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Equi-Ripple LowPass VI

LabVIEW 2013 Help

Edition Date: June 2013

Part Number: 371361K-01

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Owning Palette: Filters VIs

Requires: Full Development System

Generates a lowpass FIR filter with equi-ripple characteristics using the Parks-McClellan algorithm and the # of taps, pass freq, stop freq, and sampling freq: fs. The Equi-Ripple LowPass VI then applies a linear-phase, lowpass filter to the input sequence X using the Convolution VI to obtain Filtered X. Wire data to the X input to determine the polymorphic instance to use or manually select the instance.

Details  

Use the pull-down menu to select an instance of this VI.

Equi-Ripple LowPass (DBL)

X is the input signal to filter.
# of taps must be greater than 2. The default is 32. If # of taps is less than or equal to 2, the VI sets Filtered X to an empty array and returns an error through the Parks-McClellan VI.
pass freq must be greater than zero and observe the Nyquist criterion. The default is 0.2 Hz. If pass freq is less than or equal to zero or does not meet the Nyquist criterion, the VI sets Filtered X to an empty array and returns an error through the Parks-McClellan VI.
stop freq must be greater than the pass freq and observe the Nyquist criterion. The default is 0.3 Hz. If stop freq is less than or equal to pass freq or does not meet the Nyquist criterion, the VI sets Filtered X to an empty array and returns an error through the Parks-McClellan VI.
sampling freq: fs is the frequency in Hz at which you want to sample X and must be greater than 0. The default is 1.0 Hz.
Filtered X contains the result of filtering the input sequence X by convolution. This VI calculates the number of elements, k, in Filtered X using the following equation:

k = n + m – 1,

where n is the number of elements in X and m is the number of taps.

This VI also calculates the delay associated with the output sequence using the following equation:

error returns any error or warning from the VI. You can wire error to the Error Cluster From Error Code VI to convert the error code or warning into an error cluster.

Equi-Ripple LowPass (CDB)

X is the input signal to filter.
# of taps must be greater than 2. The default is 32. If # of taps is less than or equal to 2, the VI sets Filtered X to an empty array and returns an error through the Parks-McClellan VI.
pass freq must be greater than zero and observe the Nyquist criterion. The default is 0.2 Hz. If pass freq is less than or equal to zero or does not meet the Nyquist criterion, the VI sets Filtered X to an empty array and returns an error through the Parks-McClellan VI.
stop freq must be greater than the pass freq and observe the Nyquist criterion. The default is 0.3 Hz. If stop freq is less than or equal to pass freq or does not meet the Nyquist criterion, the VI sets Filtered X to an empty array and returns an error through the Parks-McClellan VI.
sampling freq: fs is the frequency in Hz at which you want to sample X and must be greater than 0. The default is 1.0 Hz.
Filtered X contains the result of filtering the input sequence X by convolution. The number of elements, k, in Filtered X is given by the following equation.

k = n + m – 1,

where n is the number of elements in X and m is the number of taps.

A delay is also associated with the output sequence, as given by the following equation.

error returns any error or warning from the VI. You can wire error to the Error Cluster From Error Code VI to convert the error code or warning into an error cluster.

Equi-Ripple LowPass Details

The passband of the filter goes from zero (DC) to pass freq. The transition band goes from pass freq to stop freq. The stopband goes from stop freq to the Nyquist frequency.

The values for pass freq and stop freq must observe the following relationship.

0 < f0 < f1 < 0.5fs

where f0 is pass freq, f1 is stop freq, and fs is sampling freq: fs. If you violate any of these conditions, this VI sets Filtered X to an empty array and returns an error through the Parks-McClellan VI.


 

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