CMOS MAPS With a Novel Readout Scheme for High Luminosity Particle Colliders

The Super Tau-Charm Facility (STCF) is a proposed electron-positron collider producing a data sample over 50 times higher than present tau-charm factory Beijing Electron Positron Collider (BEPCII). The inner tracker (ITK) of STCF should have low material budget, as well as the capabilities for position, time, and charge measurement. One of its alternative options is semiconductor detector based on monolithic active pixel sensor (MAPS). The power consumption of MAPS needs to be sufficiently low (<100 mW/cm2) to meet the requirement of low material budget, which is in conflict with the requirement to enhance timing resolution. A novel readout scheme based on super pixels has been developed to satisfy these requirements. On the one side, it uses voltage-controlled oscillator (VCO) in super pixels to record time-of-arrival (ToA) at 500 MHz with extremely low static power consumption. On the other side, the discrimination outputs of the nonadjacent subpixels are combined through <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">or</small> gates which avoid the loss of ToA and time-over-threshold (ToT) caused by <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">or</small> gates. A group address is read out simultaneously to prevent degradation of position resolution caused by channels merging. A readout model based on MATLAB has been established. According to simulation, data loss is kept to less than 1% until the hit rate exceeds 8.5 MHz/cm2, which corresponds to more than 10 times average counting rate of STCF ITK. According to simulation, the matrix digital power is lower than 30 mW/cm2 while timing resolution of ToA is 2 ns.