SPRACN4 August   2019 66AK2G12 , 66AK2H06 , 66AK2H12 , 66AK2H14 , OMAP-L132 , OMAP-L138 , TMS320C6452 , TMS320C6454 , TMS320C6455 , TMS320C6457 , TMS320C6652 , TMS320C6654 , TMS320C6655 , TMS320C6657 , TMS320C6672 , TMS320C6674 , TMS320C6678 , TMS320C6742 , TMS320C6743 , TMS320C6745 , TMS320C6746 , TMS320C6747 , TMS320C6748

 

  1.   Using DSPLIB FFT Implementation for Real Input and Without Data Scaling
    1.     Trademarks
    2. 1 Real Input Introduction
      1. 1.1 Prerequisites
      2. 1.2 Computing a Length N/2 Complex FFT From a Length N Real Input Sequence
      3. 1.3 Returning to a Length N Real Sequence Using a Length N/2 Complex IFFT
      4. 1.4 Benchmark of the Efficient Compute of FFT
    3. 2 Fixed Point FFT With No Data Scaling
      1. 2.1 Suggested Change
      2. 2.2 Example Application
    4. 3 Summary
    5. 4 References

2 Fixed Point FFT With No Data Scaling

The FFT (DSP_fft16x16) and iFFT (DSP_ifft16x16) implementation provided with the C64x+ DSPLIB [1] apply scaling of data to avoid overflow. For more information, see the TMS320C64x+ DSP Little-Endian Library Programmer's Reference.

All stages are radix-4 except the last one, which can be radix-2 or radix-4, depending on the size of the FFT. All stages except the last one scale by two the stage output data.

It is desirable in certain use cases that the data scaling is not applied in the FFT routines. This article suggests modifications to the provided FFT source in the DSPLIB such that the data is not scaled. Also, an example is provided to demonstrate the affect of suggested change.