A FPGA-Based Architecture for Real-Time Cluster Finding in the LHCb Silicon Pixel Detector
G. Bassi, L. Giambastiani, K. Hennessy, F. Lazzari, M. J. Morello, T. Pajero, Antonio Fernández Prieto, G. Punzi
Abstract
This article describes a custom [very high speed integrated circuits (VHSIC) hardware description language (VHDL)] firmware implementation of a 2-D cluster-finder architecture for reconstructing hit positions in the new vertex pixel detector that is part of the large hadron collider beauty (LHCb) Upgrade. This firmware has been deployed to the existing field-programmable gate-array (FPGA) cards that perform the readout of the VErtex LOcator detector (VELO), as a further enhancement of the data-acquisition (DAQ) system, and will run in real-time during physics data taking, reconstructing VELO hits coordinates on-the-fly at the LHC collision rate. This preprocessing allows the first level of the software trigger to accept an 11% higher rate of events, as the ready-made hit coordinates accelerate the track reconstruction and consume significantly less electrical power. It additionally allows the raw pixel data to be dropped at the readout level, thus saving approximately 14% of the DAQ bandwidth. Detailed simulation studies have shown that the use of this real-time cluster-finding does not introduce any appreciable degradation in the tracking performance in comparison to a full-fledged software implementation. This work is part of a wider effort aimed at boosting the real-time processing capability of HEP experiments by delegating intensive tasks to dedicated computing accelerators deployed at the earliest stages of the data acquisition chain.