High-order inductorless elliptic filter with reduced number of capacitors using signal-flow graphs

In this paper a method of realizing seventh-order elliptic filter using signal-flow graphs is presented. The elliptic filter having a minimum number of capacitors is compared with the filter having a higher number of capacitors. The version with minimum number of capacitors provides area savings in IC form. Both filters (i.e. filter with minimum and one with higher number of capacitors) have a low sensitivity to component tolerances in the pass band according to Orchard´s theorem. The seventh-order elliptic filter has three parallel capacitors forming three parallel tanks, and therefore has three finite elliptic transfer-function zeros. The realizations of one and two parallel capacitors have already been presented elsewhere. The sfg derivations necessary to realize seventh-order filter having additional resistive network is presented, which is very complicated in the case of three zeros. Transfer function magnitudes are simulated using the PSpice program. Monte Carlo runs confirm the low sensitivity to component tolerances of both circuit types.