Owning Palette: Advanced FIR Filter Design VIs
Requires: Digital Filter Design Toolkit
Creates an equi-ripple filter using the Remez exchange method.
|minimum order specifies whether this VI uses the filter order you specify or calculates the minimum filter order. The default is User Defined. If you select MinEven or MinOdd, this VI ignores the order input and determines the minimum required filter order. You also must provide a ripple constraint for each band in the ripple constraint input of band specs.
|filter type specifies the type of filter that this VI creates.
|order specifies the filter order. The value of order must be greater than zero. The default is 20. order +1 equals the number of coefficients or filter taps. Increasing the value can narrow the transition band.|
|band specs specifies the target frequency response that the filter frequency response fits. Each element of the array represents one frequency band specification. You can enter one or more points in ascending order to describe the frequency response in each band. This VI connects the points to form the continuous ideal frequency response for the band. The frequency range between two consecutive bands is a transition band. The frequency response you describe with the band specs input is the signed amplitude response. You can provide negative target amplitude values. However, if the filter type input is Minimum Phase or Maximum Phase, the frequency response you describe with the band specs input is the magnitude response, and all target amplitude values must be positive.
|freqs of exact gain specifies frequency points where the amplitude must have exactly the same value as the amplitude input in band specs. If a frequency point does not appear in band specs, this VI interpolates the amplitude linearly.|
|error in describes error conditions that occur before this node runs. This input provides standard error in functionality.|
|fs specifies the sampling frequency in hertz. The value must be greater than zero. The default is 1, which is the normalized sampling frequency.|
|filter out returns a new filter.|
|actual ripples returns the actual ripple magnitude in each band specified in band specs.|
|error out contains error information. This output provides standard error out functionality.|
In the Remez exchange method, the filter frequency response best fits the target response in the Chebyshev sense. The Remez Design VI employs either complex approximation or magnitude approximation to create the design.
The design criterion for complex approximation is defined by the following equation:
The design criterion for magnitude approximation is defined by the following equation:
where D(wi) is the ideal frequency response, H(wi) is the frequency response of the designed filter, and W(i) is the positive weight at the ith frequency point. Symmetric, Antisymmetric, Differentiator, and Hilbert filter types use complex approximation. Minimum Phase and Maximum Phase filter types use magnitude approximation.
Refer to the following VIs for examples of using the DFD Remez Design VI: