ORGANIC LIGHT-EMITTING DIODE DISPLAY DEVICE AND METHOD OF DRIVING THE SAME

• US 20180190198A1
• Filed: 12/12/2017
• Published: 07/05/2018
• Est. Priority Date: 12/29/2016
• Status: Active Grant

• Current Assignee: LG Display Co., Ltd.
• Original Assignee: LG Display Co., Ltd.
• Granted Patent: US 10,460,666 B2
• Time in Patent Office: Days
• 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 2310/0251 Precharge or discharge of pixel before applying new pixel voltage
• CPC Class Codes: G09G 2310/0262 The addressing of the pixel, in a display other than an active matrix LCD, involving the control of two or more scan electrodes or two or more data electrodes, e.g. pixel voltage dependent on signals of two data electrodes
• CPC Class Codes: G09G 2320/0295 by monitoring each display pixel
• 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
• CPC Class Codes: G09G 3/3258 with pixel circuitry controlling the voltage across the light-emitting element
• CPC Class Codes: G09G 3/3266 Details of drivers for scan electrodes
• 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 organic light-emitting diode (OLED) display device can include a pixel and a data driver. The pixel includes a driving thin film transistor (TFT) to drive an OLED element, a first switching TFT to connect a data line to a gate electrode of the driving TFT, a second switching TFT to connect a reference line to a source electrode of the driving TFT and a capacitor connected between the gate electrode and the source electrode of the driving TFT. The data driver includes a first amplifier to drive the data line with a reference voltage or a data voltage, a second amplifier to drive the reference line with an initialization voltage, and a third amplifier to sense a voltage of the reference line and supply a reference sensing voltage to the second amplifier, in which the reference line voltage is based on a threshold voltage of the driving TFT.

Claims

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

a pixel including;

a driving thin film transistor (TFT) configured to drive an OLED element;

a first switching TFT configured to connect a data line to a gate electrode of the driving TFT by control of a first gate line;

a second switching TFT configured to connect a reference line to a source electrode of the driving TFT by control of a second gate line; and

a capacitor connected between the gate electrode of the driving TFT and the source electrode of the driving TFT; and

a data driver including;

a first amplifier configured to drive the data line with a reference voltage (Vref) or a data voltage (Vdata);

a second amplifier configured to drive the reference line with an initialization voltage; and

a third amplifier configured to sense a voltage of the reference line, and supply a reference sensing voltage to the second amplifier, wherein the voltage of the reference line is based on a threshold voltage (Vth) of the driving TFT.

2. The OLED display device according to claim 1, wherein the reference sensing voltage is set to the reference voltage (Vref) minus the threshold voltage (Vth) of the driving TFT.

3. The OLED display device according to claim 1, wherein an output terminal of the second amplifier is connected to the reference line, a non-inverting input terminal of the second amplifier is connected to an output terminal of the third amplifier and an inverting input terminal of the second amplifier is connected to the output terminal of the second amplifier in a voltage following manner, and

wherein the output terminal of the third amplifier is connected to the non-inverting input terminal of the second amplifier, a non-inverting input terminal of the third amplifier is connected to the reference line and an inverting input terminal of the third amplifier is connected to the output terminal of the third amplifier in a voltage following manner.

4. The OLED display device according to claim 1, wherein the data driver is configured to drive the pixel for a plurality of frames,

wherein each frame of the plurality of frames includes:

a scan period during which the first and second switching TFTs are turned on and a target driving voltage corresponding to the data voltage (Vdata) is charged in the capacitor, and

a light-emitting period during which the first and second switching TFTs are turned off and the driving TFT drives the OLED element with the target driving voltage charged in the capacitor,

wherein the scan period includes an initialization period, a sensing period, and a sampling period,

wherein, during the initialization period, the first amplifier supplies the reference voltage (Vref) to the gate electrode of the driving TFT via the data line and the first switching TFT, and the second amplifier supplies the initialization voltage to the source electrode of the driving TFT via the reference line and the second switching TFT,

wherein, during the sensing period, the first amplifier supplies the reference voltage (Vref) to the gate electrode of the driving TFT via the data line and the first switching TFT, the second amplifier enters a high impedance state, and a threshold voltage-reduced reference voltage (Vref−

Vth) is charged in the source electrode of the driving TFT and the reference line by driving of the driving TFT, and

wherein, during the sampling period, the first amplifier supplies the data voltage (Vdata) to the gate electrode of the driving TFT via the data line and the first switching TFT, the third amplifier senses the threshold voltage-reduced reference voltage (Vref−

Vth) as the reference sensing voltage and supplies the reference sensing voltage to the second amplifier, the second amplifier supplies the reference sensing voltage supplied from the third amplifier to the source electrode of the driving TFT via the reference line and the second switching TFT, and the capacitor stores a difference voltage (Vdata−

(Vref−

Vth)) between the data voltage (Vdata) and the reference sensing voltage (Vref−

Vth) as the target driving voltage.

5. The OLED display device according to claim 4, wherein the initialization voltage is less than the reference voltage (Vref) minus the threshold voltage (Vth) of the driving TFT to drive the driving TFT by a stored voltage in the capacitor of the reference voltage (Vref) minus the initialization voltage during the initialization period, and

wherein the initialization voltage is less than a threshold voltage of the OLED element to cause the OLED element not to emit light during the initialization period and the sensing period.

6. The OLED display device according to claim 5, wherein, during the initialization period, the third amplifier enters a high impedance state, and

wherein, during the sensing period, the third amplifier enters the high impedance state or performs a normal buffering operation.

7. The OLED display device according to claim 1, wherein a threshold voltage of the OLED element is greater than the reference voltage (Vref) minus the initialization voltage, and the reference voltage (Vref) minus the initialization voltage is greater than the threshold voltage (Vth) of the driving TFT.

8. The OLED display device according to claim 1, wherein the first and second gate lines are different gate lines or the same gate line.

9. A method of driving an organic light-emitting diode (OLED) display device, the method comprising:

during an initialization period, supplying a reference voltage (Vref), via a first amplifier, to a gate electrode of a driving thin film transistor (TFT) connected to an OLED element and charging an initialization voltage in a source electrode of the driving TFT;

during a sensing period, supplying the reference voltage (Vref), via the first amplifier, to the gate electrode of the driving TFT, and charging the source electrode of the driving TFT from the initialization voltage to a reference sensing voltage based on the reference voltage (Vref) minus a threshold voltage (Vth) of the driving TFT; and

during a sampling period, supplying a data voltage (Vdata), via the first amplifier, to the gate electrode of the driving TFT, sensing the reference sensing voltage, via a third amplifier, and supplying the reference sensing voltage, via a second amplifier, to the source electrode of the driving TFT.

10. The method according to claim 9, wherein the reference sensing voltage is set to the reference voltage (Vref) minus the threshold voltage (Vth) of the driving TFT.

11. The method according to claim 9, wherein an output terminal of the second amplifier is connected to the reference line, a non-inverting input terminal of the second amplifier is connected to an output terminal of the third amplifier and an inverting input terminal of the second amplifier is connected to the output terminal of the second amplifier in a voltage following manner, and

wherein the output terminal of the third amplifier is connected to the non-inverting input terminal of the second amplifier, a non-inverting input terminal of the third amplifier is connected to the reference line and an inverting input terminal of the third amplifier is connected to the output terminal of the third amplifier in a voltage following manner.

12. The method according to claim 9, wherein, during the initialization period, the first amplifier supplies the reference voltage (Vref) to the gate electrode of the driving TFT via a data line and a first switching TFT, and the second amplifier supplies the initialization voltage to the source electrode of the driving TFT via the reference line and a second switching TFT,

wherein, during the sensing period, the first amplifier supplies the reference voltage to the gate electrode of the driving TFT via the data line and the first switching TFT, the second amplifier enters a high impedance state, and a threshold voltage-reduced reference voltage (Vref−

Vth) is charged in the source electrode of the driving TFT and the reference line by driving of the driving TFT, and

wherein, during the sampling period, the first amplifier supplies the data voltage (Vdata) to the gate electrode of the driving TFT via the data line and the first switching TFT, the third amplifier senses the threshold voltage-reduced reference voltage (Vref−

Vth) of the reference line as the reference sensing voltage and supplies the reference sensing voltage to the second amplifier, the second amplifier supplies the reference sensing voltage supplied from the third amplifier to the source electrode of the driving TFT via the reference line and the second switching TFT, and the capacitor stores a difference voltage (Vdata−

(Vref−

Vth)) between the data voltage (Vdata) and the reference sensing voltage (Vref−

Vth) as a target driving voltage.

13. The method according to claim 12, wherein the initialization voltage is less than the reference voltage (Vref) minus the threshold voltage (Vth) of the driving TFT to drive the driving TFT by a stored voltage in the capacitor of the reference voltage (Vref) minus the initialization voltage during the initialization period, and

wherein the initialization voltage is less than a threshold voltage of the OLED element to cause the OLED element not to emit light during the initialization period and the sensing period.

14. The method according to claim 12, wherein, during the initialization period, the third amplifier enters a high impedance state, and

wherein, during the sensing period, the third amplifier enters the high impedance state or performs a normal buffering operation.

15. The method according to claim 9, further comprising:

during the sensing period, gradually charging the source electrode of the driving TFT from the initialization voltage to the reference voltage (Vref) minus the threshold voltage (Vth) of the driving TFT, while maintaining the gate electrode of the driving TFT at the reference voltage (Vref).

16. The method according to claim 9, wherein a threshold voltage of an OLED element connected to the driving TFT is greater than the reference voltage (Vref) minus the initialization voltage, and the reference voltage (Vref) minus the initialization voltage is greater than the threshold voltage (Vth) of the driving TFT.

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

a pixel circuit including;

a driving thin film transistor (TFT) connected to an OLED element;

a first switching TFT configured to connect a data line to a gate electrode of the driving TFT;

a second switching TFT configured to connect a reference line to a source electrode of the driving TFT; and

a capacitor connected between the gate electrode of the driving TFT and the source electrode of the driving TFT; and

a data driver including an analog compensation circuit for compensating for a threshold voltage of the driving TFT,

wherein the analog compensation circuit includes a first amplifier and a second amplifier,

wherein the first amplifier is connected to an output of the second amplifier, and

wherein the second amplifier is configured to sense a voltage of the reference line and supply a reference sensing voltage to the second amplifier, and the first amplifier is configured to supply a compensation voltage based on the reference sensing voltage to the reference line.

18. The OLED display device according to claim 17, wherein an output terminal of the first amplifier is connected to the reference line, a non-inverting input terminal of the first amplifier is connected to the output terminal of the second amplifier and an inverting input terminal of the first amplifier is connected to the output terminal of the first amplifier in a voltage following manner, and

wherein the output terminal of the second amplifier is connected to the non-inverting input terminal of the first amplifier, a non-inverting input terminal of the second amplifier is connected to the reference line and an inverting input terminal of the second amplifier is connected to the output terminal of the second amplifier in a voltage following manner.

19. The OLED display device according to claim 17, wherein the reference sensing voltage is set to a reference voltage (Vref) supplied to the gate electrode of the driving TFT minus a threshold voltage (Vth) of the driving TFT.

20. The OLED display device according to claim 17, further comprising a third amplifier configured to drive the data line with a reference voltage (Vref) or a data voltage (Vdata).