To start a design, you first choose from one
of the two available interactive design tools by making a selectionfrom the tree control on the left side of the interface. Select
Classical Design to design a filter based on specifications such aspassband / stopband edge frequencies, passband ripple, and stopband
attenuation. Select Pole-Zero Placement to design a filter byspecifying the locations of poles and zeros on the complex
plane.
The following sections detail how to work
with each alternative.
Classical filter design
This tool allows you to design multiple digital filter
types by adjusting the filter specifications manually orby interactively changing the passband and stopband cursors in the magnitude vs.
frequency graph. As the cursors move, the pole/zero plot and the text based interface change dynamically toset the values for the desired filter.
Digital filter design utility
The Classical Filter Design Interface
Classical filter parameter descriptions
Filter Type: Specifies the type of filter you want. The
default is a lowpass filter type. You also can select a highpass,bandpass, or bandstop filter type.
Filter specification
Sampling Frequency [Hz]: Specifies the sampling frequency ofthe filter in hertz
Passband Edge Frequency [Hz]: Specifies the first passband
edge frequency of the filter in hertz.
Passband Edge Frequency [Hz]: Specifies the second passband
edge frequency of the filter in hertz. This option does not appearfor lowpass or highpass filters.
Passband Ripple: Specifies the passband ripple of the filter
in units determined by the Magnitude in dB option.
Stopband Edge Frequency [Hz]: Specifies the first stopband
edge frequency of the filter in hertz.
Stopband Edge Frequency [Hz]: Specifies the second stopband
edge frequency of the filter in hertz. This option does not appearfor lowpass or highpass filters.
Stopband Attenuation: Specifies the stopband attenuation of
the filter in units determined by the Magnitude in dBoption.
Design Method: Specifies the method of filter design. The
default is Elliptic. You also can select Butterworth, Chebyshev,Inverse Chebyshev, Kaiser Window, Dolph Chebyshev Window, and Equi
Ripple FIR filter designs. Elliptic, Butterworth, Chebyshev, andInverse Chebyshev designs are IIR filter designs. Kaiser Window,
Dolph Chebyshev Window, and Equi Ripple FIR designs are FIR filterdesigns.
Design feedback
Filter Order: Returns the order of the designed filter. For
FIR filters, order +1 equals the number of coefficients or filtertaps.
Error Message: Contains details about errors that occur
during filter creation.
Magnitude in dB: Specifies whether the VI uses decibels or a linear scale to express the magnitude response and for entry of the Passband and Stopband Attenuation input parameters. If checked, the VI converts linear magnitude response to decibels.
Passband: Specifies the color of the lines in the magnitude
plot that represent the passband response and the passbandfrequencies. The default is blue. Click the color box next to the
parameter name to select a different color.
Stopband: Specifies the color of the lines in the magnitude
plot that represent the stopband attenuation and the stopbandfrequencies. The default is red. Click the color box next to the
parameter name to select a different color.
Magnitude: Contains the plot of the magnitude response. You
can drag the cursors in the plot to change the specifications. Thecolor you specify in passband represents the passband response and
the passband frequencies. The color you specify in stopbandrepresents the stopband attenuation and the stopband frequencies.
The green vertical line in the graph represents the half samplingfrequency, also known as the Nyquist frequency.
Z Plane: Contains the plot of the zeroes and poles of the
filter in the Z plane.
