Process-independent analogue data driver for polysilicon TFT AMLCD

Polycrystalline silicon (poly-Si) thin film transistor (TFT) technology is very suitable for driving an active matrix LCD (AMLCD) panel as the driver circuit, and the panel can be integrated on the same substrate. This allows the entire display system to be thin and makes the concepts of `TV on wall' and `sheet computer' possible. However, the large variation of threshold voltage of poly-Si TFT across the wafer makes it difficult to obtain analogue amplifiers with constant gain and phase margin. In this paper, an analogue data driver for the poly-Si TFT AMLCD is proposed. An operational amplifier with a gate bias-voltage generation circuit for this analogue data driver, with characteristics independent of variations in threshold voltage, will be presented. In Hspice simulation, with threshold voltage varying from 2.5 V to 4.5 V, gain variations of the proposed amplifier were reduced from +/-10 dB to +/-0.2 dB and phase margin variations were reduced from 10degrees to 0.37degrees compared with typical operational amplifier design. This enables the analogue data driver for AMLCD to be implemented in poly-Si TFT technology