Design of polysilicon TFT operational amplifier for analog TFT AMLCD driver

Poly-crystalline silicon (poly-Si) thin film transistor (TFT) technology is very suitable for driving active matrix LCD panel as the driver circuit and the panel can be integrated on the the same substrate. However, the large variation of threshold voltage of poly-Si TFT across the wafer makes it difficult to obtain amplifiers with constant gain and phase margin. An operational amplifier with characteristics independent of threshold voltage variation is presented in this paper. In HSpice simulation with threshold voltage varying from 2 V to 4 V, gain variations were reduced from 50% to 3% and phase margin variations were reduced from 10/spl deg/ to 0.37/spl deg/ in the proposed amplifier.