Melitta - Designer

The filter designer allows to compute scaled filter parameters for a range for digital filter families and types given the appropriate input parameters. The types are as follows:

The filter designer offers means to design the filters in an interactive manner (a shell), as well as in a GUI-supported manner. The filter design itself can be carried out using several methods as follows.

Design by analogue reference filter

This design method uses analogue reference filters in order to generate digital filter parameter sets for the following filter families:

The designed analogue filter transfer function are transformed into the z-transfer function by using:

Design in the discrete time domain

FIR filters only are considered in this design, either with design in the frequency domain or through windowing.

Approximation in the frequency domain

An ideal digital filter transfer function is approximated in the frequency domain by variation of the FIR filter parameters according to certain algorithms:

Window method

A finite sample of the impulse response of the ideal filter (infinte Sinc(n) function) is used to compose a FIR filter. The finite sample is shaped using the following windowing functions:

Filter decomposition

The transfer function of the digital filter can be decomposed into a product, or sum of first and/or second order stages. An option will define the ordering of the stages by pole location and/or gain.

Filter parameter implementation

The last step in the design is the computation of the scaled filter parameters of the respective IIR or FIR filter for a concrete digital filter with a given finite word length through scaling. The output can be written into C source or header files.

Filter presentation

It is possible to generate Pole/Zero plot, a Nyquist plot, a Bode plot as well as a step and impulse response for all filters. It is also possible to compare all plots mentioned before.


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Copyleft 2005, Peter Wurmsdobler.