MSc Dissertation: Lerato Mohapi


Adobe-PDF-downloadMohapi, Lerato Jerfree. An FPGA-based Digital Triggering System with Model-Integrated Configuration Environment for the Control of NIM Electronics. MSc Dissertation. Department of Electrical Engineering, University of Cape Town, 2012.



Nuclear Instrumentation Module (NIM) is a standard that defines mechanical and electrical specifications for electronic modules used in experimental particle and nuclear physics. Together with other standard analogue electronics such as pre-amplifiers, NIM electronics are used to acquire the electrical charge pulses generated by detectors, extract the quantities of interest and convert them into a digital format for processing. Detectors normally generate large volumes of data thus making it difficult for these electronic modules to cope in processing of this data. Although general purpose computers are becoming more parallel and their processing throughput continues to increase, these systems remain unsuited to the high processing rates and large data volumes for real-time processing of nuclear physics experiments.

This dissertation presents a project to develop a real-time trigger that is hardware reconfigurable, triggering on user specified events, and captures data for permanent storage and later processing. This triggering platform is planned to replace previous analogue triggering systems that involve time-consuming manual tasks of connecting analogue electronics with NIM components. These manual tasks involve a multitude of wiring connections and their timings are error prone. Multiple on-going experiments could not time-share the expensive NIM electronics, implying lengthy waits between experiments and inefficient resource usage. The new triggering platform provides significant time saving for physicists setting up experiments, together with a model-based system that speeds up the design and setting-up of  experiments, while also reducing the wear and tear of dismantling and connecting equipment.

The research methodology involved studying manual processes used by physicists and engineers to set up experiments. The new triggering platform, which automates parts of these manual processes, was tested experimentally using radioactive sources and its results compared the same experiment using the old system. Experiments to test the new system used 22Na radioactive sources, and the electronics involved were represented as blocks in the Scilab model. On average, the VHDL code was generated in 50ms, synthesized in 16s, installed on the FPGA in less than 5s. Initial experiments showed timing problems, particularly long latencies and jitter.

Solutions for these problems are briefly described in this dissertation. The synthesis results for iThemba LABS AFRODITE experimental model demonstrated space optimized VHDL code generation by occupying 10% of total FPGA LEs. These results showed that the new triggering platform allows time-sharing of multiple electronics in small to large nuclear experiments. Therefore user requirements were met in this project.


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