DSP Blockset

Implementing a Lowpass Filter

The Digital Filter block, in the DSP Blockset Filter Designs library, is useful for implementing a digital FIR or IIR filter. In this example, you create a lowpass filter using the Digital Filter block.

To learn how to create a highpass filter, see Implementing a Highpass Filter. To design and implement a new filter, see Digital Filter Design Block:

1. Define the lowpass filter coefficients in the MATLAB workspace by typing

1. lopassNum = [-0.0021 -0.0108 -0.0274 -0.0409 -0.0266 0.0374 0.1435 0.2465 0.2896 0.2465 0.1435 0.0374 -0.0266 -0.0409 -0.0274 -0.0108 -0.0021]

   You could have calculated these values using

   • Signal Processing Toolbox functions -- Type the following commands at the MATLAB command line:

   • [N Fo Ao W] = remezord([0.2 0.5],[1 0], ...
     [5.750112778453722e-002,1.000000000000001e-004]);
     lopassNum = remez(N,Fo,Ao,W,{16});
     

   • Digital Filter Design block -- Design a lowpass filter as in Creating a Lowpass Filter. Then export the filter coefficients to the MATLAB workspace to the variable lopassNum as described in the Importing and Exporting Quantized Filters section of the Filter Design Toolbox documentation.

2. Open Simulink and create a new model file.
3. In the Simulink Model browser, double-click DSP Blockset.
4. Double-click Filtering, and select the Filter Designs library.
5. Click-and-drag a Digital Filter block into your model.
6. Double-click the Digital Filter block.

1. The Block Parameters: Digital Filter dialog box opens.

7. Set the parameters to the values shown below.

1. 

   Note that you can provide the filter coefficients in several ways:

   • Type in a variable name from the MATLAB workspace, such as lopassNum.
   • Type in filter design commands from the Signal Processing Toolbox or the Filter Design Toolbox, such as fir1(5, 0.2, 'low').
   • Type in a vector of the filter coefficient values.

8. Click OK.

The Digital Filter block in your model now represents a lowpass filter.

Digital Filter Block

Implementing a Highpass Filter