Transformada de fourier

29th International Cosmic Ray Conference Pune (2005) 8, 61–64

16-point Discrete Fourier Transform based on the Radix-2 FFT algorithm implemented into Cyclone FPGA as the UHERC trigger for horizontal air showers
Z. Szadkowski
(a) University of Ł´ d´, Pomorska 151, 90-236 Ł´ d´, Poland. o z o z (b) Bergische Universit¨ t Wuppertal, Fachbereich C - Physik, D-42097 Wuppertal, Germany a

Presenter: Z. Szadkowski ([e-mail]), ger-szadkowski-Z-abs1-he15-oral

Extremely rare flux of UHERC requires sophisticated detection techniques. Standard methods oriented on the typical events may not be sensitive enough to capture rare events, crucial to fix a discrepancy in the current data or to confirm/reject some new hypothesis. Currently used triggers in water Cherenkov tanks, selecting events above some amplitude thresholds or investigating a length of traces seems to be not optimized for the horizontal and very inclined showers, interesting as potentially generated by neutrinos. Those showers could be triggered using their signatures: i.e. a curvature of the shower front, transformed on the rise time of traces or muon component giving early peak for ”old” showers. Currently available powerful and costeffective FPGAs provide sufficient resources to implement new triggers not available in the past. The paper describes the implementation of 16-point Discrete Fourier Transform based on the Radix-2 FFT algorithm into Altera Cyclone FPGA. All complex coefficients are calculated online in heavy pipelined routines. The register performance 200 MHz and relatively low resources occupancy 2000 logic elements for 10-bit FADC traces provide a powerful tool to trigger the events on the traces characteristic in the frequency domain.
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Introduction

Extensive Air Showers are investigated in several experiments utilizing different detection techniques (scintillators, water Cherenkow detectors, fluorescence detectors). Signals in detectors depend on several