Filter Design Toolbox

Constructing a Quantized Filter from a Reference

In general you construct quantized filters from reference filters. You begin with a set of unquantized (or quantized) reference filter coefficients to implement in a quantized filter.

Suppose you design a quantized filter from a fourth-order elliptic filter. You can use the Signal Processing Toolbox filter design functions to help you. First, design a filter with parameters in transfer function form.

• [b,a] = ellip(4,3,20,.6); 
  

Filters designed with a second-order section topology are more robust against quantization errors than those composed of higher order transfer functions.

Converting a Filter to Second-Order Sections Form

You can construct a quantized filter in second-order sections form as follows:

1. Create a quantized filter using the elliptic filter's transfer function parameters as reference coefficients.

• Hq = qfilt('df2t',{b,a});
  

1. This filter is not in second-order sections form and has coefficient overflow.

2. Use sos to convert the filter to second-order sections form.

• Hq = sos(Hq);
  

Working with Quantized Filters

Copying Filters to Inherit Properties