As an electric current type of light-emitting device, organic light emitting diodes (OLEDs) have found wide application in high performance displays. With the increase in the size of the display, traditional passive matrix organic light-emitting diode (PMOLED) displays require shorter driving time for a single pixel, which necessitates an increased transient current and increased power consumption. Meanwhile, application of a large current results in a large voltage drop on the ITO wire and a high working voltage of the OLED, and in turn decreases its efficiency. Active matrix organic light-emitting diode (AMOLED) displays may address these issues elegantly by means of switch transistors scanning and inputting currents for OLEDs line by line.
Among the three types of driving approaches for AMOLED, which are digital driving, current driving and voltage driving, the voltage driving approach is similar to the traditional driving approach for active matrix liquid crystal displays (AMLCDs), i.e., providing by a driving chip (IC) a voltage signal that represents a grayscale, which voltage signal would be converted inside a sub-pixel into a current signal for driving a thin film transistor, so as to drive the OLED to exhibit a luminance grayscale. This approach is advantageous in that it is fast in driving speed, simple to implement, and appropriate for driving large-sized panels, and thus is extensively applied in the industry.
However, in an AMOLED display of the voltage driving type, the current-luminance (I-L) conversion efficiency decreases as the OLED ages over time. Even if the currents are the same, the luminance displayed may be different because due to their different aging degrees the OLEDs are different in their conversion efficiencies. This leads to an issue that non-uniformity of the luminance is present in the images displayed on the display panel.
In order to improve the luminance uniformity, external compensation approaches are generally applied at present for the AMOLED display of the voltage driving type. Namely, each sub-pixel of the display panel is connected with a driving chip through a respective sense line corresponding one-to-one thereto, which driving chip detects the aging of the OLEDs in respective sub-pixels through the respective sense lines and then performs compensation of the sub-pixels in accordance with the detection. Nevertheless, in the above display panel, each sub-pixel is connected to a respective sense line, leading to increased wirings in the display panel, which is disadvantageous for fabrication of a high resolution display panel. Moreover, the number of the signal channels of the driving chip will be doubled, resulting in an increased area of the driving chip and a high cost.