The Study of Digital Filtering on VLBI Data Acquisition

A digital filter for bandwidth selection has obvious advantages on VLBI (Very Long Baseline Interferometry)data acquisition compared with the analog filter. This paper first reviews the development of digital filtering on VLBI data acquisition in Japan and NRAO (the National Radio Astronomy Observatory), then proposes two kinds of systematic implementation of digital filtering.The key factor to implement a filter is the speed of processing signals because of many high-speed arithmetic operations required.Reducing the computation time of digital filtering is important.The filter utilizes RAM look-up tables for tap weight multiplications.Three kinds of structures to realize the digital filter are compared here.Afterwards, the two kinds of systematic implementations are discussed in detail. With a steady advance in the technology of very high-density VLBI integrated circuits in recent years, FPGAs (Field Programmable Gate Array Integrated Circuits)are developed fast and have been proved to be powerful in many fields of digital signal processing.Finally, this paper gives a hardware layout to implement digital filtering based on FPGAs.