Log-domain linear transformation filters revised: Improved building blocks and comparison results

A method for designing high-order log-domain filters has already been proposed in the literature based on the concept of the classical linear transformation (I-T) filters. For this put-pose, a substitution table containing the log-domain LT equivalent of each passive element has been introduced. Drawbacks of the log-domain filter topologies derived according to this table are the following: (a) a dc offset current appears at the output of all pole filters and (b) dc instability is observed in the case of the substitution of LC resonators. In addition, an alternative technique already proposed for simulating filters with LC resonators is valid only under small-signal conditions. In order to overcome the aforementioned problems, new log-domain LT equivalents of a number of passive elements are introduced in this paper. The correct operation of the novel blocks has been verified through simulation results. Also, a comparison concerning the behaviour of the log-domain LT filters and that of the filters derived according to the leapfrog and the wave methods has also been performed. Copyright (C) 2007 John Wiley & Sons, Ltd.