Altera FFT MegaCore Function - Manual (Page 47)

Figure 4-1: Scaling of Input Data Sample = 0x5000
Unity Gain in an IFFT+FFT Pair
Given sufficiently high precision, such as with floating-point arithmetic, it is theoretically possible to
obtain unity gain when an IFFT and FFT are cascaded. However, in BFP arithmetic, special attention
must be paid to the exponent values of the IFFT/FFT blocks to achieve the unity gain. This section
explains the steps required to derive a unity gain output from an Altera IFFT/FFT MegaCore pair, using
BFP arithmetic.
BFP arithmetic does not provide an input for the exponent, so you must keep track of the exponent from
the IFFT block if you are feeding the output to the FFT block immediately thereafter and divide by N at
the end to acquire the original signal magnitude.
UG-FFT
2014.12.15
Unity Gain in an IFFT+FFT Pair 4-5
Block Floating Point Scaling Altera Corporation
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