DSP Blockset

Implementing a Highpass Filter

In the previous topic, Implementing a Lowpass Filter, you learned how to create a lowpass filter. Now, create a highpass filter using the Digital Filter block:

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

1. highpassNum = [-0.0051 0.0181 -0.0069 -0.0283 -0.0061 0.0549 0.0579 -0.0826 -0.2992 0.5946 -0.2992 -0.0826 0.0579 0.0549 -0.0061 -0.0283 -0.0069 0.0181 -0.0051];

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

   • Digital Filter Design block -- Design a highpass filter as in Creating a Highpass Filter. Then export the filter coefficients to the MATLAB workspace to the variable highpassNum 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.

1. If you completed the procedure in Implementing a Lowpass Filter, you can continue to use your the same 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 highpassNum.
   • 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 highpass filter.

Implementing a Lowpass Filter

Filtering High-Frequency Noise