Introducing the MF-10: A Versatile Monolithic Active Filter Building Block

Filter design takes one of two approaches: passive or active. Passive designs combine resistors, capacitors and inductors to perform specific frequency filtering in applications where precision is less important than mass producibility. For very high frequency applications, a passive approach is quite often the only way to go. Active filters combine op amps and discrete transistors, primarily with resistors and capacitors, to provide impedance buffering and filter parameter tunability. In precision filters, it is most desirable to have an independent ‘‘handle’’ for each of three basic filter parameters: resonant frequency (fo), Q or quality factor, and the passband gain (Ho). As a general rule, the degree of tunability increases with the number of amplifiers used. The three op amp, state variable active filter, Figure 1, is most popular for 2nd order designs.