Abstract :
A commercially available transimpedance opamp, with compensation pin (AD 844 or AD 846) is surely a right choice to implement high-performance biquad in the current mode. Fabre´s remarkable article [1993] richly deserves credit. Nevertheless the author contributes to the wider and more reasonable utilisation of those circuits, especially in cases where a conventional opamp is not suitable. Its parasitic inherent features are presented here in a more characteristic way. The goal of this work is not to criticise Fabre´s paper, but to supplement it, to make it more accurate and intelligible. First, from principles of methodology the author recommends distinguishing more modes in which the given circuit can operate. These are especially applied basic modes, namely the classical voltage mode (VM) and the adjoint current mode (CM), when all subnetworks operate either with voltage or current signals. However, if a certain subcircuit (usually an active element) operates in a complementary mode (opposite to other parts) this is considered as hybrid modes, namely the voltage-current mode (V/CM) or the current-voltage mode (C/VM), respectively. The conventional opamp operates in VM whereas the current conveyor and transimpedance amplifier operate in CM
