# DIF based FFT scaling for OFDM Input

I'm working on XILINX FFT IP(PG109) in pipeline mode, which uses radix 2 DIF Lattice to perform FFT/IFFT operation. How to perform scaling of each stage in FFT, such that the effect of saturation or underflow will be less?

Input Data: An OFDM Symbol from channel.

My work : 1) Data growth will be due to addition/subtraction and rotation of vector done by twiddle factor.

2) Because of addition/subtraction there will 1 bit growth(when extreme values involves)

FOR DIF ARCHITECTURE BIT GROWTH IN LAST TWO STAGES IS PURELY DUE TO ADDITION/SUBTRACTION AS TWIDDLE VALUES ARE +/-1, +/-j.

3) For rest first N-2 stages, data grows as per note 1 . The max. real/imaginary can go to 2*sqrt(2).

4)Always data growth in every stage can't lead to overflow.(when input values are small).

But that leads to over scaling of the magnitude and if the input $$x[n]$$ has low amplitude, then the accumulation at few stages might become 0 after this division by 2.