Electronic Design

An FPGA-Based Spectrometer For Solar Observation

When the Swiss Federal Institute of Technology in Zurich wanted to construct a spectral-analysis system for use in solar and stellar radio astronomy, it turned to Acqiris, a Geneva-based maker of data-acquisition systems. The goal is to build a continuously operating 1-GHz spectrometer based on purely digital methods and implemented in FPGAs.

This system would enable the analysis of a wide spectrum of radio emissions by digital transformation of the temporal variations in the radio signal. The technique also would allow for high-quality spectral observations at a much lower cost.

The project combines a high-speed sampler with the fast electronics of an on-board FPGA real-time processing system to be developed by Acqiris. The fast-Fourier transform (FFT) computation and spectra summation will be carried out without dead time. Thus, the FFT analyzer will be suitable for high-sensitivity measurements. The aim is a total bandwidth of 1 GHz in 32,768 frequency bins. The realization of such a high data rate on a large chip is a technological challenge.

Implementation of the analyzer was done in a Xilinx Virtex-2 Pro FPGA. The design team chose a pipelined FFT, which lent itself to FPGA implementation. On the Virtex-2 Pro device are 74,448 logic cells; 328 18-by-18 embedded multipliers; 328 18-kbit block RAMs; two hard-macro PowerPC 405 CPUs; and 12 Rocket I/O serial transceivers (see the figure).

Acqiris used Mentor Graphics' FPGA tool flow to develop the FFT analyzer. The device will first be used and tested by the group for Radio Astronomy and Plasma Physics at the Institute for Astronomy at ETH in a spectrometer for solar and stellar observations.

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