Analog Filter Design (DSP Blockset)

Design and implement an analog filter.

Library

Filter Designs, in Filtering

Description

The Analog Filter Design block designs and implements a Butterworth, Chebyshev type I, Chebyshev type II, or elliptic filter in a highpass, lowpass, bandpass, or bandstop configuration. The block treats each element of the input as a distinct channel to independently filter over time.


Filter Design	Description
Butterworth	The magnitude response of a Butterworth filter is maximally flat in the passband and monotonic overall.
Chebyshev type I	The magnitude response of a Chebyshev type I filter is equiripple in the passband and monotonic in the stopband.
Chebyshev type II	The magnitude response of a Chebyshev type II filter is monotonic in the passband and equiripple in the stopband.
Elliptic	The magnitude response of an elliptic filter is equiripple in both the passband and the stopband.

The design and band configuration of the filter are selected from the Design method and Filter type pop-up menus in the dialog box. For each combination of design method and band configuration, an appropriate set of secondary parameters is displayed.

The table below lists the available parameters for each design/band combination. For lowpass and highpass band configurations, these parameters include the passband edge frequency

_p, the stopband edge frequency

_s, the passband ripple R_p, and the stopband attenuation R_s. For bandpass and bandstop configurations, the parameters include the lower and upper passband edge frequencies,

_p1 and

_p2, the lower and upper stopband edge frequencies,

_s1 and

_s2, the passband ripple R_p, and the stopband attenuation R_s. Frequency values are in rads/sec, and ripple and attenuation values are in dB.


	Lowpass	Highpass	Bandpass	Bandstop
Butterworth	Order, _p	Order, _p	Order, _p1, _p2	Order, _p1, _p2
Chebyshev Type I	Order, _p, R_p	Order, _p, R_p	Order, _p1, _p2, R_p	Order, _p1, _p2, R_p
Chebyshev Type II	Order, _s, R_s	Order, _s, R_s	Order, _s1, _s2, R_s	Order, _s1, _s2, R_s
Elliptic	Order, _p, R_p, R_s	Order, _p, R_p, R_s	Order, _p1, _p2, R_p, R_s	Order, _p1, _p2, R_p, R_s

The analog filters are designed using the Signal Processing Toolbox's filter design commands buttap, cheb1ap, cheb2ap, and ellipap, and are implemented in state-space form. Filters of order 8 or less are implemented in controller canonical form for improved efficiency.

Dialog Box

The parameters displayed in the dialog box vary for different design/band combinations. Only a portion of the parameters listed below are visible in the dialog box at any one time.

Design method: The filter design method: Butterworth, Chebyshev type I, Chebyshev type II, or Elliptic.
Filter type: The type of filter to design: Lowpass, Highpass, Bandpass, or Bandstop.
Filter order: The order of the filter, for lowpass and highpass configurations. For bandpass and bandstop configurations, the order of the final filter is twice this value.
Passband edge frequency: The passband edge frequency, in rads/sec, for the highpass and lowpass configurations of the Butterworth, Chebyshev type I, and elliptic designs.
Lower passband edge frequency: The lower passband frequency, in rads/sec, for the bandpass and bandstop configurations of the Butterworth, Chebyshev type I, and elliptic designs.
Upper passband edge frequency: The upper passband frequency, in rads/sec, for the bandpass and bandstop configurations of the Butterworth, Chebyshev type I, or elliptic designs.
Stopband edge frequency: The stopband edge frequency, in rads/sec, for the highpass and lowpass band configurations of the Chebyshev type II design.
Lower stopband edge frequency: The lower stopband edge frequency, in rads/sec, for the bandpass and bandstop configurations of the Chebyshev type II design.
Upper stopband edge frequency: The upper stopband edge frequency, in rads/sec, for the bandpass and bandstop filter configurations of the Chebyshev type II design.
Passband ripple: The passband ripple, in dB, for the Chebyshev Type I and elliptic designs.
Stopband ripple: The stopband attenuation, in dB, for the Chebyshev Type II and elliptic designs.

References

Antoniou, A. Digital Filters: Analysis, Design, and Applications. 2nd ed. New York, NY: McGraw-Hill, 1993.