Fast Fourier Transform provision appts. for multicarrier telephony transport - twiddle-factor look-up table coupled to N multiplier inputs with RAM storing transform points for multiplication by real and imaginary components of twiddle factor

摘要

The FFT appts. includes a radix-N core. The radix-N core includes at least N multipliers and a twiddle-factor lookup table storing complex twiddle factors. The table is coupled to an input of each one of the multipliers. A conventional RAM stores transform points and is coupled to another input of each one of the multipliers. An array of at least N*N adder-subtractor-accumulators. A set of holding latches hold real and imaginary portions of a first transform point. Fetches of real and imaginary portions of the first twiddle factor from the look-up table are interleaved. The real portion of the twiddle factor is multiplied by the real and imaginary portions of the first transform point. Further multiply operations in the N multipliers multiply the imaginary portion of the twiddle factor by the real and imaginary portions of the first transform point.