A high performance split-radix FFT with constant geometry architecture

High performance hardware FFTs have numerous applications in instrumentation and communication systems. This paper describes a new parallel FFT architecture which combines the split-radix algorithm with a constant geometry interconnect structure. The split-radix algorithm is known to have lower multiplicative complexity than both radix-2 and radix-4 algorithms. However, it conventionally involves an “L-shaped” butterfly datapath whose irregular shape has uneven latencies and makes scheduling difficult. This work proposes a split-radix datapath that avoids the L-shape. With this, the split-radix algorithm can be mapped onto a constant geometry interconnect structure in which the wiring in each FFT stage is identical, resulting in low multiplexing overhead. Further, we exploit the lower arithmetic complexity of split-radix to lower dynamic power, by gating the multipliers during trivial multiplications. The proposed FFT achieves 46% lower power than a parallel radix-4 design at 4.5GS/s when computing a 128-point real-valued transform.