The active filter offers the advantage of providing isolation between stages. This is possible by taking advantage of the high input impedance and low output impedance of the operational amplifier. In all cases, the order of the filter is determined by the number of capacitors at the input and in the feedback loop of the amplifier. The Double Pole, Voltage Controlled Voltage Source is better known as the Sallen-Key filter realization. This filter is configured so the DC gain is positive. In the Sallen-Key Filter realization shown in Figure 4, the DC gain is greater than one. In the realization shown in Figure 5, the DC gain is equal to one. In both cases, the order of the filters is equal to two. The poles of these filters are determined by the resistors and capacitors values of R1, R2, C1 and C2.