Organic Light Emitting Diode Display Device for Sensing Pixel Current and Pixel Current Sensing Method Thereof

• US 20140022289A1
• Filed: 12/12/2012
• Published: 01/23/2014
• Est. Priority Date: 07/19/2012
• Status: Active Grant

• Current Assignee: LG Display Co., Ltd.
• Original Assignee: LG Display Co., Ltd.
• Inventors: Lee, Ji-Eun, Kim, Bum-Sik, Kim, Seung-Tae, Ha, Won-Kyu, Oh, Kil-Hwan
• Granted Patent: US 9,035,976 B2
• Time in Patent Office: Days
• US Class Current: 345/691
• 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 2330/12 Test circuits or failure detection circuits included in a display system, as permanent part thereof
• 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 3/3283 in which the data driver supplies a variable data current for setting the current through, or the voltage across, the light-emitting elements
• 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
• CPC Class Codes: G09G 5/10 Intensity circuits

Abstract

The present invention relates to an organic light emitting diode display device capable of sensing driving current of each pixel with a simple configuration to compensate for a luminance deviation between pixels and a pixel current sensing method thereof. The organic light emitting diode display device includes a display panel including 2N (N being a natural number) pixels that share a reference line though which a reference signal is supplied and are respectively connected to 2N data lines through which data signals are applied, and a data driver for driving the 2N pixels sharing the reference line in a time division manner through the data lines, sensing currents of the time-division-driven 2N pixels as voltages through the shared reference line and outputting the sensed currents, in a sensing mode.

Claims

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

a display panel including 2N (N being a natural number) pixels that share a reference line though which a reference signal is supplied and are respectively connected to 2N data lines through which data signals are applied; and

a data driver for driving the 2N pixels sharing the reference line in a time division manner through the data lines, sensing currents of the time-division-driven 2N pixels as voltages through the shared reference line and outputting the sensed currents, in a sensing mode.

2. The OLED display device according to claim 1, wherein the data driver divides a sensing period for the 2N pixels sharing the reference line into 2N time-division sensing periods and, in each of the 2N time-division sensing periods, the data driver selects a pixel to be sensed from the 2N pixels through a data line corresponding to the pixel to be sensed and de-selects the other pixel through a data line corresponding to the other pixel.

3. The OLED display device according to claim 2, wherein, in each time-division sensing period, the data driver selects the pixel to be sensed by supplying a data voltage for sensing to the data line corresponding to the pixel to be sensed to drive the pixel, and de-selects the other pixel by supplying a black data voltage or an off voltage to the data line corresponding to the other pixel to prevent the other pixel from being driven.

4. The OLED display device according to claim 3, wherein each of the 2N pixels comprises:

a light-emitting element;

a driving thin film transistor (TFT) for driving the light-emitting element;

a first switching TFT for supplying a data signal of the corresponding data line to a first node connected to a gate electrode of the driving TFT in response to a scan signal of a scan line;

a second switching TFT for supplying a reference signal of the reference line to a second node connected between the driving TFT and the light-emitting element in response to a different scan signal of a different scan line; and

a storage capacitor for charging a voltage between the first and second nodes and providing the charged voltage as a driving voltage of the driving TFT,

wherein each of the time-division sensing periods includes;

an initialization period in which the first and second switching TFTs of each pixel are turned on such that the first and second nodes are respectively initialized to the data signal from the corresponding data line and the reference signal of the reference line;

a precharge period in which only the second switching TFT is turned off and the reference line is precharged with a precharge voltage;

a discharge period in which the first and second switching TFTs are turned on such that pixel current of the driving TFT flows to the reference line; and

a sampling period in which the first and second switching TFTs are turned off and the pixel current of the driving TFT is sampled with a saturated voltage of the reference line and held.

5. The OLED display device according to claim 4, wherein the 2N pixels that share the reference line include two pixels that are located on both sides of the shared reference line between two neighboring data lines and respectively connected to the two data lines.

6. The OLED display device according to claim 4, wherein the reference line is branched to N branch reference lines, and every two pixels from among the 2N pixels that share the reference line share the N branch reference lines, the two pixels being located on both sides of the shared branch reference lines between two neighboring data lines and respectively connected to the two data lines.

7. The OLED display device according to claim 5, wherein the first switching TFTs of the two pixels share a first scan line through which a first scan signal is supplied and the second switching TFTs of the two pixels share a second scan line through which a second scan signal is supplied.

8. The OLED display device according to claim 5, wherein the first switching TFTs of the two pixels share a first scan line through which a first scan signal is supplied, the second switching TFT of one of the two pixels is connected to a second scan line through which a second scan signal is supplied, and the second switching TFT of the other of the two pixels is connected to a third scan line through which a third scan signal is supplied,

wherein the second scan signal and the third scan signal respectively provide voltages having opposite polarities only during the discharge period to form a current path between the driving TFT of a pixel to be sensed and the shared reference line and to open a current path between the driving TFT of the other pixel and the shared reference line.

9. The OLED display device according to claim 4, wherein the data driver comprises:

a first digital-to-analog converter (DAC) for converting input data into the data signal and outputting the data signal to a data channel individually connected to the data line;

a second DAC for converting input reference data into the reference signal and outputting the reference signal to a reference channel individually connected to the reference line;

a sample and hold unit for sampling the voltage of the reference line through the reference channel, holding the sampled voltage as a sensing voltage and outputting the held sensing voltage;

an analog-to-digital converter (ADC) for converting the sensing voltage from the sample and hold unit into digital data and outputting the digital data;

a first switch through which output of the first DAC is supplied to the data channel during the initialization period to the discharge period;

a second switch through which output of the second DAC is supplied to the reference channel during the initialization period and the discharge period; and

a third switch through which the precharge voltage is supplied to the reference channel,

wherein the first, second and third switches are turned off during the sampling period.

10. The OLED display device according to claim 9, wherein the data driver further comprises a multiplexer connected between the reference channel and the sample and hold unit to selectively connect at least two reference channels to an input channel of the sample and hold unit, and the number of sample and hold units and the number of ADCs correspond to the number of output channels of the multiplexer.

11. The OLED display device according to claim 5, wherein the number of reference lines corresponds to half the number of data lines, and the number of reference channels respectively connected to the reference lines in the data driver corresponds to half the number of data lines.

12. The OLED display device according to claim 6, wherein the number of branch reference lines corresponds to half the number of data lines, and the number of reference channels respectively connected to the reference lines in the data driver corresponds to half the number of data lines.

13. A method of sensing pixel current of an OLED display device which includes 2N (N being a natural number) pixels that share a reference line though which a reference signal is supplied and are respectively connected to 2N data lines through which data signals are applied, the method comprising:

driving the 2N pixels sharing the reference line in a time division manner through the data lines in a sensing mode; and

sensing currents of the time-division-driven 2N pixels as voltages through the shared reference line and outputting the sensed currents.

14. The method according to claim 13, wherein the driving of the 2N pixels in a time division manner comprises dividing a sensing period for the 2N pixels into 2N time-division sensing periods, selecting a pixel to be sensed from the 2N pixels through a data line corresponding to the pixel and de-selecting the other pixel through a data line corresponding to the other pixel in each of the 2N time-division sensing periods.

15. The method according to claim 14, wherein each of the 2N pixels comprises:

a light-emitting element;

a driving TFT for driving the light-emitting element;

a first switching TFT for supplying the data signal of the corresponding data line to a first node connected to the gate electrode of the driving TFT in response to a scan signal of a scan line;

a second switching TFT for supplying a reference signal of the reference line to a second node connected between the driving TFT and the light-emitting element in response to a different scan signal of a different scan line; and

a storage capacitor for charging a voltage between the first and second nodes and providing the charged voltage as a driving voltage of the driving TFT,

wherein each of the time division sensing periods includes;

an initialization period in which the first and second switching TFTs of each pixel are turned on such that the first and second nodes are respectively initialized to the data signal from the corresponding data line and the reference signal of the reference line;

a precharge period in which only the second switching TFT is turned off and the reference lines is precharged with a precharge voltage;

a discharge period in which the first and second switching TFTs are turned on such that pixel current of the driving TFT flows to the reference line; and

a sampling period in which the first and second switching TFTs are turned off and the pixel current of the driving TFT is sampled with a saturated voltage of the reference line and held.

16. The method according to claim 15, wherein the 2N pixels that share the reference line include two pixels that are located on both sides of the shared reference line between two neighboring data lines and respectively connected to the two data lines, the first switching TFTs of the two pixels are turned on in response to a first scan signal during the initialization period to the discharge period and are turned off during the sampling period, the second switching TFTs of the two pixels are turned on in response to a second scan signal during the initialization period and the discharge period and are turned off during the precharge period and the sampling period.

17. The method according to claim 15, wherein the 2N pixels that share the reference line include two pixels located on both sides of the shared reference line between two neighboring data lines and respectively connected to the two data lines,

wherein the first switching TFTs of the two pixels are turned on in response to a first scan signal during the initialization period to the discharge period and are turned off during the sampling period, and the second switching TFTs of the two pixels are turned on in response to second and third scan signals, respectively, during the initialization period and are turned off during the precharge period and the sampling period,

wherein the second switching TFT of a pixel to be sensed from the two pixels is turned on and the second TFT of the other pixel is turned off during the discharge period.

18. The method according to claim 15, wherein the reference line is branched to N branch reference lines, and every two pixels from among the 2N pixels that share the reference line share the N branch reference lines, the two pixels being located on both sides of the shared branch reference lines between two neighboring data lines and respectively connected to the two data lines, the first switching TFTs of the two pixels being turned on in response to a first scan signal during the initialization period to the discharge period and turned off during the sampling period, the second switching TFTs of the two pixels being turned on in response to a second scan signal during the initialization period and the discharge period and turned off during the precharge period and the sampling period.

19. The method according to claim 15, wherein each of the time division sensing periods includes:

outputting the data signal through a data channel individually connected to the data line and outputting the reference signal to a reference channel individually connected to the reference line during the initialization period;

maintaining output of the data signal through the data channel and outputting a precharge voltage through the reference channel during the precharge period;

outputting the data signal through the data channel and outputting the reference signal through the reference channel during the discharge period;

blocking output of the data signal and reference signal, sampling and holding currents of the time-division-driven pixels through the reference channel as voltages during the sampling period;

converting the held voltage into digital data and outputting the digital data after the sampling period.

20. The method according to claim 19, wherein at least two reference channels are selectively connected to an input channel of the sample and hold unit through a multiplexer.