which is a sensing pixel, sensing a voltage discharged in accordance with characteristics of a driving thin film transistor (TFT) in the pixel driving circuit of the sensing pixel, on a data line connected to the pixel driving circuit of the sensing pixel, among data lines connected to respective pixel driving circuits of the pixels, and detecting a threshold voltage (Vth) of the driving TFT, using the measured voltage; and

driving the pixel driving circuit of the sensing pixel, using data voltage compensated for the detected threshold voltage (Vth), sensing a voltage discharged in accordance with the characteristics of the driving TFT, on the data line, and detecting a k-parameter deviation of the driving TFT, based on the measured voltage.

14. The method according to claim 13, wherein the step of detecting the threshold voltage (Vth) comprises the step of calculating a difference voltage between the measured voltage and a reference voltage supplied to the pixel driving circuit of the sensing pixel, to detect the threshold voltage (Vth).

15. The method according to claim 14, wherein the step of detecting the k-parameter variation comprises the step of detecting a variation in the voltage discharged in accordance with the characteristics of the driving TFT in the sensing pixel, based on the measured voltage, and calculating a ratio of the detected voltage variation in the sensing pixel to a predetermined or previously-detected voltage variation in a reference one of the pixels.

16. The method according to claim 15, wherein:

the pixel driving circuit comprises the driving TFT, which drives the light emitting element, a first switching TFT for supplying the voltage on the data line to a first node of the driving TFT in response to a first scan signal from a scan line, a second switching TFT for supplying a reference voltage from a reference voltage line to a second node of the driving TFT in response to a second scan signal from the scan line, and a storage capacitor for charging a voltage between the first node and the second node, and supplying the charged voltage as a driving voltage for the driving TFT; and

the step of detecting the threshold voltage (Vth) comprises the steps of;

supplying a pre-charge voltage to the data line, and then sensing the voltage on the data line at a time when the driving TFT is driven in a saturated state in accordance with discharge of the pre-charge voltage from the data line through driving of the first and second switching TFTs; and

calculating a difference voltage between the measured voltage and the reference voltage, to detect the threshold voltage (Vth).

17. The method according to claim 16, wherein the step of detecting the k-parameter deviation comprises the steps of:

supplying, in a programming period, a sum of a data voltage compensated for the detected threshold voltage (Vth) and the reference voltage to the data line, and driving the driving TFT in accordance with the driving of the first and second switching TFTs;

pre-charging, in a pre-charging period following the programming period, the data line with the pre-charge voltage, and turning off the first and second switching TFTs;

floating the data line in a discharging period following the pre-charging period, and discharging the pre-charge voltage on the data line through the first switching TFT and the driving TFT;

turning off the first switching TFT at a sensing time, which corresponds to the sensing time or each of the sensing times and follows the discharging period, and sensing the voltage on the data line;

calculating a difference voltage between the pre-charge voltage and the voltage measured at the sensing time, to detect a voltage variation in the sensing pixel; and

calculating a ratio of the voltage variation in the sensing pixel to a voltage variation in a reference one of the pixels, to detect the k-parameter deviation.

18. The method according to claim 15, wherein:

the pixel driving circuit comprises the driving TFT, which drives the light emitting element, a first switching TFT for supplying the voltage on the data line to a first node of the driving TFT in response to a first scan signal from a scan line, a second switching TFT for supplying a reference voltage from a reference voltage line to a second node of the driving TFT in response to a second scan signal from the scan line, and a storage capacitor for charging a voltage between the first node and the second node, and supplying the charged voltage as a driving voltage for the driving TFT; and

the step of detecting the threshold voltage (Vth) comprises the steps of;

supplying a first reference voltage to the reference voltage line, supplying a pre-charge voltage to the data line, sensing the voltage on the data line at a plurality of times when the driving TFT is driven in a saturated state in accordance with discharge of the pre-charge voltage from the data line through driving of the first and second switching TFTs, and outputting the measured voltages as first measured voltages;

supplying a second reference voltage different from the first reference voltage to the reference voltage line, supplying the pre-charge voltage to the data line, sensing the voltage on the data line at the plurality of times when the driving TFT is driven in the saturated state in accordance with the discharge of the pre-charge voltage from the data line through the driving of the first and second switching TFTs, and outputting the measured voltages as second measured voltages; and

detecting a time when a difference voltage between corresponding ones of the first and second measured voltages output from the data driver is equal or similar to a difference voltage between the first and second reference voltages, and calculating a difference voltage between the first measured voltage measured at the detected time and the first reference voltage or a difference voltage between the second measured voltage measured at the detected time and the second reference voltage, to detect the threshold voltage (Vth).

19. The method according to claim 18, wherein the step of detecting the k-parameter deviation comprises the steps of:

supplying, in a programming period, a sum of a data voltage compensated for the detected threshold voltage (Vth) and the reference voltage to the data line, and driving the driving TFT in accordance with the driving of the first and second switching TFTs;

pre-charging, in a pre-charging period following the programming period, the data line with the pre-charge voltage, and turning off the first and second switching TFTs;

floating the data line in a discharging period following the pre-charging period, and discharging the pre-charge voltage on the data line through the first switching TFT and the driving TFT;

turning off the first switching TFT at a sensing time, which corresponds to the sensing time or each of the sensing times and follows the discharging period, and sensing the voltage on the data line;

calculating a difference voltage between the pre-charge voltage and the voltage measured at the sensing time, to detect a voltage variation in the sensing pixel; and

calculating a ratio of the voltage variation in the sensing pixel to a voltage variation in a reference one of the pixels, to detect the k-parameter deviation.