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Butterworth Coefficients Express VI

LabVIEW 2011 FPGA Module Help

Edition Date: June 2011

Part Number: 371599G-01

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Owning Palette: Scaling VIs

Requires: FPGA Interface

Generates filter coefficients for the Butterworth Filter Express VI. Use this VI in a host VI.

Note  Large changes to inputs during run time cause invalid states and instability in the Butterworth Filter Express VI. Change the inputs gradually or reset the filter after changing the inputs.

Dialog Box Options
Block Diagram Inputs
Block Diagram Outputs

Dialog Box Options

ParameterDescription
Filter SpecificationsContains the following options:
  • Type—Specifies whether the filter type is Lowpass or Highpass.
  • Cutoff frequency (Hz)—Specifies the cutoff frequency of the filter. The allowable frequency range depends on the Expected sample rate you specify. The normalized cutoff frequency (Cutoff frequency/Expected sample rate) must be less than 0.5, which corresponds to the Nyquist frequency.
  • Expected sample rate (S/s)—Specifies the sample rate, in samples per second, of the input signal. This Express VI uses the rate you specify to calculate the normalized cutoff frequency, which is Cutoff frequency/Expected sample rate.
    Caution  The actual sample rate is specified elsewhere in the FPGA application. If the sample rate changes, you must change the Expected sample rate in this VI. Otherwise, this VI might not behave as expected.
  • Order—Specifies the filter order. You can select 1 (first-order), 2 (second-order), or 4 (fourth-order).
ImplementationContains the following options:
  • Number of channels—Specifies the number of channels to process. The number of channels must match the number of channels specified in the configuration dialog box for corresponding filter Express VI.
  • FPGA clock rate (MHz)—Specifies the design clock rate at which the compilation tools compile the FPGA VI.
Filter ResponseDisplays the actual magnitude response of the filter.

Block Diagram Inputs

ParameterDescription
cutoff frequency (Hz)Specifies the cutoff frequency of the filter in hertz. The default is 1000 Hz.
sample rate (S/s)Specifies the sampling rate of the signal in samples per second. The default is 50000 S/s.
error inDescribes error conditions that occur before this node runs.
channel indexSpecifies the index of the channel for the scaled coefficients configuration. This parameter is available only if the Number of channels option is greater than 1.

Block Diagram Outputs

ParameterDescription
scaled coefficientsReturns single-channel filter coefficients to load at run time. Scaled coefficients is a fixed-size array of 32-bit signed integers. The size of the array depends on the order you specify. You can select 1 (the array contains two elements), 2 (the array contains three elements), or 4 (the array contains six elements).

The filter coefficients must correspond to the filter type and order you specify using the Type and Order options in the Butterworth Filter Express VI. You cannot change the order or type of the filter at run time.

configurationReturns the scaled coefficients to load at run time for the channel index you specify using the channel index element of this cluster. This parameter is available only when you configure the VI such that Number of channels is greater than one.
error outContains error information. This output provides standard error out functionality.

 

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