Log-domain filter design with XFILTER
A.E.J. Ng · 2000
Log-domain synthesis procedures for both ladder and cascade-biquad filters have been presented. The ladder design procedure is based on decomposing a matrix description of a prototype ladder and establishing an exponential relationship between the linear and nonlinear variables. This, in conjunction with the direct realisability of the matrix equations, facilitates the generation of various high-order log-domain designs from a single prototype. Design equations for second order and first order sections have also been presented for the design of cascade-biquad log-domain filters. The incorporation of these synthesis procedures in XFILTER represents an early attempt to automate the log-domain filter design process, which hitherto has mainly been performed manually. Due to the generality of the mapping process, the proposed design procedures can be readily extended to weak-inversion CMOS and other realisations which employ sinh and tanh companding functions. Various design examples have been given for validation. (7 pages)