Display device

1. A display device comprising:

a sub-pixel comprising a light emitting device and a driving transistor electrically connected to a first electrode of the light emitting device and configured to drive the light emitting device; and

a reference voltage line electrically connected to the sub-pixel and applying an initialization voltage to the first electrode of the light emitting device,

wherein a voltage level of the initialization voltage changes based on a positive correlation to a length of a blank period,

wherein, after the display device is driven in a variable refresh rate mode, for a plurality of consecutive frames, when the length of the blank period increases, the voltage level of the initialization voltage increases, and when the length of the blank period decreases, the voltage level of the initialization voltage decreases.

2. The display device of claim 1 , further comprising a display panel including a display area in which the sub-pixel is disposed, and a non-display area around the display area,

wherein the non-display area includes a monitoring sub-pixel having a monitoring capacitor and a charging transistor electrically connected to one end of the monitoring capacitor which is electrically connected to the reference voltage line.

3. The display device of claim 2 , wherein the monitoring capacitor includes another end to which a base voltage is applied.

4. The display device of claim 2 , wherein the monitoring sub-pixel further includes a sensing transistor configured to switch an electrical connection between the monitoring capacitor and the reference voltage line according to a sense pulse, and

wherein, in a variable refresh rate mode, a timing at which the sense pulse of a turn-on voltage level is applied varies according to the length of the blank period.

5. The display device of claim 4 , further comprising an analog-to-digital converter configured to sense a voltage of the reference voltage line, convert the sensed voltage into a digital value, and output the digital value,

wherein a voltage at the one end of a monitoring capacitor input to the analog-to-digital converter varies according to the length of the blank period.

6. The display device of claim 5 , further comprising:

a timing controller configured to receive the digital value output from the analog-to-digital converter; and

a power management circuit configured to change the voltage level of the initialization voltage under a control of the timing controller.

7. The display device of claim 6 , wherein the timing controller includes a memory for storing a lookup table including a reference refresh rate value and a reference sensing voltage value at the reference refresh rate value, and

wherein the timing controller is configured to control the power management circuit to change the voltage level of the initialization voltage based on the reference sensing voltage value.

8. The display device of claim 6 , wherein the power management circuit further comprises a variable voltage output circuit configured to output the initialization voltage.

9. The display device of claim 8 , wherein the variable voltage output circuit comprises a resistor column comprising two or more resistors, and

wherein the power management circuit is configured to apply a voltage divided by the resistor column to an initialization voltage supply node.

10. The display device of claim 1 , further comprising a main control device configured to control a driving mode of the display device to be driven in either a variable refresh rate mode or a fixed refresh rate mode.

11. The display device of claim 1 , wherein, in a variable refresh rate mode, a plurality of frames have the same length of an active period.

12. The display device of claim 1 , further comprising an initialization voltage supply node electrically connected to the reference voltage line through a switch and supplied with the initialization voltage,

wherein, based on the length of the blank period, the voltage level of the initialization voltage applied to the initialization voltage supply node varies during an active period immediately after the blank period.

13. A display device comprising:

a display panel in which a sub-pixel for image display and a data line for providing a data voltage for image display to the sub-pixel are disposed, the sub-pixel comprising a light emitting device and a driving transistor for driving the light emitting device; and

a reference voltage line electrically connected to the sub-pixel and applying an initialization voltage to a second node of the driving transistor,

wherein the initialization voltage initializes a voltage of the second node of the driving transistor when the data voltage is input to the data line to cause the light emitting device to emit light,

wherein the initialization voltage applied during a current frame increases as a length of a blank period of a previous frame increases in a variable refresh rate mode, and

wherein, a first node of the driving transistor is a gate node, and the second node of the driving transistor is a source node or a drain node.

14. The display device of claim 13 , wherein the display panel includes a display area in which the sub-pixel is disposed, and a non-display area around the display area,

wherein the non-display area includes a monitoring sub-pixel including a monitoring capacitor and a charging transistor electrically connected to one end of the monitoring capacitor which is electrically connected to the reference voltage line.