| The vast majority of commercially available flat panel digital x-ray imagers are based on flat panel amorphous silicon (a-Si) thin film transistor (TFT) switch pixels that are derived from active matrix liquid crystal display (AMLCD) technology. In this thesis, we develop on-pixel analog-to-digital converters (A/D's) as alternate pixel architectures for large area digital x-ray imagers to incorporate off-panel components into the on-panel integrated circuit. The higher level of integration can lead to lower complexity and costs, higher speeds and better imager performance. Different voltage controlled oscillators (VCOs) were considered in this thesis including an LC tank oscillator, a relaxation oscillator, and a ring oscillator. Ring oscillators became the choice for on-pixel A/D's in this thesis due to their compact nature and higher frequency output for amorphous silicon thin film transistor based circuits. Measured results for voltage to frequency gain and estimations of phase noise and metastability are presented.;Keywords. Medical x-ray imaging, flat panel detector, thin film transistor, amorphous silicon, high dynamic range. |
