DSP Blockset

Creating a Highpass Filter

The Digital Filter Design block, located in the DSP Blockset Filter Designs library, is useful for designing and implementing a digital FIR or IIR filter. In this example, you create a highpass filter using the Digital Filter Design block. To implement a filter you already designed, see Digital Filter Block:

1. From the Filter Designs library, drag a Digital Filter Design block into a Simulink model.

1. If you created the model in Creating a Lowpass Filter, you can place this block into the same model file.

2. Double-click the new Digital Filter Design block.

1. The Filter Design and Analysis Tool (FDATool) GUI opens.

3. Set the block parameters of the GUI as shown in the following figure.
   
   
4. Click the Design Filter button at the bottom of the GUI to design the filter.

1. Your Digital Filter Design block now represents a filter with the parameters you specified.

5. In the Edit menu, select Convert Structure.

1. The Convert Structure dialog box opens.

6. Select Direct-Form FIR Transposed and click OK.

The block now implements a highpass filter with a direct form FIR transpose structure. As the wpass and wstop settings indicate, the filter passes all frequencies greater than or equal to 50% of the Nyquist frequency (half the sampling frequency), and stops frequencies less than or equal to 20% of the Nyquist frequency.

Note that this highpass filter is the "opposite" of the lowpass filter described in Creating a Lowpass Filter. The highpass filter passes the frequencies stopped by the lowpass filter, and stops the frequencies passed by the lowpass filter. In the next topic, you learn how to build a model where the lowpass filter filters out the high-frequency noise output by this highpass filter.

To learn how to create a model capable of filtering high frequency noise, see Filtering High-Frequency Noise.

Creating a Lowpass Filter

Filtering High-Frequency Noise