Compensation Pixel Circuit to Improve Image Quality for Mobile AMOLED Displays

Abstract

This paper proposes a new pixel circuit using low- temperature polycrystalline silicon thin-film transistors (LTPS TFTs) for use in mobile active matrix organic light-emitting diode (AMOLED) displays. The purpose of a pixel circuit is to supply stable and uniform currents to current-driving devices of OLEDs. The proposed pixel circuit uses overlapping compensation times to extend the period of precise sensing of V TH variations of LTPS TFTs. Moreover, the proposed circuit prevents a current from flowing into an OLED when the OLED is not operated in the emission stage to avoid image flicker. An 1.3-in panel that uses the proposed pixel circuit is fabricated. Measurement results verify that the increased T COMP of 33.3 µs results in higher contrast ratio and lower required data voltages than those at T COMP values of 4.3 and 2.2 µs. Red, green, and blue images displayed by the fabricated panel with a TCOMP of 33.3 µs with a 255 gray level are all much more uniform than with TCOMPS of 4.3 and 2.2 µs. White images with a TCOMP of 33.3 µs for 16 and 8 gray levels on the fabricated panel confirm that the serious line and spot defects in the images with T COMP values of 4.3 and 2.2 µs are effectively eliminated. Therefore, the proposed pixel circuit is suitable for use in mobile AMOLED displays.