Radix-4 Butterfly LSI in Direct-Imaging Waseda Radio Interferometer for a Pulsar Survey

In the Nyquist rate direct-imaging interferometer at Waseda University, a radix-4 butterfly LSI has been developed for the spatial-temporal (2+1)D FFT processor to survey pulsars. In (2+1)D FFT, the first 2D FFT is a 2D directional finding spatial FFT processing for an 8times 8 pixel image. The second 1D FFT is a 1D spectral finding temporal FFT processing for a 64ch frequency analysis in each 64 pixels. Since fewer multipliers are required in radix-4 FFT than in radix-2 FFT, we have implemented radix-4 algorithms in the present butterfly LSI. This implementation, using 512 radix-4 butterfly LSIs, could reduce the circuit size of the parallel and pipeline (2+1)D FFT processor. Additional functions, such as shift registers, digital filters and post-process sections, are also included in the LSI for a radio interferometric pulsar survey.