elliptical filter design
I feel the time has come to make some general statements on filter design.
For example, just to say “I like to design an elliptical filter” is completely insufficient and nobody can give a substantial answer to such a question.
Instead, the design has to follow some steps in the right order:
1.) Frequency and attenuation requirements
2.) Choice of an approximation (out of at least five alternatives)
3.) Filter order (as a consequnence of steps 1 and 2)
4.) Choice: passiv or active
5.) Selection of technology (opamp, OTA, SC, CC)
6.) Choice of synthesis procedure: Cascade design or direct (ladder simulation ,leap frog, FLF, PRB)
7.) Selection of a specific circuit (Sallen-Key, MLF, several Biquads, FDNR,………)
Did I forget something ?
You see, filter design is connected with several design steps. For example, to build a lowpass of only second order you have at least 20 alternatives.
But, how come to a decision and what governs the choice ? Several aspects, like component availability, cost, power and supply voltage requirements, frequency range, tuning capabilities, accuracy requirements, ………
And don´t think, that the problems rise with frequency; to design an active lowpass for a pole frequency of 10…100 mHz is a big problem.
Perhaps this helps somebody a bit.
Regards.