Three op amp floating immittance simulators: a retrospection

Through the use of nullor models it is shown that the recently proposed GRM circuit is a nullor equivalent of one of M.A. Reddy´s circuits (see ibid., vol.CAS-23, p.171-3, 1976), whereas the circuit of T.S. Rathore and B.M. Singhi (see Int. J. Circuit Theory Appl., vol.8, no.2, p.184-8, 1980) as well as Reddy´s second circuit evolve from the alternative form of this nullor model. Thus although these circuits have been derived by different techniques, they are equivalent and belong to the same family of three-op-amp floating-immitance (FI) simulator networks. Another result is the finding that from the three nullor models of the FI considered here, 14 additional circuits of this kind are possible which have not been disclosed or considered in the literature