‘Shadow’ Filters—A New Family of Electronically Tunable Filters
It is shown that the ‘shadow’ filter, introduced recently by Lakys and Fabre, is capable of achieving not only a constant bandwidth bandpass filter, but also several other interesting characteristics depending upon the choice of the desired output port and the port from which feedback signal is derived. Two such characteristics are illustrated in this chapter, namely constant centre frequency, variable Q, and constant value of the product of centre frequency and Q. A problem is also posed for further investigation. Finally, a suggestion is made for the design of a simple but interesting experiment for undergraduate students, using only resistors, capacitors and op-amps, which illustrates the basic concepts of filters and what the shadow technique can do to improve their quality.
KeywordsShadow filters Versatility Open problems
- 3.N.J. Fliege, Multiple biquads. Ch. 13 in The Circuits and Filters Handbook, (W.K. Chen (Ed), 2007, CRC Press)Google Scholar