Variable cut-off digital ladder filters

This paper presents a now class of transformations whose implementation to doubly terminated LC ladder filters results in variable cut-off frequency digital filters. It is shown that using this transformation and the concept of generalized delay, from a given prototype ladder structure, we can construct low-pass, high-pass, band-pass and band-stop filters with variable cut-off frequency and bandwidth. Thu resulting variable filters are canonical in the sense that a minimum number of multipliers in the prototype filter need to be adjusted. Two examples are worked out to illustrate the application of this method.