Active Stage Gains

FilterSolutions allows one to view and modify the gain of each stage of an active filter, as shown in the Modify Stages section of the Help contents. It is important to remember that the product of the stage gains is not necessarily equal to the overall filter gain as seen in the Active Control Panel. The reasons for this are summarized below.

 

Band Pass Filters

The gain of the filter as shown in the Active Control Panel is taken at the center frequency of the filter. The gain of the individual stages is taken at the center frequency of the respective stage, which will not be the same of the center frequency of the filter. To illustrate, the frequency response of a second order Butterworth band pass filter is shown below along with the frequency response of both cascaded stages.

2nd Order Band Pass Filter Gain of 1.000

 

Band Pass Stage Gains of 1.510

 

Band Stop Filters

The gain of the band stop filter as shown in the Active Control Panel is taken at the zero and infinite frequencies of the filter. The gain of the individual stages is different at zero and infinity. The stage gain in FilterSolutions is taken at zero or infinite frequency, depending on which has the higher gain, of the respective stage, which will not be the same of the zero and infinite frequencies of the filter. To illustrate, the frequency response of a second order Butterworth band stop filter is shown below along with the frequency response of both cascaded stages.

2nd Order Band Stop Gain of 1.000

 

Band Stop Stage Gains of 1.443