Shadow Filter for Orthogonal Modification of Center Frequency and Bandwidth with Constant Q Factor

Abstract

A new family of electronically tunable second order filters have been introduced in the recent past. Such filters have the capability to tune with any characteristic frequency with the help of changing the amplification of an external amplifier in the feedback. Further research in this area demonstrated the generalization of this result to nth order filters. Possibilities of independent modification of characteristic frequency and bandwidth and the product of characteristic frequency and Q factor were explored and verified in this area. However, in the previous works the independent modification of characteristic frequency and bandwidth was not achieved by keeping Q factor constant which shows a niche in design and analysis of an electronically tunable filter. Therefore, this study was aimed at addressing this particular gap in designing with an innovative idea of shadow filters for modifying characteristic frequency of second order filter cells via a feedback second order filter and external amplifier. This external amplifier is used to independently modify characteristic frequency and bandwidth by keeping Q factor constant. Further, a thorough theoretical analysis was performed and the theoretical justification is then confirmed with an example of basic passive second order filter cells.