Documentation

Analog Filter Design

Design and implement analog filters

Library

Filtering / Filter Implementations

dsparch4

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 input must be a sample-based, continuous-time, real-valued, scalar signal.

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.

Filter DesignDescription

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 following table lists the available parameters for each design/band combination. For lowpass and highpass band configurations, these parameters include the passband edge frequency Ωp, the stopband edge frequency Ωs, the passband ripple Rp, and the stopband attenuation Rs. For bandpass and bandstop configurations, the parameters include the lower and upper passband edge frequencies, Ωp1 and Ωp2, the lower and upper stopband edge frequencies, Ωs1 and Ωs2, the passband ripple Rp, and the stopband attenuation Rs. Frequency values are in rad/s, and ripple and attenuation values are in dB.

 LowpassHighpassBandpassBandstop
Butterworth

Order, Ωp

Order, Ωp

Order, Ωp1, Ωp2

Order, Ωp1, Ωp2

Chebyshev Type I

Order, Ωp, Rp

Order, Ωp, Rp

Order, Ωp1, Ωp2, Rp

Order, Ωp1, Ωp2, Rp

Chebyshev Type II

Order, Ωs, Rs

Order, Ωs, Rs

Order, Ωs1, Ωs2, Rs

Order, Ωs1, Ωs2, Rs

Elliptic

Order, Ωp, Rp, Rs

Order, Ωp, Rp, Rs

Order, Ωp1, Ωp2, Rp, Rs

Order, Ωp1, Ωp2, Rp, Rs

The Analog Filter Design block uses a state-space filter representation, and applies the filter using the State-Space block in the Simulink® Continuous library. All of the design methods use Signal Processing Toolbox™ functions to design the filter:

  • The Butterworth design uses the toolbox function butter.

  • The Chebyshev type I design uses the toolbox function cheby1.

  • The Chebyshev type II design uses the toolbox function cheby2.

  • The elliptic design uses the toolbox function ellip.

The Analog Filter Design block is built on the filter design capabilities of Signal Processing Toolbox software.

    Note:   The Analog Filter Design block does not work with the Simulink discrete solver, which is enabled when the Solver list is set to Discrete (no continuous states) in the Solver pane of the Model Configuration Parameters dialog box. Select one of the continuous solvers (such as ode4) instead.

Dialog Box

The parameters displayed in the dialog box vary for different design/band combinations. Only some 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. Tunable.

Filter type

The type of filter to design: Lowpass, Highpass, Bandpass, or Bandstop. Tunable.

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 rad/s, for the highpass and lowpass configurations of the Butterworth, Chebyshev type I, and elliptic designs. Tunable.

Lower passband edge frequency

The lower passband frequency, in rad/s, for the bandpass and bandstop configurations of the Butterworth, Chebyshev type I, and elliptic designs. Tunable.

Upper passband edge frequency

The upper passband frequency, in rad/s, for the bandpass and bandstop configurations of the Butterworth, Chebyshev type I, or elliptic designs. Tunable.

Stopband edge frequency

The stopband edge frequency, in rad/s, for the highpass and lowpass band configurations of the Chebyshev type II design. Tunable.

Lower stopband edge frequency

The lower stopband edge frequency, in rad/s, for the bandpass and bandstop configurations of the Chebyshev type II design. Tunable.

Upper stopband edge frequency

The upper stopband edge frequency, in rad/s, for the bandpass and bandstop filter configurations of the Chebyshev type II design. Tunable.

Passband ripple in dB

The passband ripple, in dB, for the Chebyshev Type I and elliptic designs. Tunable.

Stopband attenuation in dB

The stopband attenuation, in dB, for the Chebyshev Type II and elliptic designs. Tunable.

References

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

Supported Data Types

  • Double-precision floating point

See Also

Digital Filter DesignDSP System Toolbox
butterSignal Processing Toolbox
cheby1Signal Processing Toolbox
cheby2Signal Processing Toolbox
ellipSignal Processing Toolbox

See the following sections for related information:

Introduced before R2006a

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