Design and Evaluation of RC Active Filters for Hybrid Thick Film Implementation

The resistance-capacitance (RC) active simulation of low sensitivity inductance--capacitance (LC) ladder filters has received a great deal of attention in recent years. Most known methods for the design of either RC active driving point impedances or general impedance converters (GIC's) use the well-known two opamp structure of Antoniou. Recently, some general second-order driving point impedances using only one opamp were introduced. In this paper both structures are considered for hybrid thick film implementation. They are compared with respect to sensitivity to component tolerances and tuning errors, and a method is given for optimizing the single opamp driving point branches with a view to realization in hybrid thick film form. Furthermore, a method is developed that permits the substrate area requirements of thick film RC active filters to be assessed. Finally, sensitivity and substrate area performance functions are introduced and applied, providing an "optimized" design of single opamp branches. Using the methods reported in this paper, typical improvements of close to 40 percent in circuit yield and ten percent in substrate area were achieved.