AMOLED driving circuit with subthreshold current compensating capability for high PPI display panel

In this paper, we presents an external compensating driving circuit using the novel sentinel voltage control method for active-matrix organic light-emitting diode (A MOLED) displays. The pixel driving current is gradually increased by the ramp voltage at gate and converted to voltage in real time. When the sensed voltage is equal to the sentinel voltage, the gate voltage stops changing. Thus, the gate voltage is pinched at the value corresponding to the target driving current. The pixel contains only three thin-film transistors (TFTs) and one capacitor, which is suitable for high PPI display. Owing to the small area of the high PPI pixel, the driving TFT may operate at the low level current, even in the subthreshold region where the current exponentially varies with its gate voltage.