Butterworth Order Estimation VI

Owning Palette: Advanced IIR Filtering VIs

Requires: Full Development System

Estimates the Butterworth filter order.

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	filter type specifies the type of filter that this VI creates. 0 Lowpass (default) 1 Highpass 2 Bandpass 3 Bandstop
	sampling freq: fs is the sampling frequency in hertz. The value must be greater than zero. The default is 1.0 Hz, which is the normalized sampling frequency.
	freq specs specifies the band edge frequencies of the filter in hertz. lower pass freq specifies the first passband edge frequency in hertz. lower stop freq specifies the first stopband edge frequency in hertz. higher pass freq specifies the second passband edge frequency in hertz. The VI ignores this input for lowpass and highpass filters. higher stop freq specifies the second stopband edge frequency in hertz. The VI ignores this input for lowpass and highpass filters.
	ripple specs specifies the ripple level in the passband and stopband of the filter. passband specifies the ripple level in the passband. The default is 0.1. stopband specifies the ripple level in the stopband. The default is 60. dB/linear? specifies whether this VI applies a decibel scale or a linear scale to the ripple levels. If the value is TRUE, this VI applies a decibel scale to the ripple level. If the value is FALSE, this VI applies a linear scale to the ripple level. The default is TRUE.
	error in describes error conditions that occur before this node runs. This input provides standard error in functionality.
	estimated order returns the minimum order value that the filter requires to meet the specifications you set.
	high cutoff freq returns the high cutoff frequency. The cutoff frequency corresponds to the half-power frequency or the 3 dB frequency.
	low cutoff freq returns the low cutoff frequency. The cutoff frequency corresponds to the half-power frequency or the 3 dB frequency.
	error out contains error information. This output provides standard error out functionality.

Butterworth Order Estimation Details

The Butterworth Order Estimation VI uses the formula below to estimate the order of a Butterworth filter:

where    N is the estimated order

A_p the passband ripple in dB

A_s is the stopband ripple in dB

[ ] means Round Toward +Infinity

Ω_p and Ω_s are calculated as:

Lowpass filter:

Highpass filter:

Bandpass filter:

Bandstop filter:

where the various Ω values equal as follows:

Related Information

Passband Ripple and Stopband Attenuation