An optimal design of RC active filters using grounded capacitors

It is desirable, from the point of view of integration, to have all the capacitors grounded in RC active filters. Recently, such a network was reported with only a preliminary design procedure. An optimal design is presented in this paper for the above network. The new design leads to a simpler configuration, simultaneously minimizes the worst‐case deviation in both the pole‐Q(Qp) and the pole frequency ωp and also guarantees that the network is free from unstable modes of operation during activation. Although this design is based on Qp and ωp, it is also suitable for notch and allpass sections. It is shown that the gains of the operational amplifiers (o.a.s.), controlling the poles of the filter, can all be made equal to (4Q2p‐1)1/3; this choice of the gains minimizes the effect of the finite bandwidths of the amplifiers on Qp and ωp. A simple scheme is proposed to compensate for this effect. The effect of compensation on the zeros, in the case of notch and allpass sections, is also studied. It is found that the effect on the notch frequency is negligible, while, for allpass filters, compensation for the poles automatically provides compensation for the zeros. A simple tuning scheme using only resistors is also presented, and the theoretical results are verified experimentally.