DSP Blockset

Example: Chebyshev Type II Lowpass Filter.   In the model below, the Sine Wave block generates two sinusoids, one at 100 Hz and 400 Hz, each with a frame size of 128 samples. The sinusoids are then summed point-by-point, and the resulting signal is passed through a lowpass IIR filter to attenuate the higher frequency sinusoid. Both signals are displayed on the scope.

To build the model, make the following settings:

• In the Sine Wave block, set:
• Amplitude = 10
• Frequency = [100 400]
• Phase offset = 0
• Sample time = 0.001
• Samples per frame = 128
• In the Matrix Sum block, set Sum along = Rows.
• In the Digital IIR Filter Design block, set:
• Design method = Chebyshev II
• Filter type = Lowpass
• Filter order = 8
• Stopband edge frequency = 0.5
• Stopband attenuation in dB = 20

This specifies a Chebyshev type II lowpass filter with a stopband edge frequency of 250 Hz, which will attenuate the sinusoid at 400 Hz but retain the sinusoid at 100 Hz. Note that half the sample frequency in this case is 500 Hz, so that the normalized Stopband edge frequency is 0.5, as specified.

• In the Matrix Concatenation block, set:
• Number of input = 2
• Concatenation method = Horizontal
• Set the Stop time in the Parameters dialog box to inf, and start the simulation by selecting Start from the Simulation menu.

Use the default setting in the Spectrum Scope block. As the simulation begins running, right-click in the plot area of the scope, and select Autoscale from the pop-up menu. You can also change the styles and colors of the plotted lines by selecting either CH 1 or CH 2 from the right-click pop-up menu.

The scope window displays both the original signal and the filtered result, which shows the expected attenuation of the 400 Hz component. Stop the simulation at any time by selecting Stop from the Simulation menu.

Discrete-Time IIR Filters

Designing Continuous-Time Classical IIR Filters