PIXEL AND ORGANIC LIGHT-EMITTING DIODE (OLED) DISPLAY HAVING THE SAME

• US 20160379569A1
• Filed: 09/13/2016
• Published: 12/29/2016
• Est. Priority Date: 04/04/2014
• Status: Active Grant

• Current Assignee: Samsung Display Company Limited (Samsung Electronics Co. Ltd.)
• Original Assignee: Samsung Display Company Limited (Samsung Electronics Co. Ltd.)
• Inventors: Lee, Jae-Sic, Lee, Seung-Kyu
• Granted Patent: US 10,170,048 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• 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 2320/0233 Improving the luminance or brightness uniformity across the screen
• CPC Class Codes: G09G 2320/0238 Improving the black level
• CPC Class Codes: G09G 2330/028 Generation of voltages supplied to electrode drivers in a matrix display other than LCD
• 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 3/3275 Details of drivers for data 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

A pixel and an organic light-emitting diode (OLED) display having the same are disclosed. In one aspect, a pixel includes an OLED including an anode and a cathode and configured to emit light corresponding to data signals applied during first and second frame periods. Each of the first and second frame periods includes a first discharge period and a light-emitting period subsequent to the first discharge period. The pixel also includes a pixel circuit configured to control light emission of the OLED, apply a first voltage to the anode during the light-emitting period, apply a second voltage to the cathode, the second voltage having a voltage level less than that of the first voltage, and apply a third voltage to the anode so as to discharge the anode during the first discharge period. The second voltage has different voltage levels during the first and second frame periods.

Claims

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

a plurality of scan lines;

a plurality of light-emitting lines;

plurality of light emitting control signals to the light emitting lines;

a plurality of data lines crossing the scan lines and the light-emitting lines;

a plurality of pixels; and

a voltage generator configured to output a third voltage and a fourth voltage different from the third voltage to the pixels, wherein each of the pixels includes;

a pixel circuit configured to receive a first voltage, the third voltage and the fourth voltage; and

an OLED including an anode connected to the pixel circuit and a cathode configured to receive a second voltage having a voltage level lower than that of the first voltage;

wherein the difference between the second voltage and the third voltage is substantially constant, and wherein the pixel circuit is configured to apply the third voltage to the anode.

2. The OLED display of claim 1, wherein the pixel circuit comprises:

a driving transistor electrically connected between a second node applied with the first voltage and the anode of the OLED, wherein the driving transistor has i) a control electrode electrically connected to a first node applied with the fourth voltage, ii) an input electrode, and iii) an output electrode;

a switching transistor including i) an input electrode configured to receive a data signal applied to a corresponding data line of the data lines, ii) an output electrode electrically connected to the input electrode of the driving transistor, and iii) a control electrode configured to receive a scan signal applied to a corresponding scan line of the scan lines;

a storage capacitor electrically connected between the first node and the second node;

a first control transistor including i) an input electrode electrically connected to the output electrode of the driving transistor, ii) an output electrode electrically connected to the first node, and iii) a control electrode configured to receive the scan signal applied to the corresponding scan line;

a second control transistor including i) an input electrode electrically connected to the output electrode of the driving transistor, ii) an output electrode electrically connected to the anode of the OLED, and iii) a control electrode electrically connected to a corresponding light-emitting line of the light-emitting lines applied with a first control signal; and

a first discharge transistor including i) an input electrode configured to receive the third voltage, ii) an output electrode electrically connected to the anode of the OLED, and iii) a control electrode configured to receive a second control signal,

wherein the first discharge transistor is configured to apply the third voltage to the anode of the OLED.

3. The OLED display of claim 2, wherein the second control signal comprises the scan signal applied to a scan line subsequent to the corresponding scan line.

4. The OLED display of claim 2, wherein the pixel circuit further comprises a second discharge transistor including i) an input electrode configured to receive the fourth voltage having a voltage level less than that of the data signal applied to the corresponding data line, ii) an output electrode electrically connected to the first node, and iii) a control electrode configured to receive a third control signal, wherein the second discharge transistor is configured to apply the fourth voltage to the control node.

5. The OLED display of claim 4, wherein the third control signal comprises a scan signal applied to the scan line preceding the corresponding scan line.

6. The OLED display of claim 4, wherein the pixel circuit further comprises a third control transistor including i) an input electrode electrically connected to the second node, ii) an output electrode electrically connected to the input electrode of the driving transistor, and iii) a control electrode configured to receive the first control signal applied to the corresponding light-emitting line.

8. The OLED display of claim 1, wherein the voltage generator comprises a first voltage generator configured to generate the third voltage and comprising a differential amplifier including i) an inverting input terminal configured to receive a first reference voltage, ii) a non-inverting input terminal configured to receive a second reference voltage corresponding to the second voltage, and iii) an output terminal configured to output a voltage difference between the first reference voltage and the second reference voltage as the third voltage.

9. The OLED display of claim 1, wherein the discharge voltage generator comprises a second voltage generator configured to generate the fourth voltage and comprising a voltage dividing circuit including a plurality of resistors electrically connected in series between the first voltage and the second voltage so as to output the fourth voltage divided by the resistors.

10. The OLED display of claim 1, wherein the second voltage comprises a voltage level in a range of about −

4 volts to about −

2 volts.

11. The OLED display of claim 1, wherein the difference between the second voltage and the third voltage is less than a light-emitting threshold voltage of the OLED.

7. (canceled)

12. A pixel for an organic light-emitting diode (OLED) display, comprising:

an OLED including an anode and a cathode configured to receive a second voltage; and

a pixel circuit configured to 1) receive a first voltage, ii) apply a third voltage to the anode before the OLED emits the light in a frame period, iii) receive a fourth voltage different from the third voltage,

wherein the difference between the second voltage and the third voltage is substantially constant during the frame period.

13. The pixel of claim 12, wherein the pixel circuit comprises:

a driving transistor electrically connected between the anode of the OLED and a second node applied with the first voltage, the driving transistor has i) a control electrode electrically connected to a first node applied with the fourth voltage ii) an input electrode and iii) an output electrode;

a switching transistor including an input electrode configured to receive the data signal, an output electrode electrically connected to the input electrode of the driving transistor, and a control electrode configured to receive a scan signal;

a storage capacitor electrically connected between the first node and the second node;

a first control transistor including i) an input electrode electrically connected to the output electrode of the driving transistor, ii) an output electrode electrically connected to the first node, and iii) a control electrode configured to receive the scan signal;

a second control transistor including i) an input electrode electrically connected to the output electrode of the driving transistor, ii) an output electrode electrically connected to the anode of the OLED, and iii) a control electrode configured to receive a first control signal; and

a first discharge transistor including i) an input electrode configured to receive the third voltage, ii) an output electrode electrically connected to the anode of the OLED, and iii) a control electrode configured to receive a second control signal, wherein the first discharge transistor is configured to apply the third voltage to the anode of the OLED before the OLED emits the light in the frame period.

14. The pixel of claim 13, wherein the pixel circuit further comprises a second discharge transistor including i) an input electrode configured to receive the fourth voltage, ii) an output electrode electrically connected to the first node, and iii) a control electrode configured to receive a third control signal,

wherein the second discharge transistor is configured to apply the fourth voltage to the first node before the OLED emits the light in the frame period.

15. The pixel of claim 14, wherein the pixel circuit further comprises a third control transistor including i) an input electrode electrically connected to the second node, ii) an output electrode electrically connected to the input electrode of the driving transistor, and iii) a control electrode configured to receive the first control signal.

16. The pixel of claim 12, wherein the second voltage comprises a voltage level in a range of about −

4 volts to about −

2 volts.

17. The pixel of claim 12, wherein the difference between the second voltage and the third voltage is less than a light-emitting threshold voltage of the OLED.

18. The pixel of claim 12, wherein the fourth voltage has a voltage level lower than that of the data signal.