[SOLVED] Active LF Filter Design Topology

[jpanhalt]

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 the attached design using three AD8055 op-amp sections.  Only the first section is shown.

Analog Devices calls it an MFB, but TI and others with similar design programs do not include feedback resistors R3A and R4A.   Perhaps obviously, the design is pretty sensitive to the value of those resistors.  I have seen similar topology called VCVS (voltage-controlled variable state), but all of the examples of that I have seen use the non-inverting input of the op-amp for signal input.

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 to share that explains how to calculate the values for those two resistors?

Regards, John

[jpanhalt]

SOLVED:

It is a variation on the Single Amplifier Biquad (SAB) originally designed by Delyiannia and Friend.   Schaumann and Van Valkenburg's  text (Oxford University Press, 2001) has a nice description and worked example beginning around p. 170.

Regards, John