Filter Design Toolbox

To Scale Transfer Function Coefficients

To scale the transfer function coefficients of a filter in FDATool, follow these steps:

1. Design a filter, or import a filter into FDATool. This is your reference filter.

1. Under Current Filter Information, the characteristics of your filter are structure, source, order, and whether the filter is stable.

2. Click Set Quantization Parameters.

1. The bottom half of the FDATool window (the quantization region) shows the options for quantizing a filter, including options for scaling filter transfer function coefficients and setting the property values for the quantization properties of the filter.

3. Select Turn quantization on to quantize the filter in Current Filter Information.

1. You can review the transfer function coefficients for your filter. Select View Filter Coefficients from the Analysis menu. The analysis area changes to list the coefficients for the reference and quantized filters. Scroll through the list to review the coefficients and to check for coefficient overflow or underflow that can occur during quantization.

   Notice that the left column in the analysis area contains symbols. They indicate whether the quantized coefficient over- or underflowed during quantization. A minus sign signals that the coefficient on that line overflowed toward positive infinity. A plus sign indicates an overflow toward negative infinity. Coefficients marked with zero had reference values that underflowed to zero.

4. Click Scale transfer-fnc coeffs <=1.
5. Review the scaled coefficients to see that no overflow warning appears at the end of the list of coefficients

• Warning: 1 overflow in coefficients.
  

1. and no plus, zero, or minus symbols appear in the left column.

Once you have scaled a filter, you cannot remove the scale factors. You must recreate the filter from the beginning by redesigning or reimporting the filter.

Scaling Transfer Function Coefficients

Scaling Inputs and Outputs of Quantized Filters