Analog Filter Design

Design and implement analog filters

• 

Libraries:
DSP System Toolbox / Filtering / Filter Designs

Description

The Analog Filter Design block designs and implements a Butterworth, Chebyshev type I, Chebyshev type II, elliptic, or bessel filter in a highpass, lowpass, bandpass, or bandstop configuration.

You select the design and band configuration of the filter from the Design method and Filter type drop-down lists in the dialog box. For each combination of design method and band configuration, an appropriate set of secondary parameters is displayed. For more details, see Design/Band Combination Table.

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

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 you set the Solver list 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.

Examples

Filter input with Butterworth Filter in Simulink

This example shows how to use the Analog Filter Design block.

Open the Simulink model.

model = "ex_analog_filter_design";
open_system(model);

The Analog Filter Design block returns the filtered input as a scalar. Run the model.

sim(model);

Extended Examples

Sigma-Delta A/D Conversion

Model analog-to-digital conversion by implementing a sigma-delta algorithm.

• Open Script

Ports

Input

Port_1 — Input signal

scalar

Input signal to filter, specified as a sample-based, continuous-time, real-valued scalar value.

Data Types: double

Output

Port_1 — Output signal

scalar

Filtered signal, returned as a real double scalar value.

Data Types: double

Parameters

Design method — Filter design

Butterworth (default) | Chebyshev I | Chebyshev II | Elliptic | Bessel

The filter design methods are:

• Butterworth — The magnitude response of a Butterworth filter is maximally flat in the passband and monotonic overall. The Butterworth design uses the toolbox function butter.

• Chebyshev I — The magnitude response of a Chebyshev I filter is equiripple in the passband and monotonic in the stopband. The Chebyshev I design uses the toolbox function cheby1.

• Chebyshev II — The magnitude response of a Chebyshev II filter is monotonic in the passband and equiripple in the stopband. The Chebyshev II design uses the toolbox function cheby2.

• Elliptic — The magnitude response of an elliptic filter is equiripple in both the passband and the stopband. The elliptic design uses the toolbox function ellip.

• Bessel — The magnitude response of a bessel filter is maximally flat in the passband and monotonic overall. The filter has a maximally flat linear phase response. The bessel design uses the function besself.

Tunable: Yes

Filter type — Filter type

Lowpass (default) | Highpass | Bandpass | Bandstop

The type of filter to design:

• Lowpass

• Highpass

• Bandpass

• Bandstop

Tunable: Yes

Filter order — Filter order

8 (default) | scalar value

The order of the filter when Filter type is set to:

• Lowpass

• Highpass

The order of the final filter is twice the value of Filter order when Filter type is set to:

• Bandpass

• Bandstop

.

Passband edge frequency (rad/s) — Passband edge frequency

30 (default) | scalar value

The passband edge frequency, in rad/s.

Tunable: Yes

Dependencies

This parameter appears only when Design method is set to:

• Butterworth

• Chebyshev I

• Elliptic

• Bessel

and Filter type is set to:

• Lowpass

• Highpass

Lower passband edge frequency (rad/s) — Lower passband edge frequency

30 (default) | scalar value

The lower passband edge frequency, specified in rad/s.

Tunable: Yes

Dependencies

This parameter appears only when Design method is set to:

• Butterworth

• Chebyshev I

• Elliptic

• Bessel

and Filter type is set to:

• Bandpass

• Bandstop

Upper passband edge frequency (rad/s) — Upper passband edge frequency

80 (default) | scalar value

The upper passband edge frequency, specified in rad/s.

Tunable: Yes

Dependencies

This parameter appears only when Design method is set to:

• Butterworth

• Chebyshev I

• Elliptic

• Bessel

and Filter type is set to:

• Bandpass

• Bandstop

Stopband edge frequency (rad/s) — Stopband edge frequency

30 (default) | scalar value

The stopband edge frequency, specified in rad/s.

Tunable: Yes

Dependencies

This parameter appears only when Design method is set to:

• Chebyshev II

and Filter type is set to:

• Lowpass

• Highpass

Lower stopband edge frequency (rad/s) — Lower stopband edge frequency

30 (default) | scalar value

The lower stopband edge frequency, in rad/s.

Tunable: Yes

Dependencies

This parameter appears only when Design method is set to:

• Chebyshev II

and Filter type is set to:

• Bandpass

• Bandstop

Upper stopband edge frequency (rad/s) — Upper stopband edge frequency

80 (default) | scalar value

The upper stopband edge frequency, specified in rad/s.

Tunable: Yes

Dependencies

This parameter appears only when Design method is set to:

• Chebyshev II

and Filter type is set to:

• Bandpass

• Bandstop

Passband ripple in dB — Passband ripple

2 (default) | scalar value

The passband ripple, specified in dB.

Tunable: Yes

Dependencies

This parameter appears only when Design method is set to:

• Chebyshev I

• Elliptic

Stopband attenuation in dB — Stopband attenuation

40 (default) | scalar value

The stopband attenuation, in dB.

Tunable: Yes

Dependencies

This parameter appears only when Design method is set to:

• Chebyshev II

• Elliptic

Block Characteristics

Data Types	double
Direct Feedthrough	no
Multidimensional Signals	no
Variable-Size Signals	no
Zero-Crossing Detection	no

More About

Design/Band Combination Table

This table lists the available parameters for each design/band combination. For lowpass and highpass band configurations, these parameters include:

• The passband edge frequency Ω_p.

• The stopband edge frequency Ω_s

• The passband ripple R_p

• The stopband attenuation R_s

For bandpass and bandstop configurations, the parameters include:

• The lower and upper passband edge frequencies, Ω_p1 and Ω_p2

• The lower and upper stopband edge frequencies, Ω_s1 and Ω_s2

• The passband ripple R_p

• The stopband attenuation R_s

Frequency values are in rad/s, and ripple and attenuation values are in dB.

Filter Design Type	Lowpass	Highpass	Bandpass	Bandstop
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
Bessel	Order, Ωp	Order, Ωp	Order, Ωp1, Ωp2	Order, Ωp1, Ωp2

References

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

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using Simulink® Coder™.

This block is not recommended for production code generation.

Consider using the Model Discretizer (Simulink) to map this continuous block into a discrete equivalent that supports code generation. To access the Model Discretizer, on the Apps tab, under Apps, under Control Systems, click Model Discretizer.

Version History

Introduced before R2006a