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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 filters are designed using the filter design commands in Signal Processing Toolbox™ software's buttap, cheb1ap, cheb2ap, and ellipap functions, 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 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
buttapSignal Processing Toolbox
cheb1apSignal Processing Toolbox
cheb2apSignal Processing Toolbox
ellipapSignal Processing Toolbox

See the following sections for related information:

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