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Filter Wizard Design Equation(s)

Question asked by jpa on Jan 17, 2017
Latest reply on Jan 18, 2017 by Matt.Duff

I am working on a 500 kHz active filter and turned to the filter wizard of Analog Devices. Given a center frequency of 500 kHz, 20 kHz passband, gain of 10 dB, it came up with a design using three AD8055 op-amp sections (attached below).

 

Analog Devices calls it an MFB, but TI and others with similar design programs do not include feedback resistors R3A and R4A from the output to the non-inverting input. Perhaps obviously, the design is pretty sensitive to the value of those resistors.

 

1) What is the topology called? That is, is there a more specific name for it that includes the feedback resistors?
2) Does anyone have a link that explains how to calculate the values for those two resistors?

 

Regards, John

 

PS: It simulates fine and works fine on the bench, but that is not my question. 

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