Stability of Active-RC LPF Designed by Cascade Method

This paper studies the stability of active-RC lowpass filter (LPF) designed by cascade method. The influence of the gain bandwidth product (GBW) and phase margin (PM) of the non-ideal operational amplifier (Op-Amp) on the stability of the first order and second order structures is discussed. This paper also derives the transfer function of the first order and second order structures adopting a two-poles integrator model of Op-Amp. Routh-Hurwitz (RH) array is used for stability analysis and the concept of minimum phase margin (MPM) is defined. The design process of active-RC LPF under extreme conditions of large bandwidth and low power dissipation is given. How to do trade-offs in Op-Amp's power dissipation, GBW and PM is defined, the visualization of results is presented as well. The proposed analysis method can be used in the design of other types of active filters.