Fliege notch filter
The Fliege notch topology is shown in Figure 4. The
advantages of this circuit over the twin-T are as follows:
• Only four precision components—two Rs and two Cs—
are required for tuning the center frequency. One nice
feature of this circuit is that slight mismatches of components
are okay—the center frequency will be affected,
but not the notch depth.
• The Q of the filter can be adjusted independently from
the center frequency by using two noncritical resistors
of the same value.