Investigation of source-follower type analog buffer using low temperature poly-Si TFTs

A new source follower circuit using low-temperature polycrystalline silicon thin film transistors (LTPS-TFTs) as analog buffer for the integrated data driver circuit of active matrix liquid crystal displays (AMLCDs) and active matrix light emitting diodes (AMOLEDs) is proposed and measured. Threshold voltage compensation circuit with two n-type thin film transistors, a capacitor, and four switches structure is used to enhance image quality for the display. The threshold voltage difference of driving TFTs and the unsaturated of output voltage are eliminated in this circuit. An active load is added and a calibration operation is applied to study the effects on the source follower circuit, the transistor operation mode region is also discussed. The proposed circuit is capable of minimizing the variation from both the signal timing and the device characteristics through the simulation and measured results.