AF120

~National ~ Semiconductor Active Filters AF120 Generalized Impedance Converter, GIC General Description The AF120 contains a pair: of operational amplifiers and four precision thin film resistors connected as shown below. A gyrator may be formed by adding one external capacitor; or a frequency dependent negative resistance FDN R may be formed by adding two external capacitors. In the gyrator mode, ZIN a: jWC, which is equivalent to a grounded inductor. In the FDNR mode, ZIN a: - 1/ w 2 C1C2. The AF120 may also be used in pairs to form ungrounded inductors or inductor networks. Thus, with appropriate transformations, the G IC makes possible an active realization of any low-frequency ladder filter network. The advantage of ladder filters being, of course, that they exhibit lower sensitivity to component variations than any other type of filter realization. Temperature coefficient of the internal resistors is equal and opposite in sign to that of poly- styrene capacitors, thus RC prod...