CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2020-0104740, filed on Aug. 20, 2020, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

Technical Field

The present disclosure relates to a display device in which a pixel driving voltage is supplied to pixel circuits of all pixels.

Description of the Related Art

Electroluminescent display devices are broadly classified into inorganic light-emitting display devices and organic light-emitting display devices according to a material of an emission layer. Organic light-emitting display devices in an active matrix include organic light-emitting diodes (hereinafter, referred to as OLEDs) configured to self-emit light and have advantages such as a high response speed, a high luminous efficiency, a high luminance, and a wide viewing angle. In the organic light-emitting display device, the OLED is formed in each of pixels. The organic light-emitting display devices may not only have a high response speed, a high luminous efficiency, a high luminance, and a wide viewing angle but also express a black gradation in complete black, and thus may have a high contract ratio and color reproduction ratio.

Organic light-emitting display devices do not require a backlight unit and may be implemented on a plastic substrate, a thin glass substrate, or a metal substrate which is made of a flexible material. Accordingly, flexible displays can be implemented using organic light-emitting display devices.

In flexible displays, the size and shape of a screen are variable in a manner of rolling, folding, or bending a display panel. The flexible displays may be implemented as rollable displays, bendable displays, foldable displays, slideable displays, or the like. Such flexible displays may be applied not only to mobile devices such as smartphones and tablet personnel computers (PCs) but also to televisions (TVs), vehicle displays, and wearable devices, and application fields thereof are expanding.

Pixels of organic light-emitting display devices each include an OLED, a driving element that drives the OLED by controlling a current flowing in the OLED according to a gate-source voltage (Vgs), and a storage capacitor that maintains a gate voltage of the driving element.

The driving element may be implemented as a transistor. In order to make image quality of an entire screen of the organic light-emitting display device uniform, the driving elements of all pixels should have uniform electrical characteristics. However, due to a process deviation and an element characteristic deviation caused in a manufacturing process of a display panel, the driving elements of the pixels may have a difference in electrical characteristics, and the difference may be increased as a driving time of the pixels elapses. In order to compensate for an electrical characteristic deviation between the driving elements of the pixels, internal compensation technology or external compensation technology may be applied to the organic light-emitting display device.

In the internal compensation technology, a threshold voltage of the driving element is sampled for each subpixel using an internal compensation circuit embedded in each of the pixels, thereby compensating for the gate-source voltage (Vgs) of the driving element by as much as the threshold voltage. In the external compensation technology, a current or voltage of the driving elements, which varies according to the electrical characteristics of the driving elements, is sensed in real time using an external compensation circuit. In the external compensation technology, pixel data (digital data) of an input image is modulated by as much as an electrical characteristic deviation (or change) of the driving element sensed for each pixel, thereby compensating for the electrical characteristic deviation (or change) of the driving element in real time in each of the pixels.

BRIEF SUMMARY

As the efficiency of an organic light-emitting diode (OLED) is improved, a current flowing to the OLED in a low gradation may be decreased. This is because a time for a parasitic capacitance of the OLED to be charged is delayed due to a low current. Therefore, in an OLED with high efficiency, low gradation expression characteristics may be degraded, and a flicker in which luminance periodically fluctuates may be visible in a low speed driving mode.

One or more embodiments of the present disclosure may solve the above-mentioned problems and other technical problems in the related art.

The present disclosure is directed to providing a pixel circuit with improved low gradation expression characteristics and reduced a flicker in a low speed driving mode, and a display device using the same.

It should be noted that technical benefits of the present disclosure are not limited to the above-described benefits, and other benefits of the present disclosure will be apparent to those skilled in the art from the following descriptions.

According to an aspect of the present disclosure, there is provided a pixel circuit including a light-emitting element including an anode and a cathode, a driving element which includes a gate electrode connected to a first node, a first electrode connected to a second node, and a second electrode connected to a third node and which supplies a current to the light-emitting element, a first switch element configured to connect the first node to the third node in a sampling step, a second switch element configured to supply a data voltage to the second node in the sampling step, a third switch element configured to supply a pixel driving voltage to the second node in a emission step after the sampling step, a fourth switch element configured to connect the third node to the anode of the light-emitting element in the emission step, a first capacitor connected to the first node, a second capacitor connected between the third node and the anode of the light-emitting element, and a third capacitor connected between the anode and the cathode of the light-emitting element.

According to an aspect of the present disclosure, there is provided a display device including the pixel circuit.

According to an aspect of the present disclosure, there is provided a display device comprising: a data driver configured to supply data voltages to data lines; a gate driver configured to supply an (N−1)th scan signal generated as a pulse of a gate-on voltage to a first gate line in an initialization step, supply an Nth scan signal generated as the pulse of the gate-on voltage to a second gate line in a sampling step after the initialization step, and supply an emitting signal generated as the gate-on voltage to a third gate line in a emission step after the sampling step, wherein N is a positive integer which is greater than or equal to 1; a power source configured to output a pixel driving voltage and a low potential power voltage and an initialization voltage which are lower than the pixel driving voltage; and a red subpixel, a green subpixel, and a blue subpixel including pixel circuits connected to the data lines and the first gate line to the third gate line, wherein the pixel circuit includes: a light-emitting element including an anode and a cathode; a driving element which includes a gate electrode connected to a first node, a first electrode connected to a second node, and a second electrode connected to a third node and which supplies a current to the light-emitting element; a first switch element configured to connect the first node to the third node in the sampling step; a second switch element configured to supply the data voltage to the second node in the sampling step; a third switch element configured to supply the pixel driving voltage to the second node in the emission step after the sampling step; a fourth switch element configured to connect the third node to the anode of the light-emitting element in the emission step; a first capacitor connected to the first node; a second capacitor connected between the third node and the anode of the light-emitting element; and a third capacitor connected between the anode and the cathode of the light-emitting element.

