On the exact realization of log-domain elliptic filters using the signal flow graph approach

Abstract

Logarithmic (LOG)-domain filters can be designed using the signal flow graph (SFG) synthesis approach and an appropriate set of operators. Following the above procedure, all-pole LOG-domain filters that exactly emulate the operation of the inductor-capacitor LC ladder prototype filter can be implemented. In the case of elliptic LOG-domain filters, the transmission zeros are not precisely realized. This is due to the fact that floating capacitors are used, in order to approximately perform the required differentiations. In this paper an alternative SFG representation of the prototype system is done, in such a way that the corresponding filter configuration can be implemented using only LOG-domain lossless integrators and amplifiers. A third-order LOG-domain elliptic filter was simulated in order to confirm the validity of the proposed technique.