Leakage-Prevention Mechanism to Maintain Driving Capability of Compensation Pixel Circuit for Low Frame Rate AMOLED Displays

Abstract

A new leakage-prevention pixel circuit is proposed to maintain the driving capability of its driving thin-film transistors (TFTs) at a low frame rate of 15 Hz for use in active-matrix organic light-emitting diode (AMOLED) displays. The proposed leakage-prevention mechanism generates a compensating leakage current that reduces the source-to-drain voltage of the switching TFT, thereby lessening the fluctuation of the stored driving voltage when the frame rate is reduced from 60 to 15 Hz. Moreover, the proposed circuit can compensate for the threshold voltage variation in low-temperature polycrystalline silicon TFTs (LTPS TFTs) and current–resistance drops in VDD lines. To validate the performance of the compensation and leakage prevention, simulation models based on the measurement of the fabricated LTPS TFTs and an organic light-emitting diode (OLED) are established. The experimental results confirm that the leakage current of the gate node is successfully suppressed from 50.34 to 1.25 pA by the proposed leakage-prevention mechanism. Also, within the long emission period, the highly uniform OLED currents at low, medium, and high gray levels are achieved, verifying the feasibility of the proposed pixel circuit.