Build an adjustable high frequency notch filter:
02/06/03 EDN-Design Ideas / Although you can obtain
universal, resistor-programmable switched-capacitor
filters that are configurable as notch filters, most
cannot operate at bandwidths higher than 100 kHz.
Further, the typically 16
Closing the loop deepens notches: 02/07/2002
EDN - Design Ideas / Notch filters remove a single
unwanted frequency from an input signal. They are
also a vital component of pulse-shaping networks,
such as time-averaging filters. You can tune a
state-variable filter over a wide range by changing
the time constants of its integrating amplifiers
(references 1, 2, and 3). .
RC Notch Filter Twin T: The twin T notch filter
can be used block an unwanted frequency or if placed
around an op-amp as a bandpass filter. The notch
frequency occurs where the capacitive reactance
equals the resistance Xc=R and if the values are
close, the attenuation can be very high and the
notch frequency virtually eliminated.