A stable n-channel mirrorable current source for versatile analog design with thin film transistors

Amorphous silicon (a-Si:H) thin film transistors (TFTs) are widely used as the active element in large area sensor and display systems. Circuit design with the TFT is constrained by the absence of p-channel devices, and thereby a current source, due to low device mobility. Moreover, the device is also prone to a bias dependent threshold voltage instability. We present a mirrorable current source built with only n-channel devices, which is immune to the variation in threshold voltage, thereby effectively increasing the application spectrum of the TFT