Design and applications of the operational floating amplifier (OFA): The most universal operational amplifier

Abstract

The operational floating amplifier (OFA) is the most universal type of operational amplifier. Both input and output ports are floating ports, i.e., free from restrictive ground connections. The floating input port enables the OFA to accurately equate two voltages between the two input terminals, like a standard operational amplifier, but in addition to that the OFA is able to accurately equate two currents through the two terminals of the floating output port. Specific applications are given, such as current amplifiers, voltage-to-current converters, gyrators, hybrids, and filters. The concept of the OFA allows these analog transfer functions to be realized with the absolute minimum number of accurate internal and external elements necessary to accurately determine the transfer. The OFA does not need accurate internal matched elements, except for offset, to obtain accurate overall transfer functions. This is in contrast to other current-output devices, such as the current conveyer, which transfer depends on the accuracy of internal current mirrors. Several designs of class A and class AB OFAs based on different topologies are presented and compared. This paper gives an overview of the application, the specification, and the design.