New Development on Digital Architecture for Efficient Pixel Readout ASIC at Extreme Hit Rate for HEP Detectors at HL-LHC

A novel region-based pixel digital architecture for latency buffering and trigger matching able to withstand extended trigger latencies and unprecedented data rates at the High-Luminosity LHC upgrade is presented. The architecture features above 99.5% efficiency at nominal 3 GHz/cm2 pixel hit rate and 1 MHz trigger rate with 12.5 μs trigger latency foreseen at HL-LHC. The overall inefficiency is dominated by dead-time in analogue front-end channels. The digital architecture is organized in pixel regions composed of 4×4 pixels. Charge information is retrieved from each pixel by means of Time-over-Threshold (ToT) using 5-bit counters. A common digital logic shared among pixels stores hits information for the whole trigger latency, handles the local configuration, performs trigger matching and sends zero-suppressed hit data to the chip periphery upon a trigger request. Data compression based on priority queues has been introduced in order to save area and power in the pixel region. The logic has been implemented in a commercial 65 nm CMOS pixel ASIC demonstrator prototyped as part of the Italian INFN CHIPIX65 project. Design specifications, implementation details and simulation results are discussed.