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DFD Remez Design VI

LabVIEW 2013 Digital Filter Design Toolkit Help

Edition Date: June 2013

Part Number: 371988F-01

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Owning Palette: Advanced FIR Filter Design VIs

Requires: Digital Filter Design Toolkit

Creates an equi-ripple filter using the Remez exchange method.

Details  Examples

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.

0User Defined—Specifies to use the value in order.
1MinEven—Specifies to calculate the minimum even order value and use this value to design the filter.
2MinOdd—Specifies to calculate the minimum odd order value and use this value to design the filter.
filter type specifies the type of filter that this VI creates.

0Symmetric (default)—Creates a filter with a symmetric impulse response.
1Antisymmetric—Creates a filter with an antisymmetric impulse response. The Symmetric and Antisymmetric options determine the symmetry of the filter impulse response and consequently determine the symmetry of the zero phase frequency amplitude response specified by the band specifications.
2Differentiator—Creates a filter with an antisymmetric impulse response. This filter type differs from Antisymmetric by having an additional weighting of 1/ on amplitude response. This option uses a built-in weighting function that is inversely proportional to frequency to achieve a constant percentage error ripple versus the amplitude of the frequency response.
3Hilbert—Creates a filter with an antisymmetric impulse response that behaves in the same way as Antisymmetric.
4Minimum Phase—Creates a minimum phase filter. Minimum phase filters sometimes are called minimum energy delay or minimum delay filters. A minimum phase FIR filter has all the zeroes inside or on the unit circle of the z-plane.
5Maximum Phase—Creates a maximum phase filter. A maximum phase FIR filter has a time-reversed impulse response of a minimum phase filter, where the zeroes of a maximum phase filter are all outside or on the unit circle of the z-plane.
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.
freq specifies one frequency point in hertz.
amplitude specifies the amplitude on freq in linear scale.
weight specifies the relative importance of the ripple size. Increasing weight reduces the ripple size and brings the filter closer to the frequency response specified in freq. This VI linearly interpolates the weight values of the frequencies between points. For example, to design a lowpass filter whose passband ripple is half the stopband ripple, set the passband weight to 2 and the stopband weight to 1.
ripple constraint specifies the ripple constraint in the current band using linear scale. The default is 0, which means that no constraint is applied. If you enter a positive value, the ripple level in the current band will be at a level lower than the value you specify. You must leave at least one band unconstrained if you set minimum order to User Defined.
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.

DFD Remez Design Details

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.

Examples

Refer to the following VIs for examples of using the DFD Remez Design VI:

  • EquiRipple Filter Design - DFD VI: labview\examples\Digital Filter Design\AALXMPL
  • Advanced Remez FIR Filter Design VI: labview\examples\Digital Filter Design\Floating-Point Filters\Conventional
  • Arbitrary Shape Lowpass Filter Design VI: labview\examples\Digital Filter Design\Floating-Point Filters\Conventional

 

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