FPGA-Based DAQ System for Multi-Channel Detectors

In this article a data acquisition (DAQ) system is presented consisting of FPGA-based electronics and an object-oriented readout software that has been developed for the needs of multi-channel detectors. The design goal of the DAQ electronics was to develop an affordable and scalable multi-channel system that is flexible enough to be easily adapted to the experiment requirements. The analog circuitry is integrated on separate analog boards for easy adaptation to different experiments. The heart of the electronics is a hierarchical system of up to 81 FPGAs organized in three layers. It digitizes up to 480 channels with 12 bit ADCs at 10 to 40 MHz sampling rate. The electronics are interfaced by a PCI-bridge to a commercial Processor PMC board. The Object-oriented Real-time Control and Acquisition system (ORCA) contains drivers for the basic functions of the DAQ electronics. Only the experiment specific parts of the FPGA implementation needs to be changed for new applications. The power of a FPGA based DAQ electronics together with ORCA could be demonstrated by developing the detector readout of the Neutron Time Projection Chamber at Lawrence Livermore National Laboratory (nTPC within only 2 months - covering modification of the trigger logic in the FPGA, the readout drivers and design of nTPC specific ORCA dialogs. The DAQ electronics are currently used by four experiments: The fluorescence detector of the Pierre Auger Southern Observatory, the nTPC experiment, an ultrasound computer tomograph and the KATRIN neutrino experiment. The first part of the article introduces the concept and the features of the DAQ electronics and shows how it is integrated in the ORCA software. The second part focuses on the application of the DAQ electronics for the KATRIN experiment. The flexibility gained by the co-design of functions realized in hardware and software is demonstrated.