Fully differential feedback amplifiers (FDA), such as National’s LMH6550, LMH6551, and the newly released LMH6552, are used to provide balanced low-distortion amplification and level shifting to wide bandwidth differential signals. This paper provides two conceptual diagrams: the first is of an FDA where two forward paths amplify the two complementary halves of the differential signal, and the second of a fully differential amplifier noise model.


The paper also discusses factors that must be considered when choosing between current and voltage mode FDAs. Where low-noise, wide-bandwidth applications require the FDA to be configured for larger than unity gain, CFB FDAs can offer an elegant solution.