How would one minimize quantization error in radix-8 based FFT?

Started by Mr. Ken February 7, 2007
My design is 4096-point FFT, which splits into 4 stages of radix-8 FFT.
The system twiddle factor is 15-bits and gives acceptable quantization
However the design is bogged down by the trivial twiddle factor within
W81 = 2 * pi * 1/8 = 0.707, which can be reasonably done with 181/256.

However the quantization of 181/256 causes system quantization error from
to 30+dB, and this error absorbed quantization error variations with system
factors varying between 13~20bits.

Consideration is the system memory (4096 point, 13b) won't be widdened to
accomodate this 0.707.

Are there any means to fix this problem?