RC-Active Ladder Filters Based on Simulating Inductors

The RC-active filters in this category can be readily obtained by replacing inductors with selected active circuits. Three ba­sic types of active circuits are employed and discussed in the following.

Generalized Impedance Converters. The GIC is a two-port circuit, usually employing two op-amps as shown in Fig. 5(a), where the impedances Zi are usually either a resistor or a capacitor. The impedance relations between the input and terminating impedances of a GIC are given by

Z|nl Z„Z

which is a so-called frequency-dependent negative resistance (FDNR). Applications of FDNRs are discussed in the next subsection.

The GIC is used in a very similar way to that of a gyrator. In particular, the gyrator simulating a grounded inductor, as shown in Fig. 4(a), can be replaced with a GIC given by Eq. (12). The GICs can also be used to simulate floating inductors as shown in Fig. 5(b), which was first proposed by Gorski – Popiel. It is noted that, unlike the gyrator, the GICs with the

RC-Active Ladder Filters Based on Simulating Inductors

ks R = L Ik ks

L

Figure 5. (a) Active implementation of GIC and its corresponding symbol. K(s) is the conversion factor. (b) Floating-inductor simulation using GIC. This simulation uses a resistor connecting two GICs. The required capacitors are hidden in the GICs.

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