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Xilinx FIR Compiler Data input/output format


Xilinx FIR Compiler Data input/output format

I would like for the FPGA Xilinx FIR compiler/filter to take fixed point 1.31 (32-bit) data as input and output. In the attached display capture you see my data path settings. Unfortunately, the output is fixed point 32.0, not 1.31 (even 2.30 as indicated in the attached figure would be fine).

How do I have 1.31 in and 1.31 out?

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Re: Xilinx FIR Compiler Data input/output format

Hi rykowski,


I looked at the FIR compiler documentation and noticed the following on page 59:

For this example the coefficients are signed with a coefficient width of 10 bits and a coefficient fractional width of 5 bits (using the Mathworks Fix format notation Fix10_5). The specified coefficients range between -12.34 and +13.88. Considering the coefficient bit width as integer only, 10 bits give a maximum positive value of 511 and a maximum negative value of -512. The fractional bit width is 5 bits; this gives a maximum representable positive number of 511/(2^5)=15.96875 and a maximum representation negative number of -512/(2^5)=-16. All coefficients are scaled by the factor 15.96875/13.88=1.1504863 (=+1.2176dB) prior to quantization. The overall scaling factor is calculated as defined previously and displayed in the Vivado IDE.

It looks like fix32_30 as you have in your screenshot represents 1 bit for the sign, 1 bit for the coefficient width and 30 bits for the fractional width. Have you tried making the input and output signed? I would contact xilinx and see what they have to say about how to define the FIR compiler.

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