Filters

Remove or enhance frequency components using signal processing filters

Use these examples to learn how to design signal processing filters to remove or enhance frequency components.

Featured Examples

Analog Anti-Aliasing Filter

An analog implementation of an anti-aliasing filter for use with an A-to-D converter. The filter cut-off frequency is set to 500Hz in order to match the A-to-D converter sampling frequency of 1kHz. The test signal incorporates a desired 50Hz sinusoid plus a higher frequency component at 1100Hz that cannot be captured with a 1kHz A-to-D sampling frequency. The scope shows the captured signal without and with anti-aliasing. With the anti-alias filter the 50Hz sine wave amplitude is correctly measured with an amplitude of 1 and corresponding power of 0.5W, i.e., 27dBm for a 1ohm reference load.

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Band-Pass Filter Using Three Mutually-Coupled Inductors

An implementation of a band-pass filter using three mutually-coupled inductors. The model can be used to validate filter parameters which are chosen to provide a band-pass centered on 100MHz. A band-limited noise source is up-shifted by a 100MHz oscillator and applied to the filter. The response is then down-shifted by the oscillator. The model StopFcn callback takes FFTs of the source and response and estimates the filter frequency response.

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Controllable Phase Shifter

An implementation of a first order phase shifting filter. The filter is characterized by the transfer function H(s) = (sC - gm1)/(sC + gm1). Double-click on the Set Design Parameters block to set the desired phase shift, amplitude of the input signal, and the frequency of the input signal. The block mask calls a function which sets the parameter values in the model workspace.

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Fourth-Order Sallen-Key Lowpass Filter

An implementation of a fourth-order Sallen-Key low-pass filter using Operational Amplifiers (OPAs). The filter design parameters, cut-off frequency (f1) and DC gain (K), are specified by double-clicking on the Set Design Parameters block. Pass-band ripple is predefined to be 1dB using a Chebyshev response. The block mask calls a function which sets the parameter values in the model workspace.

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Low-Pass Filter Using Operational Transconductance Amplifiers

Model a second-order active low-pass filter. The filter is characterized by the transfer function H(s) = 1 / ( (s/w1)^2 + (1/Q)*(s/w1) + 1 ) where w1 = 2*pi*f1, f1 is the cut-off frequency and Q is the quality factor. Double-click on the Set Design Parameters block to set parameters f1 and Q. The block mask calls a function which sets the parameter values in the model workspace.

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