Inductor and Capacitor Tuning

When passive filters ideal elements are replaced with real parts with nonideal values, an expected degradation in filter performance occurs. It is possible to tune the circuit inductors and/or capacitors such that some, or even most, of the degradations are transferred from the filter pass band to the stop band. The effect of this translation is that degradation in the pass band is minimized.

Whenever any inductor or capacitor value in a passive LC filter is modified, an "L tune", "C tune", or "Tune" button is available in the passive filter tool bar, as shown below. Depressing this button causes all filter inductors or capacitors to automatically assume new values that will minimize the pass band error in the filter.

 

"L tune" Button on Passive Filters

Example:

The following pass band and stop band error is the result of inserting non ideal capacitor values into a low pass filter:

Pass Band Error Resulting From Nonideal Capacitor Values

 

Stop Band Error Resulting From Nonideal Capacitor Values

 

After inductor tuning, the passband error is minimized at the expense of the stop band error.

Pass Band Error After Inductor Tuning

 

Stop Band Error After Inductor Tuning