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DFD Butterworth Design VI

LabVIEW 2013 Digital Filter Design Toolkit Help

Edition Date: June 2013

Part Number: 371988F-01

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Owning Palette: Advanced IIR Filter Design VIs

Requires: Digital Filter Design Toolkit

Creates a digital Butterworth infinite impulse response (IIR) filter.

You can use the DFD Butterworth Order Estimation VI to estimate order.

Details  Examples

filter type specifies the type of filter that this VI creates.

0Lowpass (default)
1Highpass
2Bandpass
3Bandstop
order specifies the digital filter order. The value of order must be greater than zero. The default is 2. If you set filter type to Lowpass or Highpass, the digital filter order you specify must equal the analog prototype filter order. If you set filter type to Bandstop or Bandpass, the digital filter order you specify must be an even number that equals two times the analog prototype filter order. Increasing the value can narrow the transition band.
high cutoff freq specifies the high cutoff frequency in hertz. The value must be greater than low cutoff freq. The default is 0.45. This VI uses this input only for bandpass and bandstop filter design. The cutoff frequency that you specify corresponds to the half-power frequency or the 3 dB frequency.
low cutoff freq specifies the low cutoff frequency in hertz. The default is 0.12. The cutoff frequency that you specify corresponds to the half-power frequency or the 3 dB frequency.
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.
error out contains error information. This output provides standard error out functionality.

DFD Butterworth Design Details

Butterworth filters have the following characteristics:

  • Smooth frequency response at all frequencies and monotonically decreasing or increasing magnitude response in the transition band.
  • Maximally flat at frequencies of zero and one-half the sampling frequency.

Butterworth filters do not always provide an acceptable accurate approximation of the ideal frequency response because the filter has slow roll off in the transition band. Use Chebyshev, Inverse Chebyshev, or Elliptic filters to achieve a sharper roll off.

Examples

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

  • Extract the Sine Wave - DFD VI: labview\examples\Digital Filter Design\AALXMPL
  • IIR Filter Design - DFD VI: labview\examples\Digital Filter Design\AALXMPL

 

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