Leapfrog‐type active RC filters with reduced number of operational amplifiers

Abstract

AbstractIt is known that the active RC filter which simulates a ladder‐type filter has a lower element‐sensitivity than a cascade‐connected active RC filter. Many methods to construct this type of filter have recently been proposed. This paper introduces a method in which an active RC filter is used to realize the relationship between the node voltages and the closed‐circuit currents in a circuit obtained by scaling the impedance of each element of the original LC filter with the s‐function. By choosing the scaling function appropriately, the inverting‐integration circuit in a conventional leapfrog‐type filter can be replaced by an inverting double integrator with two capacitors; and the noninverting‐integration circuit in the same filter can be replaced by an RC first‐order, low‐pass circuit. This reduces operational amplifiers in the circuit to less than half a conventional leapfrog‐type active filter. The element‐sensitivity was analyzed, and the conditions for a low element‐sensitivity were obtained. A fifth‐order Cheby‐shev low‐pass filter was constructed, and its measured element‐sensitivity was compared with the results of a computer simulation.