How to Add external frequency inputs in the analog filter design block simulink in matlab

Question

I want to be able to externally have inputs for the lower passband edge frequency and higher passband edge frequencies for the butterworth filter block in the simulink signal processing toolbox in matlab. How can I achieve this. Currently you'll have to click the block to specify these frequencies and this is not possible at runtime.

Regards, Alfred

Answer 1

Basically you are asking for a filter that has time varying parameters. The Butterworth filter block does not allow for this, and cannot be modified to do so, so you are going to have to roll your own. This can be achieved in several ways:

1. Determining the difference equations that you need to implement, then creating a filter out of fundamental blocks (product, summation and unit delay blocks) where the "parameters" you want to change are fed into the product blocks as signals.
2. Using a block such as Transfer Fcn Direct Form II Time Varying. (This assumes you can parameterize the changes you need as a gain-scheduled signal.)
3. Write an S-Function (or perhaps a MATLAB Function block) to implement any detailed/specific functionality.