Active RC LPFs with Single-Element Pole Frequency Tuning

New low-pass filter (LPF) architectures based on differential difference operational amplifiers (DDOA) are studied in this paper. The feature of the proposed LPF is that when tuning the cut-off frequency, the LPF gain remains unchanged at zero frequency. As a tuning element, it is possible to use digital potentiometers. The basic equations for two LPF modifications are presented, which provide parametric synthesis of circuits. The results of computer simulation of tunable responses were given in Micro-cap CAD.