Implementation of a Fully-Differential Operational Amplifier with Wide-Input Range, High-Impedance Common-Mode Feedback

Stabilizing the common-mode in fully-differential amplifiers is a well-known challenge. Conventional approaches usually are not able to deal with output nodes that have both: a high impedance and a high voltage swing. In this work, we implement a common-mode feedback architecture that was previously proposed in [2] but not yet realized. A two-stage fully-differential operational amplifier in a 0.25μm CMOS technology is used to demonstrate the feasibility of the new architecture. Measurements of the overall amplifier verify that the studied common-mode feedback is indeed a good candidate for opamps with high output impedance and rail-to-rail swing.