On-panel analog output buffer for data driver with consideration of device characteristic variation in LTPS technology

Abstract

A class-A analog output buffer for the data driver with consideration of device variation in low temperature poly-silicon (LTPS) technology is proposed. With high enough mobility, LTPS thin-film transistor (TFT) has been suitable for the realization with driver circuits on the LCD panel to meet system-on-panel (SoP) applications. However, the device characteristics of poly-Si TFTs have poor uniformity and suffer from huge variations in different locations due to the poly-silicon grain structures. Besides, the variation on device characteristic of the N-type TFT is much worse than that of P-type TFT. Therefore, replacing the critical part of the analog circuit by P-TFTs is a good design solution for suppressing device characteristic variation in order to improve manufacturing yield of the analog circuit on panel. A class-A output buffer realized with P-TFTs as the input stage has been designed and fabricated in a 8-mu m LTPS technology. From the experimental results, this proposed analog output buffer with P-TFTs as input stage can be operated at 50-kHz operation frequency with at least a 1-to-9 V output swing for using in the on-panel data drivers to provide a uniform brightness and high resolution display.