Fixed Point Model - 2023.2 English

Vitis Libraries

Release Date
2023-12-20
Version
2023.2 English

Once working with the fixed point model, the recommended scaling mode to start with is SSR_FFT_NO_SCALING. The input bit-widths should be selected as follows. Create an initial fixed point model with type ap_fixed<WL, IL>. The overall input type is std::complex <ap_fixed<WL, IL>, essentially storing the real and imaginary parts of the input. These parts are:

  • IL: Integer bits, selected based on the input range
  • WL: Word Length = IL + FL, where FL is the Fraction Bit Width, selected based on input resolution

In this case, 1-D SSR FFT internally does not use any scaling because of scaling mode selection. Therefore, no potential scaling errors will be seen at the output. With scaling mode set to no scaling, you can experiment with other fixed point parameters such as integer bits and fraction bits used to represent the input samples. The simplistic approach would be to select bits required to represent the input based on the input range and resolution but depending on the other input characteristic user can optimize these bit widths.