An external compensation method for AMOLED using the concept of ramp-stop

In this paper, we propose an external feedback method to compensate the device variation for active-matrix organic light-emitting diode. The pixel data current is controlled by ramping the gate voltage and converted to the sensed voltage V_sense in real time. When V_sense is equal to a preset voltage V_data, the switching block outputs the low potential to stop the ramping. Therefore, the gate voltage is locked at the value corresponding to the target data current. This circuit is implemented with three thin-film transistors in the active area and some functional blocks in driver integrated circuit (IC), namely, sentinel block, current-voltage converting block, and switching block. Unlike the other usual methods of external compensation requiring double number of connections between driver IC and glass, by using the common ramping signal and a simple circuit made on glass, the proposed method can be implemented with only one pin per column.