The Timepix chip evolved from the Medipix2 development. The pixels have identical size to those of Medipix2 but the functionality within each pixel has been changed. In Timepix each pixel can be programmed to count hits like Medipix2, or to record Time-Over-Threshold (providing rough analog information), or to measure arrival time of the first particle to impinge on the pixel. The Timepix development was driven by the requirements for TPC readout and supported by the EUDet project.
The Timepix chip