Bandstop Filter

Design bandstop filter

  • Library:
  • DSP System Toolbox / Filtering / Filter Designs

Description

This block brings the filter design capabilities of the filterbuilder function to the Simulink® environment.

Ports

Input

expand all

Input signal to filter, specified as a scalar, vector, or matrix.

Data Types: single | double

Output

expand all

Filtered output signal, specified as a scalar, vector, or matrix.

Data Types: single | double

Parameters

expand all

This button opens the Filter Visualization Tool (fvtool) from the Signal Processing Toolbox™ product. You can use the tool to display:

  • Magnitude response, phase response, and group delay in the frequency domain.

  • Impulse response and step response in the time domain.

  • Pole-zero information.

The tool also helps you evaluate filter performance by providing information about filter order, stability, and phase linearity. For more information on FVTool, see the Signal Processing Toolbox documentation.

Specify whether the block implements an FIR or IIR filter.

Note

The design methods and structures for FIR filters are not the same as the methods and structures for IIR filters.

Select Minimum to have the block implement a filter with minimum order. When you select Specify, you must enter the filter order using the Order parameter.

Tip

When you set the Impulse response to IIR, you can specify different numerator and denominator orders. To specify a different denominator order, select the Denominator order check box.

Specify the filter order as a positive integer.

Dependencies

To enable this parameter, set Order mode to Specify.

Select this check box to specify a different denominator order. When you select this check box, you can specify the denominator order as a positive integer in the resulting text box.

Dependencies

To enable this parameter, set the Impulse response to IIR and the Order mode to Specify.

Select the type of filter to implement. Your choice determines the type of filter and the design methods and structures that are available to implement your filter.

Dependencies

  • This parameter applies only when you set Impulse response to FIR.

  • Selecting Decimator or Interpolator activates the Decimation Factor or the Interpolation Factor options respectively.

  • Selecting Sample-rate converter activates both factors.

Specify the decimation factor as a positive integer.

Dependencies

To enable this parameter, set the Filter type to Decimator or Sample-rate converter.

Specify the interpolation factor as a positive integer.

Dependencies

To enable this parameter, set the Filter type to Interpolator or Sample-rate converter.

When you set the Order mode to Specify, this parameter allows you to choose the filter features that the block uses to define the frequency response characteristics. Depending on the Impulse response you choose, you can set the Frequency constraints to one of:

  • Passband and stopband edges — Specify the frequencies for the edges for the stop- and passbands.

  • Passband edges — For IIR filters, define the filter by specifying frequencies for the edges of the passband.

  • Stopband edges — For IIR filters, define the filter by specifying frequencies for the edges of the stopbands.

  • Half power (3dB) frequencies — For IIR filters, define the filter response by specifying the locations of the 3 dB points. The 3 dB point is the frequency for the point three decibels below the passband value.

  • Half power (3dB) frequencies and passband width — For IIR filters, define the filter by specifying frequencies for the 3 dB points in the filter response and the width of the passband.

  • Half power (3dB) frequencies and stopband width — For IIR filters, define the filter by specifying frequencies for the 3 dB points in the filter response and the width of the stopband.

  • Cutoff (6dB) frequencies — For FIR filters, define the filter response by specifying the locations of the 6 dB points. The 6 dB point is the frequency for the point 6 dB below the passband value.

Dependencies

To enable this parameter, set the Order mode to Specify. The available Frequency constraints will depend on whether the Impulse response is FIR or IIR.

Use this parameter to specify whether your frequency settings are normalized or in absolute frequency. Select Normalized (0 to 1) to enter frequencies in normalized form. To enter frequencies in absolute values, select one of the frequency units from the drop-down list—Hz, kHz, MHz, or GHz.

Fs, specified in the units you selected for Frequency units, defines the sampling frequency at the filter input. When you provide an input sampling frequency, all frequencies in the specifications are in the selected units as well.

Dependencies

To enable this parameter, set Filter type to Single-rate, Decimator, or Sample-rate converter and Frequency units to one of the unit options (Hz, kHz, MHz, or GHz).

When you design an interpolator, Fs represents the sampling frequency at the filter output rather than the filter input.

Dependencies

To enable this parameter, set Filter type to Interpolator and Frequency units to one of the unit options (Hz, kHz, MHz, or GHz).

Enter the frequency at the edge of the end of the first passband. Specify the value in either normalized frequency units or the absolute units you select in Frequency units.

Enter the frequency at the edge of the start of the stopband. Specify the value in either normalized frequency units or the absolute units you select in Frequency units.

Enter the frequency at the edge of the end of the stopband. Specify the value in either normalized frequency units or the absolute units you select in Frequency units.

Enter the frequency at the edge of the start of the second passband. Specify the value in either normalized frequency units or the absolute units you select in Frequency units.

Specify the lower frequency 3 dB point as a positive scalar between zero and one.

Dependencies

To enable this parameter, set Impulse response to IIR, Order mode to Specify, and Frequency constraints to Half power (3dB) frequencies, Half power (3dB) frequencies and passband width, or Half power (3dB) frequencies and stopband width.

Specify the higher frequency 3 dB point as a positive scalar between zero and one.

Dependencies

To enable this parameter, set Impulse response to IIR, Order mode to Specify, and Frequency constraints to Half power (3dB) frequencies, Half power (3dB) frequencies and passband width, or Half power (3dB) frequencies and stopband width.

Specify the lower frequency 6 dB point as a positive scalar between zero and one.

Dependencies

To enable this parameter, set Frequency constraints to Cutoff (6dB) frequencies.

Specify the higher frequency 6 dB point as a positive scalar between zero and one.

Dependencies

To enable this parameter, set Frequency constraints to Cutoff (6dB) frequencies.

Specify the width of the passband as a positive scalar, in units corresponding to the Frequency units parameter.

Dependencies

To enable this parameter, set Frequency constraints to Half power (3dB) frequencies and passband width.

Specify the width of the stopband as a positive scalar, in units corresponding to the Frequency units parameter.

Dependencies

To enable this parameter, set Frequency constraints to Half power (3dB) frequencies and stopband width.

Specify the magnitude constraints for the filter design.

Dependencies

To enable this parameter, set Order mode to Specify. The available options depend on the value of the Frequency constraints parameter.

Specify the units for any parameter you provide in magnitude specifications:

  • Linear — Specify the magnitude in linear units.

  • dB — Specify the magnitude in decibels (default).

  • Squared — Specify the magnitude in squared units.

Dependencies

To enable this parameter, set Order mode to Minimum.

Specify the filter ripple allowed in the first passband in the units you choose for Magnitude units. Values must be real, positive scalars. If you are specifying values in linear units, they must be smaller than 1.

Dependencies

To enable this parameter, set the Order mode to Minimum.

Enter the filter attenuation in the stopband in the units you choose for Magnitude units. Values must be real, positive scalars. If you are specifying values in linear units, they must be smaller than 1.

Dependencies

To enable this parameter, set the Order mode to Minimum.

Enter the filter ripple allowed in the second passband in the units you choose for Magnitude units. Values must be real, positive scalars. If you are specifying values in linear units, they must be smaller than 1.

Dependencies

To enable this parameter, set the Order mode to Minimum.

Lists the design methods available for the frequency and magnitude specifications you entered. When you change the specifications for a filter, such as changing the impulse response, the methods available to design filters changes as well. The default IIR design method is usually Butterworth, and the default FIR method is Equiripple.

Selecting this parameter directs the design to scale the filter coefficients to reduce the chances that the inputs or calculations in the filter overflow and exceed the representable range of the filter. Clearing this option removes the scaling.

Dependencies

To enable this parameter, set Impulse response to IIR.

Density factor controls the density of the frequency grid over which the design method optimization evaluates your filter response function. The number of equally spaced points in the grid is the value you enter for Density factor times (filter order + 1.

Increasing the value creates a filter that more closely approximates an ideal equiripple filter but increases the time required to design the filter. The default value of 16 represents a reasonable balance between the accurate approximation to the ideal filter and the time to design the filter.

Dependencies

To enable this parameter, set Impulse response to FIR and Design method to Equiripple.

Specify the phase constraint of the filter as Linear, Maximum, or Minimum.

Dependencies

To enable this parameter, set Impulse response to FIR and Design method to Equiripple.

When you select this parameter, the design method determines and designs a minimum order filter to meet your specifications.

Dependencies

To enable this parameter, set Impulse response to FIR, Order mode to Minimum, and Design method to Kaiser window.

Specifies that the resulting filter design matches either the passband, stopband, or both bands.

Dependencies

To enable this parameter, set Impulse response to IIR.

For the filter specifications and design method you select, this parameter lists the filter structures available to implement your filter. By default, FIR filters use direct-form structure, and IIR filters use direct-form II filters with SOS.

Select this check box to implement the filter as a subsystem of basic Simulink blocks. Clear the check box to implement the filter as a high-level subsystem.

The high-level implementation provides better compatibility across various filter structures, especially filters that would contain algebraic loops when constructed using basic elements.

Dependencies

When you select this check box, the block enables the following optimization parameters:

  • Optimize for zero gains — Terminate chains that contain Gain blocks with a gain of zero.

  • Optimize for unit gains — Remove Gain blocks that scale by a factor of one.

  • Optimize for delay chains — Substitute delay chains made up of n unit delays with a single delay of n.

  • Optimize for negative gains — Use subtraction in Sum blocks instead of negative gains in Gain blocks.

Select this check box to scale unit gains between sections in SOS filters.

Dependencies

To enable this parameter, set Impulse response to IIR.

When the Filter type parameter specifies a multirate filter, select the rate processing rule for the block:

  • Enforce single-rate processing — When you select this option, the block maintains the sample rate of the input.

  • Allow multirate processing — When you select this option, the block adjusts the rate at the output to accommodate an increased or reduced number of samples.

Dependencies

To enable this parameter, set the Impulse response to FIR and set Filter type to a multirate filter.

Select this check box to enable the specification of coefficients using MATLAB® variables. The available coefficient names differ depending on the filter structure. Using symbolic names allows tuning of filter coefficients in generated code.

Block Characteristics

Data Types

double | single

Multidimensional Signals

No

Variable-Size Signals

No

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Introduced in R2006b