Design of analog-to-digital converters for energy sensitive hybrid pixel detectors

An important feature of hybrid semiconductor pixel detectors is the fact that detector and readout electronics are manufactured separately, allowing the use of industrial state-of-the-art CMOS processes to manufacture the readout electronics. As the feature size of these processes decreases, faster and more complex electronics can be designed and manufactured. Furthermore, most new CMOS processes are optimised for use with digital circuits, making the design of precise analog electronics a difficult task. Hence, the sooner the data is converted to the digital domain, the better the technology can be used. We have studied the possibility of adding energy sensitivity to the single photon counting capability of pixel detectors. To know not only the number of X-ray photons but also their energies (or wavelenghts), will increase the information content of the resulting image, given the same X-ray dose. In order to do this, a small and low power ADC is added to each pixel. We have studied different types of analog-to-digital converters that can be implemented inside the pixel electronics of a pixel detector.