Differential mode feedback is the designer's to create,
external to the fully differential op amp. CMFB is internal
to the op amp, making it work properly (set the average
of the + and - outputs to mid-rail).
Differential mode feedback is the designer's to create,
external to the fully differential op amp. CMFB is internal
to the op amp, making it work properly (set the average
of the + and - outputs to mid-rail).
CMFB is absolutely required for a true differential amplifier to set the common mode output voltage which would be otherwise undefined. Depending on the differential feedback topology, it can also increase common mode rejection as an additional benefit.