SC leapfrog filters without additional adder stages

In an arbitrary SC leapfrog filter, additional adders or inverters must generally be introduced to perform the necessary signal inversions and summations. Thus an additional (third) amplifier per second-order resonator, or biquad, is required. In this paper, we present a simple method of eliminating these extra stages, so that the number of amplifiers and capacitors in the original biquad blocks remains unchanged.