On the design of optimal switched capacitor filters based on the use of lossy frequency-dependent negative resistance (FDNR) prototype structures

The approach described in this paper is based on the SC simulation of the FDNR element obtained by Bruton transformation. The authors describe a class of SC filter design techniques based on the SC realization of lossy-FDNR subcircuits. The approach will be shown to lead to designs which are optimal in terms of active and passive component count, which feature very low sensitivity, and which offer minimised capacitance spread-an important requirement for efficient integrated circuit realization. An example filter design is given using a prewarping technique. The paper presents an alternative design strategy using optimisation to achieve the desired frequency response together with minimised capacitance spread. Finally, the effect of parasitic capacitances in the new structure is examined, and a modified structure is presented to reduce the capacitance spread still further