Documentation

Variable Rate CIC Filters

Supported Variable Rate CIC Filter Types

The coder supports HDL code generation for variable rate CIC filters, including the following filter types:

  • CIC Decimators (dsp.CICDecimator, mfilt.cicdecim)

  • CIC Interpolators (dsp.CICInterpolator, mfilt.cicinterp)

  • Multirate cascade with one CIC stage (mfilt.cascade)

Code Generation Options for Variable Rate CIC Filters

A variable rate CIC filter has a programmable rate change factor. It is assumed that the filter is designed with the maximum rate expected, and that the Decimation Factor (for CIC Decimators) or Interpolation Factor (for CIC Interpolators) is set to this maximum rate change factor.

Two properties support variable rate CIC filters:

  • AddRatePort: When AddRatePort is set 'on', the coder generates rate and load_rate ports. When the load_rate signal is asserted, the rate port loads in a rate factor.

  • TestbenchRateStimulus: Specifies the rate stimulus. If you do not specify TestbenchRateStimulus, the coder uses the maximum rate change factor specified in the filter object.

You can also specify these properties in the GUI using the Add rate port checkbox and the Testbench rate stimulus edit box, shown in the following figures.

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